Faculty Profiles - KOBAYASHI Hiroshi

Papers - KOBAYASHI Hiroshi

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Faint warm debris disks around nearby bright stars explored by AKARI and IRSF

Daisuke Ishihara, Nami Takeuchi, Hiroshi Kobayashi, Takahiro Nagayama, Hidehiro Kaneda, Shu-ichiro Inutsuka, Hideaki Fujiwara, Takashi Onaka

ASTRONOMY & ASTROPHYSICS Vol. 601 page： A72 2017.5

Language：English Publishing type：Research paper (scientific journal) Publisher：EDP SCIENCES S A

Context. Debris disks are important observational clues for understanding planetary-system formation process. In particular, faint warm debris disks may be related to late planet formation near 1 au. A systematic search of faint warm debris disks is necessary to reveal terrestrial planet formation.
Aims. Faint warm debris disks show excess emission that peaks at mid-IR wavelengths. Thus we explore debris disks using the AKARI mid-IR all-sky point source catalog (PSC), a product of the second generation unbiased IR all-sky survey.
Methods. We investigate IR excess emission for 678 isolated main-sequence stars for which there are 18 mu m detections in the AKARI mid-IR all-sky catalog by comparing their fluxes with the predicted fluxes of the photospheres based on optical to near-IR fluxes and model spectra. The near-IR fluxes are first taken from the 2MASS PSC. However, 286 stars with Ks < 4.5 in our sample have large flux errors in the 2MASS photometry due to saturation. Thus we have measured accurate J, H, and Ks band fluxes, applying neutral density (ND) filters for Simultaneous InfraRed Imager for Unbiased Survey (SIRIUS) on IRSF, the phi 1.4m near-IR telescope in South Africa, and improved the flux accuracy from 14% to 1.8% on average.
Results. We identified 53 debris-disk candidates including eight new detections from our sample of 678 main-sequence stars. The detection rate of debris disks for this work is similar to 8%, which is comparable with those in previous works by Spitzer and Herschel.
Conclusions. The importance of this study is the detection of faint warm debris disks around nearby field stars. At least nine objects have a large amount of dust for their ages, which cannot be explained by the conventional steady-state collisional cascade model.

DOI： 10.1051/0004-6361/201526215

Web of Science

Size Dependence of Dust Distribution around the Earth Orbit

Ueda Takahiro, Kobayashi Hiroshi, Takeuchi Taku, Ishihara Daisuke, Kondo Toru, Kaneda Hidehiro

ASTRONOMICAL JOURNAL Vol. 153 ( 5 ) 2017.5

Detection of Submillimeter-wave [C i] Emission in Gaseous Debris Disks of 49 Ceti and β Pictoris Reviewed

Aya E Higuchi, Aki Sato, Takashi Tsukagoshi, Nami Sakai, Kazunari Iwasaki, Munetake Momose, Hiroshi Kobayashi, Daisuke Ishihara, Sakae Watanabe, Hidehiro Kaneda, Satoshi Yamamoto

Astrophysical Journal Vol. 839 ( 1 ) page： L14 2017.4

Orbital Evolution of Moons in Weakly Accreting Circumplanetary Disks

Yuri I Fujii, Hiroshi Kobayashi, Sanemichi Z Takahashi, Oliver Gressel

Astronomical Journal Vol. 153 ( 4 ) page： 194 2017.4

Detection of Submillimeter-wave [CI] Emission in Gaseous Debris Disks of 49 Ceti and beta Pictoris

Aya E. Higuchi, Aki Sato, Takashi Tsukagoshi, Nami Sakai, Kazunari Iwasaki, Munetake Momose, Hiroshi Kobayashi, Daisuke Ishihara, Sakae Watanabe, Hidehiro Kaneda, Satoshi Yamamoto

ASTROPHYSICAL JOURNAL LETTERS Vol. 839 ( 1 ) page： L14 2017.4

Language：English Publishing type：Research paper (scientific journal) Publisher：IOP PUBLISHING LTD

We have detected [C I] P-3(1)-P-3(0) emissions in the gaseous debris disks of 49 Ceti and beta Pictoris with the 10 m telescope of the Atacama Submillimeter Telescope Experiment, which is the first detection of such emissions. The line profiles of [C I] are found to resemble those of CO(J = 3-2) observed with the same telescope and the Atacama Large Millimeter/submillimeter Array. This result suggests that atomic carbon (C) coexists with CO in the debris disks. and is likely formed by the photodissociation of CO. Assuming an optically thin [C I] emission with the excitation temperature ranging from 30 to 100. K, the column density of C is evaluated to be (2.2 +/- 0.2). x. 10(17) and (2.5 +/- 0.7). x. 10(16). cm(-2) for 49 Ceti and beta Pictoris, respectively. The C/CO column density ratio is thus derived to be 54 +/- 19 and 69 +/- 42 for 49 Ceti and beta Pictoris, respectively. These ratios are higher than those of molecular clouds and diffuse clouds by an order of magnitude. The unusually high ratios of C to CO are likely attributed to a lack of H-2 molecules needed to reproduce CO molecules efficiently from C. This result implies a small number of H-2 molecules in the gas disk,. i.e., there is an appreciable contribution of secondary gas from dust grains.

DOI： 10.3847/2041-8213/aa67f4

Web of Science

Orbital Evolution of Moons in Weakly Accreting Circumplanetary Disks

Fujii Yuri I., Kobayashi Hiroshi, Takahashi Sanemichi Z., Gressel Oliver

ASTRONOMICAL JOURNAL Vol. 153 ( 4 ) 2017.4

Evolutionary Description of Giant Molecular Cloud Mass Functions on Galactic Disks Reviewed

Masato I.N. Kobayashi, Shu-ichiro Inutsuka, Hiroshi Kobayashi, Kenji Hasegawa

Astrophysical Journal Vol. 836 ( 2 ) page： 175 2017.2

Evolutionary Description of Giant Molecular Cloud Mass Functions on Galactic Disks

Masato I. N. Kobayashi, Shu-ichiro Inutsuka, Hiroshi Kobayashi, Kenji Hasegawa

ASTROPHYSICAL JOURNAL Vol. 836 ( 2 ) 2017.2

Language：English Publishing type：Research paper (scientific journal) Publisher：IOP PUBLISHING LTD

Recent radio observations show that giant molecular cloud (GMC) mass functions noticeably vary across galactic disks. High-resolution magnetohydrodynamics simulations show that multiple episodes of compression are required for creating a molecular cloud in the magnetized interstellar medium. In this article, we formulate the evolution equation for the GMC mass function to reproduce the observed profiles, for which multiple compressions are driven by a network of expanding shells due to H II regions and supernova remnants. We introduce the cloudcloud collision (CCC) terms in the evolution equation in contrast to previous work (Inutsuka et al.). The computed time evolution suggests that the GMC mass function slope is governed by the ratio of GMC formation timescale to its dispersal timescale, and that the CCC effect is limited only in the massive end of the mass function. In addition, we identify a gas resurrection channel that allows the gas dispersed by massive stars to regenerate GMC populations or to accrete onto pre-existing GMCs. Our results show that almost all of the dispersed gas contributes to the mass growth of pre-existing GMCs in arm regions whereas less than 60% contributes in inter-arm regions. Our results also predict that GMC mass functions have a single power-law exponent in the mass range < 10(5.5) M-circle dot (where M-circle dot represents the solar mass), which is well characterized by GMC self-growth and dispersal timescales. Measurement of the GMC mass function slope provides a powerful method to constrain those GMC timescales and the gas resurrecting factor in various environments across galactic disks.

DOI： 10.3847/1538-4357/836/2/175

Web of Science

Sintering-induced Dust Ring Formation in Protoplanetary Disks: Application to the HL Tau Disk Reviewed

Satoshi Okuzumi, Munetake Momose, Sin-iti Sirono, Hiroshi Kobayashi, Hidekazu Tanaka

Astrophysical Journal Vol. 821 ( 2 ) page： id 82, 24 2016.4

From Planetesimals to Planets in Turbulent Protoplanetary Disks. I. Onset of Runaway Growth Reviewed

Hiroshi Kobayashi, Hidekazu Tanaka, Satoshi Okuzumi

Astrophysical Journal Vol. 817 ( 2 ) page： id. 105, 10 2016.2

Resolution Dependence of Disruptive Collisions between Planetesimals in the Gravity Regime Reviewed

H. Genda, T. Fujita, H. Kobayashi, H. Tanaka, Y. Abe

Icarus Vol. 262 page： 58 2015.12

Comet C/2012 S1 (ISON) coma composition at ~4 au from HST observations Reviewed

E. Zubko, G. Videen, D. C. Hines, Y. Shkuratov, V. Kaydash, K. Muinonen, M. M. Knight, M. L. Sitko, C. M. Lisse, M. Mutchler, D. H. Wooden, J.-Y. Li, H. Kobayashi

Planetary and Space Science Vol. 118 page： 138 2015.12

Warm Debris Disks Produced by Giant Impacts During Terrestrial Planet Formation

H. Genda, H. Kobayashi, E. Kokubo

Astrophysical Journal Vol. 810 page： 136(8p) 2015.11

Significant gas-to-dust ratio asymmetry and variation in the disk of HD 142527 and the indication of gas depletion

Takayuki Muto, Takashi Tsukagoshi, Munetake Momose, Tomoyuki Hanawa, Hideko Nomura, Misato Fukagawa, Kazuya Saigo, Akimasa Kataoka, Yoshimi Kitamura, Sanemichi Z Takahashi, Shu-ichiro Inutsuka, Taku Takeuchi, Hiroshi Kobayashi, Eiji Akiyama, Mitsuhiko Honda, Hideaki Fujiwara, Hiroshi Shibai

Publications of the Astronomical Society of Japan page： psv098 2015.11

Cohesion of Amorphous Silica Spheres: Toward a Better Understanding of The Coagulation Growth of Silicate Dust Aggregates Reviewed

Hiroshi Kimura, Koji Wada, Hiroki Senshu, Hiroshi Kobayashi

Astrophysical Journal Vol. 812 page： 1 2015.10

Planetary and meteoritic Mg/Si and δ30Si variations inherited from solar nebula chemistry Reviewed

N. Dauphas, F. Poitrasson, C. Burkhardt, H. Kobayashi, K. Kurosawa

Earth and Planetary Science Letter Vol. 427 page： 236 2015.10

Formation of terrestrial planets in disks evolving via disk winds and implications for the origin of the solar system's terrestrial planets

M. Ogihara, H. Kobayashi, S. Inutsuka, T. Suzuki

Astronomy & Astrophysics Vol. 579 page： A65 2015.6

Orbital Evolution of Planetesimals in Gaseous Disks

Hiroshi Kobayashi

Earth, Planets and Space Vol. 67 page： 60 2015.4

Debris disc formation induced by planetary growth Reviewed

Hiroshi Kobayashi, Torsten Loehne

Monthly Notices of the Royal Astronomical Society Vol. 442 ( 4 ) page： 464-8602 2014.8

N-body Simulations of Terrestrial Planet Formation under the Influence of a Hot Jupiter Reviewed

Ogihara, Masahiro; Kobayashi, Hiroshi; Inutsuka, Shu-ichiro

The Astrophysical Journal Vol. 787 ( 2 ) page： id 172(16p) 2014.6

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Papers - KOBAYASHI Hiroshi