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Kengo Tomida

Section

Graduate School of Science

Job title

Associate Professor

Degree

博士（理学）（総合研究大学院大学）

researchmap

https://researchmap.jp/tomidakn

J-GLOBAL ID

201901000889761941

e-Rad No.

70772367

ORCID

https://orcid.org/0000-0001-8105-8113

Research History 7

2020/03 - Present

Tohoku University　Astronomical Institute　Associate Professor
2019/04 - 2024/03

National Institutes of Natural Sciences　International Research Collaboration Center
2015/10 - 2020/03

Osaka University　Graduate School of Science Department of Earth and Space Science　Assistant Professor
2018/10 - 2019/09

Princeton University　Department of Astrophysical Sciences　Visiting Fellow
2014/12 - 2015/09

Princeton University　Department of Astrophysical Sciences　Postdoctoral Research Associate
2014/04 - 2014/11

Princeton University　Department of Astrophysical Sciences　Research Fellow of Japan Society for the Promotion of Science
2012/04 - 2014/03

Princeton University　Department of Astrophysical Sciences　JSPS Postdoctoral Fellow for Research Abroad

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Education 2

The Graduate University for Advanced Studies　School of Physical Sciences　Department of Astronomical Science

2007/04 - 2012/03
Kyoto University

2003/04 - 2007/03

Committee Memberships 3

Astronomical Society of Japan　Delegate

2022/04 - 2026/03
理論天文学宇宙物理学懇談会　運営委員

2020/10 - 2022/11
The Astronomical Society of Japan　Editor of the Astronomical Herald

2017/06 - 2021/06

Professional Memberships 4

International Astronomical Union

2020/05 - Present
American Astronomical Society
理論天文学宇宙物理学懇談会
THE ASTRONOMICAL SOCIETY OF JAPAN

Research Areas 3

Informatics / High-performance computing /
Natural sciences / Theoretical studies related to particle-, nuclear-, cosmic ray and astro-physics /
Natural sciences / Astronomy /

Awards 7

2023 North American Top Cited Paper Awards

2023/11　IOP Publishing　The Athena ++ Adaptive Mesh Refinement Framework: Design and Magnetohydrodynamic Solvers
Tohoku University Distinguished Researcher

2023/05　Tohoku University
HPCI Software Award

2023/04　Athena++
The Young Scientists' Award

2023/04　The Commendation for Science and Technology by the Minister of Education, Culture, Sports, Science and Technology
Osaka University Prize

2018/11　Osaka University
The ASJ Young Astronomer Award

2018/03　The Astronomical Society of Japan
President's award

2011/04　The Graduate University for Advanced Studies

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Papers 87

Formation and Early Evolution of Protoplanetary Disks under Nonuniform Cosmic-Ray Ionization

Erika Nishio, Kengo Tomida, Yuki Kudoh, Shigeo S. Kimura

The Astrophysical Journal　2025/07/20

DOI： 10.3847/1538-4357/addbe2 　
Connecting a Magnetized Disk to a Convective Low-mass Protostar: A Global 3D Model of Boundary Layer Accretion

Shinsuke Takasao, Takashi Hosokawa, Kengo Tomida, Kazunari Iwasaki

The Astrophysical Journal　2025/05/20

DOI： 10.3847/1538-4357/adc37b 　
Comparative Analysis of Hall Effect Implementations in Hall Magnetohydrodynamics

Kazunari Iwasaki, Kengo Tomida

The Astrophysical Journal　2025/05/01

DOI： 10.3847/1538-4357/adc2f7 　
Isolated Black Holes as Potential PeVatrons and Ultrahigh-energy Gamma-Ray Sources

Shigeo S. Kimura, Kengo Tomida, Masato I. N. Kobayashi, Koki Kin, Bing Zhang

The Astrophysical Journal Letters　2025/03/10

DOI： 10.3847/2041-8213/adb841 　
Spin-down of Solar-mass Protostars in Magnetospheric Accretion Paradigm

Shinsuke Takasao, Masanobu Kunitomo, Takeru K. Suzuki, Kazunari Iwasaki, Kengo Tomida

The Astrophysical Journal　2025/02/10

DOI： 10.3847/1538-4357/ada364 　
Dynamics near the inner dead-zone edges in a proprotoplanetary disk

Kazunari Iwasaki, Kengo Tomida, Shinsuke Takasao, Satoshi Okuzumi, Takeru K Suzuki

Publications of the Astronomical Society of Japan　2024/08/01

DOI： 10.1093/pasj/psae036 　
Metallicity Dependence of Molecular Cloud Hierarchical Structure at Early Evolutionary Stages

Masato I. N. Kobayashi, Kazunari Iwasaki, Kengo Tomida, Tsuyoshi Inoue, Kazuyuki Omukai, Kazuki Tokuda

The Astrophysical Journal　954　(1)　38-38　2023/08/22
Publisher: American Astronomical Society
DOI： 10.3847/1538-4357/ace34e 　

ISSN： 0004-637X

eISSN： 1538-4357

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Abstract The formation of molecular clouds out of H i gas is the first step toward star formation. Its metallicity dependence plays a key role in determining star formation throughout cosmic history. Previous theoretical studies with detailed chemical networks calculate thermal equilibrium states and/or thermal evolution under one-zone collapsing background. The molecular cloud formation in reality, however, involves supersonic flows, and thus resolving the cloud internal turbulence/density structure in three dimensions is still essential. We here perform magnetohydrodynamics simulations of 20 km s⁻¹ converging flows of warm neutral medium (WNM) with 1 μG mean magnetic field in the metallicity range from the solar (1.0 Z_⊙) to 0.2 Z_⊙ environment. The cold neutral medium (CNM) clumps form faster with higher metallicity due to more efficient cooling. Meanwhile, their mass functions commonly follow ${dn}/{dm}\propto {m}^{-1.7}$ at three cooling times regardless of the metallicity. Their total turbulence power also commonly shows the Kolmogorov spectrum with its 80% in the solenoidal mode, while the CNM volume alone indicates the transition toward Larson’s law. These similarities measured at the same time in units of the cooling time suggest that the molecular cloud formation directly from the WNM alone requires a longer physical time in a lower-metallicity environment in the 1.0–0.2 Z_⊙ range. To explain the rapid formation of molecular clouds and subsequent massive star formation possibly within ≲10 Myr as observed in the Large/Small Magellanic Clouds, the H i gas already contains CNM volume instead of pure WNM.
Early Planet Formation in Embedded Disks (eDisk). VII. Keplerian Disk, Disk Substructure, and Accretion Streamers in the Class 0 Protostar IRAS 16544–1604 in CB 68

Miyu Kido, Shigehisa Takakuwa, Kazuya Saigo, Nagayoshi Ohashi, John J. Tobin, Jes K. Jørgensen, Yuri Aikawa, Yusuke Aso, Frankie J. Encalada, Christian Flores, Sacha Gavino, Itziar de Gregorio-Monsalvo, Ilseung Han, Shingo Hirano, Patrick M. Koch, Woojin Kwon, Shih-Ping Lai, Chang Won Lee, Jeong-Eun Lee, Zhi-Yun Li, Zhe-Yu Daniel Lin, Leslie W. Looney, Shoji Mori, Suchitra Narayanan, Adele L. Plunkett, Nguyen Thi Phuong, Jinshi Sai (Insa Choi), Alejandro Santamaría-Miranda, Rajeeb Sharma, Patrick D. Sheehan, Travis J. Thieme, Kengo Tomida, Merel L. R. van ’t Hoff, Jonathan P. Williams, Yoshihide Yamato, Hsi-Wei Yen

The Astrophysical Journal　953　(2)　190-190　2023/08/01
Publisher: American Astronomical Society
DOI： 10.3847/1538-4357/acdd7a 　

ISSN： 0004-637X

eISSN： 1538-4357

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Abstract We present observations of the Class 0 protostar IRAS 16544–1604 in CB 68 from the “Early Planet Formation in Embedded Disks (eDisk)” ALMA Large program. The ALMA observations target continuum and lines at 1.3 mm with an angular resolution of ∼5 au. The continuum image reveals a dusty protostellar disk with a radius of ∼30 au seen close to edge-on and asymmetric structures along both the major and minor axes. While the asymmetry along the minor axis can be interpreted as the effect of the dust flaring, the asymmetry along the major axis comes from a real nonaxisymmetric structure. The C¹⁸O image cubes clearly show the gas in the disk that follows a Keplerian rotation pattern around a ∼0.14 M_⊙ central protostar. Furthermore, there are ∼1500 au scale streamer-like features of gas connecting from northeast, north–northwest, and northwest to the disk, as well as the bending outflow as seen in the ¹²CO (2–1) emission. At the apparent landing point of the NE streamer, there is SO (6₅–5₄) and SiO (5–4) emission detected. The spatial and velocity structure of the NE streamer can be interpreted as a free-falling gas with a conserved specific angular momentum, and the detection of the SO and SiO emission at the tip of the streamer implies the presence of accretion shocks. Our eDisk observations have unveiled that the Class 0 protostar in CB 68 has a Keplerian-rotating disk with a flaring and nonaxisymmetric structure associated with accretion streamers and outflows.
Early Planet Formation in Embedded Disks (eDisk). IV. The Ringed and Warped Structure of the Disk around the Class I Protostar L1489 IRS

Yoshihide Yamato, Yuri Aikawa, Nagayoshi Ohashi, John J. Tobin, Jes K. Jørgensen, Shigehisa Takakuwa, Yusuke Aso, Jinshi Sai (Insa Choi), Christian Flores, Itziar de Gregorio-Monsalvo, Shingo Hirano, Ilseung Han, Miyu Kido, Patrick M. Koch, Woojin Kwon, Shih-Ping Lai, Chang Won Lee, Jeong-Eun Lee, Zhi-Yun Li, Zhe-Yu Daniel Lin, Leslie W. Looney, Shoji Mori, Suchitra Narayanan, Nguyen Thi Phuong, Kazuya Saigo, Alejandro Santamaría-Miranda, Rajeeb Sharma, Travis J. Thieme, Kengo Tomida, Merel L. R. van ’t Hoff, Hsi-Wei Yen

The Astrophysical Journal　951　(1)　11-11　2023/06/28
Publisher: American Astronomical Society
DOI： 10.3847/1538-4357/accd71 　

ISSN： 0004-637X

eISSN： 1538-4357

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Abstract Constraining the physical and chemical structure of young embedded disks is crucial for understanding the earliest stages of planet formation. As part of the Early Planet Formation in Embedded Disks Atacama Large Millimeter/submillimeter Array Large Program, we present high spatial resolution (∼0.″1 or ∼15 au) observations of the 1.3 mm continuum and ¹³CO J = 2–1, C¹⁸O J = 2–1, and SO J_N = 6₅–5₄ molecular lines toward the disk around the Class I protostar L1489 IRS. The continuum emission shows a ring-like structure at 56 au from the central protostar and tenuous, optically thin emission extending beyond ∼300 au. The ¹³CO emission traces the warm disk surface, while the C¹⁸O emission originates from near the disk midplane. The coincidence of the radial emission peak of C¹⁸O with the dust ring may indicate a gap-ring structure in the gaseous disk as well. The SO emission shows a highly complex distribution, including a compact, prominent component at ≲30 au, which is likely to originate from thermally sublimated SO molecules. The compact SO emission also shows a velocity gradient along a direction tilted slightly (∼15°) with respect to the major axis of the dust disk, which we interpret as an inner warped disk in addition to the warp around ∼200 au suggested by previous work. These warped structures may be formed by a planet or companion with an inclined orbit, or by a gradual change in the angular momentum axis during gas infall.
Early Planet Formation in Embedded Disks (eDisk). I. Overview of the Program and First Results

Nagayoshi Ohashi, John J. Tobin, Jes K. Jørgensen, Shigehisa Takakuwa, Patrick Sheehan, Yuri Aikawa, Zhi-Yun Li, Leslie W. Looney, Jonathan P. Williams, Yusuke Aso, Rajeeb Sharma, Jinshi Sai (Insa Choi), Yoshihide Yamato, Jeong-Eun Lee, Kengo Tomida, Hsi-Wei Yen, Frankie J. Encalada, Christian Flores, Sacha Gavino, Miyu Kido, Ilseung Han, Zhe-Yu Daniel Lin, Suchitra Narayanan, Nguyen Thi Phuong, Alejandro Santamaría-Miranda, Travis J. Thieme, Merel L. R. van ’t Hoff, Itziar de Gregorio-Monsalvo, Patrick M. Koch, Woojin Kwon, Shih-Ping Lai, Chang Won Lee, Adele Plunkett, Kazuya Saigo, Shingo Hirano, Ka Ho Lam, Shoji Mori

The Astrophysical Journal　951　(1)　8-8　2023/06/28
Publisher: American Astronomical Society
DOI： 10.3847/1538-4357/acd384 　

ISSN： 0004-637X

eISSN： 1538-4357

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Abstract We present an overview of the Large Program, “Early Planet Formation in Embedded Disks (eDisk),” conducted with the Atacama Large Millimeter/submillimeter Array (ALMA). The ubiquitous detections of substructures, particularly rings and gaps, in protoplanetary disks around T Tauri stars raise the possibility that at least some planet formation may have already started during the embedded stages of star formation. In order to address exactly how and when planet formation is initiated, the program focuses on searching for substructures in disks around 12 Class 0 and 7 Class I protostars in nearby (<200 pc) star-forming regions through 1.3 mm continuum observations at a resolution of ∼7 au (0.″04). The initial results show that the continuum emission, mostly arising from dust disks around the sample protostars, has relatively few distinctive substructures, such as rings and spirals, in marked contrast to Class II disks. The dramatic difference may suggest that substructures quickly develop in disks when the systems evolve from protostars to Class II sources, or alternatively that high optical depth of the continuum emission could obscure internal structures. Kinematic information obtained through CO isotopologue lines and other lines reveals the presence of Keplerian disks around protostars, providing us with crucial physical parameters, in particular, the dynamical mass of the central protostars. We describe the background of the eDisk program, the sample selection and their ALMA observations, and the data reduction, and we also highlight representative first-look results.
The Athena++ Adaptive Mesh Refinement Framework: Multigrid Solvers for Self-gravity

Kengo Tomida, James M. Stone

The Astrophysical Journal Supplement Series　2023/05/01

DOI： 10.3847/1538-4365/acc2c0 　
Three-dimensional Simulations of Magnetospheric Accretion in a T Tauri Star: Accretion and Wind Structures Just Around the Star

Shinsuke Takasao, Kengo Tomida, Kazunari Iwasaki, Takeru K. Suzuki

The Astrophysical Journal　941　(1)　2022/12/01

DOI： 10.3847/1538-4357/ac9eb1 　

ISSN： 0004-637X

eISSN： 1538-4357
Interaction of a Relativistic Magnetized Collisionless Shock with a Dense Clump

Sara Tomita, Yutaka Ohira, Shigeo S. Kimura, Kengo Tomida, Kenji Toma

The Astrophysical Journal Letters　2022/09/01

DOI： 10.3847/2041-8213/ac88be 　
Osaka Feedback Model. II. Modeling Supernova Feedback Based on High-resolution Simulations

Yuri Oku, Kengo Tomida, Kentaro Nagamine, Ikkoh Shimizu, Renyue Cen

The Astrophysical Journal Supplement Series　262　(1)　9-9　2022/09/01
Publisher: American Astronomical Society
DOI： 10.3847/1538-4365/ac77ff 　

ISSN： 0067-0049

eISSN： 1538-4365

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Abstract Feedback from supernovae (SNe) is an essential mechanism that self-regulates the growth of galaxies, and a better model of SN feedback is still needed in galaxy-formation simulations. In the first part of this paper, using an Eulerian hydrodynamic code Athena++, we find the universal scaling relations for the time evolution of momentum and radius for a superbubble, when the momentum and time are scaled by those at the shell-formation time. In the second part of this paper, we develop a SN feedback model based on the Athena++ simulation results utilizing Voronoi tessellation around each star particle, and implement it into the GADGET3-Osaka smoothed particle hydrodynamic code. Our feedback model was demonstrated to be isotropic and conservative in terms of energy and momentum. We examined the mass/energy/metal loading factors and find that our stochastic thermal feedback model produced galactic outflow that carries metals high above the galactic plane but with weak suppression of star formation. Additional mechanical feedback further suppressed star formation and brought the simulation results into better agreement with the observations of the Kennicutt–Schmidt relation, with all the results being within the uncertainties of observed data. We argue that both thermal and mechanical feedback are necessary for the SN feedback model of galaxy evolution when an individual SN bubble is unresolved.
Universal Properties of Dense Clumps in Magnetized Molecular Clouds Formed through Shock Compression of Two-phase Atomic Gases

Kazunari Iwasaki, Kengo Tomida

The Astrophysical Journal　2022/08/01

DOI： 10.3847/1538-4357/ac75cc 　
Nature of Supersonic Turbulence and Density Distribution Function in the Multiphase Interstellar Medium

Masato I. N. Kobayashi, Tsuyoshi Inoue, Kengo Tomida, Kazunari Iwasaki, Hiroki Nakatsugawa

The Astrophysical Journal　2022/05/01

DOI： 10.3847/1538-4357/ac5a54 　
OPTAB: Public code for generating gas opacity tables for radiation hydrodynamics simulations

Hirose, S., Hauschildt, P., Minoshima, T., Tomida, K., Sano, T.

Astronomy and Astrophysics　659　2022

DOI： 10.1051/0004-6361/202141076 　

ISSN： 1432-0746 0004-6361
Osaka Feedback Model II: Modeling Supernova Feedback Based on High-Resolution Simulations

Yuri Oku, Kengo Tomida, Kentaro Nagamine, Ikkoh Shimizu, Renyue Cen

Proceedings of the International Astronomical Union　17　(S373)　181-185　2021/08
Publisher: Cambridge University Press (CUP)
DOI： 10.1017/s1743921322004860 　

ISSN： 1743-9213

eISSN： 1743-9221

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Abstract Feedback from supernovae (SNe) is an essential mechanism that self-regulates the growth of galaxies. We build an SN feedback model based on high-resolution simulations of superbubble and SN-driven outflows for the physical understanding of the galaxy–CGM connection. Using an Eulerian hydrodynamic code Athena++, we find universal scaling relations for the time evolution of superbubble momentum, when the momentum and time are scaled by those at the shell-formation time. We then develop an SN feedback model utilizing Voronoi tessellation, and implement it into the GADGET3-Osaka smoothed particle hydrodynamic code. We show that our stochastic thermal feedback model produces galactic outflow that carries the metals high above the galactic plane but with weak suppression of star formation. Additional mechanical feedback further suppresses star formation. Therefore, we argue that both thermal and mechanical feedback is necessary for the SN feedback model of galaxy evolution when an individual SN bubble is unresolved.
Magnetohydrodynamic effect on first star formation: pre-stellar core collapse and protostar formation

Kenji Eric Sadanari, Kazuyuki Omukai, Kazuyuki Sugimura, Tomoaki Matsumoto, Kengo Tomida

Monthly Notices of the Royal Astronomical Society　505　(3)　4197-4214　2021/06/23

DOI： 10.1093/mnras/stab1330 　

ISSN： 0035-8711 1365-2966

eISSN： 1365-2966
Misaligned Twin Molecular Outflows from the Class 0 Protostellar Binary System VLA 1623A Unveiled by ALMA

Chihomi Hara, Ryohei Kawabe, Fumitaka Nakamura, Naomi Hirano, Shigehisa Takakuwa, Yoshito Shimajiri, Takeshi Kamazaki, James Di Francesco, Masahiro N. Machida, Motohide Tamura, Kazuya Saigo, Tomoaki Matsumoto, Kengo Tomida

The Astrophysical Journal　912　(1)　34-34　2021/05/01
Publisher: American Astronomical Society
DOI： 10.3847/1538-4357/abb810 　

ISSN： 0004-637X 1538-4357

eISSN： 1538-4357
ALMA Observation of the Protoplanetary Disk around WW Cha: Faint Double-peaked Ring and Asymmetric Structure

Kanagawa, K.D., Hashimoto, J., Muto, T., Tsukagoshi, T., Takahashi, S.Z., Hasegawa, Y., Konishi, M., Nomura, H., Liu, H.B., Dong, R., Kataoka, A., Momose, M., Ono, T., Sitko, M., Takami, M., Tomida, K.

Astrophysical Journal　909　(2)　212-212　2021/03/01
Publisher: American Astronomical Society
DOI： 10.3847/1538-4357/abdfc5 　

ISSN： 1538-4357 0004-637X
Erratum: Pre-explosion Spiral Mass Loss of a Binary Star Merger (Astrophysical Journal (2017) 850 (59) DOI: 10.3847/1538-4357/aa95b9)

Pejcha, O., Metzger, B.D., Tyles, J.G., Tomida, K.

Astrophysical Journal　922　(2)　2021

DOI： 10.3847/1538-4357/ac3764 　

ISSN： 1538-4357 0004-637X
Transition Region from Turbulent to Dead Zone in Protoplanetary Disks: Local Shearing Box Simulations

Fulvia Pucci, Kengo Tomida, James Stone, Shinsuke Takasao, Hantao Ji, Shoichi Okamura

The Astrophysical Journal　907　(1)　13-13　2021/01/01
Publisher: American Astronomical Society
DOI： 10.3847/1538-4357/abc9c0 　

eISSN： 1538-4357
Bimodal Behavior and Convergence Requirement in Macroscopic Properties of the Multiphase Interstellar Medium Formed by Atomic Converging Flows

Masato I. N. Kobayashi, Tsuyoshi Inoue, Shu-ichiro Inutsuka, Kengo Tomida, Kazunari Iwasaki, Kei E. I. Tanaka

The Astrophysical Journal　905　(2)　95-95　2020/12/17
Publisher: American Astronomical Society
DOI： 10.3847/1538-4357/abc5be 　

eISSN： 1538-4357
Salt, Hot Water, and Silicon Compounds Tracing Massive Twin Disks

Kei E. I. Tanaka, Yichen Zhang, Tomoya Hirota, Nami Sakai, Kazuhito Motogi, Kengo Tomida, Jonathan C. Tan, Viviana Rosero, Aya E. Higuchi, Satoshi Ohashi, Mengyao Liu, Koichiro Sugiyama

The Astrophysical Journal Letters　900　(1)　2020/09/01
Publisher: American Astronomical Society
DOI： 10.3847/2041-8213/abadfc 　

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We report results of $0\buildrel{\prime\prime}\over{.} 05$-resolution observations toward the O-type proto-binary system IRAS 16547-4247 with the Atacama Large Millimeter/submillimeter Array. We present dynamical and chemical structures of the circumbinary disk, circumstellar disks, outflows, and jets, illustrated by multi-wavelength continuum and various molecular lines. In particular, we detect sodium chloride, silicon compounds, and vibrationally excited water lines as probes of the individual protostellar disks at a scale of 100 au. These are complementary to typical hot-core molecules tracing the circumbinary structures on a 1000 au scale. The H₂O line tracing inner disks has an upper-state energy of ${E}_{u}/k\gt 3000\,{\rm{K } }$, indicating a high temperature of the disks. On the other hand, despite the detected transitions of NaCl, SiO, and SiS not necessarily having high upper-state energies, they are enhanced only in the vicinity of the protostars. We posit that these molecules are the products of dust destruction, which only happens in the inner disks. This is the second detection of alkali metal halide in protostellar systems after the case of the disk of Orion Source I, and also one of few massive protostellar disks associated with high-energy transition water and silicon compounds. These new results suggest that these "hot-disk" lines may be common in innermost disks around massive protostars, and have great potential for future research of massive star formation. We also tentatively find that the twin disks are counter-rotating, which might give a hint of the origin of the massive proto-binary system IRAS 16547-4247....
Protostellar Collapse: Regulation of the Angular Momentum and Onset of an Ionic Precursor

March, , P., Tomida, K., Tanaka, K.E.I., Commer?on, B., Chabrier, G.

Astrophysical Journal　900　(2)　180-180　2020/09/01
Publisher: American Astronomical Society
DOI： 10.3847/1538-4357/abad99 　

ISSN： 1538-4357 0004-637X
Salt, Hot Water, and Silicon Compounds Tracing Massive Twin Disks Peer-reviewed

Kei E. I. Tanaka, Yichen Zhang, Tomoya Hirota, Nami Sakai, Kazuhito Motogi, Kengo Tomida, Jonathan C. Tan, Viviana Rosero, Aya E. Higuchi, Satoshi Ohashi, Mengyao Liu, Koichiro Sugiyama

The Astrophysical Journal　2020/08/25
Publisher: arXiv e-prints
DOI： 10.3847/2041-8213/abadfc 　

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We report results of 0.05"-resolution observations toward the O-type proto-binary system IRAS 16547-4247 with the Atacama Large Millimeter/submillimeter Array (ALMA). We present dynamical and chemical structures of the circumbinary disk, circumstellar disks, outflows and jets, illustrated by multi-wavelength continuum and various molecular lines. In particular, we detect sodium chloride, silicon compounds, and vibrationally-excited water lines as probes of the individual protostellar disks at a scale of 100 au. These are complementary to typical hot-core molecules tracing the circumbinary structures on a 1000-au scale. The H2O line tracing inner-disks has an upper-state energy of Eu/k>3000K, indicating a high temperature of the disks. On the other hand, despite the detected transitions of NaCl, SiO, and SiS not necessarily having high upper-state energies, they are enhanced only in the vicinity of the protostars. We interpret that these molecules are the products of dust destruction, which only happens in the inner disks. This is the second detection of alkali metal halide in protostellar systems after the case of the disk of Orion Source I, and also one of few massive protostellar disks associated with high-energy transition water and silicon compounds. These new results suggest these "hot-disk" lines may be common in innermost disks around massive protostars, and have great potential for future research of massive star formation. We also tentatively find that the twin disks are counter-rotating, which might give a hint of the origin of the massive proto-binary system IRAS 16547-4247....
FRagmentation and Evolution of Dense Cores Judged by ALMA (FREJA). I. Overview: Inner ∼1000 au Structures of Prestellar/Protostellar Cores in Taurus Peer-reviewed

Kazuki Tokuda, Kakeru Fujishiro, Kengo Tachihara, Tatsuyuki Takashima, Yasuo Fukui, Sarolta Zahorecz, Kazuya Saigo, Tomoaki Matsumoto, Kengo Tomida, Masahiro N. Machida, Shu-ichiro Inutsuka, Philippe André, Akiko Kawamura, Toshikazu Onishi

The Astrophysical Journal　899　(1)　2020/08/07

DOI： 10.3847/1538-4357/ab9ca7 　

ISSN： 0004-637X

eISSN： 1538-4357
The Athena++ Adaptive Mesh Refinement Framework: Design and Magnetohydrodynamic Solvers Peer-reviewed

James M. Stone, Kengo Tomida, Christopher J. White, Kyle G. Felker

The Astrophysical Journal Supplement Series　2020/07/01

DOI： 10.3847/1538-4365/ab929b 　
A low-velocity bipolar outflow from a deeply embedded object in Taurus revealed by the Atacama Compact Array Peer-reviewed

Fujishiro, Kakeru, Tokuda, Kazuki, Tachihara, Kengo, Takashima, Tatsuyuki, Fukui, Yasuo, Zahorecz, Sarolta, Saigo, Kazuya, Matsumoto, Tomoaki, Tomida, Kengo, Machida, Masahiro N., Inutsuka, Shu-ichiro, André, Philippe, Kawamura, Akiko, Onishi, Toshikazu

The Astrophysical Journal　899　(1)　L10-L10　2020/06
Publisher: arXiv e-prints
DOI： 10.3847/2041-8213/ab9ca8 　

eISSN： 2041-8213

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The first hydrostatic core, the first quasi-hydrostatic object formed during the star formation process, is still the observational missing link between the prestellar and protostellar phases, mainly due to its short lifetime. Although we have not established a clear method to identify this rare object, recent theoretical studies predict that the first core has millimeter continuum emission and low-velocity outflow with a wide opening angle. An extensive continuum/outflow survey toward a large number of $"$starless$"$ cores in nearby star-forming regions works as a pathfinder. We observed 32 prestellar cores in Taurus with an average density of $\gtrsim$10$^5$ cm$^{-3}$ in 1.3 mm continuum and molecular lines using the Atacama Large Millimeter/submillimeter Array$-$Atacama Compact Array (ALMA$-$ACA) stand-alone mode. Among the targets, MC35-mm centered at one of the densest $"$starless$"$ cores in Taurus has blueshifted/redshifted wings in the $^{12}$CO (2-1) line, indicating that there is deeply embedded object driving molecular outflow. The observed velocities and sizes of the possible outflow lobes are 2-4 km s$^{-1}$, and $\sim$2 $\times$10$^3$ au, respectively, and the dynamical time is calculated to be $\sim$10$^3$ yr. In addition to this, the core is one of the strongest N$_2$D$^{+}$ (3-2) emitters in our sample. All of the observed signatures do not conflict with any of the theoretical predictions about the first hydrostatic core so far, and thus MC35-mm is unique as the only first-core candidate in the Taurus molecular cloud....
Turbulent dissipation, CH$^+$ abundance, H$_2$ line luminosities, and polarization in the cold neutral medium Peer-reviewed

Moseley, Eric R., Draine, B. T., Tomida, Kengo, Stone, James M.

Monthly Notices of the Royal Astronomical Society　500　(3)　3290-3308　2020/06
Publisher: arXiv e-prints
DOI： 10.1093/mnras/staa3384 　

ISSN： 1365-2966 0035-8711
GW Ori: Interactions between a Triple-star System and Its Circumtriple Disk in Action Peer-reviewed

Bi, Jiaqing, van der Marel, Nienke, Dong (董若冰), Ruobing, Muto, Takayuki, Martin, Rebecca G., Smallwood, Jeremy L., Hashimoto, Jun, Liu, Hauyu Baobab, Nomura, Hideko, Hasegawa, Yasuhiro, Takami, Michihiro, Konishi, Mihoko, Momose, Munetake, Kanagawa, Kazuhiro D., Kataoka, Akimasa, Ono, Tomohiro, Sitko, Michael L., Takahashi, Sanemichi Z., Tomida, Kengo, Tsukagoshi, Takashi

The Astrophysical Journal　895　(1)　L18-L18　2020/05
Publisher: American Astronomical Society
DOI： 10.3847/2041-8213/ab8eb4 　

ISSN： 2041-8205

eISSN： 2041-8213

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GW Ori is a hierarchical triple system with a rare circumtriple disk. We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of 1.3 mm dust continuum and ¹²CO J = 2 - 1 molecular gas emission of the disk. For the first time, we identify three dust rings in the GW Ori disk at ∼46, 188, and 338 au, with estimated dust mass of 74, 168, and 245 Earth masses, respectively. To our knowledge, its outermost ring is the largest dust ring ever found in protoplanetary disks. We use visibility modeling of dust continuum to show that the disk has misaligned parts, and the innermost dust ring is eccentric. The disk misalignment is also suggested by the CO kinematics. We interpret these substructures as evidence of ongoing dynamical interactions between the triple stars and the circumtriple disk....
Disk Structure around the Class I Protostar L1489 IRS Revealed by ALMA: A Warped-disk System Peer-reviewed

Sai, Jinshi, Ohashi, Nagayoshi, Saigo, Kazuya, Matsumoto, Tomoaki, Aso, Yusuke, Takakuwa, Shigehisa, Aikawa, Yuri, Kurose, Ippei, Yen, Hsi-Wei, Tomisaka, Kohji, Tomida, Kengo, Machida, Masahiro N.

The Astrophysical Journal　893　(1)　51-51　2020/04
Publisher: American Astronomical Society
DOI： 10.3847/1538-4357/ab8065 　

eISSN： 1538-4357

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We have observed the Class I protostar L1489 IRS with the Atacama Millimeter/submillimeter Array (ALMA) in Band 6. The C¹⁸O J = 2-1 line emission shows flattened and non-axisymmetric structures in the same direction as its velocity gradient due to rotation. We discovered that the C¹⁸O emission shows dips at a radius of ∼200-300 au while the 1.3 mm continuum emission extends smoothly up to r ∼ 400 au. At the radius of the C¹⁸O dips, the rotational axis of the outer portion appears to be tilted by ∼15° from that of the inner component. Both the inner and outer components with respect to the C¹⁸O dips exhibit the r^-0.5 Keplerian rotation profiles until r ∼ 600 au. These results not only indicate that a Keplerian disk extends up to ∼600 au but also that the disk is warped. We constructed a three-dimensional warped-disk model rotating at the Keplerian velocity, and demonstrated that the warped-disk model reproduces main observed features in the velocity channel maps and the PV diagrams. Such a warped-disk system can form by mass accretion from a misaligned envelope. We also discuss a possible disk evolution scenario based on comparisons of disk radii and masses between Class I and Class II sources....
Formation and Evolution of Disks Around Young Stellar Objects Peer-reviewed

Zhao, B., Tomida, K., Hennebelle, P., Tobin, J.J., Maury, A., Hirota, T., S{\'a}nchez-Monge, ?., Kuiper, R., Rosen, A., Bh, are, A., Padovani, M., Lee, Y.-N.

Space Science Reviews　216　(3)　2020/04

DOI： 10.1007/s11214-020-00664-z 　

ISSN： 1572-9672 0038-6308
The Detection of Dust Gap-ring Structure in the Outer Region of the CR Cha Protoplanetary Disk Peer-reviewed

Kim, Seongjoong, Takahashi, Sanemichi, Nomura, Hideko, Tsukagoshi, Takashi, Lee, Seokho, Muto, Takayuki, Dong, Ruobing, Hasegawa, Yasuhiro, Hashimoto, Jun, Kanagawa, Kazuhiro, Kataoka, Akimasa, Konishi, Mihoko, Liu, Hauyu Baobab, Momose, Munetake, Sitko, Michael, Tomida, Kengo

The Astrophysical Journal　888　(2)　2020/01

DOI： 10.3847/1538-4357/ab5d2b 　

ISSN： 0004-637X

eISSN： 1538-4357
Impact of the Hall effect in star formation, improving the angular momentum conservation Peer-reviewed

March, , P., Tomida, K., Commer?on, B., Chabrier, G.

Astronomy and Astrophysics　631　2019/11

DOI： 10.1051/0004-6361/201936215 　

ISSN： 1432-0746 0004-6361
Disc formation in magnetized dense cores with turbulence and ambipolar diffusion Peer-reviewed

Lam, K.H., Li, Z.-Y., Chen, C.-Y., Tomida, K., Zhao, B.

Monthly Notices of the Royal Astronomical Society　489　(4)　2019/11

DOI： 10.1093/mnras/stz2436 　

ISSN： 1365-2966 0035-8711
Nonideal MHD Simulation of HL Tau Disk: Formation of Rings Peer-reviewed

Xiao 晓 Hu 胡, Zhaohuan 照寰 Zhu 朱, Satoshi 住聡 Okuzumi 奥, Xue-Ning 雪宁 Bai 白, Lile 力乐 Wang 王, Kengo 田賢吾 Tomida 富, James M. Stone

The Astrophysical Journal　2019/11/01

DOI： 10.3847/1538-4357/ab44cb 　
A centrally concentrated sub-solar-mass starless core in the Taurus L1495 filamentary complex Peer-reviewed

Tokuda, Kazuki, Tachihara, Kengo, Saigo, Kazuya, André, Phillipe, Miyamoto, Yosuke, Zahorecz, Sarolta, Inutsuka, Shu-ichiro, Matsumoto, Tomoaki, Takashima, Tatsuyuki, Machida, Masahiro N., Tomida, Kengo, Taniguchi, Kotomi, Fukui, Yasuo, Kawamura, Akiko, Tatematsu, Ken'ichi, Kandori, Ryo, Onishi, Toshikazu

Publications of the Astronomical Society of Japan　71　(4)　2019/08

DOI： 10.1093/pasj/psz051 　

ISSN： 0004-6264

eISSN： 2053-051X
Giant Protostellar Flares: Accretion-driven Accumulation and Reconnection-driven Ejection of Magnetic Flux in Protostars Peer-reviewed

Shinsuke Takasao, Kengo Tomida, Kazunari Iwasaki, Takeru K. Suzuki

The Astrophysical Journal　878　(1)　2019/06/06

DOI： 10.3847/2041-8213/ab22bb 　

ISSN： 2041-8205

eISSN： 2041-8213
Acceleration and escape processes of high-energy particles in turbulence inside hot accretion flows Peer-reviewed

Shigeo S Kimura, Kengo Tomida, Kohta Murase

Monthly Notices of the Royal Astronomical Society　485　(1)　163-178　2019/05/01
Publisher: Oxford University Press ({OUP})
DOI： 10.1093/mnras/stz329 　

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The Early Stage of Molecular Cloud Formation by Compression of Two-phase Atomic Gases Peer-reviewed

Kazunari Iwasaki, Kengo Tomida, Tsuyoshi Inoue, Shu-ichiro Inutsuka

The Astrophysical Journal　2019/03/01

DOI： 10.3847/1538-4357/ab02ff 　
Extremely Dense Cores Associated with Chandra Sources in Ophiuchus A: Forming Brown Dwarfs Unveiled? Peer-reviewed

Kawabe, Ryohei, Hara, Chihomi, Nakamura, Fumitaka, Saigo, Kazuya, Kamazaki, Takeshi, Shimajiri, Yoshito, Tomida, Kengo, Takakuwa, Shigehisa, Tsuboi, Yohko, Machida, Masahiro N., Di Francesco, James, Friesen, Rachel, Hirano, Naomi, Oasa, Yumiko, Tamura, Motohide, Tamura, Yoichi, Tsukagoshi, Takashi, Wilner, David

The Astrophysical Journal　866　(2)　141　2018/10

DOI： 10.3847/1538-4357/aae153 　

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On the basis of various data such as ALMA, JVLA, Chandra, Herschel, and Spitzer, we confirmed that two protostellar candidates in Oph A are bona fide protostars or proto-brown dwarfs (proto-BDs) in extremely early evolutionary stages. Both objects are barely visible across infrared (IR; i.e., near-IR to far-IR) bands. The physical nature of the cores is very similar to that expected in first hydrostatic cores (FHSCs), objects theoretically predicted in the evolutionary phase prior to stellar core formation with gas densities of ∼10^11-12 cm^-3. This suggests that the evolutionary stage is close to the FHSC formation phase. The two objects are associated with faint X-ray sources, suggesting that they are in very early phase of stellar core formation with magnetic activity. In addition, we found the CO outflow components around both sources, which may originate from the young outflows driven by these sources. The masses of these objects are calculated to be ∼0.01-0.03 M _☉ from the dust continuum emission. These physical properties are consistent with that expected from the numerical model of forming brown dwarfs. These facts (the X-ray detection, CO outflow association, and FHSC-like spectral energy distributions) strongly indicate that the two objects are proto-BDs or will be in the very early phase of protostars, which will evolve to more massive protostars if they gain enough mass from their surroundings. The ages of these two objects are likely to be within ∼10³ years after the protostellar core (or second core) formation, taking into account the outflow dynamical times (≲500 years)....
Parametric Study of the Rossby Wave Instability in a Two-dimensional Barotropic Disk. II. Nonlinear Calculations Peer-reviewed

Tomohiro Ono, Takayuki Muto, Kengo Tomida, Zhaohuan Zhu

The Astrophysical Journal　2018/09/01

DOI： 10.3847/1538-4357/aad54d 　
Warm CO Gas Generated by Possible Turbulent Shocks in a Low-mass Star-forming Dense Core in Taurus Peer-reviewed

Kazuki Tokuda, Toshikazu Onishi, Kazuya Saigo, Tomoaki Matsumoto, Tsuyoshi Inoue, Shu-ichiro Inutsuka, Yasuo Fukui, Masahiro N. Machida, Kengo Tomida, Takashi Hosokawa, Akiko Kawamura, Kengo Tachihara

The Astrophysical Journal　862　(1)　2018/07/17

DOI： 10.3847/1538-4357/aac898 　

ISSN： 0004-637X

eISSN： 1538-4357
A Three-dimensional Simulation of a Magnetized Accretion Disk: Fast Funnel Accretion onto a Weakly Magnetized Star Peer-reviewed

Shinsuke Takasao, Kengo Tomida, Kazunari Iwasaki, Takeru K. Suzuki

The Astrophysical Journal　857　(1)　2018/04/06
Publisher: Institute of Physics Publishing
DOI： 10.3847/1538-4357/aab5b3 　

ISSN： 1538-4357 0004-637X
Pre-explosion Spiral Mass Loss of a Binary Star Merger Peer-reviewed

Ondřej Pejcha, Brian D. Metzger, Jacob G. Tyles, Kengo Tomida

The Astrophysical Journal　850　(1)　2017/11/17

DOI： 10.3847/1538-4357/aa95b9 　

ISSN： 0004-637X

eISSN： 1538-4357
ALMA Observations of SMM11 Reveal an Extremely Young Protostar in Serpens Main Cluster Peer-reviewed

Yusuke Aso, Nagayoshi Ohashi, Yuri Aikawa, Masahiro N. Machida, Kazuya Saigo, Masao Saito, Shigehisa Takakuwa, Kengo Tomida, Kohji Tomisaka, Hsi-Wei Yen, Jonathan P. Williams

The Astrophysical Journal　850　(1)　L2　2017/11/10

DOI： 10.3847/2041-8213/aa9701 　

ISSN： 2041-8205

eISSN： 2041-8213
A Detached Protostellar Disk around a ∼0.2 M ⊙ Protostar in a Possible Site of a Multiple Star Formation in a Dynamical Environment in Taurus Peer-reviewed

Kazuki Tokuda, Toshikazu Onishi, Kazuya Saigo, Takashi Hosokawa, Tomoaki Matsumoto, Shu-ichiro Inutsuka, Masahiro N. Machida, Kengo Tomida, Masanobu Kunitomo, Akiko Kawamura, Yasuo Fukui, Kengo Tachihara

The Astrophysical Journal　849　(2)　101-101　2017/11/06

DOI： 10.3847/1538-4357/aa8e9e 　

ISSN： 0004-637X

eISSN： 1538-4357
ALMA Observations of the Protostar L1527 IRS: Probing Details of the Disk and the Envelope Structures Peer-reviewed

Yusuke Aso, Nagayoshi Ohashi, Yuri Aikawa, Masahiro N. Machida, Kazuya Saigo, Masao Saito, Shigehisa Takakuwa, Kengo Tomida, Kohji Tomisaka, Hsi-Wei Yen

The Astrophysical Journal　849　(1)　56-56　2017/10/30

DOI： 10.3847/1538-4357/aa8264 　

ISSN： 0004-637X

eISSN： 1538-4357
Alma Observations of the Transition from Infall Motion to Keplerian Rotation around the Late-phase Protostar TMC-1A (vol 812 , 2015) Peer-reviewed

Yusuke Aso, Nagayoshi Ohashi, Kazuya Saigo, Shin Koyamatsu, Yuri Aikawa, Masahiko Hayashi, Masahiro N. Machida, Masao Saito, Shigehisa Takakuwa, Kengo Tomida, Kohji Tomisaka, Hsi-Wei Yen

ASTROPHYSICAL JOURNAL　836　(1)　2017/02

DOI： 10.3847/1538-4357/836/1/148 　

ISSN： 0004-637X

eISSN： 1538-4357
Grand-design Spiral Arms in a Young Forming Circumstellar Disk Peer-reviewed

Kengo Tomida, Masahiro N. Machida, Takashi Hosokawa, Yuya Sakurai, Chia Hui Lin

The Astrophysical Journal　835　(1)　2017/01/20

DOI： 10.3847/2041-8213/835/1/L11 　

ISSN： 2041-8205

eISSN： 2041-8213
Grand design spiral arms in a young forming circumstellar disk . Peer-reviewed

Tomida, K., Machida, M. N., Hosokawa, T., Sakurai, Y., Lin, C. H.

Memorie della Societa Astronomica Italiana　2017

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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. <P />...
The origin of rotation profiles in star-forming clouds Peer-reviewed

Takahashi, Sanemichi Z., Tomida, Kengo, Machida, Masahiro N., Inutsuka, Shu-ichiro

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　463　(2)　1390-1399　2016/12

DOI： 10.1093/mnras/stw1994 　

ISSN： 0035-8711

eISSN： 1365-2966
Binary stellar mergers with marginally bound ejecta: excretion discs, inflated envelopes, outflows, and their luminous transients Peer-reviewed

Pejcha, Ondřej, Metzger, Brian D., Tomida, Kengo

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　461　(3)　2527-2539　2016/09

DOI： 10.1093/mnras/stw1481 　

ISSN： 0035-8711

eISSN： 1365-2966
Cool and luminous transients from mass-losing binary stars Peer-reviewed

Pejcha, Ondřej, Metzger, Brian D., Tomida, Kengo

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　455　(4)　4351-4372　2016/07

DOI： 10.1088/1742-6596/728/7/072021 　

ISSN： 0035-8711

eISSN： 1365-2966
Cool and luminous transients from mass-losing binary stars Peer-reviewed

Pejcha, Ondřej, Metzger, Brian D., Tomida, Kengo

11TH PACIFIC RIM CONFERENCE ON STELLAR ASTROPHYSICS: PHYSICS AND CHEMISTRY OF THE LATE STAGES OF STELLAR EVOLUTION, PTS 1-6　728　2016/07

DOI： 10.1088/1742-6596/728/7/072021 　 10.1093/mnras/stv2592 　

ISSN： 1742-6588
Revealing a Detailed Mass Distribution of a High-density Core MC27/L1521F in Taurus with ALMA Peer-reviewed

Tokuda, Kazuki, Onishi, Toshikazu, Matsumoto, Tomoaki, Saigo, Kazuya, Kawamura, Akiko, Fukui, Yasuo, Inutsuka, Shu-ichiro, Machida, Masahiro N., Tomida, Kengo, Tachihara, Kengo, André, Philippe

ASTROPHYSICAL JOURNAL　826　(1)　2016/07

DOI： 10.3847/0004-637X/826/1/26 　

ISSN： 0004-637X

eISSN： 1538-4357
Cool and Luminous Transients from Mass-Losing Binary Stars Peer-reviewed

Pejcha, Ondrej, Metzger, Brian D., Tomida, Kengo

Monthly Notices of the Royal Astronomical Society　455　(4)　4351-4372　2016/01
Publisher: Oxford University Press
DOI： 10.1093/mnras/stv2592 　

ISSN： 1365-2966 0035-8711
ALMA Observations of a High-density Core in Taurus: Dynamical Gas Interaction at the Possible Site of a Multiple Star Formation Peer-reviewed

Onishi, T., Tokuda, K., Saigo, K., Kawamura, A., Fukui, Y., Matsumoto, T., Inutsuka, S. -i., Machida, M., Tomida, K., Tachihara, K.

REVOLUTION IN ASTRONOMY WITH ALMA: THE THIRD YEAR　499　211-214　2015/12
Keplerian and Infall Motions Around the Late-Phase Protostar TMC-1A Peer-reviewed

Aso, Y., Ohashi, N., Saigo, K., Takakuwa, S., Yen, H. -W., Koyamatsu, S., Aikawa, Y., Machida, M. N., Saito, M., Tomida, K., Tomida, K.

REVOLUTION IN ASTRONOMY WITH ALMA: THE THIRD YEAR　499　285-286　2015/12

ISSN： 1050-3390
ALMA Observations of the Transition from Infall Motion to Keplerian Rotation around the Late-phase Protostar TMC-1A Peer-reviewed

Aso, Yusuke, Ohashi, Nagayoshi, Saigo, Kazuya, Koyamatsu, Shin, Aikawa, Yuri, Hayashi, Masahiko, Machida, Masahiro N., Saito, Masao, Takakuwa, Shigehisa, Tomida, Kengo, Tomisaka, Kohji, Yen, Hsi-Wei

The Astrophysical Journal　812　(1)　27-27　2015/10/06

DOI： 10.1088/0004-637X/812/1/27 　

ISSN： 0004-637X

eISSN： 1538-4357
SMA and ALMA Studies of Protoplanetary-Disk Formation around Low-mass Protostars Peer-reviewed

Takakuwa, Shigehisa, Yen, Hsi-Wei, Ohashi, Nagayoshi, Chou, Ti-Lin, Aso, Yusuke, Saigo, Kazuya, Saito, Masao, Machida, Masahiro N., Tomida, Kengo, Aikawa, Yuri, Tomisaka, Kohji, Koyamatsu, Shin, Takahashi, Sanemichi Z.

FROM INTERSTELLAR CLOUDS TO STAR-FORMING GALAXIES: UNIVERSAL PROCESSES?　(315)　126-129　2015/08

DOI： 10.1017/S1743921316007389 　

ISSN： 1743-9213

eISSN： 1743-9221
Extremely Bright Submillimeter Galaxies beyond the Lupus-I Star-forming Region Peer-reviewed

Tamura, Y., Kawabe, R., Shimajiri, Y., Tsukagoshi, T., Nakajima, Y., Oasa, Y., Wilner, D. J., Chandler, C. J., Saigo, K., Tomida, K., Yun, M. S., Taniguchi, A., Kohno, K., Hatsukade, B., Aretxaga, I., Austermann, J. E., Dickman, R., Ezawa, H., Goss, W. M., Hayashi, M., Hughes, D. H., Hiramatsu, M., Inutsuka, S., Ogasawara, R., Ohashi, N., Oshima, T., Scott, K. S., Wilson, G. W.

The Astrophysical Journal　808　(2)　121-121　2015/08
Publisher: {IOP} Publishing
DOI： 10.1088/0004-637X/808/2/121 　

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We report detections of two candidate distant submillimeter galaxies (SMGs), MM J154506.4-344318 and MM J154132.7-350320, which are discovered in the AzTEC/ASTE 1.1 mm survey toward the Lupus-I star-forming region. The two objects have 1.1 mm flux densities of 43.9 and 27.1 mJy, and have Herschel/SPIRE counterparts as well. The Submillimeter Array counterpart to the former SMG is identified at 890 μm and 1.3 mm. Photometric redshift estimates using all available data from the mid-infrared to the radio suggest that the redshifts of the two SMGs are {z}_{photo}≃ 4-5 and 3, respectively. Near-infrared objects are found very close to the SMGs and they are consistent with low-z ellipticals, suggesting that the high apparent luminosities can be attributed to gravitational magnification. The cumulative number counts at {S}_1.1{mm}≥slant 25 mJy, combined with the other two 1.1 mm brightest sources, are {0.70}_-0.34^+0.56 deg^-2, which is consistent with a model prediction that accounts for flux magnification due to strong gravitational lensing. Unexpectedly, a z\gt 3 SMG and a Galactic dense starless core (e.g., a first hydrostatic core) could be similar in the mid-infrared to millimeter spectral energy distributions and spatial structures at least at ≳ 1\prime\prime . This indicates that it is necessary to distinguish the two possibilities by means of broadband photometry from the optical to centimeter and spectroscopy to determine the redshift, when a compact object is identified toward Galactic star-forming regions.
RADIATION MAGNETOHYDRODYNAMIC SIMULATIONS OF PROTOSTELLAR COLLAPSE: NONIDEAL MAGNETOHYDRODYNAMIC EFFECTS AND EARLY FORMATION OF CIRCUMSTELLAR DISKS Peer-reviewed

Kengo Tomida, Satoshi Okuzumi, Masahiro N. Machida

ApJ　801　(2)　117-117　2015/03/10

DOI： 10.1088/0004-637x/801/2/117 　

ISSN： 0004-637X

eISSN： 1538-4357
ALMA Observations of a High-density Core in Taurus: Dynamical Gas Interaction at the Possible Site of a Multiple Star Formation Peer-reviewed

Kazuki Tokuda, Toshikazu Onishi, Kazuya Saigo, Akiko Kawamura, Yasuo Fukui, Tomoaki Matsumoto, Shu-ichiro Inutsuka, Masahiro N. Machida, Kengo Tomida, Kengo Tachihara

FROM INTERSTELLAR CLOUDS TO STAR-FORMING GALAXIES: UNIVERSAL PROCESSES?　(315)　2015

DOI： 10.1017/S174392131600836X 　

ISSN： 1743-9213

eISSN： 1743-9221
FORMATION OF A KEPLERIAN DISK IN THE INFALLING ENVELOPE AROUND L1527 IRS: TRANSFORMATION FROM INFALLING MOTIONS TO KEPLER MOTIONS Peer-reviewed

Nagayoshi Ohashi, Kazuya Saigo, Yusuke Aso, Yuri Aikawa, Shin Koyamatsu, Masahiro N. Machida, Masao Saito, Sanemichi Z. Takahashi, Shigehisa Takakuwa, Kengo Tomida, Kohji Tomisaka, Hsi-Wei Yen

ApJ　796　(2)　131-131　2014/11

DOI： 10.1088/0004-637x/796/2/131 　

ISSN： 0004-637X

eISSN： 1538-4357
ALMA OBSERVATIONS OF INFALLING FLOWS TOWARD THE KEPLERIAN DISK AROUND THE CLASS I PROTOSTAR L1489 IRS Peer-reviewed

Hsi-Wei Yen, Shigehisa Takakuwa, Nagayoshi Ohashi, Yuri Aikawa, Yusuke Aso, Shin Koyamatsu, Masahiro N. Machida, Kazuya Saigo, Masao Saito, Kengo Tomida, Kohji Tomisaka

ApJ　793　(1)　1-1　2014/08/27

DOI： 10.1088/0004-637x/793/1/1 　

ISSN： 0004-637X

eISSN： 1538-4357
ALMA OBSERVATIONS OF A HIGH-DENSITY CORE IN TAURUS: DYNAMICAL GAS INTERACTION AT THE POSSIBLE SITE OF A MULTIPLE STAR FORMATION Peer-reviewed

Kazuki Tokuda, Toshikazu Onishi, Kazuya Saigo, Akiko Kawamura, Yasuo Fukui, Tomoaki Matsumoto, Shu-ichiro Inutsuka, Masahiro N. Machida, Kengo Tomida, Kengo Tachihara

ApJ　789　(1)　L4　2014/06/11

DOI： 10.1088/2041-8205/789/1/l4 　

ISSN： 2041-8205

eISSN： 2041-8213
RADIATION MAGNETOHYDRODYNAMIC SIMULATIONS OF PROTOSTELLAR COLLAPSE: LOW-METALLICITY ENVIRONMENTS Peer-reviewed

Kengo Tomida

ApJ　786　(2)　98-98　2014/04/22

DOI： 10.1088/0004-637x/786/2/98 　

ISSN： 0004-637X

eISSN： 1538-4357
On the role of the H 2 ortho:para ratio in gravitational collapse during star formation Peer-reviewed

Neil Vaytet, Kengo Tomida, Gilles Chabrier

A&A　563　A85　2014/03

DOI： 10.1051/0004-6361/201322855 　

ISSN： 0004-6361

eISSN： 1432-0746
Expected Observations of Star Formation Process: From Molecular Cloud Core to First Hydrostatic Core Peer-reviewed

Kohji Tomisaka, Akimasa Kataoka, Masahiro N. Machida, Kengo Tomida, Kazuya Saigo

LABYRINTH OF STAR FORMATION　36　133-137　2014

DOI： 10.1007/978-3-319-03041-8_24 　

ISSN： 1570-6591
Radiation Magnetohydrodynamic Simulations of Protostellar Core Formation Peer-reviewed

Kengo Tomida

LABYRINTH OF STAR FORMATION　36　35-39　2014

DOI： 10.1007/978-3-319-03041-8_6 　

ISSN： 1570-6591
Molecular Evolution in the First Hydrostatic Core Phase Adapting Three-Dimensional Radiation Hydrodynamic Simulations Peer-reviewed

Furuya, K., Aikawa, Y., Tomida, K., Matsumoto, T., Saigo, K., Tomisaka, K., Hersant, F., Wakelam, V.

2013/10

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We investigate the molecular evolution that develops as star formation proceeds from molecular cloud cores to first hydrostatic cores in three spatial dimensions. We perform a radiation hydrodynamic simulation in order to trace fluid parcels, in which molecular evolution is investigated, using a gas-grain chemical network model. The abundances of gaseous molecules in the warm envelope and the outer layer of the first core (T 〈 500 K) are mainly determined via evaporation of ice mantles, which are formed in a cold era (̃10 K). We find that large organic molecules, such as CH₃OH, are associated with the first core (r 〈 10 AU). This result suggest that first cores and the surrounding warm envelopes could be observed as very compact hot corinos without stellar signatures, and large organic molecules could be useful to trace first cores.
Spatially Resolving an Extremely Young Intermediate-mass Protostar in Orion Peer-reviewed

Takahashi, S., Saigo, K., Ho, P. T. P., Tomida, K.

NEW TRENDS IN RADIO ASTRONOMY IN THE ALMA ERA: THE 30TH ANNIVERSARY OF NOBEYAMA RADIO OBSERVATORY　476　397-398　2013/10
RMHD Simulations of Protostellar Collapse: Low-Metallicity Environment Peer-reviewed

Tomida, Kengo

2013/07

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We investigate star formation processes in low-metallicity environments using 3D radiation hydrodynamic and magnetohydrodynamic simulations in comparison with models with solar abundance. The entropy at the center of first cores becomes lower because radiation cooling is more efficient due to lower dust opacities. As a result, first cores are smaller and have shorter lifetimes. This implies that first cores tend to be more gravitationally-unstable and susceptible to fragmentation. On the other hand, the structure of proto-stellar cores after the second collapse depends on metallicities very weakly. This is because the gravitational energy released in the second collapse dominates the thermodynamical properties of protostellar cores. This result suggests that the initial conditions of stellar evolution only weakly depend on the environmental parameters.
Radiation Magnetohydrodynamic Simulations of Protostellar Core Formation Peer-reviewed

Kengo Tomida

NUMERICAL MODELING OF SPACE PLASMA FLOWS ASTRONUM-2012　474　110-115　2013/04
RADIATION MAGNETOHYDRODYNAMIC SIMULATIONS OF PROTOSTELLAR COLLAPSE: PROTOSTELLAR CORE FORMATION Peer-reviewed

Tomida, Kengo, Tomisaka, Kohji, Matsumoto, Tomoaki, Hori, Yasunori, Okuzumi, Satoshi, Machida, Masahiro N., Saigo, Kazuya

The Astrophysical Journal　763　(1)　6-6　2013

DOI： 10.1088/0004-637x/763/1/6 　 10.1088/0004-637X/763/1/6 　

ISSN： 0004-637X

eISSN： 1538-4357
EXPLICIT-IMPLICIT SCHEME FOR RELATIVISTIC RADIATION HYDRODYNAMICS Peer-reviewed

Takahashi, Hiroyuki R., Ohsuga, Ken, Sekiguchi, Yuichiro, Inoue, Tsuyoshi, Tomida, Kengo

The Astrophysical Journal　764　(2)　122-122　2013

DOI： 10.1088/0004-637x/764/2/122 　 10.1088/0004-637X/764/2/122 　

ISSN： 0004-637X
SPATIALLY RESOLVING SUBSTRUCTURES WITHIN THE MASSIVE ENVELOPE AROUND AN INTERMEDIATE-MASS PROTOSTAR: MMS 6/OMC-3 Peer-reviewed

Takahashi, Satoko, Saigo, Kazuya, Ho, Paul T. P., Tomida, Kengo

The Astrophysical Journal　752　(1)　10-10　2012

DOI： 10.1088/0004-637x/752/1/10 　 10.1088/0004-637X/752/1/10 　

ISSN： 0004-637X
CHEMISTRY IN THE FIRST HYDROSTATIC CORE STAGE BY ADOPTING THREE-DIMENSIONAL RADIATION HYDRODYNAMIC SIMULATIONS Peer-reviewed

Furuya, Kenji, Aikawa, Yuri, Tomida, Kengo, Matsumoto, Tomoaki, Saigo, Kazuya, Tomisaka, Kohji, Hersant, Franck, Wakelam, Valentine

The Astrophysical Journal　758　(2)　86-86　2012

DOI： 10.1088/0004-637x/758/2/86 　 10.1088/0004-637X/758/2/86 　

ISSN： 0004-637X

eISSN： 1538-4357
Observational Identification of First Cores: Non-LTE Radiative Transfer Simulation Peer-reviewed

Tomisaka, Kohji, Tomida, Kengo

PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN　63　(5)　1151-1164　2011/10

DOI： 10.1093/pasj/63.5.1151 　

ISSN： 0004-6264

eISSN： 2053-051X
Molecular Evolution of A First Core in 3 Dimensional Hydrodynamic Calculations Peer-reviewed

Furuya, K., Aikawa, Y., Matsumoto, T., Tomida, K., Saigo, K., Tomisaka, K., Hersant, F., Wakelam, V.

2011/05

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It is well established that stars are formed by gravitational collapse of molecular cloud cores. Collapsing cores initially undergo isothermal collapse. The isothermal condition breaks down at the density of ̃ 10^-13 g cm^-3, and the temperature starts rising. Increasing gas pressure decelerates the contraction, and the cores come to hydrostatic equilibrium with a radius of a few AU and a mass of ̃ 0.01 M_☉, which is called the first cores (e.g. Larson 1969). Observation of the first cores is important but challenging, since their lifetime is short (̃ 1000 yr). The mechanical property of the first cores have been studied by multi-dimensional hydrodynamic calculations considering interstellar magnetic fields and radiative transfer (e.g. Tomisaka 2002; Machida et al.2008; Tomida et al. 2010). In contrast, their chemical property is yet to be understood. It is important to reveal their chemical property in terms of which lines we should use to observe the first cores. In addition, the first cores evolve to protoplanetary disks (Saigo et al. 2008; Machida et al. 2010), hence the compositions of the first cores restrict the initial compositions of disks. We investigate molecular evolution of star forming cores that are initially rotating molecular cloud cores and collapse to form the first cores. The results of three dimensional hydrodynamic calculations (Matsumoto & Hanawa 2003) are adopted as physical models of the core. We trace trajectories of test particles in the hydrodynamic calculations, and molecular evolution is solved using low temperature chemical network (Garrod & Herbst 2006) at T < 100 K and high temperature network (Harada et al. 2010) at T > 100 K along the trajectories. We also consider three body reactions and collisional dissociations (Willacy et al. 1998). Trace particles fall into the first core almost spherically, and rotate in the first core where the spiral arms transports angular momentum. In our model with barotropic approximation, we find that in outer regions (R > 5 AU), the composition is similar to the low temperature chemistry. In intermediate regions (R ̃3 AU), hot-core like species, such as HCOOCH_3 and CH_3OCH_3 are generated. In central regions (R < 1 AU), complex molecules, such as HC_7N, HC_9N and NH_2CN, are formed in the gas phase.
EXPOSED LONG-LIFETIME FIRST CORE: A NEW MODEL OF FIRST CORES BASED ON RADIATION HYDRODYNAMICS (vol 725, L239, 2010) Peer-reviewed

Kengo Tomida, Masahiro N. Machida, Kazuya Saigo, Kohji Tomisaka, Tomoaki Matsumoto

ASTROPHYSICAL JOURNAL LETTERS　732　(1)　2011/05

DOI： 10.1088/2041-8205/732/1/L18 　

ISSN： 2041-8205
Hydrodynamical-Chemical Models from Prestellar Cores to Protostellar Cores Peer-reviewed

Aikawa, Yuri, Furuya, Kenji, Wakelam, Valentine, Hersant, Frank, Matsumoto, Tomoaki, Saigo, Kazuya, Tomida, Kengo, Tomisaka, Koji, Garrod, Robin, Herbst, Eric

Proceedings of the International Astronomical Union　7　(S280)　33-42　2011

DOI： 10.1017/s1743921311024847 　 10.1017/S1743921311024847 　

ISSN： 1743-9213
RADIATION MAGNETOHYDRODYNAMICS SIMULATION OF PROTO-STELLAR COLLAPSE: TWO-COMPONENT MOLECULAR OUTFLOW Peer-reviewed

Tomida, Kengo, Tomisaka, Kohji, Matsumoto, Tomoaki, Ohsuga, Ken, Machida, Masahiro N., Saigo, Kazuya

The Astrophysical Journal　714　(1)　L58-L63　2010

DOI： 10.1088/2041-8205/714/1/l58 　 10.1088/2041-8205/714/1/L58 　

ISSN： 2041-8205
EXPOSED LONG-LIFETIME FIRST CORE: A NEW MODEL OF FIRST CORES BASED ON RADIATION HYDRODYNAMICS Peer-reviewed

Tomida, Kengo, Machida, Masahiro N., Saigo, Kazuya, Tomisaka, Kohji, Matsumoto, Tomoaki

The Astrophysical Journal　725　(2)　L239-L244　2010

DOI： 10.1088/2041-8205/725/2/l239 　 10.1088/2041-8205/725/2/L239 　

ISSN： 2041-8205

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Misc. 6

Three-dimensional Simulations of Magnetospheric Accretion in a T Tauri Star: Accretion and Wind Structures Just Around the Star (vol 941, 73, 2022)

Shinsuke Takasao, Kengo Tomida, Kazunari Iwasaki, Takeru K. Suzuki

ASTROPHYSICAL JOURNAL　946　(1)　2023/03

DOI： 10.3847/1538-4357/acc39b 　

ISSN： 0004-637X

eISSN： 1538-4357
Modeling Hadronic Gamma-Ray Emissions from Solar Flares and Prospects for Detecting Nonthermal Signatures from Protostars

Shigeo S. Kimura, Shinsuke Takasao, Kengo Tomida

The Astrophysical Journal　2023/02/01

DOI： 10.3847/1538-4357/acb649 　

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We investigate gamma-ray emission in the impulsive phase of solar flares and the detectability of non-thermal signatures from protostellar flares. Energetic solar flares emit high-energy gamma rays of GeV energies, but their production mechanism and emission site are still unknown. Young stellar objects, including protostars, also exhibit luminous X-ray flares, but the triggering mechanism of the flaring activity is still unclear due to the strong obscuration. Non-thermal signatures in mm/sub-mm and gamma-ray bands are useful to probe protostellar flares owing to their strong penetration power. We develop a non-thermal emission model of the impulsive phase of solar flares, where cosmic-ray protons accelerated at the termination shock produce high-energy gamma rays via hadronuclear interaction with the evaporation plasma. This model can reproduce gamma-ray data in the impulsive phase of a solar flare. We apply our model to protostellar flares and show that Cherenkov Telescope Array will be able to detect gamma rays of TeV energies if particle acceleration in protostellar flares is efficient. Non-thermal electrons accelerated together with protons can emit strong mm and sub-mm signals via synchrotron radiation, whose power is consistent with the energetic mm/sub-mm transients observed from young stars. Future gamma-ray and mm/sub-mm observations from protostars, coordinated with a hard X-ray observation, will unravel the triggering mechanism of non-thermal particle production in protostellar flares.
Non-ideal magnetohydrodynamic simulations of the first star formation: the effect of ambipolar diffusion

Kenji Eric Sadanari, Kazuyuki Omukai, Kazuyuki Sugimura, Tomoaki Matsumoto, Kengo Tomida

2022/12/15

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In the present-day universe, magnetic fields play such essential roles in star formation as angular momentum transport and outflow driving, which control circumstellar disc formation/fragmentation and also the star formation efficiency. While only a much weaker field has been believed to exist in the early universe, recent theoretical studies find that strong fields can be generated by turbulent dynamo during the gravitational collapse. Here, we investigate the gravitational collapse of a cloud core ($\sim 10^{3}\ \rm cm^{-3}$) up to protostar formation ($\sim 10^{20}\ \rm cm^{-3}$) by non-ideal magnetohydrodynamics (MHD) simulations considering ambipolar diffusion (AD), the dominant non-ideal effects in the primordial-gas. We systematically study rotating cloud cores either with or without turbulence and permeated with uniform fields of different strengths. We find that AD can slightly suppress the field growth by dynamo especially on scales smaller than the Jeans-scale at the density range $10^{10}-10^{14}\ \rm cm^{-3}$, while we could not see the AD effect on the temperature evolution, since the AD heating rate is always smaller than compression heating. The inefficiency of AD makes the field as strong as $10^{3}-10^{5} \rm\ G$ near the formed protostar, much stronger than in the present-day cases, even in cases with initially weak fields. The magnetic field affects the inflow motion when amplified to the equipartition level with turbulence on the Jeans-scale, although disturbed fields do not launch winds. This might suggest that dynamo amplified fields have smaller impact on the dynamics in the later accretion phase than other processes such as ionisation feedback.
相対論的無衝突衝撃波での乱流ダイナモによる磁場増幅

冨田沙羅, 大平豊, 木村成生, 富田賢吾, 當真賢二

日本天文学会年会講演予稿集　2022　2022

ISSN： 1347-0639
L1495領域のフィラメント雲に埋もれた褐色矮星前駆体候補の高密度コア

徳田一起, SAROLTA Zahorecz, 立原研悟, 宮本洋輔, 福井康雄, 犬塚修一郎, PHILLIPE Andre, 西合一矢, 河村晶子, 立松健一, 松本倫明, 町田正博, 富田賢吾, 谷口琴美, 神鳥亮, 高嶋辰幸, 大西利加

日本天文学会年会講演予稿集　2019　2019

ISSN： 1347-0639
おおかみ座I分子雲方向に偶然検出された極高光度サブミリ波銀河の性質

田村陽一, 川邊良平, 西合一矢, 島尻芳人, 塚越崇, 谷口暁星, 河野孝太郎, 中島康, 大朝由美子, 富田賢吾, WILNER D., CHANDLER C., DICKMAN R., GOSS M., YUN M. S.

日本天文学会年会講演予稿集　2014　2014

ISSN： 1347-0639

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Books and Other Publications 1

Protostars and planets VII

Shu-ichiro Inutsuka, Yuri Aikawa, Takayuki Muto, Kengo Tomida, Motohide Tamura

Astronomical Society of the Pacific　2023

ISBN: 9781583819555

Research Projects 16

Multi-scale Star Formation: From the Galactic Disk to Protoplanetary Disks

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research Fund for the Promotion of Joint International Research (Fostering Joint International Research (B))

Category: Fund for the Promotion of Joint International Research (Fostering Joint International Research (B))

Institution: Tohoku University

2022/10/07 - 2028/03/31
Exploration of high-energy astrophysical phenomena in star and planet formation processes

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A)

Category: Grant-in-Aid for Scientific Research (A)

Institution: Tohoku University

2021/04/05 - 2026/03/31
Study of Planet Formation in Protostellar Disks with the ALMA Large Program

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A)

Category: Grant-in-Aid for Scientific Research (A)

Institution: Kagoshima University

2021/04/05 - 2025/03/31
大規模並列計算に対応した輻射磁気流体シミュレーションコードAthena++の開発

Offer Organization: 公益財団法人稲盛財団

System: 稲盛研究助成

Institution: 東北大学

2024/04 - 2025/03
Hosting Protostar and Planets VII and Its Follow-up Workshop

Kengo Tomida

Offer Organization: Japan Science and Technology Agency

Institution: Tohoku University

2022/08 - 2024/03
Observational Studies on the Formation of Star Clusters in Giant Molecular Clouds

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area)

Category: Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area)

Institution: Osaka Prefecture University

2018/06/29 - 2023/03/31
Protoplanetary disks and formation of terrestrial planets

Xuening Bai, Hidekazu Tanaka, Shoji Mori, Chris Ormel, Zhuo Chen

Offer Organization: Tohoku University, Tsinghua University

System: Tohoku University-Tsinghua University Collaborative Research Fund

Institution: Tohoku University, Tsinghua University

2021/04 - 2023/03
Toward a unified view of the universe: from large scale structures to planets

Offer Organization: MEXT

2020/09 - 2023/03
Developement of a public code generating opacity and equation of state tables for radiation hydrodynamics simulations

Hirose Shigenobu

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research

Category: Grant-in-Aid for Scientific Research (C)

Institution: Japan Agency for Marine-Earth Science and Technology

2018/04/01 - 2021/03/31

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We have developed a public code Optab that outputs Rosseland, Planck, and two-temperature Planck mean gas opacity tables for radiation hydrodynamics simulations in astrophysics. The code is developed for modern high performance computing, being written in Fortran 90 and using Message Passing Interface and Hierarchical Data Format, Version 5. The purpose of this work is to provide a platform on which users can generate opacity tables for their own research purposes. Therefore, the code has been designed so that a user can easily modify, change, or add opacity sources in addition to those already implemented, which include bremsstrahlung, photoionization, Rayleigh scattering, line absorption, and collision-induced absorption.
Radiation Transfer Modeling of Star and Disk Formation for ALMA

Kengo Tomida, Kei Tanaka

Offer Organization: National Astronomical Observatory of Japan

System: The ALMA Joint Scientific Research Program

2018/01 - 2020/12
Exploration of the origin of the initial mass function using multi-scale simulations

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research Grant-in-Aid for Young Scientists (A)

Category: Grant-in-Aid for Young Scientists (A)

Institution: Osaka University

2016/04/01 - 2020/03/31
Accelerating astrophysical magnetohydrodynamic simulations using advanced techniques

Tomida Kengo

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research

Category: Grant-in-Aid for Challenging Exploratory Research

Institution: Osaka University

2016/04/01 - 2020/03/31

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Athena++ is a new public magnetohydrodynamic simulation code which I develop in collaboration with Princeton University and others. In this project, I optimized the code to achieve better performance and also implemented new physics modules including self-gravity. The code achieves good performance and scalability even with more than half a million threads thanks to the new parallelization based on dynamical scheduling as well as thorough optimization to modern architectures. I implemented a new self-gravity solver based on the Full Multigrid method, which is very efficient and scalable. The code and documentation are publicly distributed on the Internet, and we held schools on computational astrophysics and a users' meeting.
Multi-scale radiation magnetohydrodynamic simualtions of star formation with Athena++

Kengo Tomida

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research

Category: Fund for the Promotion of Joint International Research (Fostering Joint International Research)

Institution: Osaka University

2018 - 2019

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I developed the Athena++ public radiation MHD simulation code in collaboration with Professor Stone's group at Princeton University. In this project, I extended the self-gravity solver using the Multigrid method to adaptive mesh refinement (AMR), and extended it to radiation transfer. I implemented a new self-gravity solver which is compatible with AMR. The implementation requires some additional cost on AMR but it works stably. Then I extended it to the simplest diffusion approximation of radiation transfer. The solver works when distribution of the diffusion coefficient is relatively smooth. However, it converges slowly when the diffusion coefficient is highly non-uniform and/or the system is strongly non-linear. I will try other methods for this and improve the stability of the scheme.
Probing Planet Formation from Detailed Structures in Protoplanetary Disks

Muto Takayuki, Momose Munetake, Fukagawa Misato, Tsukagoshi Takashi, Hanawa Tomoyuki, Soon Kang-Lou, Kataoka Akimasa, Kanagawa Kazuhiro D., Tanaka Hidekazu, Ono Tomohiro, Tomida Kengo

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research Grant-in-Aid for Young Scientists (B)

Category: Grant-in-Aid for Young Scientists (B)

Institution: Kogakuin University

2014/04/01 - 2018/03/31

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High resolution observations of protoplanetary disks are now available with large telescopes and many protoplanetary disks show various structures. The goal of this research is to develope the methods to derive implications on physical status of protoplanetary disks and on planet formation processes from such observations. From the modeling work of the disk around HD 142527, we have found that there is a location in the disk where the dust particles are strongly concentrated. In the work on the shape of the gap structures produced by a planet embedded in the disk, our group is one of the first to derive the estimate of the planet mass in the disk around the HL Tau, in which several ring-like structures are found in the ALMA long-baseline campaign observations. In the work of linear stability analyses of Rossby wave instability, we have derived the marginally stable conditions of the instability, which have been a mystery over several decades.
星・惑星形成から星系形成へ-マルチスケール輻射磁気流体計算による研究

富田賢吾

Offer Organization: 日本学術振興会

System: 科学研究費助成事業特別研究員奨励費

Category: 特別研究員奨励費

Institution: 東京大学

2014 - 2014

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本研究では星形成過程のうち、分子雲コアからファーストコア・星周円盤に至るスケールをngr3mhdコードで、また円盤近傍の小スケールの構造をAthena++コードによりシミュレーションし、これらを組み合わせて分子雲から原始星に至る星形成過程全体の一貫したモデルを構築することを目的としている。 ngr3mhdコードを用いたシミュレーションについては、双極性拡散(ambipolar diffusion)を取り入れたシミュレーションを行い、この効果により磁場が拡散して磁場による角運動量輸送が強く抑制され、これまで想定されていたよりも早い段階で星周円盤の形成が可能であることを示した。形成された円盤は星形成過程の初期では半径数AU程度と小さいが、その後のガス降着により成長すると考えられる。近年の電波干渉計による星周円盤の観測では、若い原始星周囲の星周円盤は小さいことが分かっており、この結果は観測とも整合的である。原始星周辺の小スケール構造を扱うシミュレーションには新規にAthena++コードの開発を進めている。本コードはこれまでPrinceton大学にて開発されてきたAthenaコードを完全に再設計するものであり、これまでよりも柔軟な格子配置、特に任意の領域に高解像度の格子を動的に配置する解適合細分化格子(Adaptive Mesh Refinement, AMR)を可能にすること、及び従来の磁気流体に加え自己重力や輻射輸送などの多くの物理過程を実装することを目的としている。またコードの性能にも重点を置いており、現代的なスーパーコンピューターで高性能が実現できるよう最適化を行っている。多様な座標系に適用可能な一般的なMHDソルバーの開発は順調に終了し、現在テストを進めている。またAMRについては現在設計を進めている段階である。
3次元多重格子輻射磁気流体力学シミュレーションを用いた星形成現象の系統的研究

富田賢吾

Offer Organization: 日本学術振興会

System: 科学研究費助成事業特別研究員奨励費

Category: 特別研究員奨励費

Institution: 総合研究大学院大学

2009 - 2011

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原始星形成過程においてファーストコア(星形成の初期に形成される過渡的な準平衡天体)の中心温度が約2000Kに達すると水素分子が解離する。この反応は吸熱反応であり、それによって力学平衡を保てなくなりファーストコアは崩壊する。この過程(セカンドコラプス)は水素分子が完全に解離するまで続き、解離が終了すると再び断熱的となり再び準平衡天体が形成される。これがセカンドコアまたは原始星コアであり、以後周囲からのガス降着で成長する、いわば星の種である。今年度はこれまでのシミュレーションを拡張し、このセカンドコラプス以後の段階を調べるために計算コードに現実的状態方程式と非理想MHD効果を新たに導入した。これら新しい物理過程を導入することにより、世界で初めて分子雲コアから原始星コアに至る星形成過程を直接輻射磁気流体計算することに成功した。理想MHDの計算では磁場による効率の良い角運動量輸送の結果原始星コアはほぼ無回転であり、星周円盤が形成されない"Magnetic Braking Catastrophe"と呼ばれる問題があるが、抵抗性MHDでは磁場の散逸により角運動量輸送が抑制され、原始星コア周囲に星周円盤が短時間で形成されることを示した。また、回転によってトロイダル磁場が増幅され、その磁気圧勾配によって高速の細いジェットが駆動されることもわかった。これは観測されているアウトフローの構造と整合的な結果である。並行して、前年度までに引き続いて輻射磁気流体計算の結果から観測的性質の予測を行い、その結果に基づいて観測グループと共同で実際にALMAの初期科学運用やSMAなどに観測提案も提出した。特に国立天文台の大橋教授らのグループと共同で提出した観測提案は9倍の厳しい競争を勝ち抜いて採択され、近く観測結果とシミュレーションを直接比較することが可能になると期待している。

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Teaching Experience 6

Computational Astrophysics　Tohoku University
Physics of the Insterstellar Medium　Tohoku University
Practice on Astrophysics II　Tohoku University
Theoretical Mechanics　Tohoku University
Mechanics II　Osaka University
Theoretical Mechanics 2 Exercise　Osaka University

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