酒井 剛
| 基盤理工学専攻 | 教授 |
| Ⅲ類（理工系） | 教授 |
| 量子科学研究センター | 教授 |
| 宇宙・電磁環境研究センター | 教授 |
研究者情報
経歴
研究活動情報
論文
- FAUST. XIII. Dusty cavity and molecular shock driven by IRS7B in the Corona Australis cluster
G. Sabatini; L. Podio; C. Codella; Y. Watanabe; M. De Simone; E. Bianchi; C. Ceccarelli; C. J. Chandler; N. Sakai; B. Svoboda; L. Testi; Y. Aikawa; N. Balucani; M. Bouvier; P. Caselli; E. Caux; L. Chahine; S. Charnley; N. Cuello; F. Dulieu; L. Evans; D. Fedele; S. Feng; F. Fontani; T. Hama; T. Hanawa; E. Herbst; T. Hirota; A. Isella; I. Jímenez-Serra; D. Johnstone; B. Lefloch; R. Le Gal; L. Loinard; H. B. Liu; A. López-Sepulcre; L. T. Maud; M. J. Maureira; F. Menard; A. Miotello; G. Moellenbrock; H. Nomura; Y. Oba; S. Ohashi; Y. Okoda; Y. Oya; J. Pineda; A. Rimola; T. Sakai; D. Segura-Cox; Y. Shirley; C. Vastel; S. Viti; N. Watanabe; Y. Zhang; Z. E. Zhang; S. Yamamoto
Astronomy & Astrophysics, EDP Sciences, 684巻, 掲載ページ L12-L12, 出版日 2024年04月10日, 査読付, Context. The origin of the chemical diversity observed around low-mass protostars probably resides in the earliest history of these systems.
Aims. We aim to investigate the impact of protostellar feedback on the chemistry and grain growth in the circumstellar medium of multiple stellar systems.
Methods. In the context of the ALMA Large Program FAUST, we present high-resolution (50 au) observations of CH3OH, H2CO, and SiO and continuum emission at 1.3 mm and 3 mm towards the Corona Australis star cluster.
Results. Methanol emission reveals an arc-like structure at ∼1800 au from the protostellar system IRS7B along the direction perpendicular to the major axis of the disc. The arc is located at the edge of two elongated continuum structures that define a cone emerging from IRS7B. The region inside the cone is probed by H2CO, while the eastern wall of the arc shows bright emission in SiO, a typical shock tracer. Taking into account the association with a previously detected radio jet imaged with JVLA at 6 cm, the molecular arc reveals for the first time a bow shock driven by IRS7B and a two-sided dust cavity opened by the mass-loss process. For each cavity wall, we derive an average H2 column density of ∼7 × 1021 cm−2, a mass of ∼9 × 10−3 M⊙, and a lower limit on the dust spectral index of 1.4.
Conclusions. These observations provide the first evidence of a shock and a conical dust cavity opened by the jet driven by IRS7B, with important implications for the chemical enrichment and grain growth in the envelope of Solar System analogues.
研究論文（学術雑誌） - The ALMA Survey of 70 μm Dark High-mass Clumps in Early Stages (ASHES). X. Hot Gas Reveals Deeply Embedded Star Formation
Natsuko Izumi; Patricio Sanhueza; Patrick M. Koch; Xing Lu; Shanghuo Li; Giovanni Sabatini; Fernando A. Olguin; Qizhou Zhang; Fumitaka Nakamura; Ken’ichi Tatematsu; Kaho Morii; Takeshi Sakai; Daniel Tafoya
The Astrophysical Journal, American Astronomical Society, 963巻, 2号, 掲載ページ 163-163, 出版日 2024年03月01日, 査読付, Abstract
Massive infrared dark clouds (IRDCs) are considered to host the earliest stages of high-mass star formation. In particular, 70 μm dark IRDCs are the colder and more quiescent clouds. At a scale of about 5000 au using formaldehyde (H2CO) emission, we investigate the kinetic temperature of dense cores in 12 IRDCs obtained from the pilot Atacama Large Millimeter/submillimeter Array Survey of 70 μm dark High-mass clumps in Early Stages (ASHES). Compared to the 1.3 mm dust continuum and other molecular lines, such as C18O and deuterated species, we find that H2CO is mainly sensitive to low-velocity outflow components rather than to quiescent gas expected in the early phases of star formation. The kinetic temperatures of these components range from 26 to 300 K. The Mach number reaches about 15 with an average value of about 4, suggesting that the velocity distribution of gas traced by H2CO is significantly influenced by a supersonic nonthermal component. In addition, we detect warm line emission from HC3N and OCS in 14 protostellar cores, which requires high excitation temperatures (Eu/k ∼ 100 K). These results show that some of the embedded cores in the ASHES fields are in an advanced evolutionary stage, previously unexpected for 70 μm dark IRDCs.
研究論文（学術雑誌） - Observations of high-order multiplicity in a high-mass stellar protocluster
Shanghuo Li; Patricio Sanhueza; Henrik Beuther; Huei-Ru Vivien Chen; Rolf Kuiper; Fernando A. Olguin; Ralph E. Pudritz; Ian W. Stephens; Qizhou Zhang; Fumitaka Nakamura; Xing Lu; Rajika L. Kuruwita; Takeshi Sakai; Thomas Henning; Kotomi Taniguchi; Fei Li
Nature Astronomy, Springer Science and Business Media LLC, 8巻, 4号, 掲載ページ 472-481, 出版日 2024年01月15日, 査読付, Abstract
The dominant mechanism forming multiple stellar systems in the high-mass regime (M* ≳ 8 M⊙) remained unknown because direct imaging of multiple protostellar systems at early phases of high-mass star formation is very challenging. High-mass stars are expected to form in clustered environments containing binaries and higher-order multiplicity systems. So far only a few high-mass protobinary systems, and no definitive higher-order multiples, have been detected. Here we report the discovery of one quintuple, one quadruple, one triple and four binary protostellar systems simultaneously forming in a single high-mass protocluster, G333.23–0.06, using Atacama Large Millimeter/submillimeter Array high-resolution observations. We present a new example of a group of gravitationally bound binary and higher-order multiples during their early formation phases in a protocluster. This provides the clearest direct measurement of the initial configuration of primordial high-order multiple systems, with implications for the in situ multiplicity and its origin. We find that the binary and higher-order multiple systems, and their parent cores, show no obvious sign of disk-like kinematic structure. We conclude that the observed fragmentation into binary and higher-order multiple systems can be explained by core fragmentation, indicating its crucial role in establishing the multiplicity during high-mass star cluster formation.
研究論文（学術雑誌） - Digging into the Interior of Hot Cores with ALMA: Spiral Accretion into the High-mass Protostellar Core G336.01–0.82
Fernando A. Olguin; Patricio Sanhueza; Huei-Ru Vivien Chen; Xing Lu; Yoko Oya; Qizhou Zhang; Adam Ginsburg; Kotomi Taniguchi; Shanghuo Li; Kaho Morii; Takeshi Sakai; Fumitaka Nakamura
The Astrophysical Journal Letters, American Astronomical Society, 959巻, 2号, 掲載ページ L31-L31, 出版日 2023年12月01日, 査読付, Abstract
We observed the high-mass star-forming core G336.01–0.82 at 1.3 mm and 0.″05 (∼150 au) angular resolution with the Atacama Large Millimeter/submillimeter Array (ALMA) as part of the Digging into the Interior of Hot Cores with ALMA survey. These high-resolution observations reveal two spiral streamers feeding a circumstellar disk at opposite sides in great detail. Molecular line emission from CH3OH shows velocity gradients along the streamers consistent with infall. Similarly, a flattened envelope model with rotation and infall implies a mass larger than 10 M☉ for the central source and a centrifugal barrier of 300 au. The location of the centrifugal barrier is consistent with local peaks in the continuum emission. We argue that gas brought by the spiral streamers is accumulating at the centrifugal barrier, which can result in future accretion burst events. A total high infall rate of ∼4 × 10−4M☉ yr−1 is derived by matching models to the observed velocity gradient along the streamers. Their contribution accounts for 20%–50% the global infall rate of the core, indicating streamers play an important role in the formation of high-mass stars.
研究論文（学術雑誌）, 英語 - Laboratory Measurement of CH2DOH Line Intensities in the Millimeter-wave Region
Takahiro Oyama; Yuki Ohno; Akemi Tamanai; Yoshimasa Watanabe; Satoshi Yamamoto; Takeshi Sakai; Shaoshan Zeng; Riouhei Nakatani; Nami Sakai
The Astrophysical Journal, 957巻, 掲載ページ 4, 出版日 2023年11月01日, 査読付
研究論文（学術雑誌）, 英語 - The ALMA Survey of 70 μm Dark High-mass Clumps in Early Stages (ASHES). IX. Physical Properties and Spatial Distribution of Cores in IRDCs
Kaho Morii; Patricio Sanhueza; Fumitaka Nakamura; Qizhou Zhang; Giovanni Sabatini; Henrik Beuther; Xing Lu; Shanghuo Li; Guido Garay; James M. Jackson; Fernando A. Olguin; Daniel Tafoya; Ken’ichi Tatematsu; Natsuko Izumi; Takeshi Sakai; Andrea Silva
The Astrophysical Journal, American Astronomical Society, 950巻, 2号, 掲載ページ 148-148, 出版日 2023年06月01日, Abstract
The initial conditions found in infrared dark clouds (IRDCs) provide insights on how high-mass stars and stellar clusters form. We have conducted high-angular resolution and high-sensitivity observations toward thirty-nine massive IRDC clumps, which have been mosaicked using the 12 and 7 m arrays from the Atacama Large Millimeter/submillimeter Array. The targets are 70 μm dark massive (220–4900 M⊙), dense (>104 cm−3), and cold (∼10–20 K) clumps located at distances between 2 and 6 kpc. We identify an unprecedented number of 839 cores, with masses between 0.05 and 81 M⊙ using 1.3 mm dust continuum emission. About 55% of the cores are low-mass (<1 M⊙), whereas ≲1% (7/839) are high-mass (≳27 M⊙). We detect no high-mass prestellar cores. The most massive cores (MMC) identified within individual clumps lack sufficient mass to form high-mass stars without additional mass feeding. We find that the mass of the MMCs is correlated with the clump surface density, implying denser clumps produce more massive cores. There is no significant mass segregation except for a few tentative detections. In contrast, most clumps show segregation once the clump density is considered instead of mass. Although the dust continuum emission resolves clumps in a network of filaments, some of which consist of hub-filament systems, the majority of the MMCs are not found in the hubs. Our analysis shows that high-mass cores and MMCs have no preferred location with respect to low-mass cores at the earliest stages of high-mass star formation.
研究論文（学術雑誌） - Development of seven-beam optics using dielectric lenses for a new 72–116 GHz receiver in the Nobeyama 45 m telescope
Yasumasa Yamasaki; Yutaka Hasegawa; Sho Yoneyama; Sana Kawashita; Tsubasa Chinen; Sho Masui; Chiaki Nosohara; Heyang Sun; Shuto Dakie; Akira Kameyama; Ikko Fujitomo; Yuma Nishikawa; Hideo Ogawa; Ken’ichi Tatematsu; Atsushi Nishimura; Chieko Miyazawa; Toshikazu Takahashi; Jun Maekawa; Alvaro Gonzalez; Takafumi Kojima; Hiroaki Imada; Keiko Kaneko; Ryo Sakai; Takeshi Sakai; Toshikazu Onishi
Publications of the Astronomical Society of Japan, Oxford University Press (OUP), 出版日 2023年03月28日, Abstract
We developed a new seven-beam heterodyne receiver “7BEE” in the 72–116 GHz band for the Nobeyama 45 m telescope to investigate the early stage of star formation by deriving the deuterium fraction of dense cores. The optics for the receiver employs wideband corrugated horns covering the 72–116 GHz band and dielectric lenses to couple the incoming radiation from the antenna on to the feeds. One of the important aspects in the lens design is the anti-reflection (AR) structure to mitigate the reflections on the lens surfaces. Triangular grooves, which gradually change the effective refractive index from air to dielectric, were adopted as a basic AR design since the return loss can be in the order of 20 dB or better. The main goal of this study is to compare the radio frequency (RF) characteristics of the lenses with different patterns and sizes of AR grooving structures. We confirmed that concentric grooves degraded beam symmetry, cross-polarization characteristics, and aperture efficiency due to the birefringence of the grooves, which gave rise to wavefront distortions. Straight grooves of two different gap widths, 1.2 mm and 1.7 mm, were compared and showed similar good performance in terms of beam patterns and noise contribution. However, the latter showed a few percent higher aperture efficiency. Therefore, the straight grooves with 1.7 mm gap width were adopted as the AR structure of our lens.
研究論文（学術雑誌） - The ALMA Survey of 70 μm Dark High-mass Clumps in Early Stages (ASHES). VII. Chemistry of Embedded Dense Cores
Shanghuo Li; Patricio Sanhueza; Xing Lu; Chang Won Lee; Qizhou Zhang; Stefano Bovino; Giovanni Sabatini; Tie Liu; Kee-Tae Kim; Kaho Morii; Daniel Tafoya; Ken’ichi Tatematsu; Takeshi Sakai; Junzhi Wang; Fei Li; Andrea Silva; Natsuko Izumi; David Allingham
The Astrophysical Journal, American Astronomical Society, 939巻, 2号, 掲載ページ 102-102, 出版日 2022年11月01日, 査読付, Abstract
We present a study of the chemistry toward 294 dense cores in 12 molecular clumps, using data obtained from the ALMA Survey of 70 μm dark High-mass clumps in Early Stages. We identified 97 protostellar cores and 197 prestellar core candidates, based on the detection of outflows and molecular transitions of high upper-energy levels (Eu/k > 45 K). The detection rate of the N2D+ emission toward the protostellar cores is 38%, which is higher than 9% for the prestellar cores, indicating that N2D+ does not exclusively trace prestellar cores. The detection rates of the DCO+ emission are 35% for the prestellar cores and 49% for the protostellar cores, which are higher than those for N2D+, implying that DCO+ appears more frequently than N2D+ in both prestellar and protostellar cores. Both the N2D+ and DCO+ abundances appear to decrease from the prestellar to the protostellar stage. The DCN, C2D, and 13CS emission lines are rarely seen in the dense cores of early evolutionary phases. The detection rate of the H2CO emission toward dense cores is 52%, three times higher than that for CH3OH (17%). In addition, the H2CO detection rate, abundance, line intensities, and line widths increase with the core evolutionary status, suggesting that the H2CO line emission is sensitive to protostellar activity.
研究論文（学術雑誌） - The ALMA Survey of 70 μm Dark High-mass Clumps in Early Stages (ASHES). VI. The Core-scale CO Depletion
Sabatini, Giovanni; Bovino, Stefano; Sanhueza, Patricio; Morii, Kaho; Li, Shanghuo; Redaelli, Elena; Zhang, Qizhou; Lu, Xing; Feng, Siyi; Tafoya, Daniel; Izumi, Natsuko; Sakai, Takeshi; Tatematsu, Ken'ichi; Allingham, David
The Astrophysical Journal, American Astronomical Society, 936巻, 1号, 掲載ページ id. 80-80, 出版日 2022年09月, 査読付, Abstract
Studying the physical and chemical properties of cold and dense molecular clouds is crucial for the understanding of how stars form. Under the typical conditions of infrared dark clouds, CO is removed from the gas phase and trapped onto the surface of dust grains by the so-called depletion process. This suggests that the CO-depletion factor (fD) can be a useful chemical indicator for identifying cold and dense regions (i.e., prestellar cores). We have used the 1.3 mm continuum and C18O (2–1) data observed at the resolution of ∼5000 au in the ALMA Survey of 70 μm Dark High-mass Clumps in Early Stages (ASHES) to construct averaged maps of fD in 12 clumps to characterize the earliest stages of the high-mass star formation process. The average fD determined for 277 of the 294 ASHES cores follows an unexpected increase from the prestellar to the protostellar stage. If we exclude the temperature effect due to the slight variations in the NH3 kinetic temperature among different cores, we explain this result as a dependence primarily on the average gas density, which increases in cores where protostellar conditions prevail. This shows that fD determined in high-mass star-forming regions at the core scale is insufficient to distinguish among prestellar and protostellar conditions for the individual cores and should be complemented by information provided by additional tracers. However, we confirm that the clump-averaged fD values correlate with the luminosity-to-mass ratio of each source, which is known to trace the evolution of the star formation process.
研究論文（学術雑誌）, 英語 - FAUST
Charlotte VASTEL; F. Alves; C. Ceccarelli; M. Bouvier; I. Jiménez-Serra; T. Sakai; P. Caselli; L. Evans; F. Fontani; R. Le Gal; C. J. Chandler; B. Svoboda; L. Maud; C. Codella; N. Sakai; A. Lόpez-Sepulcre; G. Moellenbrock; Y. Aikawa; N. Balucani; E. Bianchi; G. Busquet; E. Caux; S. Charnley; N. Cuello; M. De Simone; F. Dulieu; A. Durân; D. Fedele; S. Feng; L. Francis; T. Hama; T. Hanawa; E. Herbst; T. Hirota; M. Imai; A. Isella; D. Johnstone; B. Lefloch; L. Loinard; M. Maureira; N. M. Murillo; S. Mercimek; S. Mori; F. Menard; A. Miotello; R. Nakatani; H. Nomura; Y. Oba; S. Ohashi; Y. Okoda; J. Ospina-Zamudio
Astronomy & Astrophysics, {EDP} Sciences, 664巻, 出版日 2022年08月,
研究論文（学術雑誌） - FAUST. V. Hot methanol in the [BHB2007] 11 protobinary system; hot corino versus shock origin
Vastel, C; Alves, F; Ceccarelli, C; Bouvier, M; Jiménez-Serra, I; Sakai, T; Caselli, P; Evans, L; Fontani, F; Le Gal, R; Chandler, C. J; Svoboda, B; Maud, L; Codella, C; Sakai, N; López-Sepulcre, A; Moellenbrock, G; Aikawa, Y; Balucani, N; Bianchi, E; Busquet, G; Caux, E; Charnley, S; Cuello, N; De Simone, M; Dulieu, F; Durân, A; Fedele, D; Feng, S; Francis, L; Hama, T; Hanawa, T; Herbst, E; Hirota, T; Imai, M; Isella, A; Johnstone, D; Lefloch, B; Loinard, L
Astronomy & Astrophysics, 664巻, 掲載ページ id. A171, 出版日 2022年08月, 査読付
研究論文（学術雑誌）, 英語 - Chemical and Physical Characterization of the Isolated Protostellar Source CB68: FAUST IV
Imai, Muneaki; Oya, Yoko; Svoboda, Brian; Liu; Hauyu Baobab; Lefloch, Bertrand; Viti, Serena; Zhang, Yichen; Ceccarelli, Cecilia; Codella, Claudio; Chandler, Claire J; Sakai, Nami; Aikawa, Yuri; Alves, Felipe O; Balucani, Nadia; Bianchi, Eleonora; Bouvier, Mathilde; Busquet, Gemma; Caselli, Paola; Caux, Emmanuel; Charnley, Steven; Choudhury, Spandan; Cuello, Nicolas; Simone, Marta De; Dulieu, Francois; Durán, Aurora; Evans, Lucy; Favre, Cécile; Fedele, Davide; Feng, Siyi; Fontani, Francesco
The Astrophysical Journal, 934巻, 1号, 掲載ページ id. 70, 出版日 2022年07月, 査読付
研究論文（学術雑誌）, 英語 - Laboratory Measurement of Millimeter-wave Transitions of 13CH2DOH for Astronomical Use
Ohno, Yuki; Oyama, Takahiro; Tamanai, Akemi; Zeng, Shaoshan; Watanabe, Yoshimasa; Nakatani, Riouhei; Sakai, Takeshi; Sakai, Nami
The Astrophysical Journal, 932巻, 2号, 掲載ページ id. 101, 出版日 2022年06月, 査読付
研究論文（学術雑誌）, 英語 - Nobeyama Survey of Inward Motions toward Cores in Orion Identified by SCUBA-2
Tatematsu, Ken'ichi; Yeh, You-Ting; Hirano, Naomi; Liu, Sheng-Yuan; Liu, Tie; Dutta, Somnath; Sahu, Dipen; Evans, Neal J., II; Juvela, Mika; Yi, Hee-Weon; Lee, Jeong-Eun; Sanhueza, Patricio; Li, Shanghuo; Eden, David; Kim, Gwanjeong; Lee, Chin-Fei; Wu, Yuefang; Kim, Kee-Tae; Tóth, L. Viktor; Choi, Minho; Kang, Miju; Thompson, Mark A; Fuller, Gary A; Li, Di; Wang, Ke; Sakai, Takeshi; Kandori, Ryo; Hsu, Shih-Ying; Chiong, Chau-Ching; Almasop" Collaboration
The Astrophysical Journal, 931巻, 1号, 掲載ページ id. 33, 出版日 2022年05月, 査読付
研究論文（学術雑誌）, 英語 - Digging into the Interior of Hot Cores with ALMA (DIHCA). II. Exploring the Inner Binary (Multiple) System Embedded in G335 MM1 ALMA1
Olguin, Fernando A; Sanhueza, Patricio; Ginsburg, Adam; Chen, Huei-Ru Vivien; Zhang, Qizhou; Li, Shanghuo; Lu, Xing; Sakai, Takeshi
The Astrophysical Journal, 929巻, 1号, 掲載ページ id. 68, 出版日 2022年04月, 査読付
研究論文（学術雑誌）, 英語 - Misaligned Rotations of the Envelope, Outflow, and Disks in the Multiple Protostellar System of VLA 1623-2417: FAUST. III
Ohashi, Satoshi; Codella, Claudio; Sakai, Nami; Chandler, Claire J; Ceccarelli, Cecilia; Alves, Felipe; Fedele, Davide; Hanawa, Tomoyuki; Durán, Aurora; Favre, Cécile; López-Sepulcre, Ana; Loinard, Laurent; Mercimek, Seyma; Murillo, Nadia M; Podio, Linda; Zhang, Yichen; Aikawa, Yuri; Balucani, Nadia; Bianchi, Eleonora; Bouvier, Mathilde; Busquet, Gemma; Caselli, Paola; Caux, Emmanuel; Charnley, Steven; Choudhury, Spandan; Cuello, Nicolas; De Simone, Marta; Dulieu, Francois; Evans, Lucy; Feng
The Astrophysical Journal, American Astronomical Society, 927巻, 1号, 掲載ページ id. 54-54, 出版日 2022年03月, 査読付,Abstract
We report a study of the low-mass Class 0 multiple system VLA 1623AB in the Ophiuchus star-forming region, using H13CO+ (J = 3–2), CS (J = 5–4), and CCH (N = 3–2) lines as part of the ALMA Large Program FAUST. The analysis of the velocity fields revealed the rotation motion in the envelope and the velocity gradients in the outflows (about 2000 au down to 50 au). We further investigated the rotation of the circumbinary VLA 1623A disk, as well as the VLA 1623B disk. We found that the minor axis of the circumbinary disk of VLA 1623A is misaligned by about 12° with respect to the large-scale outflow and the rotation axis of the envelope. In contrast, the minor axis of the circumbinary disk is parallel to the large-scale magnetic field according to previous dust polarization observations, suggesting that the misalignment may be caused by the different directions of the envelope rotation and the magnetic field. If the velocity gradient of the outflow is caused by rotation, the outflow has a constant angular momentum and the launching radius is estimated to be 5–16 au, although it cannot be ruled out that the velocity gradient is driven by entrainments of the two high-velocity outflows. Furthermore, we detected for the first time a velocity gradient associated with rotation toward the VLA 16293B disk. The velocity gradient is opposite to the one from the large-scale envelope, outflow, and circumbinary disk. The origin of its opposite gradient is also discussed.
研究論文（学術雑誌）, 英語 - The ALMA Survey of 70 mu m Dark High-mass Clumps in Early Stages (ASHES). V. Deuterated Molecules in the 70 mu m Dark IRDC G14.492-00.139
Takeshi Sakai; Patricio Sanhueza; Kenji Furuya; Ken'ichi Tatematsu; Shanghuo Li; Yuri Aikawa; Xing Lu; Qizhou Zhang; Kaho Morii; Fumitaka Nakamura; Hideaki Takemura; Natsuko Izumi; Tomoya Hirota; Andrea Silva; Andres E. Guzman; Nami Sakai; Satoshi Yamamoto
ASTROPHYSICAL JOURNAL, IOP Publishing Ltd, 925巻, 2号, 出版日 2022年02月, We have observed the 70 mu m dark infrared dark cloud (IRDC) G14.492-00.139 in the N2D+ J = 3-2, DCO+ J = 3-2, DCN J = 3-2, and (CO)-O-18 J = 2-1 lines, using the Atacama Large Millimeter/submillimeter Array (ALMA) as part of the ALMA Survey of 70 mu m Dark High-mass Clumps in Early Stages. We find that the spatial distribution is different among the observed emission from the deuterated molecular lines. The N2D+ emission traces relatively quiescent regions, while both the DCO+ and DCN emission emanate mainly from regions with signs of active star formation. In addition, the DCO+/N2D+ ratio is found to be lower in several dense cores than in starless cores embedded in low-mass star-forming regions. By comparing the observational results with chemical-model calculations, we discuss the origin of the low DCO+/N2D+ ratio in this IRDC clump. The low DCO+/N2D+ ratio can be explained if the temperature of the dense cores is in the range between the sublimation temperatures of N-2 (similar to 20 K) and CO (similar to 25 K). The results suggest that the dense cores in G14.492-00.139 are warmer and denser than the dense cores in low-mass star-forming regions.
研究論文（学術雑誌）, 英語 - The ALMA Survey of 70 μm Dark High-mass Clumps in Early Stages (ASHES). IV. Star Formation Signatures in G023.477
Morii, Kaho; Sanhueza; Patricio, Nakamura; Fumitaka, Jackson; James M., Li; Shanghuo, Beuther; Henrik, Zhang; Qizhou, Feng; Siyi, Tafoya; Daniel, Guzmán; Andrés E; Izumi; Natsuko, Sakai; Takeshi, Lu; Xing, Tatematsu; Ken'ichi, Ohashi; Satoshi, Silva; Andrea, Olguin; Fernando A; Contreras, Yanett
The Astrophysical Journal, American Astronomical Society, 923巻, 2号, 掲載ページ id. 147-147, 出版日 2021年12月, 査読付, Abstract
With a mass of ∼1000 M⊙ and a surface density of ∼0.5 g cm−2, G023.477+0.114, also known as IRDC 18310-4, is an infrared dark cloud (IRDC) that has the potential to form high-mass stars and has been recognized as a promising prestellar clump candidate. To characterize the early stages of high-mass star formation, we have observed G023.477+0.114 as part of the Atacama Large Millimeter/submillimeter Array (ALMA) Survey of 70 μm Dark High-mass Clumps in Early Stages. We have conducted ∼1.″2 resolution observations with ALMA at 1.3 mm in dust continuum and molecular line emission. We have identified 11 cores, whose masses range from 1.1 to 19.0 M⊙. Ignoring magnetic fields, the virial parameters of the cores are below unity, implying that the cores are gravitationally bound. However, when magnetic fields are included, the prestellar cores are close to virial equilibrium, while the protostellar cores remain sub-virialized. Star formation activity has already started in this clump. Four collimated outflows are detected in CO and SiO. H2CO and CH3OH emission coincide with the high-velocity components seen in the CO and SiO emission. The outflows are randomly oriented for the natal filament and the magnetic field. The position-velocity diagrams suggest that episodic mass ejection has already begun even in this very early phase of protostellar formation. The masses of the identified cores are comparable to the expected maximum stellar mass that this IRDC could form (8–19 M⊙). We explore two possibilities on how IRDC G023.477+0.114 could eventually form high-mass stars in the context of theoretical scenarios.
研究論文（学術雑誌）, 英語 - Molecular Cloud Cores with High Deuterium Fractions: Nobeyama Mapping Survey
Tatematsu; Ken'ichi, Kim; Gwanjeong, Liu; Tie, Evans; Neal J; II, Yi; Hee-Weon, Lee; Jeong-Eun, Wu; Yuefang, Hirano; Naomi, Liu; Sheng-Yuan, Dutta; Somnath, Sahu; Dipen, Sanhueza; Patricio, Kim; Kee-Tae, Juvela; Mika, Tóth; L. Viktor; Fehér; Orsolya, He; Jinhua, Ge; Jixing; Feng, Siyi; Choi, Minho; Kang, Miju; Thompson; Mark A; Fuller; Gary A., Li; Di, Ristorcelli; Isabelle, Wang, Ke; di Francesco; James, Eden; David; Ohashi, Satoshi; Kandori, Ryo; Vastel, Charlotte; Hirota, Tomoya; Sakai, Tak
The Astrophysical Journal Supplement Series, 256巻, 2号, 掲載ページ id. 25, 出版日 2021年10月, 査読付
研究論文（学術雑誌）, 英語 - Exploring the 100 au Scale Structure of the Protobinary System NGC 2264 CMM3 with ALMA
Yoshiki Shibayama; Yoshimasa Watanabe; Yoko Oya; Nami Sakai; Ana López-Sepulcre; Sheng-Yuan Liu; Yu-Nung Su; Yichen Zhang; Takeshi Sakai; Tomoya Hirota; Satoshi Yamamoto
The Astrophysical Journal, 918巻, 1号, 掲載ページ id. 32, 出版日 2021年09月, 査読付
研究論文（学術雑誌）, 英語 - Gravity Driven Magnetic Field at ~1000 au Scales in High-mass Star Formation
Patricio Sanhueza; Josep Miquel Girart; Marco Padovani; Daniele Galli; Charles L. H. Hull; Qizhou Zhang; Paulo Cortes; Ian W. Stephens; Manuel Fernandez-Lopez; James M. Jackson; Pau Frau; Patrick M. Kock; Benjamin Wu; Luis A. Zapata; Fernando Olguin; Xing Lu; Andrea Silva; Ya-Wen Tang; Takeshi Sakai; Andres E. Guzman; Ken'ichi Tatematsu; Fumitaka Nakamura; Huei-Ru Vivien Chen
The Astrophysical Journal Letters, 915巻, 1号, 掲載ページ id. L10, 出版日 2021年07月, 査読付
研究論文（学術雑誌）, 英語 - Erratum: “The Perseus ALMA Chemistry Survey (PEACHES). I. The Complex Organic Molecules in Perseus Embedded Protostars” (2021, ApJ, 910, 20)
Yao-Lun Yang; Nami Sakai; Yichen Zhang; Nadia M. Murillo; Ziwei E. Zhang; Aya E. Higuchi; Shaoshan Zeng; Ana López-Sepulcre; Satoshi Yamamoto; Bertrand Lefloch; Mathilde Bouvier; Cecilia Ceccarelli; Tomoya Hirota; Muneaki Imai; Yoko Oya; Takeshi Sakai; Yoshimasa Watanabe
The Astrophysical Journal, American Astronomical Society, 913巻, 2号, 掲載ページ 155-155, 出版日 2021年06月01日
研究論文（学術雑誌） - The ALMA Survey of 70 μm Dark High-mass Clumps in Early Stages (ASHES). III. A Young Molecular Outflow Driven by a Decelerating Jet
Daniel Tafoya; Patricio Sanhueza; Qizhou Zhang; Shanghuo Li; Andrés E. Guzmán; Andrea Silva; Eduardo de la Fuente; Xing Lu; Kaho Morii; Ken'ichi Tatematsu; Yanett Contreras; Natsuko Izumi; James M. Jackson; Fumitaka Nakamura; Takeshi Sakai
The Astrophysical Journal, American Astronomical Society, 913巻, 2号, 掲載ページ id.131-131, 出版日 2021年06月, 査読付, Abstract
We present a spatio-kinematical analysis of the CO (J = 2 → 1) line emission, observed with the Atacama Large Millimeter/submillimeter Array (ALMA), of the outflow associated with the most massive core, ALMA1, in the 70 μm dark clump G010.991–00.082. The position–velocity (PV) diagram of the molecular outflow exhibits a peculiar S-shaped morphology that has not been seen in any other star-forming region. We propose a spatio-kinematical model for the bipolar molecular outflow that consists of a decelerating high-velocity component surrounded by a slower component whose velocity increases with distance from the central source. The physical interpretation of the model is in terms of a jet that decelerates as it entrains material from the ambient medium, which has been predicted by calculations and numerical simulations of molecular outflows in the past. One side of the outflow is shorter and shows a stronger deceleration, suggesting that the medium through which the jet moves is significantly inhomogeneous. The age of the outflow is estimated to be τ ≈ 1300 yr, after correction for a mean inclination of the system of ≈57°.
研究論文（学術雑誌）, 英語 - Spectrometer Using superconductor MIxer Receiver (SUMIRE) for laboratory submillimeter spectroscopy
Watanabe, Yoshimasa; Chiba, Yutaro; Sakai, Takeshi; Tamanai, Akemi; Suzuki, Rikako; Sakai, Nami
Publications of the Astronomical Society of Japan, 73巻, 2号, 掲載ページ 372-393, 出版日 2021年04月, 査読付
研究論文（学術雑誌）, 英語 - FAUST. II. Discovery of a Secondary Outflow in IRAS 15398-3359: Variability in Outflow Direction during the Earliest Stage of Star Formation?
Yuki Okoda; Yoko Oya; Logan Francis; Doug Johnstone; Shu-ichiro Inutsuka; Cecilia Ceccarelli; Claudio Codella; Claire Chandler; Nami Sakai; Yuri Aikawa; Felipe O. Alves; Nadia Balucani; Eleonora Bianchi; Mathilde Bouvier; Paola Caselli; Emmanuel Caux; Steven Charnley; Spandan Choudhury; Marta De Simone; Francois Dulieu; Aurora Duran; Lucy Evans; Cecile Favre; Davide Fedele; Siyi Feng; Francesco Fontani; Tetsuya Hama; Tomoyuki Hanawa; Eric Herbst; Tomoya Hirota; Muneaki Imai; Andrea Isella; Izaskun Jimenez-Serra; Claudine Kahane; Bertrand Lefloch; Laurent Loinard; Ana Lopez-Sepulcre; Luke T. Maud; Maria Jose Maureira; Francois Menard; Seyma Mercimek; Anna Miotello; George Moellenbrock; Shoji Mori; Nadia M. Murillo; Riouhei Nakatani; Hideko Nomura; Yasuhiro Oba; Ross O'Donoghue; Satoshi Ohashi; Juan Ospina-Zamudio; Jaime E. Pineda; Linda Podio; Albert Rimola; Takeshi Sakai; Dominique Segura-Cox; Yancy Shirley; Brian Svoboda; Vianney Taquet; Leonardo Testi; Charlotte Vastel; Serena Viti; Naoki Watanabe; Yoshimasa Watanabe; Arezu Witzel; Ci Xue; Yichen Zhang; Bo Zhao; Satoshi Yamamoto
ASTROPHYSICAL JOURNAL, IOP PUBLISHING LTD, 910巻, 1号, 出版日 2021年03月, We have observed the very low-mass Class 0 protostar IRAS 15398-3359 at scales ranging from 50 to 1800 au, as part of the Atacama Large Millimeter/Submillimeter Array Large Program FAUST. We uncover a linear feature, visible in H2CO, SO, and (CO)-O-18 line emission, which extends from the source in a direction almost perpendicular to the known active outflow. Molecular line emission from H2CO, SO, SiO, and CH3OH further reveals an arc-like structure connected to the outer end of the linear feature and separated from the protostar, IRAS 15398-3359, by 1200 au. The arc-like structure is blueshifted with respect to the systemic velocity. A velocity gradient of 1.2 km s(-1) over 1200 au along the linear feature seen in the H2CO emission connects the protostar and the arc-like structure kinematically. SO, SiO, and CH3OH are known to trace shocks, and we interpret the arc-like structure as a relic shock region produced by an outflow previously launched by IRAS 15398-3359. The velocity gradient along the linear structure can be explained as relic outflow motion. The origins of the newly observed arc-like structure and extended linear feature are discussed in relation to turbulent motions within the protostellar core and episodic accretion events during the earliest stage of protostellar evolution.
研究論文（学術雑誌）, 英語 - Digging into the Interior of Hot Cores with ALMA (DIHCA). I. Dissecting the High-mass Star-forming Core G335.579-0.292 MM1
Olguin, Fernando A; Sanhueza, Patricio; Guzmán; Andrés E; Lu, Xing; Saigo, Kazuya; Zhang, Qizhou; Silva, Andrea; Chen, Huei-Ru Vivien; Li, Shanghuo; Ohashi, Satoshi; Nakamura, Fumitaka; Sakai, Takeshi; Wu, Benjamin
The Astrophysical Journal, 909巻, 2号, 掲載ページ id. 199, 出版日 2021年03月, 査読付
研究論文（学術雑誌）, 英語 - The Perseus ALMA Chemistry Survey (PEACHES). I. The Complex Organic Molecules in Perseus Embedded Protostars
Yang, Yao-Lun; Sakai, Nami; Zhang, Yichen; Murillo, Nadia M; Zhang, Ziwei E; Higuchi, Aya E; Zeng, Shaoshan; López-Sepulcre, Ana; Yamamoto, Satoshi; Lefloch, Bertrand; Bouvier, Mathilde; Ceccarelli, Cecilia; Hirota, Tomoya; Imai, Muneaki; Oya, Yoko; Sakai, Takeshi; Watanabe, Yoshimasa
The Astrophysical Journal, American Astronomical Society, 910巻, 1号, 掲載ページ id. 20-20, 出版日 2021年03月, 査読付
研究論文（学術雑誌）, 英語 - HCN J = 4-3, HNC J = 1-0, H13CN J = 1-0, and HC3N J = 10-9 Maps of Galactic Center Region. II. Physical Properties of Dense-gas Clumps and Probability of Star Formation
Tanaka, Kunihiko; Nagai, Makoto; Kamegai, Kazuhisa; Iino, Takahiro; Sakai, Takeshi
The Astrophysical Journal, 903巻, 2号, 掲載ページ id. 111, 出版日 2020年11月, 査読付
研究論文（学術雑誌）, 英語 - The ALMA Survey of 70 μm Dark High-mass Clumps in Early Stages (ASHES). II. Molecular Outflows in the Extreme Early Stages of Protocluster Formation
Li, Shanghuo; Sanhueza, Patricio; Zhang, Qizhou; Nakamura, Fumitaka; Lu, Xing; Wang, Junzhi; Liu, Tie; Tatematsu, Ken'ichi; Jackson, James M; Silva, Andrea; Guzmán, Andrés E; Sakai, Takeshi; Izumi, Natsuko; Tafoya, Daniel; Li, Fei; Contreras, Yanett; Morii, Kaho; Kim, Kee-Tae
The Astrophysical Journal, American Astronomical Society, 903巻, 2号, 掲載ページ id. 119-119, 出版日 2020年11月, 査読付
研究論文（学術雑誌）, 英語 - FAUST I. The hot corino at the heart of the prototypical Class I protostar L1551 IRS5
E Bianchi; C J Chandler; C Ceccarelli; C Codella; N Sakai; A López-Sepulcre; L T Maud; G Moellenbrock; B Svoboda; Y Watanabe; T Sakai; F Ménard; Y Aikawa; F Alves; N Balucani; M Bouvier; P Caselli; E Caux; S Charnley; S Choudhury; M De Simone; F Dulieu; A Durán; L Evans; C Favre; D Fedele; S Feng; F Fontani; L Francis; T Hama; T Hanawa; E Herbst; T Hirota; M Imai; A Isella; I Jiménez-Serra; D Johnstone; C Kahane; B Lefloch; L Loinard; M J Maureira; S Mercimek; A Miotello; S Mori; R Nakatani; H Nomura; Y Oba; S Ohashi; Y Okoda; J Ospina-Zamudio; Y Oya; J Pineda; L Podio; A Rimola; D Segura Cox; Y Shirley; V Taquet; L Testi; C Vastel; S Viti; N Watanabe; A Witzel; C Xue; Y Zhang; B Zhao; S Yamamoto
Monthly Notices of the Royal Astronomical Society: Letters, Oxford University Press (OUP), 498巻, 1号, 掲載ページ L87-L92, 出版日 2020年10月11日,ABSTRACT
The study of hot corinos in solar-like protostars has been so far mostly limited to the Class 0 phase, hampering our understanding of their origin and evolution. In addition, recent evidence suggests that planet formation starts already during Class I phase, which therefore represents a crucial step in the future planetary system chemical composition. Hence, the study of hot corinos in Class I protostars has become of paramount importance. Here, we report the discovery of a hot corino towards the prototypical Class I protostar L1551 IRS5, obtained within the ALMA (Atacama Large Millimeter/submillimeter Array) Large Program FAUST (Fifty AU STudy of the chemistry in the disc/envelope system of solar-like protostars). We detected several lines from methanol and its isotopologues (13CH3OH and CH2DOH), methyl formate, and ethanol. Lines are bright towards the north component of the IRS5 binary system, and a possible second hot corino may be associated with the south component. The methanol lines' non-LTE analysis constrains the gas temperature (∼100 K), density (≥1.5 × 108 cm−3), and emitting size (∼10 au in radius). All CH3OH and 13CH3OH lines are optically thick, preventing a reliable measure of the deuteration. The methyl formate and ethanol relative abundances are compatible with those measured in Class 0 hot corinos. Thus, based on this work, little chemical evolution from Class 0 to I hot corinos occurs.
研究論文（学術雑誌） - Molecular Cloud Cores with a High Deuterium Fraction: Nobeyama Single-pointing Survey
Gwanjeong Kim; Ken’ichi Tatematsu; Tie Liu; Hee-Weon Yi; Jinhua He; Naomi Hirano; Sheng-Yuan Liu; Minho Choi; Patricio Sanhueza; L. Viktor Tóth; Neal J. Evans II; Siyi Feng; Mika Juvela; Kee-Tae Kim; Charlotte Vastel; Jeong-Eun Lee; Quang Nguyễn Lu’o’; Miju Kang; Isabelle Ristorcelli; Orsolya Fehér; Yuefang Wu; Satoshi Ohashi; Ke Wang; Ryo Kandori; Tomoya Hirota; Takeshi Sakai; Xing Lu; Mark A. Thompson; Gary A. Fuller; Di Li; Hiroko Shinnaga; Jungha Kim
The Astrophysical Journal Supplement Series, American Astronomical Society, 249巻, 2号, 掲載ページ 33-33, 出版日 2020年08月12日
研究論文（学術雑誌） - A new off-point-less observing method for millimeter and submillimeter spectroscopy with a frequency-modulating local oscillator
Taniguchi, Akio; Tamura, Yoichi; Kohno, Kotaro; Takahashi, Shigeru; Horigome, Osamu; Maekawa, Jun; Sakai, Takeshi; Kuno, Nario; Minamidani, Tetsuhiro
Publications of the Astronomical Society of Japan, Oxford University Press (OUP), 72巻, 1号, 掲載ページ id. 2, 出版日 2020年02月, 査読付,Abstract
We propose a new observing method for single-dish millimeter and submillimeter spectroscopy using a heterodyne receiver equipped with a frequency-modulating local oscillator (FMLO). Unlike conventional switching methods, which extract astronomical signals by subtracting the reference spectra of off-sources from those of on-sources, the FMLO method does not need to obtain any off-source spectra; rather, it estimates them from the on-source spectra themselves. The principle uses high-dump-rate (10 Hz) spectroscopy with radio frequency modulation achieved by fast sweeping of a local oscillator of a heterodyne receiver. Because sky emission (i.e., off-source) fluctuates as $1/f$ and is spectrally correlated, it can be estimated and subtracted from time series spectra (a timestream) by principal component analysis. Meanwhile, astronomical signals remain in the timestream since they are modulated to a higher time-frequency domain. The FMLO method therefore achieves (1) a remarkably high observation efficiency, (2) reduced spectral baseline wiggles, and (3) software-based sideband separation. We developed an FMLO system for the Nobeyama $45\:$m telescope and a data reduction procedure for it. Frequency modulation was realized by a tunable and programmable first local oscillator. With observations of Galactic sources, we demonstrate that the observation efficiency of the FMLO method is dramatically improved compared to conventional switching methods. Specifically, we find that the time to achieve the same noise level is reduced by a factor of 3.0 in single-pointed observations and by a factor of 1.2 in mapping observations. The FMLO method can be applied to observations of fainter ($\sim$mK) spectral lines and larger ($\sim$deg$^{2}$) mapping. It offers much more efficient and baseline-stable observations compared to conventional switching methods.
研究論文（学術雑誌）, 英語 - The ALMA Survey of 70 μm Dark High-mass Clumps in Early Stages (ASHES). I. Pilot Survey: Clump Fragmentation
Sanhueza, Patricio; Contreras, Yanett; Wu, Benjamin; Jackson, James M; Guzmán; Andrés E; Zhang, Qizhou; Li, Shanghuo; Lu, Xing; Silva, Andrea; Izumi, Natsuko; Liu, Tie; Miura, Rie E; Tatematsu, Ken’ichi; Sakai, Takeshi; Beuther, Henrik; Garay, Guido; Ohashi, Satoshi; Saito, Masao; Nakamura, Fumitaka; Saigo; Kazuya Veena; V. S; Nguyen-Luong, Quang; Tafoya, Daniel
The Astrophysical Journal, 886巻, 2号, 掲載ページ id. 102, 出版日 2019年12月, 査読付
研究論文（学術雑誌）, 英語 - Sulfur-bearing Species Tracing the Disk/Envelope System in the Class I Protostellar Source Elias 29
Oya, Yoko; López-Sepulcre, Ana; Sakai, Nami; Watanabe, Yoshimasa; Higuchi, Aya E; Hirota, Tomoya; Aikawa, Yuri; Sakai, Takeshi; Ceccarelli, Cecilia; Lefloch, Bertrand; Caux, Emmanuel; Vastel, Charlotte; Kahane, Claudine; Yamamoto, Satoshi
The Astrophysical Journal, 881巻, 2号, 掲載ページ id. 112, 出版日 2019年08月, 査読付
研究論文（学術雑誌）, 英語 - Development of mm/submm broadband anti-reflection coating exploiting the various expanded PTFEs measured with THz-TDS
Tai Oshima; Keisuke Yoshioka; Tatsuya Takekoshi; Kah Wuy Chin; Shinsuke Uno; Takeshi Sakai
ISSTT 2019 - 30th International Symposium on Space Terahertz Technology, Proceedings Book, 掲載ページ 118, 出版日 2019年
研究論文（国際会議プロシーディングス） - An unbiased spectral line survey observation toward the low-mass star-forming region L1527
Yoshida, Kento; Sakai, Nami; Nishimura, Yuri; Tokudome, Tomoya; Watanabe, Yoshimasa; Sakai, Takeshi; Takano, Shuro; Yamamoto, Satoshi
Publications of the Astronomical Society of Japan, psy136巻, 出版日 2019年01月, 査読付
研究論文（学術雑誌）, 英語 - Deuterium Fractionation Survey Toward Protostellar Sources in the Perseus Molecular Cloud: HNC Case
Imai, Muneaki; Sakai, Nami; López-Sepulcre, Ana; Higuchi, Aya E; Zhang, Yichen; Oya, Yoko; Watanabe, Yoshimasa; Sakai, Takeshi; Ceccarelli, Cecilia; Lefloch, Bertrand; Yamamoto, Satoshi
The Astrophysical Journal, 869巻, 1号, 掲載ページ id. 51, 出版日 2018年12月, 査読付
研究論文（学術雑誌）, 英語 - Series-connected array of superconductor-insulator-superconductor junctions in the 100 GHz-band heterodyne mixer for FOREST on the Nobeyama 45 m telescope
Nakajima, Taku; Inoue, Hirofumi; Fujii, Yumi; Miyazawa, Chieko; Iwashita, Hiroyuki; Sakai, Takeshi; Noguchi, Takashi; Mizuno, Akira
Publications of the Astronomical Society of Japan, psy112巻, 出版日 2018年10月, 査読付
研究論文（学術雑誌）, 英語 - Rotation in the NGC 1333 IRAS 4C Outflow
Zhang, Yichen; Higuchi, Aya E; Sakai, Nami; Oya, Yoko; López-Sepulcre, Ana; Imai, Muneaki; Sakai, Takeshi; Watanabe, Yoshimasa; Ceccarelli, Cecilia; Lefloch, Bertrand; Yamamoto, Satoshi
The Astrophysical Journal, 864巻, 1号, 掲載ページ id. 76, 出版日 2018年09月, 査読付
研究論文（学術雑誌）, 英語 - Depletion of 15N in the center of L1544: Early transition from atomic to molecular nitrogen?
Furuya, K; Watanabe, Y; Sakai, T; Aikawa, Y; Yamamoto, S
Astronomy & Astrophysics, 615巻, 掲載ページ id. L16, 出版日 2018年07月, 査読付
研究論文（学術雑誌）, 英語 - Infall Signatures in a Prestellar Core Embedded in the High-mass 70 μm Dark IRDC G331.372-00.116
Contreras, Yanett; Sanhueza, Patricio; Jackson, James M; Guzmán, Andrés E; Longmore, Steven; Garay, Guido; Zhang, Qizhou; Nguyễn-Lu'o'ng, Quang; Tatematsu, Ken'ichi; Nakamura, Fumitaka; Sakai, Takeshi; Ohashi, Satoshi; Liu, Tie; Saito, Masao; Gomez, Laura; Rathborne, Jill; Whitaker, Scott
The Astrophysical Journal, 861巻, 1号, 掲載ページ id. 14, 出版日 2018年07月, 査読付
研究論文（学術雑誌）, 英語 - Magnetic fields at the onset of high-mass star formation
H. Beuther; J. D. Soler; W. Vlemmings; H. Linz; Th. Henning; R. Kuiper; R. Rao; R. Smith; T. Sakai; K. Johnston; A. Walsh; S. Feng
Astronomy and Astrophysics, EDP Sciences, 614巻, 掲載ページ id. A64, 出版日 2018年06月01日, 査読付, Context. The importance of magnetic fields at the onset of star formation related to the early fragmentation and collapse processes is largely unexplored today. Aims. We want to understand the magnetic field properties at the earliest evolutionary stages of high-mass star formation. Methods. The Atacama Large Millimeter Array is used at 1.3 mm wavelength in full polarization mode to study the polarized emission, and, using this, the magnetic field morphologies and strengths of the high-mass starless region IRDC 18310-4. Results. Polarized emission is clearly detected in four sub-cores of the region
in general it shows a smooth distribution, also along elongated cores. Estimating the magnetic field strength via the Davis-Chandrasekhar-Fermi method and following a structure function analysis, we find comparably large magnetic field strengths between ~0.3-5.3 mG. Comparing the data to spectral line observations, the turbulent-to-magnetic energy ratio is low, indicating that turbulence does not significantly contribute to the stability of the gas clump. A mass-to-flux ratio around the critical value 1.0 - depending on column density - indicates that the region starts to collapse, which is consistent with the previous spectral line analysis of the region. Conclusions. While this high-mass region is collapsing and thus at the verge of star formation, the high magnetic field values and the smooth spatial structure indicate that the magnetic field is important for the fragmentation and collapse process. This single case study can only be the starting point for larger sample studies of magnetic fields at the onset of star formation.
研究論文（学術雑誌）, 英語 - HCN J = 4-3, HNC J = 1-0, H13CN J = 1-0, and HC3N J = 10-9 Maps of the Galactic Center Region. I. Spatially Resolved Measurements of Physical Conditions and Chemical Composition
Tanaka, Kunihiko; Nagai, Makoto; Kamegai, Kazuhisa; Iino, Takahiro; Sakai, Takeshi
The Astrophysical Journal Supplement Series, 236巻, 2号, 掲載ページ id. 40, 出版日 2018年06月, 査読付
研究論文（学術雑誌）, 英語 - Chemical Survey toward Young Stellar Objects in the Perseus Molecular Cloud Complex
Higuchi, Aya E; Sakai, Nami; Watanabe, Yoshimasa; López-Sepulcre, Ana; Yoshida, Kento; Oya, Yoko; Imai, Muneaki; Zhang, Yichen; Ceccarelli, Cecilia; Lefloch, Bertrand; Codella, Claudio; Bachiller, Rafael; Hirota, Tomoya; Sakai, Takeshi; Yamamoto, Satoshi
The Astrophysical Journal Supplement Series, 236巻, 2号, 掲載ページ id. 52, 出版日 2018年06月, 査読付
研究論文（学術雑誌）, 英語 - ALMA Observations of the IRDC Clump G34.43+00.24 MM3: Complex Organic and Deuterated Molecules
Takeshi Sakai; Takahiro Yanagida; Kenji Furuya; Yuri Aikawa; Patricio Sanhueza; Nami Sakai; Tomoya Hirota; James M. Jackson; Satoshi Yamamoto
Astrophysical Journal, Institute of Physics Publishing, 857巻, 1号, 掲載ページ id. 35, 出版日 2018年04月10日, 査読付, We have observed complex organic molecules (COMs) and deuterated species toward a hot core/corino (HC) associated with the infrared dark cloud clump G34.43+00.24 MM3 with the Atacama Large Millimeter/submillimeter Array. We have detected six normal-COMs (CH3OH, CH3CHO, CH3CH2CN, CH3OCH3, HCOOCH3, and NH2CHO), one deuterated-COM (CH2DCN), and two deuterated fundamental molecules (D2CO and DNC) toward G34.43+00.24 MM3 HC. None of these lines, except for CH3OH, are detected toward the shocked regions in our data, which suggests that COMs do not originate in shocks. The abundance of the COMs relative to CH3OH in G34.43+00.24 MM3 HC is found to be similar to those in high-mass hot cores, rather than those in hot corinos in low-mass star-forming regions. This result suggests that the physical conditions of the warm-up phase of G34.43+00.24 MM3 HC are similar to those of high-mass sources. On the other hand, the D2CO abundance relative to CH3OH in G34.43+00.24 MM3 HC is higher than that of other hot cores, and seems to be comparable to that of hot corinos. The relatively high D2CO/CH3OH ratio of G34.43+00.24 MM3 HC implies a long cold starless phase of G34.43+00.24 MM3 HC.
研究論文（学術雑誌）, 英語 - Discovery of Striking Difference of Molecular-emission-line Richness in the Potential Proto-binary System NGC 2264 CMM3
Yoshimasa Watanabe; Nami Sakai; Ana Lopez-Sepulcre; Takeshi Sakai; Tomoya Hirota; Sheng-Yuan Liu; Yu-Nung Su; Satoshi Yamamoto
ASTROPHYSICAL JOURNAL, IOP PUBLISHING LTD, 847巻, 2号, 掲載ページ id. 108, 出版日 2017年10月, 査読付, We have conducted an interferometric line survey in the 0.8 mm band toward the young high-mass protostar candidate NGC 2264 CMM3 with ALMA. CMM3 is resolved into the two continuum peaks, CMM3A and CMM3B, at an angular separation of 0 ''.9. Thus, CMM3 is found to be a binary system candidate. We have detected molecular outflows associated with CMM3A and CMM3B each, indicating active star formation. In addition to the two peaks, six faint continuum peaks are detected around CMM3A and CMM3B, most of which are thought to be evolved low-mass protostars. CMM3A is found to be rich in molecular line emission including complex organic molecules such as HCOOCH3 and CH3OCH3. The emission of complex organic molecules is distributed within a compact region around the continuum peak of CMM3A. Hence, CMM3A apparently harbors a hot core. On the other hand, CMM3B is deficient in molecular line emission, although its continuum flux is almost comparable to that of CMM3A. Possible origins of the striking difference between CMM3A and CMM3B are discussed.
研究論文（学術雑誌）, 英語 - On-Wafer Capacitance Measurement of Nb-Based SIS Junctions with a 4-K Probe Station
Takafumi Kojima; Matthias Kroug; Konomi Sato; Takeshi Sakai; Yoshinori Uzawa
IEEE Transactions on Applied Superconductivity, 27巻, 4号, 出版日 2017年06月, 査読付, © 2017 IEEE. This paper presents a method for measuring the capacitance of superconductor-insulator-superconductor (SIS) junctions with a 4-K probe station. The probe station can be used to perform on-wafer characterization of sample lots at frequencies ranging from dc to microwave. In our study, we evaluated SIS junctions that had a variety of areas, and estimated the capacitance after subtracting the parasitic elements of the probe contact pad. The results show that the RNC products for the evaluated junctions were uniform within +/-5% across the wafer.
研究論文（学術雑誌） - Vertical structure of the transition zone from infalling rotating envelope to disc in the Class 0 protostar, IRAS 04368+2557
Nami Sakai; Yoko Oya; Aya E. Higuchi; Yuri Aikawa; Tomoyuki Hanawa; Cecilia Ceccarelli; Bertrand Lefloch; Ana Lopez-Sepulcre; Yoshimasa Watanabe; Takeshi Sakai; Tomoya Hirota; Emmanuel Caux; Charlotte Vastel; Claudine Kahane; Satoshi Yamamoto
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, OXFORD UNIV PRESS, 467巻, 1号, 掲載ページ L76-L80, 出版日 2017年05月, 査読付, We have resolved for the first time the radial and vertical structures of the almost edge-on envelope/disc system of the low-mass Class 0 protostar L1527. For that, we have used Atacama Large Millimetre/submillimetre Array (ALMA) observations with a spatial resolution of 0.25 x 0.13 arcsec(2) and 0.37 x 0.23 arcsec(2) at 0.8 and 1.2 mm, respectively. The L1527 dust continuum emission has a deconvolved size of 78 x 21 au(2), and shows a flared disc-like structure. A thin infalling-rotating envelope is seen in the CCH emission outward of about 150 au, and its thickness is increased by a factor of 2 inward of it. This radius lies between the centrifugal radius (200 au) and the centrifugal barrier of the infalling-rotating envelope (100 au). The gas stagnates in front of the centrifugal barrier and moves towards vertical directions. SO emission is concentrated around and inside the centrifugal barrier. The rotation speed of the SO emitting gas is found to be decelerated around the centrifugal barrier. A part of the angular momentum could be extracted by the gas that moves away from the mid-plane around the centrifugal barrier. If this is the case, the centrifugal barrier would be related to the launching mechanism of low-velocity outflows, such as disc winds.
研究論文（学術雑誌）, 英語 - L483: Warm Carbon-chain Chemistry Source Harboring Hot Corino Activity
Yoko Oya; Nami Sakai; Yoshimasa Watanabe; Aya E. Higuchi; Tomoya Hirota; Ana Lopez-Sepulcre; Takeshi Sakai; Yuri Aikawa; Cecilia Ceccarelli; Bertrand Lefloch; Emmanuel Caux; Charlotte Vastel; Claudine Kahane; Satoshi Yamamoto
ASTROPHYSICAL JOURNAL, IOP PUBLISHING LTD, 837巻, 2号, 掲載ページ id. 174, 出版日 2017年03月, 査読付, The Class 0 protostar, L483, has been observed in various molecular lines in the 1.2 mm band at a subarcsecond resolution with ALMA. An infalling-rotating envelope is traced by the CS line, while a very compact component with a broad velocity width is observed for the CS, SO, HNCO, NH2CHO, and HCOOCH3 lines. Although this source is regarded as the warm carbon-chain chemistry (WCCC) candidate source at a 1000 au scale, complex organic molecules characteristic of hot corinos such as NH2CHO and HCOOCH3 are detected in the vicinity of the protostar. Thus, both hot corino chemistry and WCCC are seen in L483. Although such a mixed chemical character source has been recognized as an intermediate source in previous single-dish observations, we here report the first spatially resolved detection. A kinematic structure of the infalling-rotating envelope is roughly explained by a simple ballistic model with a protostellar mass of 0.1-0.2 M-circle dot and a radius of the centrifugal barrier (half of the centrifugal radius) of 30-200 au, assuming an inclination angle of 80 degrees (0 degrees for face-on). The broad-line emission observed in the above molecules most likely comes from the disk component inside the centrifugal barrier. Thus, a drastic chemical change is seen around the centrifugal barrier.
研究論文（学術雑誌）, 英語 - Low Leakage Current Nb-Based Tunnel Junctions with an Extra Top Al Layer
Mizuki Ikeya; Takashi Noguchi; Takafumi Kojima; Takeshi Sakai
IEICE TRANSACTIONS ON ELECTRONICS, IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG, E100C巻, 3号, 掲載ページ 291-297, 出版日 2017年03月, 査読付, In this paper, we describe the fabrication of low leakage Superconductor/Insulator/Superconductor (SIS) junctions with a Nb/Al/AlOx/Al/Nb structure. In other words, an extra Al layer was added onto the top of the insulator in a conventional Nb/Al/AlOx/Nb junction. We measured the current and voltage (IV) characteristics of both the Nb/Al/AlOx/Al/Nb and Nb/Al/AlOx/Nb junctions at the temperature of liquid helium, and found that the sub-gap leakage current in the Nb/Al/AlOx/Al/Nb junctions was much lower than that of the Nb/Al/AlOx/Nb junctions. Our analysis of the IV characteristics indicates that the quality of the AlOx insulator used in the Nb/Al/AlOx/Al/Nb junction was close to ideal, while the insulator used in the Nb/Al/AlOx/Nb junction had possible defects. According to the scanning transmission electron microscope (STEM) images and energy-dispersive X-ray spectroscopy (EDX) analyses, it was evident that the Nb atoms diffused into the bottom electrode of the Nb/Al/AlOx/Nb junction, while a smaller number diffused into the bottom electrode of the Nb/Al/AlOx/Al/Nb junction. Therefore, we conclude that the extra Al layer effectively acted as a buffer layer that prevented the Nb atoms from diffusing into the insulator and bottom electrode. The presence of the top Al layer is expected to favorably improve the quality of junctions with a very high current density, and support the extension of the RF and IF bandwidths of SIS mixers.
研究論文（学術雑誌）, 英語 - Astrochemical Properties of Planck Cold Clumps
Ken'ichi Tatematsu; Tie Liu; Satoshi Ohashi; Patricio Sanhueza; Quang Nguyen Luong; Tomoya Hirota; Sheng-Yuan Liu; Naomi Hirano; Minho Choi; Miju Kang; Mark A. Thompson; Gary Fuller; Yuefang Wu; Di Li; James Di Francesco; Kee-Tae Kim; Ke Wang; Isabelle Ristorcelli; Mika Juvela; Hiroko Shinnaga; Maria Cunningham; Masao Saito; Jeong-Eun Lee; L. Viktor Toth; Jinhua He; Takeshi Sakai; Jungha Kim
ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES, IOP PUBLISHING LTD, 228巻, 2号, 掲載ページ id. 20, 出版日 2017年02月, 査読付, We observed 13 Planck cold clumps with the James Clerk Maxwell Telescope/SCUBA-2 and with the Nobeyama 45 m radio telescope. The N2H+ distribution obtained with the Nobeyama telescope is quite similar to SCUBA-2 dust distribution. The 82 GHz HC3N, 82 GHz CCS, and 94 GHz CCS emission are often distributed differently with respect to the N2H+ emission. The CCS emission, which is known to be abundant in starless molecular cloud cores, is often very clumpy in the observed targets. We made deep single-pointing observations in DNC, (HNC)-C-13, N2D+, and cyclic-C3H2 toward nine clumps. The detection rate of N2D+ is 50%. Furthermore, we observed the NH3 emission toward 15 Planck cold clumps to estimate the kinetic temperature, and confirmed that most targets are cold (less than or similar to 20 K). In two of the starless clumps we observed, the CCS emission is distributed as it surrounds the N2H+ core (chemically evolved gas), which resembles the case of L1544, a prestellar core showing collapse. In addition, we detected both DNC and N2D+. These two clumps are most likely on the verge of star formation. We introduce the chemical evolution factor (CEF) for starless cores to describe the chemical evolutionary stage, and analyze the observed Planck cold clumps.
研究論文（学術雑誌）, 英語 - Vertical Structure of the Transition Zone from Infalling Rotating Envelope to Disk in the Class 0 Protostar, IRAS04368+2557
Nami Sakai; Yoko Oya; Aya E. Higuchi; Yuri Aikawa; Tomoyuki Hanawa; Cecilia Ceccarelli; B. Lefloch; Ana López-Sepulcre; Yoshimasa Watanabe; Takeshi Sakai; Tomoya Hirota; Emmanuel Caux; Charlotte Vastel; Claudine Kahane; Satoshi Yamamoto
Monthly Notices of the Royal Astronomical Society: Letters, Oxford University Press (OUP), 掲載ページ slx002-slx002, 出版日 2017年01月13日, 査読付
研究論文（学術雑誌） - DISCOVERY OF A HOT CORINO IN THE BOK GLOBULE B335
Muneaki Imai; Nami Sakai; Yoko Oya; Ana Lopez-Sepulcre; Yoshimasa Watanabe; Cecilia Ceccarelli; Bertrand Lefloch; Emmanuel Caux; Charlotte Vastel; Claudine Kahane; Takeshi Sakai; Tomoya Hirota; Yuri Aikawa; Satoshi Yamamoto
ASTROPHYSICAL JOURNAL LETTERS, IOP PUBLISHING LTD, 830巻, 2号, 掲載ページ id. L37, 出版日 2016年10月, 査読付, We report the first evidence of a hot corino in a Bok globule. This is based on ALMA observations in the 1.2 mm band toward the low-mass Class 0 protostar IRAS 19347+ 0727 in B335. Saturated complex organic molecules (COMs), CH3CHO, HCOOCH3, and NH2CHO, are detected in a compact region within a few 10 au around the protostar. Additionally, CH3OCH3, C2H5OH, C2H5CN, and CH3COCH3 are tentatively detected. Carbon-chain related molecules, CCH and c-C3H2, are also found in this source, whose distributions are extended over a scale of a few 100 au. On the other hand, sulfur-bearing molecules CS, SO, and SO2 have both compact and extended components. Fractional abundances of the COMs relative to H-2 are found to be comparable to those in known hot corino sources. Though the COMs lines are as broad as 5-8 km s(-1), they do not show obvious rotation motion in the present observation. Thus, the COMs mainly exist in a structure whose distribution is much smaller than the synthesized beam (0 ''.58 x 0 ''.52).
研究論文（学術雑誌）, 英語 - SUBARCSECOND ANALYSIS OF THE INFALLING-ROTATING ENVELOPE AROUND THE CLASS I PROTOSTAR IRAS 04365+2535
Nami Sakai; Yoko Oya; Ana Lopez-Sepulcre; Yoshimasa Watanabe; Takeshi Sakai; Tomoya Hirota; Yuri Aikawa; Cecilia Ceccarelli; Bertrand Lefloch; Emmanuel Caux; Charlotte Vastel; Claudine Kahane; Satoshi Yamamoto
ASTROPHYSICAL JOURNAL LETTERS, IOP PUBLISHING LTD, 820巻, 2号, 掲載ページ id. L34, 出版日 2016年04月, 査読付, Subarcsecond images of the rotational line emission of CS and SO have been obtained toward the Class I protostar IRAS 04365+2535 in TMC-1A with ALMA. A compact component around the protostar is clearly detected in the CS and SO emission. The velocity structure of the compact component of CS reveals infalling-rotating motion conserving the angular momentum. It is well explained by a ballistic model of an infalling-rotating envelope with the radius of the centrifugal barrier (one-half of the centrifugal radius) of 50 au, although the distribution of the infalling gas is asymmetric around the protostar. The distribution of SO is mostly concentrated around the radius of the centrifugal barrier of the simple model. Thus, a drastic change in chemical composition of the gas infalling onto the protostar is found to occur at a 50 au scale probably due to accretion shocks, demonstrating that the infalling material is significantly processed before being delivered into the disk.
研究論文（学術雑誌）, 英語 - THE DEUTERIUM FRACTION IN MASSIVE STARLESS CORES AND DYNAMICAL IMPLICATIONS
Shuo Kong; Jonathan C. Tan; Paola Caselli; Francesco Fontani; Thushara Pillai; Michael J. Butler; Yoshito Shimajiri; Fumitaka Nakamura; Takeshi Sakai
ASTROPHYSICAL JOURNAL, IOP PUBLISHING LTD, 821巻, 2号, 掲載ページ id. 94, 出版日 2016年04月, 査読付, We study deuterium fractionation in two massive starless/early-stage cores, C1-N and C1-S, in Infrared Dark Cloud G028.37+ 00.07, which was first identified by Tan et al. with ALMA. Line emission from multiple transitions of N2H+ and N2D+ were observed with the ALMA, CARMA, SMA, JCMT, NRO 45 m, and IRAM 30 m telescopes. By simultaneously fitting the spectra, we estimate the excitation conditions and deuterium fraction, D-frac(N2H+) [N2D+]/[N2H+], with values of D-frac(N2H+) similar or equal to 0.2-0.7, several orders of magnitude above the cosmic [D]/[H] ratio. Additional observations of o-H2D+ are also presented that help constrain the ortho-to-para ratio of H-2, which is a key quantity affecting the degree of deuteration. We then present chemodynamical modeling of the two cores, especially exploring the implications for the collapse rate relative to free-fall, aff. In order to reach the high level of observed deuteration of N2H+, we find that the most likely evolutionary history of the cores involves collapse at a relatively slow rate, less than or similar to one-tenth of free-fall.
研究論文（学術雑誌）, 英語 - SPECTRAL-LINE SURVEY AT MILLIMETER AND SUBMILLIMETER WAVELENGTHS TOWARD AN OUTFLOW-SHOCKED REGION, OMC 2-FIR 4
Shimajiri Yoshito; Sakai Takeshi; Kitamura Yoshimi; Tsukagoshi Takashi; Saito Masao; Nakamura Fumitaka; Momose Munetake; Takakuwa Shigehisa; Yamaguchi Takahiro; Sakai Nami; Yamamoto Satoshi; Kawabe Ryohei
ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES, 221巻, 2号, 出版日 2015年12月, 査読付 - Hierarchical fragmentation and collapse signatures in a high-mass starless region
H. Beuther; Th. Henning; H. Linz; S. Feng; S. E. Ragan; R. J. Smith; S. Bihr; T. Sakai; R. Kuiper
ASTRONOMY & ASTROPHYSICS, EDP SCIENCES S A, 581巻, 掲載ページ id.A119, 出版日 2015年09月, 査読付, Aims. We study the fragmentation and collapse properties of the dense gas during the onset of high-mass star formation.
Methods. We observed the massive (similar to 800 M-circle dot) starless gas clump IRDC18310-4 with the Plateau de Bure Interferometer (PdBI) at subarcsecond resolution in the 1.07mm continuum and N2H+(3-2) line emission.
Results. Zooming from a single-dish low-resolution map to previous 3mm PdBI data, and now the new 1.07mm continuum observations, the substructures hierarchically fragment on the increasingly smaller spatial scales. While the fragment separations may still be roughly consistent with pure thermal Jeans fragmentation, the derived core masses are almost two orders of magnitude larger than the typical Jeans mass at the given densities and temperatures. However, the data can be reconciled with models using non-homogeneous initial density structures, turbulence, and/or magnetic fields. While most subcores remain (far-) infrared dark even at 70 mu m, we identify weak 70 mu m emission toward one core with a comparably low luminosity of similar to 16 L-circle dot, supporting the notion of the general youth of the region. The spectral line data always exhibit multiple spectral components toward each core with comparably small line widths for the individual components (in the 0.3 to 1.0 km s(-1) regime). Based on single-dish (CO)-O-18(2-1) data we estimate a low virial-to-gas-mass ratio <= 0.25. We propose that the likely origin of these spectral properties may be the global collapse of the original gas clump that results in multiple spectral components along each line of sight. Even within this dynamic picture the individual collapsing gas cores appear to have very low levels of internal turbulence.
研究論文（学術雑誌）, 英語 - SPECTRAL LINE SURVEY TOWARD THE YOUNG MASSIVE PROTOSTAR NGC 2264 CMM3 IN THE 4 mm, 3 mm, AND 0.8mm BANDS
Yoshimasa Watanabe; Nami Sakai; Ana Lopez-Sepulcre; Ryuta Furuya; Takeshi Sakai; Tomoya Hirota; Sheng-Yuan Liu; Yu-Nung Su; Satoshi Yamamoto
ASTROPHYSICAL JOURNAL, IOP PUBLISHING LTD, 809巻, 2号, 掲載ページ id. 162, 出版日 2015年08月, 査読付, Spectral line survey observations are conducted toward the high-mass protostar candidate NGC 2264 CMM3 in the 4, 3, and 0.8 mm bands with the Nobeyama 45 m telescope and the Atacama Submillimeter Telescope Experiment (ASTE) 10 m telescope. In total, 265 emission lines are detected in the 4 and 3 mm bands, and 74 emission lines in the 0.8 mm band. As a result, 36 molecular species and 30 isotopologues are identified. In addition to the fundamental molecular species, many emission lines of carbon-chain molecules such as HC5N, C4H, CCS, and C3S are detected in the 4 and 3 mm bands. Deuterated molecular species are also detected with relatively strong intensities. On the other hand, emission lines of complex organic molecules such as HCOOCH3 and CH3OCH3 are found to be weak. For the molecules for which multiple transitions are detected, rotation temperatures are derived to be 7-33 K except for CH3OH. Emission lines with high upper-state energies (E-u > 150 K) are detected for CH3OH, indicating the existence of a hot core. In comparison with the chemical composition of the Orion KL, carbon-chain molecules and deuterated molecules are found to be abundant in NGC 2264 CMM3, while sulfur-bearing species and complex organic molecules are deficient. These characteristics indicate the chemical youth of NGC 2264 CMM3 in spite of its location at the center of the cluster forming core, NGC 2264 C.
研究論文（学術雑誌）, 英語 - ALMA OBSERVATIONS OF THE IRDC CLUMP G34.43+00.24 MM3: DNC/HNC RATIO
Takeshi Sakai; Nami Sakai; Kenji Furuya; Yuri Aikawa; Tomoya Hirota; Jonathan B. Foster; Patricio Sanhueza; James M. Jackson; Satoshi Yamamoto
ASTROPHYSICAL JOURNAL, IOP PUBLISHING LTD, 803巻, 2号, 掲載ページ id. 70, 出版日 2015年04月, 査読付, We have observed the clump G34.43+00.24 MM3 associated with an infrared dark cloud in DNC J = 3-2, (HNC)-C-13 J = 3-2, and N2H+ J = 3-2 with the Atacama Large Millimeter/submillimeter Array (ALMA). The N2H+ emission is found to be relatively weak near the hot core and the outflows, and its distribution is clearly anti-correlated with the CS emission. This result indicates that a young outflow is interacting with cold ambient gas. The (HNC)-C-13 emission is compact and mostly emanates from the hot core, whereas the DNC emission is extended around the hot core. Thus, the DNC and (HNC)-C-13 emission traces warm regions near the protostar differently. The DNC emission is stronger than the (HNC)-C-13 emission toward most parts of this clump. The DNC/HNC abundance ratio averaged within a 15 '' x15 '' area around the phase center is higher than 0.06. This ratio is much higher than the value obtained by the previous single-dish observations of DNC and (HNC)-C-13 J = 1-0 (similar to 0.003). It seems likely that the DNC and HNC emission observed with the single-dish telescope traces lower density envelopes, while that observed with ALMA traces higher density and highly deuterated regions. We have compared the observational results with chemical-model results in order to investigate the behavior of DNC and HNC in the dense cores. Taking these results into account, we suggest that the low DNC/HNC ratio in the high-mass sources obtained by the single-dish observations are at least partly due to the low filling factor of the high density regions.
研究論文（学術雑誌）, 英語 - Submillimeter-Wave Observations toward the Low-Mass Protostar IRAS 15398-3359 at Subarcsecond Resolution
Oya Yoko; Sakai Nami; Watanabe Yoshimasa; Yamamoto Satoshi; Sakai Takeshi; Hirota Tomoya; Lindberg Johan E; Bisschop Suzannne E; Jorgensen Jes K; van Dishoeck Ewine F
REVOLUTION IN ASTRONOMY WITH ALMA: THE THIRD YEAR, 499巻, 掲載ページ 221-222, 出版日 2015年, 査読付 - Low-noise 1.5 THz waveguide-type hot-electron bolometer mixers using relatively thick NbTiN superconducting film
Shiino T; Furuya R; Soma T; Watanabe Y; Sakai T; Jiang L; Maezawa H; Yamakura T; Sakai N; Yamamoto S
Japanese Journal of Applied Physics, 54巻, 3号, 出版日 2015年, 査読付
研究論文（学術雑誌）, 英語 - DENSE MOLECULAR CLUMPS ASSOCIATED WITH THE LARGE MAGELLANIC CLOUD SUPERGIANT SHELLS LMC 4 AND LMC 5
Kosuke Fujii; Tetsuhiro Minamidani; Norikazu Mizuno; Toshikazu Onishi; Akiko Kawamura; Erik Muller; Joanne Dawson; Ken'ichi Tatematsu; Tetsuo Hasegawa; Tomoka Tosaki; Rie E. Miura; Kazuyuki Muraoka; Takeshi Sakai; Takashi Tsukagoshi; Kunihiko Tanaka; Hajime Ezawa; Yasuo Fukui
ASTROPHYSICAL JOURNAL, IOP PUBLISHING LTD, 796巻, 2号, 掲載ページ id. 123, 出版日 2014年12月, 査読付, We investigate the effects of supergiant shells (SGSs) and their interaction on dense molecular clumps by observing the Large MagellanicCloud (LMC) star-forming regions N48 and N49, which are located between two SGSs, LMC4 and LMC 5. (CO)-C-12 (J = 3-2, 1-0) and (CO)-C-13(J = 1-0) observations with the ASTE and Mopra telescopes have been carried out toward these regions. A clumpy distribution of dense molecular clumps is revealed with 7 pc spatial resolution. Large velocity gradient analysis shows that the molecular hydrogen densities (n(H-2)) of the clumps are distributed from low to high density (10(3)-10(5) cm(-3)) and their kinetic temperatures (T-kin) are typically high (greater than 50 K). These clumps seem to be in the early stages of star formation, as also indicated from the distribution of Ha, young stellar object candidates, and IR emission. We found that the N48 region is located in the high column density Hi envelope at the interface of the two SGSs and the star formation is relatively evolved, whereas the N49 region is associated with LMC 5 alone and the star formation is quiet. The clumps in the N48 region typically show high n(H-2) and T-kin, which are as dense and warm as the clumps in LMC massive cluster-forming areas (30 Dor, N159). These results suggest that the large-scale structure of the SGSs, especially the interaction of two SGSs, works efficiently on the formation of dense molecular clumps and stars.
研究論文（学術雑誌）, 英語 - A Substellar-mass Protostar and its Outflow of IRAS 15398–3359 Revealed by Subarcsecond-resolution Observations of H2CO and CCH
Oya, Y; Sakai, N; Sakai, T; Watanabe, Y; Hirota, T; Lindberg, J. E; Bisschop, S. E; Jørgensen, J. K; van Dishoeck; E. F; Yamamoto, S
The Astrophysical Journal, IOP PUBLISHING LTD, 795巻, 2号, 掲載ページ id. 152, 出版日 2014年11月, 査読付, Subarcsecond (0 ''.5) images of H2CO and CCH line emission have been obtained in the 0.8 mm band toward the low-mass protostar IRAS 15398-3359 in the Lupus 1 cloud as one of the Cycle 0 projects of the Atacama Large Millimeter/Submillimeter Array. We have detected a compact component concentrated in the vicinity of the protostar and a well-collimated outflow cavity extending along the northeast-southwest axis. The inclination angle of the outflow is found to be about 20 degrees, or almost edge-on, based on the kinematic structure of the outflow cavity. This is in contrast to previous suggestions of a more pole-on geometry. The centrally concentrated component is interpreted by use of a model of the infalling rotating envelope with the estimated inclination angle and the mass of the protostar is estimated to be less than 0.09 M-circle dot. Higher spatial resolution data are needed to infer the presence of a rotationally supported disk for this source, hinted at by a weak high-velocity H2CO emission associated with the protostar.
研究論文（学術雑誌）, 英語 - ALMA OBSERVATIONS OF THE IRDC CLUMP G34.43+00.24 MM3: 278 GHz CLASS I METHANOL MASERS
Takahiro Yanagida; Takeshi Sakai; Tomoya Hirota; Nami Sakai; Jonathan B. Foster; Patricio Sanhueza; James M. Jackson; Kenji Furuya; Yuri Aikawa; Satoshi Yamamoto
ASTROPHYSICAL JOURNAL LETTERS, IOP PUBLISHING LTD, 794巻, 1号, 掲載ページ id. L10, 出版日 2014年10月, 査読付, We have observed a molecular clump (MM3) associated with the infrared dark cloud G34.43+00.24 in the CH3OH J(K) = 9(-1)-8(0) E, 5(0)-4(0) E, and 5(-1)-4(-1) E lines at sub-arcsecond resolution by using the Atacama Large Millimeter/submillimeter Array. By comparing the CH3OH J(K) = 9(-1)-8(0) E emission with the CH3OH 5(0)-4(0) E and 5(-1)-4(-1) E emission, we have found that the CH3OH J(K) = 9(-1)-8(0) E emission is masing. We have clearly shown that the CH3OH J(K) = 9(-1)-8(0) masers arise from the post shocked gas in the interacting regions between the outflows and ambient dense gas. Toward the strongest peak of the CH3OH maser emission, SiO J = 6-5 emission is very weak. This indicates that the CH3OH maser emission traces relatively old shocks or weak shocks.
研究論文（学術雑誌）, 英語 - DISTRIBUTED LOW-MASS STAR FORMATION IN THE IRDC G34.43+00.24
Jonathan B. Foster; Hector G. Arce; Marc Kassis; Patricio Sanhueza; James M. Jackson; Susanna C. Finn; Stella Offner; Takeshi Sakai; Nami Sakai; Satoshi Yamamoto; Andres E. Guzman; Jill M. Rathborne
ASTROPHYSICAL JOURNAL, IOP PUBLISHING LTD, 791巻, 2号, 掲載ページ id. 108, 出版日 2014年08月, 査読付, We have used deep near-infrared observations with adaptive optics to discover a distributed population of low-mass protostars within the filamentary Infrared Dark Cloud G34.43+00.24. We use maps of dust emission at multiple wavelengths to determine the column density structure of the cloud. In combination with an empirically verified model of the magnitude distribution of background stars, this column density map allows us to reliably determine overdensities of red sources that are due to embedded protostars in the cloud. We also identify protostars through their extended emission in the K band, which comes from excited H-2 in protostellar outflows or reflection nebulosity. We find a population of distributed low-mass protostars, suggesting that low-mass protostars may form earlier than, or contemporaneously with, high-mass protostars in such a filament. The low-mass protostellar population may also produce the narrow line-width SiO emission observed in some clouds without high-mass protostars. Finally, we use a molecular line map of the cloud to determine the virial parameter per unit length along the filament and find that the highest mass protostars form in the most bound portion of the filament, as suggested by theoretical models.
研究論文（学術雑誌）, 英語 - A CHEMICAL VIEW OF PROTOSTELLAR-DISK FORMATION IN L1527
Nami Sakai; Yoko Oya; Takeshi Sakai; Yoshimasa Watanabe; Tomoya Hirota; Cecilia Ceccarelli; Claudine Kahane; Ana Lopez-Sepulcre; Bertrand Lefloch; Charlotte Vastel; Sandrine Bottinelli; Emmanuel Caux; Audrey Coutens; Yuri Aikawa; Shigehisa Takakuwa; Nagayoshi Ohashi; Hsi-Wei Yen; Satoshi Yamamoto
ASTROPHYSICAL JOURNAL LETTERS, IOP PUBLISHING LTD, 791巻, 2号, 掲載ページ id. L38, 出版日 2014年08月, 査読付, Subarcsecond images of the rotational line emissions of CCH, CS, H2CO, and CH3OH have been obtained toward the low-mass protostar IRAS 04368 + 2557 in L1527 as one of the early science projects of the Atacama Large Millimeter/submillimeter Array. The intensity distributions of CCH and CS show a double-peaked structure along the edge-on envelope with a dip toward the protostar position, whereas those of H2CO and CH3OH are centrally peaked. By analyzing the position-velocity diagrams along the envelope, CCH and CS are found to reside mainly in the envelope, where the gas is infalling with conservation of its angular momentum. They are almost absent inward of the centrifugal barrier (a half of the centrifugal radius). Although H2CO exists in the infalling rotating envelope, it also resides in the disk component inside the centrifugal barrier to some extent. On the other hand, CH3OH seems to exist around the centrifugal barrier and in the disk component. Hence, the drastic chemical change occurs at the centrifugal barrier. A discontinuous infalling motion as well as the gas-grain interaction would be responsible for the chemical change. This result will put an important constraint on initial chemical compositions for chemical evolution of protostellar disks.
研究論文（学術雑誌）, 英語 - DNC/HNC and N2D+/N2H+ ratios in high-mass star-forming cores
F. Fontani; T. Sakai; K. Furuya; N. Sakai; Y. Aikawa; S. Yamamoto
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, OXFORD UNIV PRESS, 440巻, 1号, 掲載ページ 448-456, 出版日 2014年05月, 査読付, Chemical models predict that the deuterated fraction (the column density ratio between a molecule containing D and its counterpart containing H) of N2H+, D-frac(N2H+), high in massive pre-protostellar cores, is expected to rapidly drop by an order of magnitude after the protostar birth, while that of HNC, D-frac(HNC), remains constant for much longer. We tested these predictions by deriving D-frac(HNC) in 22 high-mass star-forming cores divided in three different evolutionary stages, from high-mass starless core candidates (HMSCs, eight) to high-mass protostellar objects (HMPOs, seven) to ultracompact H ii regions (UCHIIs, seven). For all of them, D-frac(N2H+) was already determined through IRAM 30 m Telescope observations, which confirmed the theoretical rapid decrease of D-frac(N2H+) after protostar birth. Therefore, our comparative study is not affected by biases introduced by the source selection. We have found average D-frac(HNC) of 0.012, 0.009 and 0.008 in HMSCs, HMPOs and UCHIIs, respectively, with no statistically significant differences among the three evolutionary groups. These findings confirm the predictions of the chemical models, and indicate that large values of D-frac(N2H+) are more suitable than large values of D-frac(HNC) to identify cores on the verge of forming high-mass stars, likewise what was found in the low-mass regime.
研究論文（学術雑誌）, 英語 - Kinematic structure of massive star-forming regions I. Accretion along filaments
J. Tackenberg; H. Beuther; Th Henning; H. Linz; T. Sakai; S. E. Ragan; O. Krause; M. Nielbock; M. Hennemann; J. Pitann; A. Schmiedeke
ASTRONOMY & ASTROPHYSICS, EDP SCIENCES S A, 565巻, 掲載ページ id. A101, 出版日 2014年05月, 査読付, Context. The mid- and far-infrared view on high-mass star formation, in particular with the results from the Herschel space observatory, has shed light on many aspects of massive star formation. However, these continuum studies lack kinematic information.
Aims. We study the kinematics of the molecular gas in high-mass star-forming regions.
Methods. We complemented the PACS and SPIRE far-infrared data of 16 high-mass star-forming regions from the Herschel key project EPoS with N2H+ molecular line data from the MOPRA and Nobeyama 45 m telescope. Using the full N2H+ hyperfine structure, we produced column density, velocity, and linewidth maps. These were correlated with PACS 70 mu m images and PACS point sources. In addition, we searched for velocity gradients.
Results. For several regions, the data suggest that the linewidth on the scale of clumps is dominated by outflows or unresolved velocity gradients. IRDC18454 and G11.11 show two velocity components along several lines of sight. We find that all regions with a diameter larger than 1 pc show either velocity gradients or fragment into independent structures with distinct velocities. The velocity profiles of three regions with a smooth gradient are consistent with gas flows along the filament, suggesting accretion flows onto the densest regions.
Conclusions. We show that the kinematics of several regions have a significant and complex velocity structure. For three filaments, we suggest that gas flows toward the more massive clumps are present.
研究論文（学術雑誌）, 英語 - Change in the chemical composition of infalling gas forming a disk around a protostar
Nami Sakai; Takeshi Sakai; Tomoya Hirota; Yoshimasa Watanabe; Cecilia Ceccarelli; Claudine Kahane; Sandrine Bottinelli; Emmanuel Caux; Karine Demyk; Charlotte Vastel; Audrey Coutens; Vianney Taquet; Nagayoshi Ohashi; Shigehisa Takakuwa; Hsi-Wei Yen; Yuri Aikawa; Satoshi Yamamoto
NATURE, NATURE PUBLISHING GROUP, 507巻, 7490号, 掲載ページ 78-+, 出版日 2014年03月, 査読付, IRAS 04368+2557 is a solar-type (low-mass) protostar embedded in a protostellar core (L1527) in the Taurus molecular cloud(1,2), which is only 140 parsecs away from Earth, making it the closest large star-forming region. The protostellar envelope has a flattened shape with a diameter of a thousand astronomical units (1 AU is the distance from Earth to the Sun), and is infalling and rotating(3-5). It also has a protostellar disk with a radius of 90 AU (ref. 6), from which a planetary system is expected to form(7,8). The interstellar gas, mainly consisting of hydrogen molecules, undergoes a change in density of about three orders of magnitude as it collapses from the envelope into the disk, while being heated from 10 kelvin to over 100 kelvin in the mid-plane, but it has hitherto not been possible to explore changes in chemical composition associated with this collapse. Here we report that the unsaturated hydrocarbon molecule cyclic-C3H2 resides in the infalling rotating envelope, whereas sulphur monoxide (SO) is enhanced in the transition zone at the radius of the centrifugal barrier (100 +/- 20 AU), which is the radius at which the kinetic energy of the infalling gas is converted to rotational energy. Such a drastic change in chemistry at the centrifugal barrier was not anticipated, but is probably caused by the discontinuous infalling motion at the centrifugal barrier and local heating processes there.
研究論文（学術雑誌）, 英語 - Anomalous 13C isotope abundances in C3S and C 4H observed toward the cold interstellar cloud, taurus molecular cloud-1
Nami Sakai; Shuro Takano; Takeshi Sakai; Shoichi Shiba; Yoshihiro Sumiyoshi; Yasuki Endo; Satoshi Yamamoto
Journal of Physical Chemistry A, 117巻, 39号, 掲載ページ 9831-9839, 出版日 2013年10月03日, 査読付, We have studied the abundances of the 13C isotopic species of C3S and C4H in the cold molecular cloud, Taurus Molecular Cloud-1 (Cyanopolyyne Peak), by radioastronomical observations of their rotational emission lines. The CCCS/13CCCS and CCCS/C13CCS ratios are determined to be >
206 and 48 ± 15, respectively. The CC13CS line is identified with the aid of laboratory microwave spectroscopy, and the range of the CCCS/CC13CS ratio is found to be from 30 to 206. The abundances of at least two 13C isotopic species of C3S are thus found to be different. Similarly, it is found that the abundances of the four 13C isotopic species of C4H are not equivalent. The CCCCH/13CCCCH, CCCCH/C13CCCH, CCCCH/CC13CCH, and CCCCH/CCC13CH ratios are evaluated to be 141 ± 44, 97 ± 27, 82 ± 15, and 118 ± 23, respectively. Here the errors denote 3 times the standard deviation. These results will constrain the formation pathways of C3S and C 4H, if the nonequivalence is caused during the formation processes of these molecules. The exchange reactions after the formation of these two molecules may also contribute to the nonequivalence. In addition, we have confirmed that the 12C/13C ratio of some species are significantly higher than the interstellar elemental 12C/ 13C ratio of 60-70. The observations of the 13C isotopic species provide us with rich information on chemical processes in cold interstellar clouds. © 2013 American Chemical Society.
研究論文（学術雑誌）, 英語 - Extensive [C I] Mapping toward the orion-a giant molecular cloud
Yoshito Shimajiri; Takeshi Sakai; Takashi Tsukagoshi; Yoshimi Kitamura; Munetake Momose; Masao Saito; Tai Oshima; Kotaro Kohno; Ryohei Kawabe
Astrophysical Journal Letters, 774巻, 2号, 掲載ページ L20, 出版日 2013年09月10日, 査読付, We have carried out wide-field (0.17 deg2) and high-angular resolution (21.″3 ∼ 0.04 pc) observations in the [C I] line toward the Orion-A giant molecular cloud with the Atacama Submillimeter Telescope Experiment 10 m telescope in the On-The-Fly mode. The overall features of the [C I] emission are similar to those of the 12CO (J = 1-0) emission by Shimajiri et al. in 2011
the total intensity ratio of the [C I] to CO emission ranges from 0.05 to 0.2. The optical depth of the [C I] emission is found to be 0.1-0.75, suggesting optically thin emission. The column density of the [C I] emission is estimated to be (1.0-19) × 1017 cm-2. These results are consistent with the results of the previous [C I] observations with a low-angular resolution of 2.′2. In the nearly edge-on photon-dominated regions (PDRs) and their candidates of the Orion Bar, DLSF, M 43 Shell, and Region D, the distributions of the [C I] emission coincide with those of the 12CO emission, inconsistent with the prediction by the plane-parallel PDR model. In addition, the [C I] distribution in the Orion A cloud is found to be more similar to those of the 13CO (J = 1-0), C18O (J = 1-0), and H13CO+ (J = 1-0) lines than that of the 12CO (J = 1-0) line, suggesting that the [C I] emission is not limited to the cloud surface, but is tracing the dense, inner parts of the cloud. © 2013. The American Astronomical Society. All rights reserved.
研究論文（学術雑誌）, 英語 - ALMA OBSERVATIONS OF THE IRDC CLUMP G34.43+00.24 MM3: HOT CORE AND MOLECULAR OUTFLOWS
Takeshi Sakai; Nami Sakai; Jonathan B. Foster; Patricio Sanhueza; James M. Jackson; Marc Kassis; Kenji Furuya; Yuri Aikawa; Tomoya Hirota; Satoshi Yamamoto
ASTROPHYSICAL JOURNAL LETTERS, IOP PUBLISHING LTD, 775巻, 1号, 掲載ページ L31, 出版日 2013年09月, 査読付, We have observed a cluster forming clump (MM3) associated with the infrared dark cloud G34.43+00.24 in the 1.3 mm continuum and the CH3OH, CS, (CS)-C-13, SiO, CH3CH2CN, and HCOOCH3 lines with the Atacama Large Millimeter/submillimeter Array and in K-band with the Keck telescope. We have found a young outflow toward the center of this clump in the SiO, CS, and CH3OH lines. This outflow is likely driven by a protostar embedded in a hot core, which is traced by the CH3CH2CN, HCOOCH3, 13CS, and high excitation CH3OH lines. The size of the hot core is about 800 x 300 AU in spite of its low mass (<1.1 M-circle dot), suggesting a high accretion rate or the presence of multiple star system harboring a few hot corinos. The outflow is highly collimated, and the dynamical timescale is estimated to be less than 740 yr. In addition, we have also detected extended emission of SiO, CS, and CH3OH, which is not associated with the hot core and the outflow. This emission may be related to past star formation activity in the clump. Although G34.43+00.24 MM3 is surrounded by a dark feature in infrared, it has already experienced active formation of low-mass stars in an early stage of clump evolution.
研究論文（学術雑誌）, 英語 - Fragmentation and dynamical collapse of the starless high-mass star-forming region IRDC 18310-4
H. Beuther; H. Linz; J. Tackenberg; Th. Henning; O. Krause; S. Ragan; M. Nielbock; R. Launhardt; S. Bihr; A. Schmiedeke; R. Smith; T. Sakai
ASTRONOMY & ASTROPHYSICS, EDP SCIENCES S A, 553巻, 掲載ページ id, A115, 出版日 2013年05月, 査読付, Context. Because of their short evolutionary time-scales, the earliest stages of high-mass star formation prior to the existence of any embedded heating source have barely been characterized until today.
Aims. We study the fragmentation and dynamical properties of a massive starless gas clump at the onset of high-mass star formation.
Methods. Based on Herschel continuum data we identify a massive gas clump that remains far-infrared dark up to 100 mu m wavelengths. The fragmentation and dynamical properties are investigated by means of Plateau de Bure Interferometer and Nobeyama 45 m single-dish spectral line and continuum observations.
Results. The massive gas reservoir (between similar to 800 and similar to 1600 M-circle dot, depending on the assumed dust properties) fragments at spatial scales of similar to 18 000 AU in four cores. Comparing the spatial extent of this high-mass region with intermediate-to low-mass starless cores from the literature, we find that linear sizes do not vary significantly over the whole mass regime. However, the high-mass regions squeeze much more gas into these similar volumes and hence have orders of magnitude larger densities. The fragmentation properties of the presented low-to high-mass regions are consistent with gravitational instable Jeans fragmentation. Furthermore, we find multiple velocity components associated with the resolved cores. Recent radiative transfer hydrodynamic simulations of the dynamic collapse of massive gas clumps also result in multiple velocity components along the line of sight because of the clumpy structure of the regions. This result is supported by a ratio between viral and total gas mass for the whole region <1.
Conclusions. This apparently still starless high-mass gas clump exhibits clear signatures of early fragmentation and dynamic collapse prior to the formation of an embedded heating source. A comparison with regions of lower mass reveals that the linear size of star-forming regions does not necessarily have to vary much for different masses, however, the mass reservoirs and gas densities are orders of magnitude enhanced for high-mass regions compared to their lower-mass siblings.
研究論文（学術雑誌）, 英語 - A New 100-GHz Band Two-Beam Sideband-Separating SIS Receiver for Z-Machine on the NRO 45-m Radio Telescope
T. Nakajima; K. Kimura; A. Nishimura; H. Iwashita; C. Miyazawa; T. Sakai; D. Iono; K. Kohno; R. Kawabe; N. Kuno; H. Ogawa; S. Asayama; T. Tamura; T. Noguchi
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF THE PACIFIC, UNIV CHICAGO PRESS, 125巻, 925号, 掲載ページ 252-262, 出版日 2013年03月, 査読付, We have developed a two-beam waveguide-type dual-polarization sideband-separating SIS receiver system in the 100-GHz band for z-machine on the 45-m radio telescope at the Nobeyama Radio Observatory. The receiver is intended for astronomical use in searching for highly redshifted spectral lines from galaxies of unknown redshift. This receiver has two beams, which have 45 '' of beam separation and allow for observation with the switch in the on-on position. The receiver of each beam is composed of an ortho-mode transducer and two sideband-separating SIS mixers, which are both based on a waveguide technique, and the receiver has four intermediate frequency bands of 4.0-8.0 GHz. Over the radio frequency range of 80-116 GHz, the single-sideband receiver noise temperature is lower than about 50 K, and the image rejection ratios are greater than 10 dB in most of the same frequency range. The new receiver system has been installed in the telescope, and we successfully observed a 12CO (J = 3-2) emission line toward a cloverleaf quasar at z = 2.56, which validates the performance of the receiver system. The SSB noise temperature of the system, including the atmosphere, is typically 150-300 K at a radio frequency of 97 GHz. We have begun a blind search of high-J CO toward high-z submillimeter galaxies.
研究論文（学術雑誌）, 英語 - Nobeyama 45m Telescope Legacy Project: Line Survey
S. Takano; Y. Aikawa; V. Chen; N. Hirano; T. Hirota; K. Kamegai; K. Kobayashi; K. Kohno; Y-J. Kuan; S. -Y. Liu; T. Nakajima; N. Ohashi; M. Ohishi; H. Ozeki; N. Sakai; T. Sakai; S. Shiba; Y. -N. Su; M. Sugimura; S. Takakuwa; T. Umemoto; K. -S. Wang; Y. Watanabe; M. Yamada; T. Yamaguchi; S. Yamamoto; Q. -Z. Zhang
NEW TRENDS IN RADIO ASTRONOMY IN THE ALMA ERA: THE 30TH ANNIVERSARY OF NOBEYAMA RADIO OBSERVATORY, ASTRONOMICAL SOC PACIFIC, 476巻, 掲載ページ 193-196, 出版日 2013年, 査読付, We carried out a new line survey project between December 2007 and May 2012. The target sources are interesting low and high -mass star forming regions (L1527, L1157 B 1, and G28.34+0.06), and nearby galaxies (NGC 1068, NGC 253, and IC 342). As a result, many molecular lines were detected: For example, various carbon chain molecules in L1527, organic molecules and PN in L1157 Bl, organic molecules and deuterated molecules in G28.34+0.06, and fundamental molecules including relatively strong HCN and CN in NGC 1068. For their details, see the related papers in this proceedings.
研究論文（国際会議プロシーディングス）, 英語 - Test Observations of a New 100 GHz Wave-Band FOur-beam REceiver System on the Nobeyama 45-m Telescope (FOREST)
Kazuyuki Muraoka; Kana Matsui; Toshiya Akashi; Nario Kuno; Hiroyuki Iwashita; Chieko Miyazawa; Makoto Koyano; Hiroyuki Baji; Jun Maekawa; Taku Nakajima; Sachiko Onodera; Takeshi Sakai; Kimihiro Kimura; Hiroyuki Maezawa; Toshikazu Onishi; Hideo Ogawa
NEW TRENDS IN RADIO ASTRONOMY IN THE ALMA ERA: THE 30TH ANNIVERSARY OF NOBEYAMA RADIO OBSERVATORY, ASTRONOMICAL SOC PACIFIC, 476巻, 掲載ページ 417-418, 出版日 2013年
研究論文（国際会議プロシーディングス）, 英語 - The 0.9 and 1.3 THz Superconducting HEB Mixer Receiver for the ASTE 10 m Telescope
Shiino T; Furuya R; Soma T; Sakai T; Watanabe Y; Sakai N; Jiang L; Ohguchi O; Maezawa H; Yamakura T; Yamamoto S; Kuno N
New Trends in Radio Astronomy in the ALMA Era: The 30th Anniversary of Nobeyama Radio Observatory, 出版日 2013年, 査読付 - Observations of Deuterated Species toward Low-Mass Prestellar and Protostellar Cores
Nishimura Yuri; Sakai Nami; Watanabe Yoshimasa; Sakai Takeshi; Hirota Tomoya; Yamamoto Satoshi
NEW TRENDS IN RADIO ASTRONOMY IN THE ALMA ERA: THE 30TH ANNIVERSARY OF NOBEYAMA RADIO OBSERVATORY, 476巻, 掲載ページ 343-344, 出版日 2013年, 査読付 - Spectral-Line Survey at Millimeter and Submillimeter Wavelengths toward an Outflow-Shocked Region, OMC2-FIR 4
Yoshito Shimajiri; T. Sakai; Y. Kitamura; T. Tsukagoshi; M. Saito; F. Nakamura; M. Momose; R. Kawabe
NEW TRENDS IN RADIO ASTRONOMY IN THE ALMA ERA: THE 30TH ANNIVERSARY OF NOBEYAMA RADIO OBSERVATORY, ASTRONOMICAL SOC PACIFIC, 476巻, 2号, 掲載ページ 341-342, 出版日 2013年, 査読付, We performed a spectral-line survey toward the three positions, an outflow shocked region, OMC2-FIR 4, in addition to the driving source of the molecular outflow, FIR 3, and the northern outflow lobe, FIR 3N, with the Nobeyama 45 m and ASTE telescopes. We detected more than 100 molecular lines. We found that the line profiles can be classified into the following two types: a single Gaussian component with a narrow (< 3 km s(-1)) velocity width and two Gaussian components with narrow and wide (> 3 km s(-1)) velocity widths. The wide components of CO, CS, HCO+, and HCN are also detected at three positions including FIR 3N, suggesting that these trace the molecular outflow. On the other hand, the wide components of SiO, SO, (CS)-S-34, CH3OH, (HCN)-C-13, and (HCN)-C-15 isotopes are detected only at the outflow shocked region, FIR 4, suggesting that these trace the outflow-shocked gas. In addition, the rotation diagram analysis revealed that the narrow components in both the two profile types correspond to the gas with a low temperature of 20-30 K, while the wide components trace a high temperature of 50-150 K. These results support our interpretation that the wide velocity components trace the molecular outflow and/or outflow-shocked gas.
研究論文（国際会議プロシーディングス）, 英語 - TENTATIVE DETECTION OF DEUTERATED METHANE TOWARD THE LOW-MASS PROTOSTAR IRAS 04368+2557 IN L1527
Nami Sakai; Yancy L. Shirley; Takeshi Sakai; Tomoya Hirota; Yoshimasa Watanabe; Satoshi Yamamoto
ASTROPHYSICAL JOURNAL LETTERS, IOP PUBLISHING LTD, 758巻, 1号, 掲載ページ id. L4, 出版日 2012年10月, 査読付, The millimeter-wave rotational transition line (J(K) = 1(0)-0(0)) of deuterated methane CH3D has tentatively been detected toward the low-mass Class 0 protostar IRAS 04368+2557 in L1527 with the Heinrich Hertz Submillimeter Telescope. This is the first detection of CH3D in interstellar clouds, if confirmed. The column density and fractional abundance of CH3D are determined to be (9.1 +/- 3.4) x 10(15) cm(-2) and (3.0 +/- 1.1) x 10(-7), respectively, where we assume the rotational temperature of 25 K. The column density and fractional abundance of the gaseous CH4 are estimated to be (1.3-4.6) x 10(17) cm(-2) and (4.3-15.2) x 10(-6), respectively, by adopting the molecular D/H ratios of 2%-7% reported for various molecules in L1527. The fractional abundance of CH4 is higher than or comparable to that found in high-mass star-forming cores by infrared observations. It is sufficiently high to trigger the efficient production of various carbon-chain molecules in a lukewarm region near the protostar, which supports the scenario of warm carbon-chain chemistry.
研究論文（学術雑誌）, 英語 - CH radio emission from Heiles Cloud 2 as a tracer of molecular cloud evolution
N. Sakai; H. Maezawa; T. Sakai; K. M. Menten; S. Yamamoto
ASTRONOMY & ASTROPHYSICS, EDP SCIENCES S A, 546巻, 掲載ページ id. A103, 出版日 2012年10月, 査読付, Aims. A mapping observation of the J = 1/2 Lambda-type doubling transition (3.3 GHz) of CH has been conducted toward Heiles Cloud 2 (HCL2) in the Taurus molecular cloud complex to reveal its molecular cloud-scale distribution.
Methods. The observations were carried out with the Effelsberg 100 m telescope.
Results. The CH emission is found to be extended over the whole region of HCL2. It is brighter in the southeastern part, which encloses the TMC-1 cyanopolyyne peak than in the northwestern part. Its distribution extends continuously from the peak of the neutral carbon emission (CI peak) to the TMC-1 ridge, as if it were connecting the distributions of the [CI] and (CO)-O-18 emissions. Since CH is an intermediate in gas-phase chemical reactions from C to CO, its emission should trace the transition region. The above distribution of the CH emission is consistent with this chemical behavior. Since the CH abundance is subject to the chemical evolutionary effect, the CH column density in HCL2 no longer follows a linear correlation wit the H-2 column density reported for diffuse and translucent clouds. More importantly, the CH line profile is found to be composed of the narrow and broad components. Although the broad component is dominant around the CI peak, the narrow component appears in the TMC-1 ridge and dense core regions such as L1527 and TMC-1A. This trend seems to reflect a narrowing of the line width during the formation of dense cores. These results suggest that the 3.3 GHz CH line is a useful tool for tracing the chemical and physical evolution of molecular clouds.
研究論文（学術雑誌）, 英語 - Extremely Strong (CO)-C-13 J=3 -> 2 Line in the "Water Fountain" IRAS 16342-3814: Evidence for the Hot-Bottom Burning
Hiroshi Imai; Sze Ning Chong; Jin-Hua He; Jun-ichi Nakashima; Chih-Hao Hsia; Takeshi Sakai; Shuji Deguchi; Nico Koning
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN, OXFORD UNIV PRESS, 64巻, 5号, 掲載ページ No. 5, 出版日 2012年10月, 査読付, We observed four "water fountain" sources in the CO J = 3 -> 2 line emission with the Atacama Submillimeter Telescope Experiment (ASTE) 10 m telescope in 2010-2011. The water fountain sources are evolved stars that form high-velocity collimated jets traced by H2O maser emission. The CO line was detected only from IRAS 16342-3814. The present work confirmed that the (CO)-C-12 to (CO)-C-13 line intensity ratio is similar to 1.5 at the systemic velocity. We discuss the origins of the very low (CO)-C-12-to-(CO)-C-13 intensity ratio, as possible evidence for "hot-bottom burning" in an oxygen-rich star, and the CO intensity variation in IRAS 16342-3814.
研究論文（学術雑誌）, 英語 - The 3 mm Spectral Line Survey toward the Lynds 1157 B1 Shocked Region. I. Data
Takahiro Yamaguchi; Shuro Takano; Yoshimasa Watanabe; Nami Sakai; Takeshi Sakai; Sheng-Yuan Liu; Yu-Nung Su; Naomi Hirano; Shigehisa Takakuwa; Yuri Aikawa; Hideko Nomura; Satoshi Yamamoto
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN, OXFORD UNIV PRESS, 64巻, 5号, 掲載ページ A105, 出版日 2012年10月, 査読付, We have conducted a spectral line survey of the 3 mm band with the 45 m telescope of Nobeyama Radio Observatory toward the L 1157 B1 shocked region, where the blue-shifted component of the bipolar outflow from the protostar IRAS 20386+6751 interacts with the ambient gas. The observed frequency ranges from 78.1 to 115.8 GHz. We have detected 129 spectral lines of 29 molecular species. In addition to various oxygen-bearing organic molecules such as CH3CHO, HCOOCH3, and HCOOH, we have detected a phosphorus-containing molecule PN, a nitrogen-bearing organic molecule NH2CHO, and a carbon-chain molecule CCS in the shocked region. These results clearly indicate that the L 1157 B1 shocked region is chemically rich, which is probably triggered by evaporation of grain mantles.
研究論文（学術雑誌）, 英語 - Initial Results from Nobeyama Molecular Gas Observations of Distant Bright Galaxies
lONO Daisuke; HATSUKADE Bunyo; KOHNO Kotaro; KAWABE Ryohei; IKARASHI Soh; ICHIKAWA Kohei; KODAMA Tadayuki; MOTOHARA Kentaro; NAKAJIMA Taku; NAKANISHI Koichiro; OHTA Kouji; OTA Kazuaki; SAITO Toshiki; SUZUKI Kenta; TADAKI Ken-ichi; TAMURA Yoichi; UEDA Junko; UMEHATA Hideki; YABE Kiyoto; YOSHIDA Tessei; YUMA Suraphong; KUNO Nario; TAKANO Shuro; IWASHITA Hiroyuki; HANDA Kazuyuki; HIGUCHI Aya; HIROTA Akihiko; ISHIKAWA Shinichi; KIMURA Kimihiro; MAEKAWA Jun; MIKOSHIBA Hiroshi; MIYAZAWA Chieko; MIYAZAWA Kazuhiko; MURAOKA Kazuyuki; OGAWA Hideo; ONODERA Sachiko; SAITO Yasufumi; SAKAI Takeshi; TAKAHASHI Shigeru; YUN Min S.
PASJ : publications of the Astronomical Society of Japan, Astronomical Society of Japan, 64巻, 4号, 掲載ページ "L2-1"-"L2-4", 出版日 2012年08月25日, 査読付
研究論文（学術雑誌）, 英語 - DISTRIBUTION OF CH3OH IN NGC 1333 IRAS4B
Nami Sakai; Cecilia Ceccarelli; Sandrine Bottinelli; Takeshi Sakai; Satoshi Yamamoto
ASTROPHYSICAL JOURNAL, IOP PUBLISHING LTD, 754巻, 1号, 掲載ページ id. 70, 出版日 2012年07月, 査読付, Distribution of the CH3OH (J(K) = 2(K)-1(K), 96.7 GHz) emission has been investigated toward NGC 1333 IRAS4B, a low-mass Class 0 protostar which harbors a hot corino, with Nobeyama Millimeter Array. The CH3OH emission is found to be prominent in the shocked region caused by an impact of the molecular outflow from the protostars. The direction of the outflow which is responsible for the shock seems to be opposite to that of a compact outflow known previously in the CO (J = 2-1), HCN (J = 1-0), H2CO (3(12)-2(11)), and CH3OH (J(K) = 7(K)-6(K)) emissions, whereas it is the same as that of the faint second outflow found in the H2CO emission. This double outflow structure can be interpreted most naturally by the existence of more than two protostars in IRAS4B. On the other hand, a centrally condensed component associated apparently with IRAS4B cannot be recognized in our CH3OH observation. Our observation suggests that, in this source, the CH3OH (J(K) = 2(K)-1(K)) emission preferentially traces the shocked regions rather than the hot corino around the protostar.
研究論文（学術雑誌）, 英語 - DNC/HNC RATIO OF MASSIVE CLUMPS IN EARLY EVOLUTIONARY STAGES OF HIGH-MASS STAR FORMATION
Takeshi Sakai; Nami Sakai; Kenji Furuya; Yuri Aikawa; Tomoya Hirota; Satoshi Yamamoto
ASTROPHYSICAL JOURNAL, IOP PUBLISHING LTD, 747巻, 2号, 掲載ページ id. 140, 出版日 2012年03月, 査読付, We have observed the (HNC)-C-13 J = 1-0 and DNC J = 1-0 lines toward 18 massive clumps, including infrared dark clouds (IRDCs) and high-mass protostellar objects (HMPOs), by using the Nobeyama Radio Observatory 45 m telescope. We have found that the (HNC)-C-13 emission is stronger than the DNC emission toward all of the observed sources. The averaged DNC/HNC ratio is indeed lower toward the observed high-mass sources (0.009 +/- 0.005) than toward the low-mass starless and star-forming cores (0.06). The kinetic temperature derived from the NH3 (J, K) = (1, 1) and (2, 2) line intensities is higher toward the observed high-mass sources than toward the low-mass cores. However, the DNC/HNC ratio of some IRDCs involving the Spitzer 24 mu m sources is found to be lower than that of HMPOs, although the kinetic temperature of the IRDCs is lower than that of the HMPOs. This implies that the DNC/HNC ratio does not depend only on the current kinetic temperature. With the aid of chemical model simulations, we discuss how the DNC/HNC ratio decreases after the birth of protostars. We suggest that the DNC/HNC ratio in star-forming cores depends on the physical conditions and history in their starless-core phase, such as its duration time and the gas kinetic temperature.
研究論文（学術雑誌）, 英語 - The onset of high-mass star formation in the direct vicinity of the Galactic mini-starburst W43
H. Beuther; J. Tackenberg; H. Linz; Th. Henning; O. Krause; S. Ragan; M. Nielbock; R. Launhardt; A. Schmiedeke; F. Schuller; P. Carlhoff; Q. Nguyen-Luong; T. Sakai
ASTRONOMY & ASTROPHYSICS, EDP SCIENCES S A, 538巻, 掲載ページ A11, 出版日 2012年02月, 査読付, Context. The earliest stages of high-mass star formation are still poorly characterized. Densities, temperatures and kinematics are crucial parameters for simulations of high-mass star formation. It is also unknown whether the initial conditions vary with environment.
Aims. We want to investigate the youngest massive gas clumps in the environment of extremely active star formation.
Methods. We selected the IRDC 18454 complex, directly associated with the W43 Galactic mini-starburst, and observed it in the continuum emission between 70 mu m and 1.2 mm with Herschel, APEX and the 30 m telescope, and in spectral line emission of N2H+ and (CO)-C-13 with the Nobeyama 45 m, the IRAM 30 m and the Plateau de Bute Interferometer.
Results. The multi-wavelength continuum study allows us to identify clumps that are infrared dark even at 70 mu m and hence the best candidates to be genuine high-mass starless gas clumps. The spectral energy distributions reveal elevated temperatures and luminosities compared to more quiescent environments. Furthermore, we identify a temperature gradient from the W43 mini-starburst toward the starless clumps. We discuss whether the radiation impact of the nearby mini-starburst changes the fragmentation properties of the gas clumps and by that maybe favors more high-mass star formation in such an environment. The spectral line data reveal two different velocity components of the gas at 100 and 50 kms(-1). While chance projection is a possibility to explain these components, the projected associations of the emission sources as well as the prominent location at the Galactic bar - spiral arm interface also allow the possibility that these two components may be spatially associated and even interacting.
Conclusions. High-mass starless gas clumps can exist in the close environment of very active star formation without being destroyed. The impact of the active star formation sites may even allow for more high-mass stars to form in these 2nd generation gas clumps. This particular region near the Galactic bar - spiral arm interface has a broad distribution of gas velocities, and cloud interactions may be possible.
研究論文（学術雑誌）, 英語 - Detection of Phosphorus Nitride in the Lynds 1157 B1 Shocked Region
Yamaguchi Takahiro; Takano Shuro; Sakai Nami; Sakai Takeshi; Liu Sheng-Yuan; Su Yu-Nung; Hirano Naomi; Takakuwa Shigehisa; Aikawa Yuri; Nomura Hideko; Yamamoto Satoshi
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN, 63巻, 5号, 掲載ページ L37-L41, 出版日 2011年10月25日, 査読付 - DETECTION OF TWO CARBON-CHAIN-RICH CORES: CB130-3 AND L673-SMM4
Tomoya Hirota; Takeshi Sakai; Nami Sakai; Satoshi Yamamoto
ASTROPHYSICAL JOURNAL, IOP PUBLISHING LTD, 736巻, 1号, 掲載ページ id. 4, 出版日 2011年07月, 査読付, We have found two dense cores, CB130-3 and L673-SMM4, where the carbon-chain molecules are extremely abundant relative to NH3, during a survey observation of radio emission lines of CCS, HC3N, HC5N, and NH3 toward dark cloud cores. Judging from the low NH3/CCS ratios, they are possible candidates for "Carbon-Chain-Producing Regions" (CCPRs) recognized as chemically young dark cloud cores. The deuterium fractionation ratios DNC/(HNC)-C-13 in CB130-3 and L673-SMM4 are found to be 1.28(-0.05)(+0.27) and 1.96(-0.01)(+0.32), respectively, which are comparable to or slightly higher than those in CCPRs found previously. We suggest that the dense cores of CB130-3 and L673-SMM4 are analogous to CCPRs, but their chemical evolutionary phase would be slightly older than those of the dense cores in the Taurus region.
研究論文（学術雑誌）, 英語 - Early Results of the 3 mm Spectral Line Survey toward the Lynds 1157 B1 Shocked Region
Mika Sugimura; Takahiro Yamaguchi; Takeshi Sakai; Tomofumi Umemoto; Nami Sakai; Shuro Takano; Yuri Aikawa; Naomi Hirano; Sheng-Yuan Liu; T. J. Millar; Hideko Nomura; Yu-Nung Su; Shigehisa Takakuwa; Satoshi Yamamoto
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN, OXFORD UNIV PRESS, 63巻, 2号, 掲載ページ 459-472, 出版日 2011年04月, 査読付, We have conducted a sensitive 3 mm observation toward the shocked region, Lynds 1157 B1, which is an interaction spot between a molecular outflow and its ambient gas. We have successfully detected the CH3CHO, HCOOCH3, and HCOOH lines, as well as the CH2DOH Line. The abundances of these molecules relative to CH3OH are found to be lower than those in the low-mass star-forming core, IRAS 16293-2422. Since these molecules are thought to evaporate from grain mantles, the observational results mean that complex molecules are less abundant in grain mantles residing in the ambient cloud surrounding a prestellar/protostellar core. Instead, efficient formation of the complex organic species and deuterated species should take place in a prestellar/protostellar core. The present result verifies the importance of an unbiased line survey of this source.
研究論文（学術雑誌）, 英語 - COMPACT MOLECULAR OUTFLOW FROM NGC 2264 CMM3: A CANDIDATE FOR VERY YOUNG HIGH-MASS PROTOSTAR
Osamu Saruwatari; Nami Sakai; Sheng-Yuan Liu; Yu-Nung Su; Takeshi Sakai; Satoshi Yamamoto
ASTROPHYSICAL JOURNAL, IOP PUBLISHING LTD, 729巻, 2号, 掲載ページ id. 147, 出版日 2011年03月, 査読付, We have conducted a high-resolution observation of the molecular outflow with the CO (J = 2-1) and CH3OH (J(K) = 5(K)-4(K), K = 0, 3) lines toward a high-mass protostar candidate, NGC 2264 CMM3, using the Submillimeter Array. A compact north-south bipolar outflow of 10 '' in size associated with CMM3 is found in both CO and CH3OH emission. The outflow dynamical age is estimated to be as young as 140-2000 yr. Together with the non-detection of any 24 mu m source with the Spitzer Space Telescope, the result suggests that CMM3 likely harbors a young massive star at its very early evolutionary stage. The CH3OH outflow lobes are slightly offset outside those of the CO outflow, which indicates that the interaction between the outflow and the dense ambient gas causes a shock around the CO peak position, and the CH3OH molecule evaporated from the grain mantles is swept away from the shock front. The interaction is particularly strong in the southern (red) lobe, as indicated by the detection of the high excitation line of CH3OH (K = 3). The outflow seems to affect the chemical composition of CMM3 significantly.
研究論文（学術雑誌）, 英語 - DENSE CLUMPS IN GIANT MOLECULAR CLOUDS IN THE LARGE MAGELLANIC CLOUD: DENSITY AND TEMPERATURE DERIVED FROM (CO)-C-13(J=3-2) OBSERVATIONS
Tetsuhiro Minamidani; Takanori Tanaka; Yoji Mizuno; Norikazu Mizuno; Akiko Kawamura; Toshikazu Onishi; Tetsuo Hasegawa; Ken'ichi Tatematsu; Tatsuya Takekoshi; Kazuo Sorai; Nayuta Moribe; Kazufumi Torii; Takeshi Sakai; Kazuyuki Muraoka; Kunihiko Tanaka; Hajime Ezawa; Kotaro Kohno; Sungeun Kim; Monica Rubio; Yasuo Fukui
ASTRONOMICAL JOURNAL, IOP PUBLISHING LTD, 141巻, 3号, 掲載ページ id. 73, 出版日 2011年03月, 査読付, In order to precisely determine the temperature and density of molecular gas in the Large Magellanic Cloud, we made observations of the optically thin (CO)-C-13(J = 3-2) transition using the ASTE 10 m telescope toward nine peaks where (CO)-C-12(J = 3-2) clumps were previously detected with the same telescope. The molecular clumps include those in giant molecular cloud (GMC) Types I (with no signs of massive star formation), II ( with H II regions only), and III (with H II regions and young star clusters). We detected (CO)-C-13(J = 3-2) emission toward all the peaks and found that their intensities are 3-12 times lower than those of (CO)-C-12(J = 3-2). We determined the intensity ratios of (CO)-C-12(J = 3-2) to (CO)-C-13(J = 3-2), R-3-2(12/13), and (CO)-C-13(J = 3-2) to (CO)-C-13(J = 1-0), R-3-2/1-0(13), at 45 '' resolution. These ratios were used in radiative transfer calculations in order to estimate the temperature and density of the clumps. The clumps have a kinetic temperature range of T-kin = 15-200 K and a molecular hydrogen gas density range of n(H-2) = 8 x 10(2)-7 x 10(3) cm(-3). We confirmed that the higher density clumps have higher kinetic temperature and that the lower density clumps have lower kinetic temperature to better accuracy than in previous work. The kinetic temperature and density increase generally from a Type I GMC to a Type III GMC. We interpret that this difference reflects an evolutionary trend of star formation in molecular clumps. The R-3-2/1-0(13) and kinetic temperature of the clumps are well correlated with the Ha flux, suggesting that the heating of molecular gas with density n(H-2) = 10(3)-10(4) cm(-3) can be explained by stellar far-ultravoilet photons.
研究論文（学術雑誌）, 英語 - LINE SURVEY OF L1157 B1 SHOCKED REGION
T. Yamaguchi; M. Sugimura; T. Sakai; N. Sakai; S. Takano; Y. Aikawa; N. Hirano; S. -L. Liu; H. Nomura; Y. -N. Su; S. Takakuwa; S. Yamamoto
CONDITIONS AND IMPACT OF STAR FORMATION: NEW RESULTS WITH HERSCHEL AND BEYOND, E D P SCIENCES, 52巻, 掲載ページ 311-+, 出版日 2011年, 査読付, We present the initial results of a spectral line survey of L1157 B1 with the Nobeyama 45 m telescope. So far, we have covered the frequencey range of 13.7 GHz (82.0-94.5 GHz and 96.3-97.5 GHz), and have detected 22 species including CH3CHO, HCOOH, HCOOCH3, HNCO, NH2CHO, CH3CN, and CCS. We have also detected the line of CH2DOH. These results demonstrate rich chemistry in this shocked region, which would mainly originate from evaporation of ice mantles by means of shocks.
研究論文（国際会議プロシーディングス）, 英語 - DISTRIBUTIONS OF CARBON-CHAIN MOLECULES IN L1527
Nami Sakai; Takeshi Sakai; Tomoya Hirota; Satoshi Yamamoto
ASTROPHYSICAL JOURNAL, IOP PUBLISHING LTD, 722巻, 2号, 掲載ページ 1633-1643, 出版日 2010年10月, 査読付, The distributions of CCH, C(4)H, c-C(3)H(2), and HC(5)N have been studied in high spatial resolution with the Plateau de Bure Interferometer, where the short-spacing data have been taken with the IRAM 30 m telescope. The distributions show clear central condensation around the protostar, confirming that these molecules are associated with the protostar's environment. The blueshifted and redshifted components are concentrated near the protostar, indicating their existence in the infalling envelope. The intensity distribution of c-C(3)H(2) shows a steep increase inward of a radius of 500-1000 AU from the protostar. By comparing the c-C(3)H(2) distribution with the H(2) column density distribution from the protostellar envelope model using the DUSTY code, the abundance of c-C(3)H(2) is found to be enhanced by a factor of about 10 within the increasing point, where the temperature becomes higher than 20-30 K. This result supports the picture of warm carbon-chain chemistry; carbon-chain molecules and their related molecules are efficiently regenerated by evaporation of CH(4) from dust grains in the warm region (about 25 K). The distributions of CCH and C(4)H have extended structures as well as an enhanced component, which implies a contribution of "remnant" carbon-chainmolecules produced in the starless-core phase in addition to the regeneration component. On the other hand, the distributions of CCH, C(4)H, and c-C(3)H(2) have a slight dip with a radius of 300-600 AU toward the protostar position, indicating that their abundances would decrease toward the central part. The present results provide a new picture of carbon-chain chemistry in the closest vicinity of a low-mass protostar.
研究論文（学術雑誌）, 英語 - LONG CARBON-CHAIN MOLECULES AND THEIR ANIONS IN THE STARLESS CORE, LUPUS-1A
Nami Sakai; Tatsuya Shiino; Tomoya Hirota; Takeshi Sakai; Satoshi Yamamoto
ASTROPHYSICAL JOURNAL LETTERS, IOP PUBLISHING LTD, 718巻, 2号, 掲載ページ L49-L52, 出版日 2010年08月, 査読付, We have recently discovered a new starless core with bright radio emissions of long carbon-chain molecules in the Lupus molecular cloud, which we have named as Lupus-1A. Toward this source, the peak intensities of the C(6)H and C(8)H lines are found to be higher than toward TMC-1 by a factor of 2-3. Even the lines of their anions, C(6)H(-) and C(8)H(-), are also brighter than in TMC-1. Moreover, the line of C(4)H(-) has been detected for the first time in a starless core. The column densities of these long carbon-chain molecules are almost comparable to those in TMC-1, and hence, this source can be regarded as the second "TMC-1 like cloud." TMC-1 has long been an outstanding molecular cloud with rich carbon-chain molecules since its discovery in 1976. In spite of extensive efforts, no comparable sources have been found so far. Lupus-1A will be used for hunting of new interstellar molecules as well as understanding of carbon-chain chemistry through critical comparison of physical and chemical properties with TMC-1. This source is important not only for astronomy but also for molecular science as an ideal spectroscopic laboratory because of narrow line shapes and bright intensities.
研究論文（学術雑誌）, 英語 - A SURVEY OF MOLECULAR LINES TOWARD MASSIVE CLUMPS IN EARLY EVOLUTIONARY STAGES OF HIGH-MASS STAR FORMATION
Takeshi Sakai; Nami Sakai; Tomoya Hirota; Satoshi Yamamoto
ASTROPHYSICAL JOURNAL, IOP PUBLISHING LTD, 714巻, 2号, 掲載ページ 1658-1671, 出版日 2010年05月, 査読付, We have observed the CH3OH J = 2-1, SiO J = 2-1, (CS)-S-34 J = 2-1, (HCO+)-C-13 J = 1-0, (HNC)-C-13 J = 1-0, CCH N = 1-0, OCS J = 8-7, and SO J(N) = 2(2)-1(1) lines toward 20 massive clumps, including Midcourse Space Experiment (MSX) 8 mu m dark sources (infrared dark clouds) and MSX 8 mu m sources, by using the Nobeyama Radio Observatory 45 m telescope. We have found that the velocity widths of the CH3OH and (CS)-S-34 lines are broader than those of the (HCO+)-C-13 line in the MSX dark sources. On the other hand, they are comparable to the velocity width of the (HCO+)-C-13 line in the MSX sources. In addition, the [SiO]/[ (HCO+)-C-13] abundance ratio is found to be enhanced in the MSX dark sources in comparison with the MSX sources. These results suggest that shocks caused by interaction between an outflow and an ambient dense gas would have substantial impact on the chemical composition of the MSX dark sources. The velocity widths of the CH3OH and (CS)-S-34 lines relative to that of the (HCO+)-C-13 line as well as the [SiO]/[ (HCO+)-C-13] abundance ratio could be used as good tools for investigating evolutionary stages of massive clumps. On the basis of the results, we discuss the chemical and physical evolution of massive clumps.
研究論文（学術雑誌）, 英語 - Searching for chameleon-like scalar fields with the ammonia method
S. A. Levshakov; P. Molaro; A. V. Lapinov; D. Reimers; C. Henkel; T. Sakai
ASTRONOMY & ASTROPHYSICS, EDP SCIENCES S A, 512巻, 掲載ページ A44, 出版日 2010年03月, 査読付, Aims. We probe the dependence of the electron-to-proton mass ratio, mu = m(e)/m(p), on the ambient matter density by means of radio astronomical observations.
Methods. The ammonia method, which has been proposed to explore the electron-to-proton mass ratio, is applied to nearby dark clouds in the Milky Way. This ratio, which is measured in different physical environments of high (terrestrial) and low (interstellar) densities of baryonic matter is supposed to vary in chameleon-like scalar field models, which predict strong dependences of both masses and coupling constant on the local matter density. High resolution spectral observations of molecular cores in lines of NH(3) (J, K) = (1, 1), HC(3)N J = 2-1, and N(2)H(+) J = 1-0 were performed at three radio telescopes to measure the radial velocity offsets, Delta V = V(rot) - V(inv), between the inversion transition of NH(3) (1,1) and the rotational transitions of other molecules with different sensitivities to the parameter Delta mu/mu = (mu(obs) - mu(lab))/mu(lab).
Results. The measured values of Delta V exhibit a statistically significant velocity offset of 23 +/- 4(stat) +/- 3(sys) m s(-1). When interpreted in terms of the electron-to-proton mass ratio variation, this infers that Delta mu/mu = (2.2 +/- 0.4(stat) +/- 0.3(sys)) x 10(-8). If only a conservative upper bound is considered, then the maximum offset between ammonia and the other molecules is vertical bar Delta V vertical bar <= 30 m s(-1). This provides the most accurate reference point at z = 0 for Delta mu/mu of vertical bar Delta mu/mu vertical bar <= 3 x 10(-8).
研究論文（学術雑誌）, 英語 - Abundance anomaly of the C-13 species of CCH
N. Sakai; O. Saruwatari; T. Sakai; S. Takano; S. Yamamoto
ASTRONOMY & ASTROPHYSICS, EDP SCIENCES S A, 512巻, 掲載ページ A31, 出版日 2010年03月, 査読付, Aims. We have observed the N = 1-0 lines of CCH and its C-13 isotopic species toward a cold dark cloud, TMC-1 and a star-forming region, L1527, to investigate the C-13 abundances and formation pathways of CCH.
Methods. The observations have been carried out with the IRAM 30 m telescope.
Results. We have successfully detected the lines of (CCH)-C-13 and (CCH)-C-13 toward the both sources and found a significant intensity difference between the two C-13 isotopic species. The [ (CCH)-C-13]/[ (CCH)-C-13] abundance ratios are 1.6 +/- 0.4 (3 sigma) and 1.6 +/- 0.1 (3 sigma) for TMC-1 and L1527, respectively. The abundance difference between (CCH)-C-13 and (CCH)-C-13 means that the two carbon atoms of CCH are not equivalent in the formation pathway. On the other hand, the [CCH]/[ (CCH)-C-13] and [CCH]/[ (CCH)-C-13] ratios are evaluated to be larger than 170 and 250 toward TMC-1, and to be larger than 80 and 135 toward L1527, respectively. Therefore, both of the C-13 species are significantly diluted in comparison with the interstellar C-12/C-13 ratio of 60. The dilution is discussed in terms of a behavior of C-13 in molecular clouds.
研究論文（学術雑誌）, 英語 - Development of the Measurement System of Image Rejection Ratio for the Sideband-Separating Receiver
Taku Nakajima; Takeshi Sakai; Nario Kuno; Hideo Ogawa
Journal of Infrared, Millimeter and Terahertz Waves, 31巻, 2号, 掲載ページ 143-150, 出版日 2010年02月, 査読付
研究論文（学術雑誌）, 英語 - DEUTERATED MOLECULES IN WARM CARBON CHAIN CHEMISTRY: THE L1527 CASE
Nami Sakai; Takeshi Sakai; Tomoya Hirota; Satoshi Yamamoto
ASTROPHYSICAL JOURNAL, IOP PUBLISHING LTD, 702巻, 2号, 掲載ページ 1025-1035, 出版日 2009年09月, 査読付, We have conducted millimeter-wave observations of deuterated species of various carbon-chain molecules toward a low-mass star-forming region, L1527, which shows extraordinary richness of carbon-chain molecules in a vicinity of the protostar (Warm Carbon Chain Chemistry; WCCC). We have detected the spectral lines of 1-C3D, C4D, C4HD, DC3N, DC5N, and c-C3HD, where 1-C3D and C4HD are detected for the first time in space. The deuterium fractionation ratios are found to be moderate (2% to 7%), although they tend to be higher than those in the starless core, TMC-1. The upper limit to the [CH2DOH]/[CH3OH] ratio is also as low as 3%. Therefore, high deuterium fractionation ratios reported for hot corino sources are not seen in L1527. The observed ratios mean that the depletion of CO onto dust grains had not proceeded far in L1527, compared to the hot corino case. This would be consistent with a short timescale of the starless core phase, as suggested for the possible origin of WCCC.
研究論文（学術雑誌）, 英語 - A THz SIS mixer with a NbTiN-ground plane and SIS microtrilayers directly grown on a quartz substrate
Akira Endo; Takashi Noguchi; Matthias Kroug; Sergey V. Shitov; Wenlei Shan; Tomonori Tamura; Takafumi Kojima; Yoshinori Uzawa; Takeshi Sakai; Hirofumi Inoue; Kotaro Kohno
IEEE Transactions on Applied Superconductivity, 19巻, 3号, 掲載ページ 400-404, 出版日 2009年06月, A new structure and a fabrication process for multi-material THz-SIS mixers are proposed. In this design, both the micrometer-sized SIS trilayers (MTLs: microtrilayers) and the ground plane are deposited directly onto the substrate. This structure is expected to possess a number of unique features, e.g., (1) the quality of the SIS junction is not affected by the physical nature of the ground plane film; (2) the heat can escape directly from the junction into the substrate. The influence of the MTL-structure on the junction quality and circuit characteristics have been investigated. Numerical calculation suggests that the extra rf loss around the junction can be kept small if the offset between the junction and the ground plane is less than 1 μm. MTL-SIS mixers have been fabricated using Nb/Al-AlN(or Al - AlOx/Nb SIS junctions and NbTiN/Al microstrip lines. The leakage current of the SIS junction can be made as small as that of the best all-Nb devices. The MTL-SIS structure will be useful in the development of future THz SIS mixers. The abstract goes here. © 2009 IEEE.
研究論文（国際会議プロシーディングス） - Discovery of the Second Warm Carbon-Chain-Chemistry Source, IRAS15398 – 3359 in Lupus
Nami Sakai; Takeshi Sakai; Tomoya Hirota; Michael Burton; Satoshi Yamamoto
The Astrophysical Journal, IOP PUBLISHING LTD, 697巻, 1号, 掲載ページ 769-786, 出版日 2009年05月, 査読付, We have conducted a search for carbon-chain molecules toward 16 protostars with the Mopra 22 m and Nobeyama 45 m telescopes, and have detected high excitation lines from several species, such as C(4)H (N = 9-8), C(4)H(2)(J = 10(0,10)-9(0,9)), CH(3)CCH(J = 5-4, K = 2), and HC(5)N(J = 32-31), toward the low-mass protostar, IRAS15398-3359 in Lupus. The C(4)H line is as bright as 2.4 K measured with the Nobeyama 45 m telescope. The kinetic temperature is derived to be 12.6 +/- 1.5 K from the K = 1 and K = 2 lines of CH(3)CCH. These results indicate that the carbon-chain molecules exist in a region of warm and dense gas near the protostar. The observed features are similar to those found toward IRAS04368+2557 in L1527, which shows warm carbon-chain chemistry (WCCC). In WCCC, carbon-chain molecules are produced efficiently by the evaporation of CH(4) from the grain mantles in a lukewarm region near the protostar. Our data clearly indicate that WCCC is no longer specific to L1527, but occurs in IRAS15398-3359. In addition, we draw attention to a remarkable contrast between WCCC and hot corino chemistry in low-mass star-forming regions. Carbon-chain molecules are deficient in hot corino sources like NGC1333 IRAS4B, whereas complex organic molecules seem to be less abundant in the WCCC sources. A possible origin for such source-to-source chemical variations is suggested to arise from the timescale of the starless-core phase in each source. If this is the case, the chemical composition provides an important clue to explore the variation of star formation processes between sources and/or molecular clouds.
研究論文（学術雑誌）, 英語 - New achievements of ASTE: the Atacama Submillimeter Telescope Experiment
Hajime Ezawa; Kotaro Kohno; Ryohei Kawabe; Satoshi Yamamoto; Hirofumi Inoue; Hiroyuki Iwashita; Hiroshi Matsuo; Takeshi Okuda; Tai Oshima; Takeshi Sakai; Kunihiko Tanaka; Nobuyuki Yamaguchi; Grant W. Wilson; Min S. Yun; Itziar Aretxaga; David Hughes; Jason Austermann; Thushara A. Perera; Kimberly S. Scott; Leonardo Bronfman; Juan R. Cortes
Ground-based and Airborne Telescopes II, SPIE, 出版日 2008年08月, 査読付 - ASTE CO (3-2) Observations of the Southern Barred Spiral Galaxy NGC 986 : a Large Gaseous Bar Filled with a Dense Molecular Medium
Kohno Kotaro; Tosaki Tomoka; Miura Rie; MURAOKA Kazuyuki; SAWADA Tsuyoshi; NAKANISHI Kouichiro; KUNO Nario; SAKAI Takeshi; SORAI Kazuo; KAMEGAI Kazuhisa; TANAKA Kunihiko; OKUDA Takeshi; ENDO Akira; HATSUKADE Bunyo; SAMESHIMA Masahiro; EZAWA Hajime; SAKAMOTO Seiichi; KAMAZAKI Takeshi; YAMAGUCHI Nobuyuki; CORTES Juan; TAMURA Yoichi; FUKUHARA Masayuki; IONO Daisuke; KAWABE Ryohei
PASJ : publications of the Astronomical Society of Japan, Astronomical Society of Japan, 60巻, 3号, 掲載ページ 457-464, 出版日 2008年06月25日, 査読付
研究論文（学術雑誌）, 英語 - A new 100-GHz band front-end system with a waveguide-type dual-polarization sideband-separating SIS receiver for the NRO 45-m radio telescope
Taku Nakajima; Takeshi Sakai; Shin'ichiro Asayama; Kimihiro Kimura; Masayuki Kawamura; Yoshinori Yonekura; Hideo Ogawa; Nario Kuno; Takashi Noguchi; Masato Tsuboi; Ryohei Kawabe
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN, OXFORD UNIV PRESS, 60巻, 3号, 掲載ページ 435-443, 出版日 2008年06月, 査読付, We developed a waveguide-type dual-polarization sideband-separating SIS receiver system of the 100-GHz band for the 45-m radio telescope at the Nobeyama Radio Observatory, Japan. This receiver is composed of an orthomode transducer and two sideband-separating SIS mixers, which are both based on a waveguide technique. The receiver has four intermediate frequency (IF) bands of 4.0-8.0 GHz. Over the radio frequency range of 80-120 GHz, the single-sideband receiver noise temperatures are 50-100 K, and the image rejection ratios (IRRs) are greater than 10 dB. We developed new matching optics for the telescope beam as well as new IF chains for the four IF signals. The new receiver system was installed in the telescope, and we successfully observed the (CO)-C-12, (CO)-C-13, and (CO)-O-18 emission lines simultaneously toward the Sagittarius 132 region to confirm the performance of the receiver system. The SSB noise temperature of the system, including the atmosphere, became approximately half of that of the previous receiver system. The IRRs of the two 2SB mixers were estimated from the (CO)-C-12 and HCO+ spectra from the W 51 giant molecular cloud, resulting in > 20 dB for one polarization and > 12 dB for the other polarization.
研究論文（学術雑誌）, 英語 - A molecular line observation toward massive clumps associated with infrared dark clouds
Takeshi Sakai; Nami Sakai; Kazuhisa Kamegai; Tomoya Hirota; Nobuyuki Yamaguchi; Shoichi Shiba; Satoshi Yamamoto
ASTROPHYSICAL JOURNAL, IOP PUBLISHING LTD, 678巻, 2号, 掲載ページ 1049-1069, 出版日 2008年05月, 査読付, We have surveyed the N2H+ J = 1-0, HC3N J = 5-4, CCS J(N) = 4(3)-3(2), NH3 (J, K) = (1, 1), (2, 2), (3, 3), and CH3OH J = 7-6 lines toward the 55 massive clumps associated with infrared dark clouds by using the Nobeyama Radio Observatory 45 m telescope and the Atacama Submillimeter Telescope Experiment 10 m telescope. The N2H+, HC3N, and NH3 lines are detected toward most of the objects. On the other hand, the CCS emission is detected toward none of the objects. The [CCS]/[N2H+] ratios are found to be mostly lower than unity even in the Spitzer 24 mu m dark objects. This suggests that most of the massive clumps are chemically more evolved than the low-mass starless cores. The CH3OH emission is detected toward 18 out of 55 objects. All the CH3OH-detected objects are associated with the Spitzer 24 mu m sources, suggesting that star formation has already started in all the CH3OH-detected objects. The velocity widths of the CH3OH J(K) = 7(0)-6(0) A(+) and 7(-1)-6(-1) E lines are broader than those of N2H+ J = 1-0. The CH3OH J(K) = 7(0)-6(0) A(+) and 7(-1)-6(-1) E lines tend to have broader line width in the MSX dark objects than in the others, the former being younger or less luminous than the latter. The origin of the broad emission is discussed in terms of the interaction between an outflow and an ambient cloud.
研究論文（学術雑誌）, 英語 - Detection of HCO2+ toward the low-mass protostar IRAS 04368+2557 in L1527
Nami Sakai; Takeshi Sakai; Yuri Aikawa; Satoshi Yamamoto
ASTROPHYSICAL JOURNAL LETTERS, UNIV CHICAGO PRESS, 675巻, 2号, 掲載ページ L89-L92, 出版日 2008年03月, 査読付, The millimeter-wave rotational emission lines (4(04)-3(03) and 5(05)-4(04)) of protonated carbon dioxide, HCO2+ (HOCO+), have been detected toward the low- mass Class 0 protostar IRAS 04368+2557 in L1527 with the IRAM 30 m telescope. This is the first detection of HCO2+ except for the Galactic center clouds. The column density of HCO2+ averaged over the beam size (29'') is determined to be 7.6 x 10(10) cm(-2), assuming a rotational temperature of 12.3 K. The fractional abundance of gaseous CO2 relative to H-2 is estimated from the column density of HCO2+ with the aid of a simplified chemical model. If the HCO2+ emission only comes from the evaporation region of CO2 near the protostar (T greater than or similar to 50 K), the fractional abundance of CO2 is estimated to be higher than. This is comparable to the elemental abundance of carbon in interstellar clouds, and hence, 6.6 x 10(-4) the direct evaporation of CO2 from dust grain is unrealistic as a source of gaseous CO2 in L1527. A narrow line width of HCO also supports this. On the other hand, the fractional abundance of CO2 is estimated to be if the source size is comparable to the beam size. These results indicate that gaseous CO2 is abundant 2.9 x 10(-7) even in the low-mass star-forming region. Possible production mechanisms of gaseous CO2 are discussed.
研究論文（学術雑誌）, 英語 - A novel THz SIS mixer with a NbTiN-ground plane and SIS micro-trilayers directly grown on a quartz substrate
Akira Endo; Takashi Noguchi; Matthias Kroug; Sergey V. Shitov; Wenlei Shan; Tomonori Tamura; Takafumi Kojima; Yoshinori Uzawa; Takeshi Sakai; Hirofumi Inoue; Kazuyuki Muraoka; Kotaro Kohno
Proceedings of the 19th International Symposium on Space Terahertz Technology, ISSTT 2008, 掲載ページ 54-59, 出版日 2008年, A new structure and fabrication process for multimaterialTHz-SIS mixers is proposed. In this design, both themicrometer-sized SIS trilayers (MTLs: micro-trilayers) andthe ground plane are deposited directly onto the substrate.This structure is expected to possess a number of uniquefeatures, e.g., (1) the quality of the SIS junction is notaffected by the physical nature of the ground plane film; (2)the heat can escape directly from the junction into thesubstrate. The influence of the MTL-structure on thejunction quality and circuit characteristics have beeninvestigated. Numerical calculation suggests that the extra rfloss around the junction can be kept small if the offsetbetween the junction and the ground plane is less than 1μm.MTL-SIS mixers have been fabricated using Nb/Al-AlOx(orAlNx)/Nb SIS junctions and NbTiN/Al microstriplines. Theleakage current of the SIS junction can be made as small asthat of the best all-Nb devices. The MTL-SIS structure willbe useful in thedevelopment of future THz SIS mixers.
研究論文（国際会議プロシーディングス） - A possible detection of CO (J=3-2) emission from the host Galaxy of GRB 980425 with the atacama submillimeter telescope experiment
Bunyo Hatsukade; Kotaro Kohno; Akira Endo; Tomoka Tosaki; Kouji Ohta; Seiichi Sakamoto; Nobuyuki Kawai; Juan R. Cortes; Kouichiro Nakanishi; Takeshi Okuda; Kazuyuki Muraoka; Takeshi Sakai; Hajime Ezawa; Nobuyuki Yamaguchi; Kazuhisa Kamegai; Ryohei Kawabe
MAPPING THE GALAXY AND NEARBY GALAXIES, SPRINGER, 掲載ページ 331-331, 出版日 2008年, 査読付
研究論文（国際会議プロシーディングス）, 英語 - Tentative detection of C4H- toward the low-mass protostar IRAS 04368+2557 in L1527
Nami Sakai; Takeshi Sakai; Satoshi Yamamoto
ASTROPHYSICAL JOURNAL LETTERS, UNIV CHICAGO PRESS, 673巻, 1号, 掲載ページ L71-L74, 出版日 2008年01月, 査読付, The millimeter-wave rotational emission line (J = 9-8) of the negative ion, C4H-, has tentatively been detected toward the low- mass Class 0 protostar IRAS 04368-2557 in L1527 with the IRAM 30 m telescope. The column density of C4H- is determined to be 1.1 x 10(10) cm(-2). The [C4H-]/[C4H] ratio is found to be 6.8 x 10(-5), which is much lower than the [C6H]/[C6H] ratio (0.093). From this result, the rate coefficient for the radiative attachment reaction between C4H and electron is estimated to be as small as cm3s on the basis of the simplified chemical model. The present observation has demonstrated the uniqueness and importance of L1527 in searching for a new carbon-chain molecule in a star-forming region.
研究論文（学術雑誌）, 英語 - Abundant carbon-chain molecules toward the low-mass protostar IRAS 04368+2557 in L1527
Nami Sakai; Takeshi Sakai; Tomoya Hirota; Satoshi Yamamoto
ASTROPHYSICAL JOURNAL, UNIV CHICAGO PRESS, 672巻, 1号, 掲載ページ 371-381, 出版日 2008年01月, 査読付, We have detected the high-excitation lines of carbon-chain molecules such as C4H2 (J = 10(0,10)-9(0,9)), C4H (N = 9-8, F-1, F-2), l-C3H2 (4(1,3)-3(1,2)), and CH3CCH (J = 5-4, K = 2) toward a low-mass star-forming region, L1527. In particular, the F1 line of C4H is as strong as 1.7 K (T-MB). The rotational temperature of C4H2 is determined to be 12: 3 +/- 0: 8 K, which is higher than that in TMC-1 (3.8 K). Furthermore, the column density of C4H2 is derived to be about 1/4 of that in TMC-1, indicating that carbon-chain molecules are abundant in L1527 for a star-forming region. Small mapping observations show that the C4H, C4H2, and c-C3H2 emissions are distributed from the infalling envelope to the inner part. Furthermore, we have detected the lines of C5H, HC7N, and HC9N in the 20 GHz region. Since the carbon-chain molecules are generally deficient in star-forming cores, the above results cannot simply be explained by the existing chemical models. The following hypothesis is proposed. If the timescale of the prestellar collapse in L1527 were shorter than those of the other star-forming cores, the carbon-chain molecules could survive in the central part of the core. In addition, regeneration processes of the carbon-chain molecules due to star formation activities would play an important role. Evaporation of CH4 from the grain mantles would drive the regeneration processes. The present observations show new chemistry in a warm and dense region near the protostars, which is named "warm carbon-chain chemistry (WCCC)."
研究論文（学術雑誌）, 英語 - Detection of C6H- toward the low-mass protostar IRAS 04368+2557 in L1527
Nami Sakai; Takeshi Sakai; Yoshihiro Osamura; Satoshi Yamamoto
ASTROPHYSICAL JOURNAL, UNIV CHICAGO PRESS, 667巻, 1号, 掲載ページ L65-L68, 出版日 2007年09月, 査読付, We have detected the J = 7-6, 8-7, and 15-14 lines of C6H- toward a low-mass star-forming region of L1527. We have also detected the J = 15/2-13/2 and 33/ 2-31/2 lines of the corresponding neutral species, C6H, and the 8(1,8)-7(1,7) line of C6H2 in L1527. This is the first detection of these three species in star-forming regions. The column density of C6H- is (5.8 +/- 1.8) x 10(10) cm(-2), which is comparable to that in TMC-1, although the column density of C6H in L1527 is about 1/5 of that in TMC-1. Hence, the N((CH-)-H-6)/N(C6H) ratio is, 0.093 +/- 0.029 which is higher than that in TMC-1 by a factor of 4. This high anion-to-neutral ratio is discussed in terms of a simplified chemical model.
研究論文（学術雑誌）, 英語 - Production pathways of CCS and CCCS inferred from their C-13 isotopic species
Nami Sakai; Masafumi Ikeda; Masaru Morita; Takeshi Sakai; Shuro Takano; Yoshihiro Osamura; Satoshi Yamamoto
ASTROPHYSICAL JOURNAL, IOP PUBLISHING LTD, 663巻, 2号, 掲載ページ 1174-1179, 出版日 2007年07月, 査読付, The rotational spectral lines (J(N) = 3(2)-2(1) and J(N) = 2(1)-1(0)) of (CCS)-C-13 and (CCS)-C-13 have been observed toward a cold dark cloud, TMC-1. The strongest hyperfine component lines of (CCS)-C-13 and (CCS)-C-13 (J(N) = 2(1)-1(0), F = 5/2-3/2) have successfully been detected. The [ (CCS)-C-13]/[ (CCS)-C-13] abundance ratio is determined to be 4.2 +/- 2.3 ( 3 sigma). The [CCS]/[ (CCS)-C-13] ratio is evaluated to be 230 +/- 130 (3 sigma), and hence, (CCS)-C-13 is found to be significantly diluted. Such a difference between the (CCS)-C-13 and (CCS)-C-13 abundances is also found in L1521E, which is a very young core with rich carbon-chain molecules. Therefore, the anomaly is not specific to TMC-1, but seems to be common for the CCS-rich clouds. Furthermore, we have also observed the J = 4-3 transition of (CCCS)-C-13 and (CCCS)-S-34 in TMC-1 and L1521E and have found that the [ (CCCS)-S-34]/[ (CCCS)-C-13]ratio is larger than 8.4 ( 3 sigma). This lower limit is considerably larger than the interstellar [C-12][S-34]/[C-13][S-32] ratio of 3, indicating that (CCCS)-C-13 is diluted as in the case of (CCS)-C-13. These results give us strong constraints on the main pathways to produce CCS and CCCS.
研究論文（学術雑誌）, 英語 - Physical and chemical properties of massive clumps in the AFGL 333 cloud
Takeshi Sakai; Tomoharu Oka; Satoshi Yamamoto
ASTROPHYSICAL JOURNAL, UNIV CHICAGO PRESS, 662巻, 2号, 掲載ページ 1043-1051, 出版日 2007年06月, 査読付, We have mapped two massive clumps, clump A and B, of the AFGL 333 cloud in the N2H+ J = 1-0, CCS J(N) = 4(3)-3(2), HC3N J = 5-4, and NH3 ( J, K) = ( 1, 1) and ( 2, 2) lines with the Nobeyama Radio Observatory 45 m telescope. Intense N2H+ emission comes from the two clumps, and its overall distribution is similar to that of (CO)-O-18 J = 1-0. On the other hand, the CCS and HC3N emissions are more intense toward clump B than toward clump A. Thus, the column density ratios of [ CCS]/[ N2H+] and [ HC3N]/[ N2H+] tend to be higher toward clump B than toward clump A, indicating that clump B is younger than clump A. This is supported by a fact that the 2MASS sources with H - K > 2 and the Spitzer 24 mu m sources are mostly associated with clump A, whereas only a few such sources exist in clump B. Clump B involves a few dense cores that are dark in the mid-infrared maps. Such cores are thought to be good candidates of starless cores for high- or intermediate-mass stars.
研究論文（学術雑誌）, 英語 - Methyl formate in the NGC 2264 IRS 1 region
Nami Sakai; Takeshi Sakai; Satoshi Yamamoto
ASTROPHYSICAL JOURNAL, UNIV CHICAGO PRESS, 660巻, 1号, 掲載ページ 363-369, 出版日 2007年05月, 査読付, Millimeter-wave spectral lines of HCOOCH3 are observed toward a massive star-forming region, NGC 2264 IRS 1, with the Nobeyama 45 m radio telescope and Nobeyama Millimeter Array. The HCOOCH3 emission is not detected toward the dense core around IRS 1, which is the brightest IR source. However, it is definitively detected toward MMS 3, which is thought to contain a high-mass equivalent of a Class 0 protostar. The column density and the fractional abundance of HCOOCH3 in MMS 3 are found to be (4-30) x 10(15) cm(-2) and (0.7-5.3) x 10(-8), respectively, assuming that the range of the excitation temperature is from 50 to 250 K. The fractional abundance is lower by an order of magnitude than that in the compact ridge of Orion KL. On the other hand, the upper limit to the fractional abundance toward IRS 1 is significantly lower than the abundance toward MMS 3. Since MMS 3 is less evolved than IRS 1, this result would indicate that HCOOCH3 preferentially exists in the younger stage of protostellar evolution, as in the case of low-mass star forming regions. The distribution of HCOOCH3 is found to be slightly offset from the dust continuum peak of MMS 3 by 13". This situation is similar to that found in the compact ridge of Orion KL, which would provide us with an important clue in exploring its peculiar chemistry.
研究論文（学術雑誌）, 英語 - A search for CO (J=3-2) emission from the host galaxy of GRB 980425 with the Atacama Submillimeter Telescope Experiment
Bunyo Hatsukade; Kotaro Kohno; Akira Endo; Tomoka Tosaki; Kouji Ohta; Seiichi Sakamoto; Nobuyuki Kawai; Juan R. Cortes; Kouichiro Nakanishi; Takeshi Okuda; Kazuyuki Muraoka; Takeshi Sakai; Paul M. Vreeswijk; Hajime Ezawa; Nobuyuki Yamaguchi; Kazuhisa Kamegai; Ryohei Kawabe
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN, OXFORD UNIV PRESS, 59巻, 1号, 掲載ページ 67-72, 出版日 2007年02月, 査読付, We report on a deep search for (CO)-C-12 (J = 3-2) line emission from the host galaxy of GRB 980425 with the Atacama Submillimeter Telescope Experiment (ASTE). We observed five points of the galaxy, covering the entire region. After combining all of the spectra, we obtained a global spectrum with a rms noise level of 3.3 mK in the T-mb scale at a velocity resolution of 10 km s(-1). No significant emission was detected, though we found a marginal emission feature in the velocity range corresponding to the redshift of the galaxy. We derived 3 sigma upper limits on the global properties: the velocity-integrated CO (3-2) intensity of I-CO(3-2) < 0.26 K km s(-1), adopting a velocity width of 67 km s(-1); an H-2 column density of N(H-2) < 3 x 10(20) cm(-2); a molecular gas mass of M(H-2) < 3 x 108 M(D, by assuming a CO line luminosity to H-2 molecular gas mass conversion factor of X-CO = 5.0 x 10(20) cm(-2) (K kna s(-1))(-1); and a star-formation rate of SFR < 0.1 M-circle dot yr(-1), based on the Schmidt law. The SFR is consistent with the previous results of Ha and mid-IR observations, thereby suggesting that there is no significant obscured star formation in the host galaxy of GRB 980425. This result implies that there is a variety of GRB hosts with regard to the presence of obscured star formation.
研究論文（学術雑誌）, 英語 - ASTE CO (3-2) observations of the barred spiral galaxy M 83: I. Correlation between CO (3-2)/CO (1-0) ratios and star formation efficiencies
Kazuyuki Muraoka; Kotaro Kohno; Tomoka Tosaki; Nario Kuno; Kouichiro Nakanishi; Kazuo Sorai; Takeshi Okuda; Seiichi Sakamoto; Akira Endo; Bunyo Hatsukade; Kazuhisa Kamegai; Kunihiko Tanaka; Juan Cortes; Hajime Ezawa; Nobuyuki Yamaguchi; Takeshi Sakai; Ryohei Kawabe
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN, OXFORD UNIV PRESS, 59巻, 1号, 掲載ページ 43-54, 出版日 2007年02月, 査読付, We present CO (J = 3-2) emission observations with the ASTE toward the 5' x 5' (or 6.6 kpc x 6.6 kpc at the distance D = 4.5 Mpc) region of the nearby barred spiral galaxy M 83. We successfully resolved the major structures, i.e., the nuclear starburst region, bar, and inner spiral arms at a resolution of 22" (480pc), showing a good spatial coincidence between CO and 6 cm continuum emissions. We found a global luminosity, L'(CO(3-2)), of 5.1 x 10(8) K km s(-1) pc(2) within the observed region. We also found L'(CO(3-2)) in a disk region (0.5 < r < 3.5 kpc) of 4.2 x 10(8) K km s(-1) pc(2), indicating that (J = 3-2) emission in the disk region significantly contributes to the global L'(CO(3-2)). From a comparison of CO (J = 3-2) data with CO (J = 1-0) intensities measured with the Nobeyama 45-m telescope, we found that the radial profile of the CO (J = 3-2)/CO (J = 1-0) integrated intensity ratio, R3-2/1-0, is almost unity in the central region (r < 0.25 kpc), whereas it drops to a constant value, 0.6-0.7, in the disk region. The radial profile of star formation efficiencies (SFEs), determined from 6 cm radio continuum and CO (J = 1-0) emission, shows the same trend as that of R3-2/1-0. At the bar-end (r similar to 2.4kpc), the amounts of molecular gas and the massive stars are enhanced when compared with other disk regions, whereas there is no excess of R3-2/1-0 and SFE in that region. This means that a simple summation of the star-forming regions at the bar-end and the disk cannot reproduce the nuclear starburst of M 83, implying that the spatial variation of the dense gas fraction traced by R3-2/1-0 governs the spatial variation of SFE in M 83.
研究論文（学術雑誌）, 英語 - Atomic carbon in the AFGL 333 cloud
Takeshi Sakai; Tomoharu Oka; Satoshi Yamamoto
ASTROPHYSICAL JOURNAL, UNIV CHICAGO PRESS, 649巻, 1号, 掲載ページ 268-279, 出版日 2006年09月, 査読付, We have mapped the W3 giant molecular cloud in the C-0 P-3(1)-P-3(0) ([C I] 492 GHz) and (CO)-C-12 J = 3-2 emission lines with the Mount Fuji Submillimeter-wave Telescope. The [C I] distribution is extended over the molecular cloud, having peaks at three star forming clouds, W3 Main, W3( OH), and AFGL 333. The [C I] emission is found to be strong in the AFGL 333 cloud, where the 12CO J 3 2 emission is relatively weak. In order to characterize the physical and chemical states of the AFGL 333 cloud, we have also observed the CO J = 1-0 isotopomer lines and the CCS and N2H+ lines with the Nobeyama Radio Observatory 45 m Telescope. The [C-0]/[CO] and [CCS]/[N2H+] abundance ratios are found to be higher in the AFGL 333 cloud than in theW3( OH) cloud, suggesting that the AFGL 333 cloud is younger than theW3(OH) cloud. In the AFGL 333 cloud we have found two massive cores without any sign of active star formation. They are highly gravitationally bound and are regarded as good candidates for a massive prestellar core.
研究論文（学術雑誌）, 英語 - A possible detection of CO (J = 32) emission from the host galaxy of GRB 980425 with atacama submillimeter telescope experiment
Bunyo Hatsukade; Kotaro Kohno; Akira Endo; Tomoka Tosaki; Kouji Ohta; Seiichi Sakamoto; Nobuyuki Kawai; Juan R. Corts; Kouichiro Nakanishi; Takeshi Okuda; Kazuyuki Muraoka; Takeshi Sakai; Hajime Ezawa; Nobuyuki Yamaguchi; Kazuhisa Kamegai; Ryohei Kawabe
Proceedings of the International Astronomical Union, 2巻, 235号, 掲載ページ 312, 出版日 2006年08月, Long-duration gamma-ray bursts (GRBs) are considered to be due to the death of massive stars. Therefore, GRBs are closely associated with the star formation of host galaxies. Since GRBs can be detected at cosmological distances, they are expected to be probes of the star formation history of the Universe. In order to determine the use of GRBs, it is essential to understand the star formation of their hosts. Multi-wavelength observations have shown that the star formation rates (SFRs) of GRB hosts derived from submillimeter/radio observations are generally higher than those from optical/UV observations (Berger et al. 2003). This implies that GRB hosts have a large amount of molecular gas and massive star formation obscured by dust. In order to solve this problem, it is necessary to derive the SFRs in a method which is independent of existing methods and not affected by dust extinction. We observed 12CO (J = 32) line emission from the host galaxy of GRB 980425 using the Atacama Submillimeter Telescope Experiment (ASTE). Five points were observed covering the entire region of the galaxy, and we find possible emission features (S/N ∼ 3 ) at the velocity range corresponding to the redshift of the galaxy. By combining all spectra of five points, we obtain a global spectrum with a ∼4 emission feature. If the features are real, this is the first detection of CO among GRB hosts. We derive the total gas mass of M(H2)=7 2 10 8M assuming a CO-to-H2 conversion factor of CO = 8.0M (K km s 1 pc 2) 1, which is deduced using the correlation between the CO and the metallicity. The dynamical mass is calculated to be Mdyn=2 10 10M, and M(H2)/Mdyn∼3% is consistent with those of nearby dwarfs and normal spirals. The derived SFR is 0.5 0.1 M yr 1 based on the Schmidt law. This SFR agrees with the results of previous H observations, suggesting that there is no significant obscured star formation in this host galaxy. This result implies that there is a variety of GRB hosts in terms of the presence of obscured star formation. © 2007 International Astronomical Union.
研究論文（国際会議プロシーディングス）, 英語 - Submillimeter-wave CI spectral lines from the NGC 1333 region
T Oka; M Iwata; H Maezawa; M Ikeda; T Ito; K Kamegai; T Sakai; S Yamamoto
ASTROPHYSICAL JOURNAL, UNIV CHICAGO PRESS, 602巻, 2号, 掲載ページ 803-815, 出版日 2004年02月, 査読付, We present large (30' x 40') maps in the C-0 P-3(1)-P-3(0) ([C I]; 492 GHz) and CO J = 3-2 (346 GHz) spectral lines of the NGC 1333 star-forming complex. We also report detections of the C-0 P-3(2)-P-3(1) (809 GHz) spectral line from 3 x 3 positions centered on HH 12. The overall extents of [C I] and CO J = 3-2 emission are similar to those of (CO)-C-13 and (CO)-O-18 J = 1 0 emission. The CO J = 3-2 intensity peak is adjacent to the illuminating star SVS 3, while the [C I] intensity peaks at 50 southwest of the reflection nebula, filling a hollow surrounded by a C-shaped dense molecular shell. We suggest that the observed [C I] distributions might be the result of nonequilibrium chemistry on the basis of the time-dependent chemical simulation. A huge expanding H I shell associated with the NGC 1333 cloud lends further support to this notion.
研究論文（学術雑誌）, 英語 - An experimental study of submillimeter-wave horn antennae for a submillimeter-wave array
M Matsunaga; Y Sekmioto; T Matsunaga; T Sakai
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN, OXFORD UNIV PRESS, 55巻, 5号, 掲載ページ 1051-1057, 出版日 2003年10月, 査読付, This paper aims to introduce two types of submillimeter-wave horn antennae designed by the authors and to present numerical findings obtained by an evaluative testing system that has also been developed by the authors. Submillimeter-wave components are widely used in radio-astronomical observation systems. There is a need to minimize (1) the various losses possibly incurred in the wave-receiving unit, and (2) the quantity of the unwanted electromagnetic waves mixing in. It is a well-known fact that a corrugated horn antenna possesses very low levels of cross-polarized field intensity, loss, and side lobes. It is for this reason that the authors have chosen to use corrugated horn antennae as two types of such antennae - one designed for use in the range of 280 GHz to 360 GHz frequencies and tested at 280 GHz, 332 GHz, and 360 GHz, and the other designed for use in the range of 385 GHz to 500 GHz frequencies and tested at 385 GHz, 442.5 GHz, and 500 GHz. The measurements of the antenna beam patterns have been found to largely correspond to those of the numerical analyses; it may be concluded that the antennae are functionally as efficient as they were designed and the testing system doubtless serves the desired purpose.
研究論文（学術雑誌）, 英語 - Distribution of the [C I] Emission in the ρ Ophiuchi Dark Cloud
Kazuhisa Kamegai; Masafumi Ikeda; Hiroyuki Maezawa; Tetsuya Ito; Mitsuhiro Iwata; Takeshi Sakai; Tomoharu Oka; Satoshi Yamamoto; Yutaro Sekimoto; Ken’ichi Tatematsu; Takashi Noguchi; Shuji Saito; Hideo Fujiwara; Hiroyuki Ozeki; Junji Inatani; Masatoshi Ohishi
The Astrophysical Journal, UNIV CHICAGO PRESS, 589巻, 1号, 掲載ページ 378-385, 出版日 2003年05月, 査読付, The P-l(1)-P-3(0) fine-structure line of the neutral carbon atom ([C I]) has been mapped over the 1.degrees8 x 1.degrees3 area of the L1688 cloud in the rho Ophiuchi region with the Mount Fuji submillimeter-wave telescope. The P-3(2)-P-3(1) line of [C I] has also been observed toward two representative positions to evaluate the excitation temperature of the [C I] lines. The overall extent of the [C I] distribution generally resembles that of the (CO)-C-13 distribution. The [C I] distribution has two major peaks; one ( peak I) is at rho Oph A, and the other (peak II) is toward the east side of the (CO)-O-18 core in the southern part of L1688. Peak II is located beyond the (CO)-O-18 core with respect to the exciting star HD 147889. The C-0 column density is 5.0 x 10(17) cm(-2) toward peak II. The spatial distribution of the [C I] emission is compared with plane-parallel photodissociation region (PDR) models, which suggest that peak II is associated with a lower density PDR front, adjacent to the dense cloud cores observed in the (CO)-O-18 line emission. Alternatively, peak II is in the early stage of chemical evolution, where C-0 has not been completely converted to CO. In this case, the difference in the [C I] and (CO)-O-18 distributions represents an evolutionary sequence. This is consistent with a picture of a shock-compressed formation of the dense cores in this region due to influences from the Sco OB2 association.
研究論文（学術雑誌）, 英語 - A 350 GHz SIS receiver on the Nobeyama 10 m submillimeter telescope
Y Sekimoto; T Sakai; G Saito; K Takematsu; K Tanaka; K Kohno; T Noguchi; H Iwashita; T Takahashi; N Satou; S Yokogawa; S Sakamoto; N Ukita; R Kawabe; T Ito; H Maezawa; S Yamamoto
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN, OXFORD UNIV PRESS, 53巻, 5号, 掲載ページ 951-958, 出版日 2001年10月, 査読付, We have developed a low-noise submillimeter-wave SIS receiver (320-360 GHz) for a 10 m submillimeter telescope, which was installed at Nobeyama in 2000 February. This receiver and a millimeter-wave SIS receiver are mounted on the ceiling of the Cassegrain receiver cabin of the 10 m telescope. Two curved mirrors couple a shaped Cassegrain beam from the subreflector to mixer horns. The minimum noise temperature measured in front of the receiver was 52 K in double sideband (DSB) at a local oscillator (LO) frequency of 354 GHz, which corresponds to three-times quantum limits (37hv/k(B)). This noise temperature contributions are resolved into the optics, mixer, and IF parts. The temperature ripple of a two-stage Gifford-McMahon cryocooler has been reduced to be 2 mK peak-to-peak at the mixer block with a helium pot temperature stabilizer. Mechanical vibration (30 mum peak-to-peak) of the cold head degrades the receiver stability.
研究論文（学術雑誌）, 英語 - Atomic carbon and CO isotope emission in the vicinity of DR 15
T Oka; S Yamamoto; M Iwata; H Maezawa; M Ikeda; T Ito; K Kamegai; T Sakai; Y Sekimoto; K Tatematsu; Y Arikawa; Y Aso; T Noguchi; SC Shi; K Miyazawa; S Saito; H Ozeki; H Fujiwara; M Ohishi; J Inatani
ASTROPHYSICAL JOURNAL, UNIV CHICAGO PRESS, 558巻, 1号, 掲載ページ 176-184, 出版日 2001年09月, 査読付, We present observations of the P-3(1)-P-3(o) fine-structure transition of atomic carbon [C I], the J = 3-2 transition of CO, and the J = 1-0 transitions of (CO)-C-13 and (CO)-O-18 toward DR 15, an H II region associated with two mid-infrared dark clouds (IRDCs). The (CO)-C-13 and (CO)-O-18 J = 1-0 emissions closely follow the dark patches seen in optical wavelength, showing two self-gravitating molecular cores with masses of 2000 and 900 M-circle dot, respectively, at the positions of the cataloged IRDCs. Our data show a rough spatial correlation between [C I] and (CO)-C-13 J = 1-0. Bright [C I] emission occurs in the relatively cold gas behind the molecular cores but does not occur in either highly excited gas traced by CO J = 3-2 emission or in the H II region/molecular cloud interface. These results are inconsistent with those predicted by standard photodissociation region models, suggesting an origin for interstellar atomic carbon unrelated to photodissociation processes.
研究論文（学術雑誌）, 英語 - Observation of the C [CSC]i[/CSC] [TSUP]3[/TSUP][ITAL]P[/ITAL][TINF]2[/TINF]–[TSUP]3[/TSUP][ITAL]P[/ITAL][TINF]1[/TINF] Line toward the Orion Kleinmann-Low Region
Satoshi Yamamoto; Hiroyuki Maezawa; Masafumi Ikeda; Tetsuya Ito; Tomoharu Oka; Gaku Saito; Mitsuhiro Iwata; Kazuhisa Kamegai; Takeshi Sakai; Yutaro Sekimoto; Ken’ichi Tatematsu; Takashi Noguchi; Sheng-Cai Shi; Yuji Arikawa; Yoshiyuki Aso; Keisuke Miyazawa; Shuji Saito; Hideo Fujiwara; Masatoshi Ohishi; Hiroyuki Ozeki; Junji Inatani
The Astrophysical Journal, American Astronomical Society, 547巻, 2号, 掲載ページ L165-L169, 出版日 2001年02月01日, 査読付
研究論文（学術雑誌） - Observation of the (CIP2)-P-3-P-3(1) line toward the Orion Kleinmann-Low region
S Yamamoto; H Maezawa; M Ikeda; T Ito; T Oka; G Saito; M Iwata; K Kamegai; T Sakai; Y Sekimoto; K Tatematsu; T Noguchi; SC Shi; Y Arikawa; Y Aso; K Miyazawa; S Saito; H Fujiwara; M Ohishi; H Ozeki; J Inatani
ASTROPHYSICAL JOURNAL, UNIV CHICAGO PRESS, 547巻, 2号, 掲載ページ L165-L169, 出版日 2001年02月, 査読付, The P-3(2)-P-3(1) fine-structure line of the neutral carbon atom (809 GHz) has been observed toward the Orion Kleinmann-Low (KL) region with the Mount Fuji submillimeter-wave telescope. The 6' x 6' area centered at Orion KL has been mapped with a grid spacing of 1'.5. The intensity distribution of the P-3(2)-P-3(1) line is found to be similar to that of the P-3(1)-P-3(0) line; these lines are rather weak toward Orion KL, while they are both bright at Orion KL's northern and southern positions. The excitation temperature determined from the intensity ratio between the P-3(2)-P-3(1) and P-3(1)-P-3(0) lines ranges from 40 to 110 K. The excitation temperature is not enhanced toward Orion KL, whereas it tends to be high in the vicinity of theta (1) Orionis C. These results indicate that the C I emission arises from a photodissociation surface illuminated by strong UV radiation from theta (1) Ori C. The relative reduction in the C I intensities toward Orion KL is found to originate from a relatively low excitation temperature rather than from the depletion of the C I column density. The origin of the low-excitation temperature of C I toward Orion KL is discussed in terms of a radiative transfer effect.
研究論文（学術雑誌）, 英語 - <title>Plan of receiver development for ASTE/LMSA</title>
Yutaro Sekimoto; Takeshi Sakai; Gaku Saito; Kotaro Kohno; Hiroyuki Iwashita; Naohisa Satou; Toshikazu Takahashi; Takashi Noguchi; Ryohei Kawabe; Hiroyuki Maezawa; Tetsuya Ito; Satoshi Yamamoto
SPIE Proceedings, SPIE, 出版日 2000年07月03日
研究論文（国際会議プロシーディングス） - The Mt. Fuji submillimeter-wave telescope
Yutaro Sekimoto; Yuji Arikawa; Yoshiyuki Aso; Hideo Fujiwara; Masafumi Ikeda; Junji Inatani; Tetsuya Ito; Mituhiro Iwata; Kazuhisa Kamegai; Hiroyuki Maezawa; Takashi Noguchi; Masatoshi Ohishi; Tomoharu Oka; Hiroyuki Ozeki; Gaku Saito; Shuji Saito; Takeshi Sakai; Sheng-Cai Shi; Ken'ichi Tatematsu; Satoshi Yamamoto
SPIE Proceedings, SPIE, 出版日 2000年07月03日
研究論文（国際会議プロシーディングス） - The Mt. Fuji submillimeter-wave telescope
Y Sekimoto; S Yamamoto; T Oka; M Ikeda; H Maezawa; T Ito; G Saito; M Iwata; K Kamegai; T Sakai; K Tatematsu; Y Arikawa; Y Aso; T Noguchi; K Miyazawa; SC Shi; S Saito; H Ozeki; H Fujiwara; J Inatani; M Ohishi; K Noda; Y Togashi
REVIEW OF SCIENTIFIC INSTRUMENTS, AMER INST PHYSICS, 71巻, 7号, 掲載ページ 2895-2907, 出版日 2000年07月, 査読付, We have developed a 1.2 m submillimeter-wave telescope at the summit of Mt. Fuji to survey emission lines of the neutral carbon atom (C-I) toward the Milky Way. A superconductor-insulator-superconductor mixer receiver on the Nasmyth focus is used to observe the 492 GHz band in SSB and the 345 GHz band in DSB simultaneously. The receiver noise temperature is 300 K in SSB and 200 K in DSB for 492 and 345 GHz, respectively. The intermediate frequency frequency is 1.8-2.5 GHz. An acousto-optical spectrometer which has the total bandwidth of 0.9 GHz and 1024 channel outputs has also been developed. The telescope was installed at the summit of Mt. Fuji (alt. 3725 m) in July 1998. It has been remotely operated via a satellite communication system from Tokyo or Nobeyama. Atmospheric opacity at Mt. Fuji was 0.4-1.0 at 492 GHz during 30% of the time and 0.07-0.5 at 345 GHz during 60% of the time from November 1998 to February 1999. The system noise temperature was 1000-3000 K in SSB at 492 GHz and 500-2000 K in DSB at 345 GHz. We observed the CI (P-3(1)-P-3(0): 492 GHz) and CO (J=3-2: 345 GHz) emission lines from nearby molecular clouds with the beam size of 2.'2 and 3.'1, respectively. We describe the telescope system and report the performance obtained in the 1998 winter. (C) 2000 American Institute of Physics. [S0034-6748(00)04907-8].
研究論文（学術雑誌）, 英語
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出版日 2008年04月, Proc. of the 19th International Symposium on Space Terahertz Technology, 掲載ページ 286-291, 英語, 速報，短報，研究ノート等（学術雑誌） - Plan of receiver development for ASTE/LMSA
Yutaro Sekimoto; Takeshi Sakai; Gaku Saito; Kotaro Kohno; Hiroyuki Iwashita; Naohisa Satou; Toshikazu Takahashi; Takashi Noguchi; Ryohei Kawabe; Hiroyuki Maezawa; Tetsuya Ito; Satoshi Yamamoto
We present a plan of heterodyne receivers for Atacama Submillimeter Telescope Experiment (ASTE), which is one of Japanese R&D project of Large Millimeter Submillimeter Array (LMSA) and Atacama Large Millimeter Array (ALMA). A new 10 m submillimeter-wave telescope has been pre-installed at Nobeyama since February 2000 and will be installed at Pampa la Bola (el. 4800 m) in northern Chile. The telescope has four receiver layouts: (1) A shaped Cassegrain optics was designed for the Nobeyama operation to achieve high beam-efficiency at millimeter-wave bands. (2) Normal gaussian optics will be replaced for the Chile operation to optimize submillimeter-wave bands up to 850 GHz. (3) It is possible to install an ALMA prototype receiver at the focus of secondary reflector. (4) an optics for submillimeter SIS photon camera. We describe the 350 GHz receiver which noise temperature was around 55 K in the frequency band of 330 - 360 GHz. The temperature ripple at the 4 K stage of two stages Gifford-McMahon refrigerator has been reduced to be less than 10 mK by employing a He-pot temperature stabilizer., SPIE-INT SOC OPTICAL ENGINEERING, 出版日 2000年, Proceedings of SPIE - The International Society for Optical Engineering, 4015巻, 掲載ページ 605-613, 英語, 査読付, 0277-786X, 0033720358, WOS:000089219700063
担当経験のある科目_授業
- 基盤理工学専攻基礎
The University of Electro-Communications - 基盤理工学専攻基礎
電気通信大学 - 電子工学実験第一
The University of Electro-Communications - 電子工学実験第一
電気通信大学 - 電気回路演習
電気通信大学 - 電気回路
The University of Electro-Communications - 力学演習
The University of Electro-Communications - 力学
電気通信大学 - 電気回路演習
The University of Electro-Communications - 電気回路演習
電気通信大学 - 電気回路
電気通信大学 - 電気回路
電気通信大学 - 力学演習
電気通信大学 - 力学演習
電気通信大学 - 力学
The University of Electro-Communications - 力学
電気通信大学 - 電子情報システム実験第一実験
電気通信大学 - 電子情報システム実験第一実験
電気通信大学 - 基礎科学実験A
The University of Electro-Communications - 電子情報システム実験第一
電気通信大学 - 電子情報システム実験第一
The University of Electro-Communications - 電子情報システム実験第一
電気通信大学 - 基礎科学実験A
電気通信大学 - 基礎科学実験A
電気通信大学
共同研究・競争的資金等の研究課題
- 次世代の天文観測用1.5THz帯IF広帯域HEBミキサの開発と分子分光への応用
酒井 剛
日本学術振興会, 科学研究費助成事業, 電気通信大学, 基盤研究(B), 24K00675
研究期間 2024年04月01日 - 2028年03月31日 - 遠赤外線微細構造輝線で切り拓く前・宇宙再電離期の銀河形成
田村 陽一; 井上 昭雄; 酒井 剛; 小嶋 崇文; 河野 孝太郎; 田中 邦彦
日本学術振興会, 科学研究費助成事業, 名古屋大学, 基盤研究(S), 22H04939
研究期間 2022年04月27日 - 2027年03月31日 - 遠赤外線酸素原子輝線の分光観測による前・宇宙再電離期の開拓
研究期間 2022年04月01日 - 2027年03月31日 - 高感度・高分解能観測で探る惑星系形成領域の化学進化
研究期間 2020年11月19日 - 2025年03月31日 - 重水素分子で探る星形成の極初期
研究期間 2020年 - 2025年03月31日 - ALMAで探る大質量星形成領域における窒素を含む複雑な有機分子の起源
研究期間 2020年04月01日 - 2023年03月31日 - テラヘルツ天文学を切り開く高感度電波分光観測用受信機の開発
研究期間 2019年 - 2022年 - 原始惑星系円盤形成領域の化学組成とその進化
研究期間 2018年 - 2022年 - 超伝導素子と超伝導回路を融合した受信分光システム
研究期間 2019年 - 2021年 - 分子雲の進化を解明する30cmサブミリ波望遠鏡による銀河面サーベイ観測
瀬田益道
研究期間 2016年 - 2019年 - 高感度2ミリ帯分光観測による隠された爆発的星形成と巨大ブラックホールの研究
研究期間 2015年 - 2019年 - 分子輝線観測による大質量星なしクランプ内部での分子雲コア形成過程の解明
研究期間 2016年 - 2018年 - 多波長ラインサーベイによる星形成から惑星系形成に至る化学進化の解明
山本 智; 高野 秀路; 前澤 裕之; 廣田 朋也; 酒井 剛; 坂井 南美; 椎野 竜哉; 徳留 智矢; 相馬 達也; 猪熊 宏士; 西村 優里; 大屋 瑶子
日本学術振興会, 科学研究費助成事業, 東京大学, 基盤研究(S), 本研究では、低質量原始星まわりの円盤形成に伴う化学進化を電波観測で探求した。また、それに必要な高感度受信機を開発した。主な成果は次の通りである。(1)多波長スペクトル線サーベイ観測により、原始星エンベロープの化学的多様性を確立した。(2)原始星近傍の衝撃波領域でスペクトル線サーベイ観測により星間塵の化学組成の知見を得た。(3)低質量原始星L1527の高空間分解能観測を行い、原始星エンベロープの遠心力バリアの位置を初めて同定した。また、円盤形成に伴い化学組成が劇的に変化していることを見出した。(4)進化の進んだClass I段階の原始星、TMC-1A、で炭素鎖分子の消失を捉えた。, 21224002
研究期間 2009年05月11日 - 2014年03月31日 - NMAの単一鏡化と多周波2SB受信化による惑星中層大気環境の変動起源の観測的探求
前澤 裕之; 徳丸 宗利; 佐川 英夫; 笠井 康子; 奥田 武志; 笠羽 康正; 川辺 良平; 酒井 剛; 寺田 直樹; 水野 亮; 奥田 武志
日本学術振興会, 科学研究費助成事業, 大阪府立大学, 基盤研究(B), ハビタブルゾーンの理解を深めるため、太陽系惑星の大気環境監視プロジェクトを実施し、G 型星である太陽の活動が惑星中層大気に与える影響について観測的研究を推進した。野辺山宇宙電波観測所の干渉計望遠群から、口径 10m の望遠鏡1台切り離して単一鏡化し、惑星大気環境監視専用望遠鏡 SPART を立ち上げた。この結果、一酸化炭素輝線(100 GHz)のかつてない高頻度観測が実現し、金星については、高度80km 付近の一酸化炭素が過去数十年の中でも低い水準に留まっていることを見出した。太陽活動の紫外線や CME に伴う高エネルギー粒子イベントの最近の低下傾向などとの関連が示唆され、G～M 型星を中心星とする地球型惑星や系外惑星、太陽系の気候を理解する上で、重要な知見が得られた。, 22340042
研究期間 2010年 - 2012年