| 町田 正博（まちだ まさひろ） | データ更新日：2024.04.05 |
教授 ／
理学研究院
地球惑星科学部門
太陽惑星系物質科学
| 1. | Takayuki Kotani, Motohide Tamura, Jun Nishikawa, Akitoshi Ueda, Masayuki Kuzuhara, Masashi Omiya, Jun Hashimoto, Masato Ishizuka, Teruyuki Hirano, Hiroshi Suto, Takashi Kurokawa, Tsukasa Kokubo, Takahiro Mori, Yosuke Tanaka, Ken Kashiwagi, Mihoko Konishi, Tomoyuki Kudo, Bun'Ei Sato, Shane Jacobson, Klaus W. Hodapp, Donald B. Hall, Wako Aoki, Tomonori Usuda, Shogo Nishiyama, Tadashi Nakajima, Yuji Ikeda, Tomoyasu Yamamuro, Jun Ichi Morino, Haruka Baba, Ko Hosokawa, Hiroyuki Ishikawa, Norio Narita, Eiichiro Kokubo, Yutaka Hayano, Hideyuki Izumiura, Eiji Kambe, Nobuhiko Kusakabe, Jungmi Kwon, Masahiro Ikoma, Yasunori Hori, Hidenori Genda, Akihiko Fukui, Yuka Fujii, Hajime Kawahara, Guyon Olivier, Nemanja Jovanovic, Hiroki Harakawa, Masahiko Hayashi, Masahide Hidai, Masahiro Machida, Taro Matsuo, Tetsuya Nagata, Masahiro Ogihara, Hideki Takami, Naruhisa Takato, Hiroshi Terada, Daehyeon Oh, The infrared Doppler (IRD) instrument for the Subaru telescope Instrument description and commissioning results, Ground-based and Airborne Instrumentation for Astronomy VII 2018, 2018.01, [URL], The Infrared Doppler (IRD) instrument is a fiber-fed high-resolution NIR spectrometer for the Subaru telescope covering the Y,J,H-bands simultaneously with a maximum spectral resolution of 70,000. The main purpose of IRD is a search for Earth-mass planets around nearby M-dwarfs by precise radial velocity measurements, as well as a spectroscopic characterization of exoplanet atmospheres. We report the current status of the instrument, which is undergoing commissioning at the Subaru Telescope, and the first light observation successfully done in August 2017. The general description of the instrument will be given including spectrometer optics, fiber injection system, cryogenic system, scrambler, and laser frequency comb. A large strategic survey mainly focused on late-type M-dwarfs is planned to start from 2019.. |
| 2. | K. Tomida, Masahiro Machida, T. Hosokawa, Y. Sakurai, C. H. Lin, Grand design spiral arms in a young forming circumstellar disk, 2017 Conference Francesco's Legacy: Star Formation in Space and Time, 2017.01, We study formation and long-term evolution of a circumstellar disk using a resistive magnetohydrodynamic simulation. While the formed circumstellar disk is initially small, it grows as accretion continues and its radius becomes as large as 200 AUs toward the end of the Class-I phase. A pair of grand-design spiral arms form due to gravitational instability in the disk, and they transfer angular momentum. Although the spiral arms disappear in a few rotations, new spiral arms form recurrently throughout the Class-0 and I phases as the disk soon becomes unstable again by gas accretion. Using synthetic observation, we compare our model with a recent high-resolution observation of Elias 2-27, whose circumstellar disk has grand design spiral arms, and find good agreement. Our model suggests that the grand design spiral arms around Elias 2-27 are consistent with material arms formed by gravitational instability. If such spiral arms commonly exist in young circumstellar disks, it implies that young circumstellar disks are considerably massive and gravitational instability is the key process of angular momentum transport.. |
| 3. | K. Tomida, Masahiro Machida, T. Hosokawa, Y. Sakurai, C. H. Lin, Grand design spiral arms in a young forming circumstellar disk, 2017 Conference Francesco's Legacy: Star Formation in Space and Time, 2017.01, We study formation and long-term evolution of a circumstellar disk using a resistive magnetohydrodynamic simulation. While the formed circumstellar disk is initially small, it grows as accretion continues and its radius becomes as large as 200 AUs toward the end of the Class-I phase. A pair of grand-design spiral arms form due to gravitational instability in the disk, and they transfer angular momentum. Although the spiral arms disappear in a few rotations, new spiral arms form recurrently throughout the Class-0 and I phases as the disk soon becomes unstable again by gas accretion. Using synthetic observation, we compare our model with a recent high-resolution observation of Elias 2-27, whose circumstellar disk has grand design spiral arms, and find good agreement. Our model suggests that the grand design spiral arms around Elias 2-27 are consistent with material arms formed by gravitational instability. If such spiral arms commonly exist in young circumstellar disks, it implies that young circumstellar disks are considerably massive and gravitational instability is the key process of angular momentum transport.. |
| 4. | K. Tomida, Masahiro Machida, T. Hosokawa, Y. Sakurai, C. H. Lin, Grand design spiral arms in a young forming circumstellar disk, 2017 Conference Francesco's Legacy: Star Formation in Space and Time, 2017.01, We study formation and long-term evolution of a circumstellar disk using a resistive magnetohydrodynamic simulation. While the formed circumstellar disk is initially small, it grows as accretion continues and its radius becomes as large as 200 AUs toward the end of the Class-I phase. A pair of grand-design spiral arms form due to gravitational instability in the disk, and they transfer angular momentum. Although the spiral arms disappear in a few rotations, new spiral arms form recurrently throughout the Class-0 and I phases as the disk soon becomes unstable again by gas accretion. Using synthetic observation, we compare our model with a recent high-resolution observation of Elias 2-27, whose circumstellar disk has grand design spiral arms, and find good agreement. Our model suggests that the grand design spiral arms around Elias 2-27 are consistent with material arms formed by gravitational instability. If such spiral arms commonly exist in young circumstellar disks, it implies that young circumstellar disks are considerably massive and gravitational instability is the key process of angular momentum transport.. |
| 5. | K. Tomida, Masahiro Machida, T. Hosokawa, Y. Sakurai, C. H. Lin, Grand design spiral arms in a young forming circumstellar disk, 2017 Conference Francesco's Legacy: Star Formation in Space and Time, 2017.01, We study formation and long-term evolution of a circumstellar disk using a resistive magnetohydrodynamic simulation. While the formed circumstellar disk is initially small, it grows as accretion continues and its radius becomes as large as 200 AUs toward the end of the Class-I phase. A pair of grand-design spiral arms form due to gravitational instability in the disk, and they transfer angular momentum. Although the spiral arms disappear in a few rotations, new spiral arms form recurrently throughout the Class-0 and I phases as the disk soon becomes unstable again by gas accretion. Using synthetic observation, we compare our model with a recent high-resolution observation of Elias 2-27, whose circumstellar disk has grand design spiral arms, and find good agreement. Our model suggests that the grand design spiral arms around Elias 2-27 are consistent with material arms formed by gravitational instability. If such spiral arms commonly exist in young circumstellar disks, it implies that young circumstellar disks are considerably massive and gravitational instability is the key process of angular momentum transport.. |
| 6. | S. I. Inutsuka, Masahiro Machida, T. Matsumoto, Y. Tsukamoto, K. Iwasaki, Low-Mass Star Formation From Molecular Cloud Cores to Protostars and Protoplanetary Disks, 6th Zermatt Symposium on Conditions and Impact of Star Formation: From Lab to Space 2015, 2016.05, [URL], This review describes realistic evolution of magnetic field and rotation of the protostars, dynamics of outflows and jets, and the formation and evolution of protoplanetary disks. Recent advances in the protostellar collapse simulations cover a huge dynamic range from molecular cloud core density to stellar density in a self-consistent manner and account for all the non-ideal magnetohydrodynamical effects, such as Ohmic resistivity, ambipolar diffusion, and Hall current. We explain the emergence of the first core, i.e., the quasi-hydrostatic object that consists of molecular gas, and the second core, i.e., the protostar. Ohmic dissipation largely removes the magnetic flux from the center of a collapsing cloud core. A fast well-collimated bipolar jet along the rotation axis of the protostar is driven after the magnetic field is re-coupled with warm gas (∼103 K) around the protostar. The circumstellar disk is born in the "dead zone", a region that is de-coupled from the magnetic field, and the outer radius of the disk increases with that of the dead zone during the early accretion phase. The rapid increase of the disk size occurs after the depletion of the envelope of molecular cloud core. The effect of Hall current may create two distinct populations of protoplanetary disks.. |
| 7. | S. I. Inutsuka, Masahiro Machida, T. Matsumoto, Y. Tsukamoto, K. Iwasaki, Low-Mass Star Formation From Molecular Cloud Cores to Protostars and Protoplanetary Disks, 6th Zermatt Symposium on Conditions and Impact of Star Formation: From Lab to Space 2015, 2016.05, [URL], This review describes realistic evolution of magnetic field and rotation of the protostars, dynamics of outflows and jets, and the formation and evolution of protoplanetary disks. Recent advances in the protostellar collapse simulations cover a huge dynamic range from molecular cloud core density to stellar density in a self-consistent manner and account for all the non-ideal magnetohydrodynamical effects, such as Ohmic resistivity, ambipolar diffusion, and Hall current. We explain the emergence of the first core, i.e., the quasi-hydrostatic object that consists of molecular gas, and the second core, i.e., the protostar. Ohmic dissipation largely removes the magnetic flux from the center of a collapsing cloud core. A fast well-collimated bipolar jet along the rotation axis of the protostar is driven after the magnetic field is re-coupled with warm gas (∼103 K) around the protostar. The circumstellar disk is born in the "dead zone", a region that is de-coupled from the magnetic field, and the outer radius of the disk increases with that of the dead zone during the early accretion phase. The rapid increase of the disk size occurs after the depletion of the envelope of molecular cloud core. The effect of Hall current may create two distinct populations of protoplanetary disks.. |
| 8. | S. I. Inutsuka, Masahiro Machida, T. Matsumoto, Y. Tsukamoto, K. Iwasaki, Low-Mass Star Formation From Molecular Cloud Cores to Protostars and Protoplanetary Disks, 6th Zermatt Symposium on Conditions and Impact of Star Formation: From Lab to Space 2015, 2016.05, [URL], This review describes realistic evolution of magnetic field and rotation of the protostars, dynamics of outflows and jets, and the formation and evolution of protoplanetary disks. Recent advances in the protostellar collapse simulations cover a huge dynamic range from molecular cloud core density to stellar density in a self-consistent manner and account for all the non-ideal magnetohydrodynamical effects, such as Ohmic resistivity, ambipolar diffusion, and Hall current. We explain the emergence of the first core, i.e., the quasi-hydrostatic object that consists of molecular gas, and the second core, i.e., the protostar. Ohmic dissipation largely removes the magnetic flux from the center of a collapsing cloud core. A fast well-collimated bipolar jet along the rotation axis of the protostar is driven after the magnetic field is re-coupled with warm gas (∼103 K) around the protostar. The circumstellar disk is born in the "dead zone", a region that is de-coupled from the magnetic field, and the outer radius of the disk increases with that of the dead zone during the early accretion phase. The rapid increase of the disk size occurs after the depletion of the envelope of molecular cloud core. The effect of Hall current may create two distinct populations of protoplanetary disks.. |
| 9. | S. I. Inutsuka, Masahiro Machida, T. Matsumoto, Y. Tsukamoto, K. Iwasaki, Low-Mass Star Formation From Molecular Cloud Cores to Protostars and Protoplanetary Disks, 6th Zermatt Symposium on Conditions and Impact of Star Formation: From Lab to Space 2015, 2016.05, [URL], This review describes realistic evolution of magnetic field and rotation of the protostars, dynamics of outflows and jets, and the formation and evolution of protoplanetary disks. Recent advances in the protostellar collapse simulations cover a huge dynamic range from molecular cloud core density to stellar density in a self-consistent manner and account for all the non-ideal magnetohydrodynamical effects, such as Ohmic resistivity, ambipolar diffusion, and Hall current. We explain the emergence of the first core, i.e., the quasi-hydrostatic object that consists of molecular gas, and the second core, i.e., the protostar. Ohmic dissipation largely removes the magnetic flux from the center of a collapsing cloud core. A fast well-collimated bipolar jet along the rotation axis of the protostar is driven after the magnetic field is re-coupled with warm gas (∼103 K) around the protostar. The circumstellar disk is born in the "dead zone", a region that is de-coupled from the magnetic field, and the outer radius of the disk increases with that of the dead zone during the early accretion phase. The rapid increase of the disk size occurs after the depletion of the envelope of molecular cloud core. The effect of Hall current may create two distinct populations of protoplanetary disks.. |
| 10. | 町田 正博, 星磁場と回転の効果による円盤の方向の空間依存性 , 日本天文学会, 2015.09, 近年の観測から星形成領域で大局磁場とジェット、アウトフローの向きが異なることが示唆されている。また、星形成領域の偏光観測によって複雑な形状の磁力線が観測されている。磁場は星の形成に関して重大な役割を果たすが、その振る舞いは単純ではない。収縮するガス雲中でローレンツ力と遠心力によって特定の方向の収縮が抑制させることによって円盤状の構造が出来る。磁場によって作られる円盤状構造をpseudo-diskと呼び、回転によって作られる構造を回転円盤と呼ぶ。. |
| 11. | 町田 正博, 星形成初期段階での空間スケールの違いによる角運動量輸送機構, 日本天文学会, 2015.03, 星は分子雲コアが重力収縮して誕生する。観測から分子雲コアの角運動量は原始星の角運動量よりも 4−5 桁程 度大きいことが分かっている。そのため、星が出来る過程でどのようにして角運動量を輸送するかを理解すること は星形成過程を解明する上で重要である。先行研究によって、星形成過程で現れるアウトフローによって分子雲コ アが持っていた角運動量の多くの割合が星間空間に微量のガスと共に放出されることが示された。しかし、今ま での研究では磁場の散逸や原始星形成後に現れるジェットなどによる角運動量輸送過程は調べられていなかった。 この研究では、星形成前の分子雲コアを初期条件として星形成過程を計算を計算した。その際、分子雲コアか ら原始星のスケールまでを空間分解して原始星形成後 500 年以上の計算を行った。この計算の初期の結果は前回 の天文学会で発表しており、(i) 星周円盤外縁から低速度アウトフローが定常的に現れ、(ii) 原始星近傍からは高 速度ジェットが非定常に出現することが示された。 今回は、星の誕生前後での角運動量輸送機構について発表する。星形成直後、星周円盤の外側では主に磁気制 動によって角運動量が輸送される。他方、円盤の外縁では磁気制動に加えてアウトフローによって角運動量が効率 的に輸送される。円盤の内側では磁場の散逸のために磁場による角運動量輸送は効果的ではない。そのため、こ の領域では円盤の面密度が上昇し重力不安定性によって非軸対称な構造が発達し、円盤中の非軸対称性によって 生じる重力トルクによる角運動量輸送効率が磁場による輸送効率をはるかに卓越する。また、より小さいスケー ル (原始星近傍) では、ジェットによる角運動量輸送が効果的となる。さらに、ジェットの非定常性は円盤中での 非軸対構造による非定常降着に起因する。ることが分かった。. |
| 12. | 町田 正博, 原始星ジェットの進化, 日本天文学会, 2014.09, 星形成領域の観測から、星形成過程で高速のジェットと低速のアウトフローが現れることが分かっている。し かし、これらのフローの駆動機構は解明されていない。原始星ジェットは、その速度から重力ポテンシャルの深 い原始星近傍で駆動すると考えられているため、数値シミュレーションによってジェットの駆動を調べるために は、駆動領域である原始星を分解する必要がある。原始星は 0.01AU 程度の半径を持つ。原始星 (近傍) へは、星 周円盤から質量が供給される。そのため、ガス降着とジェットの関係を調べるためには星周円盤を解像する必要 がある。星周円盤は、1−100AU 程度の大きさを持つ。また、円盤は、分子雲コアから供給されるガスによって成 長する。分子雲コアは、1 万 AU 以上の大きさを持つ。厳密にジェットの駆動を計算するためには、原始星、星周 円盤、分子雲コアを空間分解する必要があるが、これらは空間スケールが 6 桁以上も異なる。また、時間尺度も 大きく異なる。そのため、今までの研究ではジェットの長時間進化を計算することは難しかった。 この研究では、簡単な原始星モデルと多層格子法を用いてジェットの駆動を計算した。星が出来る前の分子雲 コアを初期条件として、中心に原始星が誕生してからおよそ 300 年間ジェットの進化を計算した。結果、ジェット の駆動は非定常であることが分かった。また、従来考えられていたように、ファーストコアから駆動したアウト フローの中をジェットが突き進むことにより星形成の初期段階において二種類のフローが現れることが分かった。 計算中、原始星からのジェットは、最大 ∼ 100km/s の速度を持ち 300AU 程度まで達した。また、低速のアウト フローは ∼ 1km/s の速度を持ち 200AU 程度まで達した。. |
| 13. | Kohji Tomisaka, Akimasa Kataoka, Masahiro Machida, Kengo Tomida, Kazuya Saigo, Expected observations of star formation process From molecular cloud core to first hydrostatic core, Conference on Labyrinth of Star Formation dedicated to Prof. Anthony Whitworth, 2012, 2014.01, [URL], We performed MHD simulations of the contraction of rotating, magnetized molecular cloud cores. In the molecular cores, B-field and angular momentum (J) vector are not always aligned. When a first hydrostatic core forms, axisymmetric structure appears and average B and J are parallel in small scale. However, in large scale, the configuration is far from this. This means that contraction process is imprinted on the snapshot. We calculated two mock observations of MHD simulations (1) the polarization of dust thermal emission to reveal the magnetic evolution and (2) the line emissions from interstellar molecules to reveal the evolution of density and velocity. Comparing the mock observations with true ones, we can answer several questions: in which case the hourglass-shaped and S-shaped magnetic fields are seen; how the distribution of polarized intensity is understood; how the first hydrostatic core should be observationally identified.. |
| 14. | Takayuki Kotani, Motohide Tamura, Hiroshi Suto, Jun Nishikawa, Bun'Ei Sato, Wako Aoki, Tomonori Usuda, Takashi Kurokawa, Ken Kashiwagi, Shogo Nishiyama, Yuji Ikeda, Donald B. Hall, Klaus W. Hodapp, Shane Jacobson, Jun Hashimoto, Jun Ichi Morino, Yasushi Okuyama, Yosuke Tanaka, Shota Suzuki, Sadahiro Inoue, Jungmi Kwon, Takuya Suenaga, Dehyun Oh, Haruka Baba, Norio Narita, Eiichiro Kokubo, Yutaka Hayano, Hideyuki Izumiura, Eiji Kambe, Tomoyuki Kudo, Nobuhiko Kusakabe, Masahiro Ikoma, Yasunori Hori, Masashi Omiya, Hidenori Genda, Akihiko Fukui, Yuka Fujii, Olivier Guyon, Hiroki Harakawa, Masahiko Hayashi, Masahide Hidai, Teruyuki Hirano, Masayuki Kuzuhara, Masahiro Machida, Taro Matsuo, Tetsuya Nagata, Hirohi Onuki, Masahiro Ogihara, Hideki Takami, Naruhisa Takato, Yasuhiro H. Takahashi, Chihiro Tachinami, Hiroshi Terada, Hajime Kawahara, Tomoyasu Yamamuro, Infrared Doppler instrument (IRD) for the Subaru telescope to search for Earth-like planets around nearby M-dwarfs, Ground-Based and Airborne Instrumentation for Astronomy V, 2014.01, [URL], We report the current status of the Infrared Doppler (IRD) instrument for the Subaru telescope, which aims at detecting Earth-like planets around nearby M darwfs via the radial velocity (RV) measurements. IRD is a fiber-fed, near infrared spectrometer which enables us to obtain high-resolution spectrum (R∼70000) from 0.97 to 1.75 μm. We have been developing new technologies to achieve 1m/s RV measurement precision, including an original laser frequency comb as an extremely stable wavelength standard in the near infrared. To achieve ultimate thermal stability, very low thermal expansion ceramic is used for most of the optical components including the optical bench.. |
| 15. | Yusuke Tsukamoto, Masahiro Machida, Shu Ichiro Inutsuka, The effect of mass accretion for formation and thermal evolution of circumstellar disks, Conference on Labyrinth of Star Formation dedicated to Prof. Anthony Whitworth, 2012, 2014.01, [URL]. |
| 16. | Kohji Tomisaka, Akimasa Kataoka, Masahiro Machida, Kengo Tomida, Kazuya Saigo, Expected observations of star formation process From molecular cloud core to first hydrostatic core, Conference on Labyrinth of Star Formation dedicated to Prof. Anthony Whitworth, 2012, 2014.01, [URL], We performed MHD simulations of the contraction of rotating, magnetized molecular cloud cores. In the molecular cores, B-field and angular momentum (J) vector are not always aligned. When a first hydrostatic core forms, axisymmetric structure appears and average B and J are parallel in small scale. However, in large scale, the configuration is far from this. This means that contraction process is imprinted on the snapshot. We calculated two mock observations of MHD simulations (1) the polarization of dust thermal emission to reveal the magnetic evolution and (2) the line emissions from interstellar molecules to reveal the evolution of density and velocity. Comparing the mock observations with true ones, we can answer several questions: in which case the hourglass-shaped and S-shaped magnetic fields are seen; how the distribution of polarized intensity is understood; how the first hydrostatic core should be observationally identified.. |
| 17. | Takayuki Kotani, Motohide Tamura, Hiroshi Suto, Jun Nishikawa, Bun'Ei Sato, Wako Aoki, Tomonori Usuda, Takashi Kurokawa, Ken Kashiwagi, Shogo Nishiyama, Yuji Ikeda, Donald B. Hall, Klaus W. Hodapp, Shane Jacobson, Jun Hashimoto, Jun Ichi Morino, Yasushi Okuyama, Yosuke Tanaka, Shota Suzuki, Sadahiro Inoue, Jungmi Kwon, Takuya Suenaga, Dehyun Oh, Haruka Baba, Norio Narita, Eiichiro Kokubo, Yutaka Hayano, Hideyuki Izumiura, Eiji Kambe, Tomoyuki Kudo, Nobuhiko Kusakabe, Masahiro Ikoma, Yasunori Hori, Masashi Omiya, Hidenori Genda, Akihiko Fukui, Yuka Fujii, Olivier Guyon, Hiroki Harakawa, Masahiko Hayashi, Masahide Hidai, Teruyuki Hirano, Masayuki Kuzuhara, Masahiro Machida, Taro Matsuo, Tetsuya Nagata, Hirohi Onuki, Masahiro Ogihara, Hideki Takami, Naruhisa Takato, Yasuhiro H. Takahashi, Chihiro Tachinami, Hiroshi Terada, Hajime Kawahara, Tomoyasu Yamamuro, Infrared Doppler instrument (IRD) for the Subaru telescope to search for Earth-like planets around nearby M-dwarfs, Ground-Based and Airborne Instrumentation for Astronomy V, 2014.01, [URL], We report the current status of the Infrared Doppler (IRD) instrument for the Subaru telescope, which aims at detecting Earth-like planets around nearby M darwfs via the radial velocity (RV) measurements. IRD is a fiber-fed, near infrared spectrometer which enables us to obtain high-resolution spectrum (R∼70000) from 0.97 to 1.75 μm. We have been developing new technologies to achieve 1m/s RV measurement precision, including an original laser frequency comb as an extremely stable wavelength standard in the near infrared. To achieve ultimate thermal stability, very low thermal expansion ceramic is used for most of the optical components including the optical bench.. |
| 18. | Yusuke Tsukamoto, Masahiro Machida, Shu Ichiro Inutsuka, The effect of mass accretion for formation and thermal evolution of circumstellar disks, Conference on Labyrinth of Star Formation dedicated to Prof. Anthony Whitworth, 2012, 2014.01, [URL]. |
| 19. | Kohji Tomisaka, Akimasa Kataoka, Masahiro Machida, Kengo Tomida, Kazuya Saigo, Expected observations of star formation process From molecular cloud core to first hydrostatic core, Conference on Labyrinth of Star Formation dedicated to Prof. Anthony Whitworth, 2012, 2014.01, [URL], We performed MHD simulations of the contraction of rotating, magnetized molecular cloud cores. In the molecular cores, B-field and angular momentum (J) vector are not always aligned. When a first hydrostatic core forms, axisymmetric structure appears and average B and J are parallel in small scale. However, in large scale, the configuration is far from this. This means that contraction process is imprinted on the snapshot. We calculated two mock observations of MHD simulations (1) the polarization of dust thermal emission to reveal the magnetic evolution and (2) the line emissions from interstellar molecules to reveal the evolution of density and velocity. Comparing the mock observations with true ones, we can answer several questions: in which case the hourglass-shaped and S-shaped magnetic fields are seen; how the distribution of polarized intensity is understood; how the first hydrostatic core should be observationally identified.. |
| 20. | Takayuki Kotani, Motohide Tamura, Hiroshi Suto, Jun Nishikawa, Bun'Ei Sato, Wako Aoki, Tomonori Usuda, Takashi Kurokawa, Ken Kashiwagi, Shogo Nishiyama, Yuji Ikeda, Donald B. Hall, Klaus W. Hodapp, Shane Jacobson, Jun Hashimoto, Jun Ichi Morino, Yasushi Okuyama, Yosuke Tanaka, Shota Suzuki, Sadahiro Inoue, Jungmi Kwon, Takuya Suenaga, Dehyun Oh, Haruka Baba, Norio Narita, Eiichiro Kokubo, Yutaka Hayano, Hideyuki Izumiura, Eiji Kambe, Tomoyuki Kudo, Nobuhiko Kusakabe, Masahiro Ikoma, Yasunori Hori, Masashi Omiya, Hidenori Genda, Akihiko Fukui, Yuka Fujii, Olivier Guyon, Hiroki Harakawa, Masahiko Hayashi, Masahide Hidai, Teruyuki Hirano, Masayuki Kuzuhara, Masahiro Machida, Taro Matsuo, Tetsuya Nagata, Hirohi Onuki, Masahiro Ogihara, Hideki Takami, Naruhisa Takato, Yasuhiro H. Takahashi, Chihiro Tachinami, Hiroshi Terada, Hajime Kawahara, Tomoyasu Yamamuro, Infrared Doppler instrument (IRD) for the Subaru telescope to search for Earth-like planets around nearby M-dwarfs, Ground-Based and Airborne Instrumentation for Astronomy V, 2014.01, [URL], We report the current status of the Infrared Doppler (IRD) instrument for the Subaru telescope, which aims at detecting Earth-like planets around nearby M darwfs via the radial velocity (RV) measurements. IRD is a fiber-fed, near infrared spectrometer which enables us to obtain high-resolution spectrum (R∼70000) from 0.97 to 1.75 μm. We have been developing new technologies to achieve 1m/s RV measurement precision, including an original laser frequency comb as an extremely stable wavelength standard in the near infrared. To achieve ultimate thermal stability, very low thermal expansion ceramic is used for most of the optical components including the optical bench.. |
| 21. | Yusuke Tsukamoto, Masahiro Machida, Shu Ichiro Inutsuka, The effect of mass accretion for formation and thermal evolution of circumstellar disks, Conference on Labyrinth of Star Formation dedicated to Prof. Anthony Whitworth, 2012, 2014.01, [URL]. |
| 22. | Kohji Tomisaka, Akimasa Kataoka, Masahiro Machida, Kengo Tomida, Kazuya Saigo, Expected observations of star formation process From molecular cloud core to first hydrostatic core, Conference on Labyrinth of Star Formation dedicated to Prof. Anthony Whitworth, 2012, 2014.01, [URL], We performed MHD simulations of the contraction of rotating, magnetized molecular cloud cores. In the molecular cores, B-field and angular momentum (J) vector are not always aligned. When a first hydrostatic core forms, axisymmetric structure appears and average B and J are parallel in small scale. However, in large scale, the configuration is far from this. This means that contraction process is imprinted on the snapshot. We calculated two mock observations of MHD simulations (1) the polarization of dust thermal emission to reveal the magnetic evolution and (2) the line emissions from interstellar molecules to reveal the evolution of density and velocity. Comparing the mock observations with true ones, we can answer several questions: in which case the hourglass-shaped and S-shaped magnetic fields are seen; how the distribution of polarized intensity is understood; how the first hydrostatic core should be observationally identified.. |
| 23. | Takayuki Kotani, Motohide Tamura, Hiroshi Suto, Jun Nishikawa, Bun'Ei Sato, Wako Aoki, Tomonori Usuda, Takashi Kurokawa, Ken Kashiwagi, Shogo Nishiyama, Yuji Ikeda, Donald B. Hall, Klaus W. Hodapp, Shane Jacobson, Jun Hashimoto, Jun Ichi Morino, Yasushi Okuyama, Yosuke Tanaka, Shota Suzuki, Sadahiro Inoue, Jungmi Kwon, Takuya Suenaga, Dehyun Oh, Haruka Baba, Norio Narita, Eiichiro Kokubo, Yutaka Hayano, Hideyuki Izumiura, Eiji Kambe, Tomoyuki Kudo, Nobuhiko Kusakabe, Masahiro Ikoma, Yasunori Hori, Masashi Omiya, Hidenori Genda, Akihiko Fukui, Yuka Fujii, Olivier Guyon, Hiroki Harakawa, Masahiko Hayashi, Masahide Hidai, Teruyuki Hirano, Masayuki Kuzuhara, Masahiro Machida, Taro Matsuo, Tetsuya Nagata, Hirohi Onuki, Masahiro Ogihara, Hideki Takami, Naruhisa Takato, Yasuhiro H. Takahashi, Chihiro Tachinami, Hiroshi Terada, Hajime Kawahara, Tomoyasu Yamamuro, Infrared Doppler instrument (IRD) for the Subaru telescope to search for Earth-like planets around nearby M-dwarfs, Ground-Based and Airborne Instrumentation for Astronomy V, 2014.01, [URL], We report the current status of the Infrared Doppler (IRD) instrument for the Subaru telescope, which aims at detecting Earth-like planets around nearby M darwfs via the radial velocity (RV) measurements. IRD is a fiber-fed, near infrared spectrometer which enables us to obtain high-resolution spectrum (R∼70000) from 0.97 to 1.75 μm. We have been developing new technologies to achieve 1m/s RV measurement precision, including an original laser frequency comb as an extremely stable wavelength standard in the near infrared. To achieve ultimate thermal stability, very low thermal expansion ceramic is used for most of the optical components including the optical bench.. |
| 24. | Yusuke Tsukamoto, Masahiro Machida, Shu Ichiro Inutsuka, The effect of mass accretion for formation and thermal evolution of circumstellar disks, Conference on Labyrinth of Star Formation dedicated to Prof. Anthony Whitworth, 2012, 2014.01, [URL]. |
| 25. | 町田 正博, 磁気制動と星周円盤の形成を適切に計算するための条件, 日本天文学会, 2013.09, [URL], 星周円盤は星形成の副産物であり惑星形成の母体であるため、その形成や進化 を理解することは重要である。しかし、理論的に星周円盤がいつ、どのように して形成するのかは未だ理解されていない。 従来、星の母体となる分子雲コアの角運動量は、原始星の角運動量よりも遥かに 大きいために 円盤形成は、収縮するガス中での角運動量保存の自然な帰結だと考えられていた。 しかし、近年、磁場の効果により原始星周囲の角運動量が外層に過剰に輸送され てしまい 回転円盤が出来ないという問題が指摘されている(Magnetic Braking Catastrophe)。 円盤形成過程は、磁場の増幅と散逸、また磁気制動とアウトフローによる角運動 量輸送などが 密接に絡み合っているために数値シミュレーションによる理解が必要となる。 しかし、シミュレーションで中心の原始星まで解像してしまうと計算のタイムス テップが 非常に短くなり円盤形成過程を計算することが出来ない。 そのため原始星近傍領域をマスクしてその内側領域を計算しないという手法(シ ンクセル法) が使用されている。 この手法を用いて円盤形成過程を計算した結果、星形成過程(少なくとも ガス降着初期段階)では回転円盤出来ないということが報告がされた(Li et al. 2011)。 しかし、研究者ごとにシンクセルの大きさや結果が大きく異なっている。 この研究では星周円盤を適切に計算するための条件を求めるために、 シンクセルの半径や境界条件などを変えて多くの計算を行った。 先ず、他の研究と同様のシンクセルを採用して過去の研究結果を再現した。 その後、シンク半径を徐々に小さくして計算結果が収束するかどうかを調べた。 その結果、ガス収縮段階において形成するファーストコアを十分な空間解像度で 分解すれば円盤形成過程が適切に計算でき、またClass 0段階の原始星周囲でも 円盤が 形成しうることが分かった。 さらに初期の分子雲コアの状態が星周円盤の形成に与える影響も調べた。. |
| 26. | 町田 正博, 原始星の進化とアウトフローの関係, 日本天文学会, 2013.03, [URL], 星形成領域の観測は、星はその誕生時に分子アウトフローというガスの放出現象を 伴うことを示唆している。このアウトフローは、広い開口角を持ち原始星周囲の ガスを 星間空間に放出する。そのため、アウトフローは原始星の進化の過程で重要な役割を 果たすと考えられているが、その駆動機構については未だ論争中である。 従来、アウトフローは、高速でコリメーションの良いジェット成分との相互作用 によっ て駆動されると考えられていた。他方、近年の 分子雲コアから原始星が誕生するまでの数値計算は、アウトフ ローは原始星の周囲に形成する円盤状天体から駆動することを示した。 後者の研究では中心星近傍からのガスの放出現象は示せたが、 長時間計算が困難だったために、計算で得られたフローを観測と比較することは 出来なかった。 この研究では、分子雲コアから原始星の形成を経て、分子雲コアが散逸するまでの 計算を行った。その際、アウトフロー駆動の内側の領域は空間 的に解像せずに分子雲コア全体を計算して、アウトフローの長時間進化を調べた。 また、中心に落下したガスから中心天体への質量降着率を導出して原始星の進化 も同時 に計算し、中心星の進化段階を決定した。 計算の結果、原始星がClass 0段階にある場合には、アウトフローは円盤に降着 するガスから エネルギーを獲得して激しく中心星近傍から放出されるが、原始星がClass I段階に 進化するとアウトフローが新たにエネルギーを獲得することが出来ず徐々に 弱くなることが分かった。 また、計算から得られたアウトフローの質量、運動量、エネルギーの時間進化は 観測と 良く一致した。 さらに、観測から得られている中心星光度とアウトフローの運動量の関係を再現する ことが出来た。 これらの結果は、原始星アウトフローは円盤からの直接駆動されるフローによっ て説明が可能 であることを意味している。 . |
| 27. | M. Tamura, H. Suto, J. Nishikawa, T. Kotani, B. Sato, W. Aoki, T. Usuda, T. Kurokawa, K. Kashiwagi, S. Nishiyama, Y. Ikeda, D. Hall, K. Hodapp, J. Hashimoto, J. Morino, S. Inoue, Y. Mizuno, Y. Washizaki, Y. Tanaka, S. Suzuki, J. Kwon, T. Suenaga, D. Oh, N. Narita, E. Kokubo, Y. Hayano, H. Izumiura, E. Kambe, T. Kudo, N. Kusakabe, M. Ikoma, Y. Hori, M. Omiya, H. Genda, A. Fukui, Y. Fujii, O. Guyon, H. Harakawa, M. Hayashi, M. Hidai, T. Hirano, M. Kuzuhara, Masahiro Machida, T. Matsuo, T. Nagata, Y. Ohnuki, M. Ogihara, S. Oshino, R. Suzuki, H. Takami, N. Takato, Y. Takahashi, C. Tachinami, H. Terada, Infrared Doppler instrument for the Subaru telescope (IRD), Ground-Based and Airborne Instrumentation for Astronomy IV, 2012.12, [URL], IRD is the near-infrared high-precision radial velocity instrument for the Subaru 8.2-m telescope. It is a relatively compact (~1m size) spectrometer with a new echelle-grating and Volume-Phase Holographic gratings covering 1-2 micron wavelengths combined with an original frequency comb using optical pulse synthesizer. The spectrometer will employ a 4096x4096-pixel HgCdTe array under testing at IfA, University of Hawaii. Both the telescope/Adaptive Optics and comb beams are fed to the spectrometer via optical fibers, while the instrument is placed at the Nasmyth platform of the Subaru telescope. Expected accuracy of the Doppler-shifted velocity measurements is about 1 m s-1. Helped with the large collecting area and high image quality of the Subaru telescope, IRD can conduct systematic radial velocity surveys of nearby middle-to-late M stars aiming for down to one Earth-mass planet. Systematic observational and theoretical studies of M stars and their planets for the IRD science are also ongoing. We will report the design and preliminary development progresses of the whole and each component of IRD.. |
| 28. | M. Tamura, H. Suto, J. Nishikawa, T. Kotani, B. Sato, W. Aoki, T. Usuda, T. Kurokawa, K. Kashiwagi, S. Nishiyama, Y. Ikeda, D. Hall, K. Hodapp, J. Hashimoto, J. Morino, S. Inoue, Y. Mizuno, Y. Washizaki, Y. Tanaka, S. Suzuki, J. Kwon, T. Suenaga, D. Oh, N. Narita, E. Kokubo, Y. Hayano, H. Izumiura, E. Kambe, T. Kudo, N. Kusakabe, M. Ikoma, Y. Hori, M. Omiya, H. Genda, A. Fukui, Y. Fujii, O. Guyon, H. Harakawa, M. Hayashi, M. Hidai, T. Hirano, M. Kuzuhara, Masahiro Machida, T. Matsuo, T. Nagata, Y. Ohnuki, M. Ogihara, S. Oshino, R. Suzuki, H. Takami, N. Takato, Y. Takahashi, C. Tachinami, H. Terada, Infrared Doppler instrument for the Subaru telescope (IRD), Ground-Based and Airborne Instrumentation for Astronomy IV, 2012.12, [URL], IRD is the near-infrared high-precision radial velocity instrument for the Subaru 8.2-m telescope. It is a relatively compact (~1m size) spectrometer with a new echelle-grating and Volume-Phase Holographic gratings covering 1-2 micron wavelengths combined with an original frequency comb using optical pulse synthesizer. The spectrometer will employ a 4096x4096-pixel HgCdTe array under testing at IfA, University of Hawaii. Both the telescope/Adaptive Optics and comb beams are fed to the spectrometer via optical fibers, while the instrument is placed at the Nasmyth platform of the Subaru telescope. Expected accuracy of the Doppler-shifted velocity measurements is about 1 m s-1. Helped with the large collecting area and high image quality of the Subaru telescope, IRD can conduct systematic radial velocity surveys of nearby middle-to-late M stars aiming for down to one Earth-mass planet. Systematic observational and theoretical studies of M stars and their planets for the IRD science are also ongoing. We will report the design and preliminary development progresses of the whole and each component of IRD.. |
| 29. | M. Tamura, H. Suto, J. Nishikawa, T. Kotani, B. Sato, W. Aoki, T. Usuda, T. Kurokawa, K. Kashiwagi, S. Nishiyama, Y. Ikeda, D. Hall, K. Hodapp, J. Hashimoto, J. Morino, S. Inoue, Y. Mizuno, Y. Washizaki, Y. Tanaka, S. Suzuki, J. Kwon, T. Suenaga, D. Oh, N. Narita, E. Kokubo, Y. Hayano, H. Izumiura, E. Kambe, T. Kudo, N. Kusakabe, M. Ikoma, Y. Hori, M. Omiya, H. Genda, A. Fukui, Y. Fujii, O. Guyon, H. Harakawa, M. Hayashi, M. Hidai, T. Hirano, M. Kuzuhara, Masahiro Machida, T. Matsuo, T. Nagata, Y. Ohnuki, M. Ogihara, S. Oshino, R. Suzuki, H. Takami, N. Takato, Y. Takahashi, C. Tachinami, H. Terada, Infrared Doppler instrument for the Subaru telescope (IRD), Ground-Based and Airborne Instrumentation for Astronomy IV, 2012.12, [URL], IRD is the near-infrared high-precision radial velocity instrument for the Subaru 8.2-m telescope. It is a relatively compact (~1m size) spectrometer with a new echelle-grating and Volume-Phase Holographic gratings covering 1-2 micron wavelengths combined with an original frequency comb using optical pulse synthesizer. The spectrometer will employ a 4096x4096-pixel HgCdTe array under testing at IfA, University of Hawaii. Both the telescope/Adaptive Optics and comb beams are fed to the spectrometer via optical fibers, while the instrument is placed at the Nasmyth platform of the Subaru telescope. Expected accuracy of the Doppler-shifted velocity measurements is about 1 m s-1. Helped with the large collecting area and high image quality of the Subaru telescope, IRD can conduct systematic radial velocity surveys of nearby middle-to-late M stars aiming for down to one Earth-mass planet. Systematic observational and theoretical studies of M stars and their planets for the IRD science are also ongoing. We will report the design and preliminary development progresses of the whole and each component of IRD.. |
| 30. | M. Tamura, H. Suto, J. Nishikawa, T. Kotani, B. Sato, W. Aoki, T. Usuda, T. Kurokawa, K. Kashiwagi, S. Nishiyama, Y. Ikeda, D. Hall, K. Hodapp, J. Hashimoto, J. Morino, S. Inoue, Y. Mizuno, Y. Washizaki, Y. Tanaka, S. Suzuki, J. Kwon, T. Suenaga, D. Oh, N. Narita, E. Kokubo, Y. Hayano, H. Izumiura, E. Kambe, T. Kudo, N. Kusakabe, M. Ikoma, Y. Hori, M. Omiya, H. Genda, A. Fukui, Y. Fujii, O. Guyon, H. Harakawa, M. Hayashi, M. Hidai, T. Hirano, M. Kuzuhara, Masahiro Machida, T. Matsuo, T. Nagata, Y. Ohnuki, M. Ogihara, S. Oshino, R. Suzuki, H. Takami, N. Takato, Y. Takahashi, C. Tachinami, H. Terada, Infrared Doppler instrument for the Subaru telescope (IRD), Ground-Based and Airborne Instrumentation for Astronomy IV, 2012.12, [URL], IRD is the near-infrared high-precision radial velocity instrument for the Subaru 8.2-m telescope. It is a relatively compact (~1m size) spectrometer with a new echelle-grating and Volume-Phase Holographic gratings covering 1-2 micron wavelengths combined with an original frequency comb using optical pulse synthesizer. The spectrometer will employ a 4096x4096-pixel HgCdTe array under testing at IfA, University of Hawaii. Both the telescope/Adaptive Optics and comb beams are fed to the spectrometer via optical fibers, while the instrument is placed at the Nasmyth platform of the Subaru telescope. Expected accuracy of the Doppler-shifted velocity measurements is about 1 m s-1. Helped with the large collecting area and high image quality of the Subaru telescope, IRD can conduct systematic radial velocity surveys of nearby middle-to-late M stars aiming for down to one Earth-mass planet. Systematic observational and theoretical studies of M stars and their planets for the IRD science are also ongoing. We will report the design and preliminary development progresses of the whole and each component of IRD.. |
| 31. | 町田 正博, 初代星周りの円盤形成と磁場の効果, 日本天文学会, 2012.09, [URL], 初代星の形成・進化を理解することは宇宙の進化を理解する上で重要である。 過去の研究から、一つのダークマターハロー中では単一の大質量初代星 が形成されると考えられてきた。 しかし、過去の研究は球対称を仮定していたために、角運動量の 効果を無視していた。その後の3次元シミュレーションも初代星形成直 後までしか計算していなかったために、初代星形成後の円盤形成段階は 調べられていなかった。 近年、シンクセル法などを用いて複数のグループが初代星形成後の進化 の計算を行った。これらの研究は、原始星誕生後に周囲の円盤が分裂して 複数の星が形成しうることを示した。 しかし、これらの計算では、(i)シンクセルが大きすぎるために分裂が盛ん に起こるであろう円盤の内側領域を計算出来ない、または、 (ii)シンクセルを用いない場合には原始星の内部構造まで計算して しまうために長時間計算が出来ないという問題があった。 この研究では、シンクセルを用いずに原始星形成後の長時間 計算を実現した。具体的には、過去の初代星の進化計算から得られた質量と 半径の関係をガスの状態方程式に組み込んだ。この手法により中心星 は質量の増加と共に半径を増大させる。そのため原始星の内部構造を計算 することは出来ないが、原始星周囲の構造を長時間計算することが可能である。 計算の結果、磁場が無い場合には、他の計算で示されているように 激しく分裂が起こり、多数の星が誕生することが分かった。 いくつかの原始星は中心近傍の比較的質量の大きな星に落下する。また、いくつかの 原始星は中心部から放出される。放出される星の最小質量は木星質量程度で ある。他方、初期宇宙に非常に弱い磁場が存在する場合には、磁気制動によって 角運動量が輸送され星周円盤が成長しない。そのため、古典的 描像のようにダークマターハローの中心に単一の大質量星が誕生する。. |
| 32. | 町田正博, 磁気星間雲中での星周円盤の形成, 日本天文学会, 2012.03, 星や円盤形成の母体となる分子雲は、磁化されておりマイクロガウス程度 の磁場を保持している。星や円盤は、この磁気星間雲 が重力収縮して形成する。星周円盤は、惑星形成の母体でもあるため、 その形成過程を理解することは星形成のみならず惑星形成の観点からも 重要である。 近年、この重力収縮するガス雲中での円盤の形成について「Magnetic Braking Catastrophe」という困難があると指摘されている。 これは、重力収縮の過程、または星形成後のガス降着段階で、磁場の効果 により角運動量が輸送されてしまい回転円盤が出来ないという問題であ る。 円盤が形成するとその回転によって磁力線が強く捻られる。 すると円盤の角運動量は、この磁力線を捻ることによって星間空間に輸送される。 円盤が回転を続ける限り磁力線が捻られ続け角運動量も輸送され続ける。 そのため、星形成過程では回転円盤が出来ないという主張である。 我々は、磁気星間雲中での星周円盤の形成過程を調べるために、磁気散逸 MHD多層格子法を用いて、星形成前の分子雲コアから星が誕生して円盤が 出来る過程の計算を行った。その結果、分子雲の磁場が強い場合でも回転円盤が 出来ることが分かった。円盤形成の初期段階では、周囲に十分なガスが 残っているために、円盤の角運動量は磁力線を通じて円盤周囲のガス に輸送される。しかし、分子雲が十分進化して、分子雲内のガスが円盤に落下し 円盤ガスよりも軽くなると角運動量を効率的に輸送できなくなる。従って、 分子雲のガスが枯渇しつつある段階では回転円盤の形成が可能となる。 さらに、初期にガス雲が重力的に非常に不安定であり円盤へのガス降着率が 大きい場合には、磁場による角運動量輸送率よりもガス降着によって持ち込 まれる角運動量の方が大きくなり、中心星が非常に若い段階でも十分に大き く重い円盤が出来ることが分かった。. |
| 33. | 町田正博、松本倫明, 星周円盤とガス惑星形成における重元素量の影響, 日本天文学会, 2011.09, 系外惑星の観測は、主星の重元素量が多い程、惑星が存在する確率が高いこと を示している。 コア・アクリーションシナリオに従うと、このような 重元素量が多い円盤中では固体コアが出来やすくガス惑星も誕生しやす いことが分かる。そのため、主星の重元素量と惑星頻度の関係は、 惑星がコア・アクリーションによって誕生したことの間接的な証拠であると 考えられている。 他方、もう一つの惑星形成シナリオである重力不安定シナリオでは、ダスト や重元素量の違いは、ガス惑星の形成にはほとんど影響を与えないと考えられ ている。しかし、この重力不安定シナリオを考える場合には、円盤の形成も 考慮する必要がある。 この講演では、円盤のサイズや質量がダストの量(重元素量)と密接に関係しており、 コア・アクリーションシナリオと同様に、金属量が高いほど重い円盤が形成し、 重力不安定によりガス惑星形成が誕生しやすいことを示す。 観測されているような分子雲コアを初期条件として、ガスに含まれるダストの量 をパラメータとして、円盤形成の計算を行った。ダストの存在量の違いは、ガス の熱進化とイオン化度を通して磁場の散逸に影響を与える。計算の結果、ダスト の量が多いほど、重くサイズの大きな円盤が出来ることが分かった。これは、 以下の2つの理由による。 (1)ダスト量が多い程、ガスが光学的に厚くなる密度が低く、初期により大きな円盤 を形成する。 (2)ガス中にダストが豊富に存在する程、ガスのイオン化度が低く 磁場がより散逸して磁場制動 による角運動量輸送が非効率的になり大きな円盤を成長させる。 これらの結果は、星形成前の分子雲コアが重元素を豊富に含むほど、重力不安定 によってガス惑星 が誕生しやすいことを示唆している。. |
| 34. | Masahiro Machida, Recent developments in simulations of low-mass star formation, 2011.04, [URL], In star forming regions, we can observe different evolutionary stages of various objects and phenomena such as molecular clouds, protostellar jets and outflows, circumstellar disks, and protostars. However, it is difficult to directly observe the star formation process itself, because it is veiled by the dense infalling envelope. Numerical simulations can unveil the star formation process in the collapsing gas cloud. Recently, some studies showed protostar formation from the prestellar core stage, in which both molecular clouds and protostars are resolved with sufficient spatial resolution. These simulations showed fragmentation and binary formation, outflow and jet driving, and circumstellar disk formation in the collapsing gas clouds. In addition, the angular momentum transfer and dissipation process of the magnetic field in the star formation process were investigated. In this paper, I review recent developments in numerical simulations of low-mass star formation.. |
| 35. | Masahiro Machida, Recent developments in simulations of low-mass star formation, 2011.04, [URL], In star forming regions, we can observe different evolutionary stages of various objects and phenomena such as molecular clouds, protostellar jets and outflows, circumstellar disks, and protostars. However, it is difficult to directly observe the star formation process itself, because it is veiled by the dense infalling envelope. Numerical simulations can unveil the star formation process in the collapsing gas cloud. Recently, some studies showed protostar formation from the prestellar core stage, in which both molecular clouds and protostars are resolved with sufficient spatial resolution. These simulations showed fragmentation and binary formation, outflow and jet driving, and circumstellar disk formation in the collapsing gas clouds. In addition, the angular momentum transfer and dissipation process of the magnetic field in the star formation process were investigated. In this paper, I review recent developments in numerical simulations of low-mass star formation.. |
| 36. | Masahiro Machida, Recent developments in simulations of low-mass star formation, 2011.04, [URL], In star forming regions, we can observe different evolutionary stages of various objects and phenomena such as molecular clouds, protostellar jets and outflows, circumstellar disks, and protostars. However, it is difficult to directly observe the star formation process itself, because it is veiled by the dense infalling envelope. Numerical simulations can unveil the star formation process in the collapsing gas cloud. Recently, some studies showed protostar formation from the prestellar core stage, in which both molecular clouds and protostars are resolved with sufficient spatial resolution. These simulations showed fragmentation and binary formation, outflow and jet driving, and circumstellar disk formation in the collapsing gas clouds. In addition, the angular momentum transfer and dissipation process of the magnetic field in the star formation process were investigated. In this paper, I review recent developments in numerical simulations of low-mass star formation.. |
| 37. | Masahiro Machida, Recent developments in simulations of low-mass star formation, 2011.04, [URL], In star forming regions, we can observe different evolutionary stages of various objects and phenomena such as molecular clouds, protostellar jets and outflows, circumstellar disks, and protostars. However, it is difficult to directly observe the star formation process itself, because it is veiled by the dense infalling envelope. Numerical simulations can unveil the star formation process in the collapsing gas cloud. Recently, some studies showed protostar formation from the prestellar core stage, in which both molecular clouds and protostars are resolved with sufficient spatial resolution. These simulations showed fragmentation and binary formation, outflow and jet driving, and circumstellar disk formation in the collapsing gas clouds. In addition, the angular momentum transfer and dissipation process of the magnetic field in the star formation process were investigated. In this paper, I review recent developments in numerical simulations of low-mass star formation.. |
| 38. | 町田正博, 低金属量下での星周円盤の形成, 日本天文学会2011年春季年会, 2011.03, [URL]. |
| 39. | Masahiro Machida, Kazuyuki Omukai, Tomoaki Matsumoto, Magnetohy drodynamics of Population III star formation, 1st Stars and Galaxies: Challenges for the Next Decade, 2010.12, [URL], The evolution of collapsing primordial clouds and the formation of Population III (Pop III) protostars are investigated with three-dimensional ideal MHD simulations. We follow the collapse of parsec-sized primordial clouds down to the formation of protostars on sub-AU scales. Pop III protostar formation is characterized by the ratio of rotational to magnetic energy of the natal cloud. When the rotational energy is larger than the magnetic energy, fragmentation occurs prior to the formation of the protostar, and a binary or multiple system appears. When the magnetic energy is greater than the rotational energy, a strong (> 100 km s-1) jet is driven by the circumstellar disk around the protostar, which does not fragment. Thus, even in the early universe, magnetic fields play an important role in the star formation process.. |
| 40. | Masahiro Machida, Kazuyuki Omukai, Tomoaki Matsumoto, Magnetohy drodynamics of Population III star formation, 1st Stars and Galaxies: Challenges for the Next Decade, 2010.12, [URL], The evolution of collapsing primordial clouds and the formation of Population III (Pop III) protostars are investigated with three-dimensional ideal MHD simulations. We follow the collapse of parsec-sized primordial clouds down to the formation of protostars on sub-AU scales. Pop III protostar formation is characterized by the ratio of rotational to magnetic energy of the natal cloud. When the rotational energy is larger than the magnetic energy, fragmentation occurs prior to the formation of the protostar, and a binary or multiple system appears. When the magnetic energy is greater than the rotational energy, a strong (> 100 km s-1) jet is driven by the circumstellar disk around the protostar, which does not fragment. Thus, even in the early universe, magnetic fields play an important role in the star formation process.. |
| 41. | Masahiro Machida, Kazuyuki Omukai, Tomoaki Matsumoto, Magnetohy drodynamics of Population III star formation, 1st Stars and Galaxies: Challenges for the Next Decade, 2010.12, [URL], The evolution of collapsing primordial clouds and the formation of Population III (Pop III) protostars are investigated with three-dimensional ideal MHD simulations. We follow the collapse of parsec-sized primordial clouds down to the formation of protostars on sub-AU scales. Pop III protostar formation is characterized by the ratio of rotational to magnetic energy of the natal cloud. When the rotational energy is larger than the magnetic energy, fragmentation occurs prior to the formation of the protostar, and a binary or multiple system appears. When the magnetic energy is greater than the rotational energy, a strong (> 100 km s-1) jet is driven by the circumstellar disk around the protostar, which does not fragment. Thus, even in the early universe, magnetic fields play an important role in the star formation process.. |
| 42. | Masahiro Machida, Kazuyuki Omukai, Tomoaki Matsumoto, Magnetohy drodynamics of Population III star formation, 1st Stars and Galaxies: Challenges for the Next Decade, 2010.12, [URL], The evolution of collapsing primordial clouds and the formation of Population III (Pop III) protostars are investigated with three-dimensional ideal MHD simulations. We follow the collapse of parsec-sized primordial clouds down to the formation of protostars on sub-AU scales. Pop III protostar formation is characterized by the ratio of rotational to magnetic energy of the natal cloud. When the rotational energy is larger than the magnetic energy, fragmentation occurs prior to the formation of the protostar, and a binary or multiple system appears. When the magnetic energy is greater than the rotational energy, a strong (> 100 km s-1) jet is driven by the circumstellar disk around the protostar, which does not fragment. Thus, even in the early universe, magnetic fields play an important role in the star formation process.. |
| 43. | 町田正博, 星周円盤の起源とその形成過程, 日本天文学会2010年秋季年会, 2010.09, [URL]. |
| 44. | 町田正博, 原始星アウトフローと星形成率の関係, 日本天文学会2010年春季年会, 2010.03, [URL]. |
| 45. | 町田正博, 周連星円盤からのアウトフロー, 日本天文学会2009年秋季年会, 2009.09, [URL]. |
| 46. | 町田正博, 低質量分子雲コア中での褐色矮星の形成可能性, 日本天文学会2009年春季年会, 2009.03, [URL]. |
| 47. | 町田正博, 巨大ガス惑星と周惑星円盤の形成過程, 日本天文学会2008年秋季年会, 2008.09, [URL]. |
| 48. | 町田正博, 異なる重元素量を持つガス雲中での星形成過程と連星頻度, 日本天文学会2008年春季年会, 2008.03, [URL]. |
| 49. | 町田正博, 近接連星と遠隔連星の形成シナリオ, 日本天文学会2007年秋季年会, 2007.09, [URL]. |
| 50. | 町田正博, 原始惑星系円盤中でのガス惑星の角運動量獲得過程, 日本天文学会2007年春季年会, 2007.03, [URL]. |
| 51. | 町田正博, 星形成過程における分子流と光学ジェットの駆動メカニズム, 日本天文学会2006年秋季年会, 2006.09, [URL]. |
| 52. | 町田正博, 磁気散逸MHDによる第二コアからの高速ジェット駆動機構の解明, 日本天文学会2006年春季年会, 2006.03, [URL]. |
| 53. | 町田正博, 原始巨大惑星へのガス降着とアウトフロー, 日本天文学会2005年秋季年会, 2005.10, [URL]. |
| 54. | 町田正博, 原始星形成：磁場と回転が平行／垂直になる場合, 日本天文学会2005年春季年会, 2005.03, [URL]. |
| 55. | Tomoaki Matsumoto, Masahiro Machida, Kohji Tomisaka, Tomoyuki Hanawa, Self-gravitational collapse of a magnetized cloud core High resolution simulations with three-dimensional MHD nested grid, Proceedings of the 18th International Conference, 2004.12, [URL], We investigate self-gravitational collapse of magnetized molecular cloud cores and formation of the outflow. We employ a nested grid in order to resolve fine structures of protostar and outflow generation, of which size is as small as 1 AU, and to follow the whole structure of the molecular cloud core, of which radius reaches 0.1-1 pc, simultaneously. The nested grid allows us to follow the evolution of the cloud core with the high dynamic range of 105-106 in the spatial resolution. In this paper, we introduce implementations of the self-gravitational MHD nested grid code and show applications to early stages in star formation: gravitational collapse of cloud core, "first core" formation, and bipolar outflow ejection. In both cases of single and binary star formation, magnetic fields play important role in the outflow formation. The outflow region has extremely low beta regions of β= 10 -6-10-3, and our code shows no sign of numerical instability even in these low-beta regions.. |
| 56. | Tomoaki Matsumoto, Masahiro Machida, Kohji Tomisaka, Tomoyuki Hanawa, Self-gravitational collapse of a magnetized cloud core High resolution simulations with three-dimensional MHD nested grid, Proceedings of the 18th International Conference, 2004.12, [URL], We investigate self-gravitational collapse of magnetized molecular cloud cores and formation of the outflow. We employ a nested grid in order to resolve fine structures of protostar and outflow generation, of which size is as small as 1 AU, and to follow the whole structure of the molecular cloud core, of which radius reaches 0.1-1 pc, simultaneously. The nested grid allows us to follow the evolution of the cloud core with the high dynamic range of 105-106 in the spatial resolution. In this paper, we introduce implementations of the self-gravitational MHD nested grid code and show applications to early stages in star formation: gravitational collapse of cloud core, "first core" formation, and bipolar outflow ejection. In both cases of single and binary star formation, magnetic fields play important role in the outflow formation. The outflow region has extremely low beta regions of β= 10 -6-10-3, and our code shows no sign of numerical instability even in these low-beta regions.. |
| 57. | Tomoaki Matsumoto, Masahiro Machida, Kohji Tomisaka, Tomoyuki Hanawa, Self-gravitational collapse of a magnetized cloud core High resolution simulations with three-dimensional MHD nested grid, Proceedings of the 18th International Conference, 2004.12, [URL], We investigate self-gravitational collapse of magnetized molecular cloud cores and formation of the outflow. We employ a nested grid in order to resolve fine structures of protostar and outflow generation, of which size is as small as 1 AU, and to follow the whole structure of the molecular cloud core, of which radius reaches 0.1-1 pc, simultaneously. The nested grid allows us to follow the evolution of the cloud core with the high dynamic range of 105-106 in the spatial resolution. In this paper, we introduce implementations of the self-gravitational MHD nested grid code and show applications to early stages in star formation: gravitational collapse of cloud core, "first core" formation, and bipolar outflow ejection. In both cases of single and binary star formation, magnetic fields play important role in the outflow formation. The outflow region has extremely low beta regions of β= 10 -6-10-3, and our code shows no sign of numerical instability even in these low-beta regions.. |
| 58. | Tomoaki Matsumoto, Masahiro Machida, Kohji Tomisaka, Tomoyuki Hanawa, Self-gravitational collapse of a magnetized cloud core High resolution simulations with three-dimensional MHD nested grid, Proceedings of the 18th International Conference, 2004.12, [URL], We investigate self-gravitational collapse of magnetized molecular cloud cores and formation of the outflow. We employ a nested grid in order to resolve fine structures of protostar and outflow generation, of which size is as small as 1 AU, and to follow the whole structure of the molecular cloud core, of which radius reaches 0.1-1 pc, simultaneously. The nested grid allows us to follow the evolution of the cloud core with the high dynamic range of 105-106 in the spatial resolution. In this paper, we introduce implementations of the self-gravitational MHD nested grid code and show applications to early stages in star formation: gravitational collapse of cloud core, "first core" formation, and bipolar outflow ejection. In both cases of single and binary star formation, magnetic fields play important role in the outflow formation. The outflow region has extremely low beta regions of β= 10 -6-10-3, and our code shows no sign of numerical instability even in these low-beta regions.. |
| 59. | 町田正博, 分子雲コアからの連星形成過程とアウトフロー, 日本天文学会2003年春季年会, 2003.03, [URL]. |
| 60. | 町田正博, 分子雲コアの分裂を誘発するディスクとバーの形成, 日本天文学会2003年秋季年会, 2003.09, [URL]. |
| 61. | 町田正博, 原始星の磁束と角運動量, 日本天文学会2004年春季年会, 2004.03, [URL]. |
| 62. | 町田正博, 分子雲の分裂条件, 日本天文学会2004年秋季年会, 2004.09, [URL]. |
| 63. | 町田正博, 非軸対称揺らぎを入れた星間分子雲の成長過程, 日本天文学会2002年秋季年会, 2002.10, [URL]. |
| 64. | 町田正博、富阪幸治、松本倫明, 非軸対称揺らぎにおける星間磁気雲の収縮過程, 日本天文学会2002年春季年会, 2002.03, [URL]. |
| 65. | 町田正博、富阪幸治、松本倫明 , ３次元MHD Nested Grid シミュレーションによる星間磁気雲の重力収縮, 日本天文学会2001年秋季年会, 2001.10, [URL]. |
| 66. | 町田正博、藤本正行、中村文隆, 初期宇宙における低質量星の形成過程, 日本天文学会2001年春季年会, 2001.03, [URL]. |
| 67. | 町田正博, SuperNova Triggered Star-Formation in Early Universe, 日本天文学会2000年秋季年会, 2000.10, [URL]. |
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九大関連コンテンツ
QIR 九州大学学術情報リポジトリ システム情報科学研究院
理学部・理学研究院
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