Updated on 2023/04/18

写真a

 
TSUBOI Yohko
 
Organization
Faculty of Science and Engineering Professor
Other responsible organization
Physics Course of Graduate School of Science and Engineering, Master's Program
Physics Course of Graduate School of Science and Engineering, Doctoral Program
Contact information
The inquiry by e-mail is 《here
External link

Degree

  • 博士(理学) ( 京都大学 )

  • 修士(理学) ( 京都大学 )

Education

  • 1999.3
     

    Kyoto University   Graduate School, Division of Natural Science   doctor course   completed

  • 1996.3
     

    Kyoto University   Graduate School, Division of Natural Science   master course   completed

  • 1994.3
     

    Kyoto University   Faculty of Science   graduated

Research History

  • 2015.4 -  

    中央大学理工学部教授

  • 2007.4 - 2015.3

    中央大学理工学部准教授

  • 2004.4 - 2007.3

    中央大学理工学部助教授   Faculty of Science and Engineering

  • 2007 -  

    - 中央大学理工学部准教授

  • 2002.4 - 2004.3

    中央大学理工学部専任講師   Faculty of Science and Engineering

  • 2001.4 - 2002.3

    ペンシルバニア州立大学天文学及び宇宙物理学科リサーチ・アソシエート

  • 1999.4 - 2001.3

    日本学術振興会海外特別研究員

  • 1999 - 2001

    日本学術振興会海外特別研究員

  • 1996.4 - 1999.3

    日本学術振興会特別研究員

  • 1996 - 1999

    日本学術振興会特別研究員

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Professional Memberships

  • アメリカ天文学会

  • 日本天文学会

  • 高エネルギー宇宙物理連絡会

Research Areas

  • Natural Science / Astronomy

Papers

  • X-ray/Hα scaling relationships in stellar flares Reviewed

    Kawai, Hiroki, Tsuboi, Yohko, search by orcid, Iwakiri, Wataru B, search by orcid, Maeda, Yoshitomo, Katsuda, Satoru, search by orcid, Sasaki, Ryo, Kohara, Junya, MAXI TEAM

    Publications of the Astronomical Society of Japan   74 ( 2 )   477 - 487   2022.4

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  • Detailed design of the science operations for the XRISM mission Reviewed

    Terada Yukikatsu

    Journal of Astronomical Telescopes, Instruments, and Systems   7   2021.7

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  • Erratum: Optical and X-ray observations of stellar flares on an active M dwarf AD Leonis with Seimei Telescope, SCAT, NICER, and OISTER Reviewed

    Namekata, Kosuke

    Publications of the Astronomical Society of Japan   73 ( 2 )   485 - 485   2021.4

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  • The RS CVn-type Star GT Mus Shows Most Energetic X-Ray Flares Throughout the 2010s Reviewed

    Sasaki, Ry

    The Astrophysical Journal Letters   910 ( 1 )   13   2021.3

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  • Optical and X-ray observations of stellar flares on an active M dwarf AD Leonis with the Seimei Telescope, SCAT, NICER, and OISTER Reviewed

    Namekata, Kosuke

    Publications of the Astronomical Society of Japan   72 ( 4 )   15   2020.8

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  • Inverse First Ionization Potential Effects in Giant Solar Flares Found from Earth X-Ray Albedo with Suzaku/XIS Reviewed

    Katsuda, Sator

    The Astrophysical Journal Letters   891 ( 2 )   13   2020.3

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  • Detection of polarized gamma-ray emission from the Crab nebula with the Hitomi Soft Gamma-ray Detector Reviewed

    Hitomi Collaboratio

    Publications of the Astronomical Society of Japan   70 ( 6 )   2018.12

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  • The 7-year MAXI/GSC X-Ray Source Catalog in the High Galactic Latitude Sky (3MAXI) Reviewed

    Kawamuro, T

    The Astrophysical Journal Letters   238 ( 2 )   15   2018.10

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  • Hitomi X-ray observation of the pulsar wind nebula G21.5-0.9 Reviewed

    Hitomi Collaboratio

    Publications of the Astronomical Society of Japan   70 ( 3 )   2018.6

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  • Hitomi (ASTRO-H) X-ray Astronomy Satellite Reviewed

    Takahashi, Tadayuki

    Journal of Astronomical Telescopes   4   2018.4

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  • The 7-year MAXI/GSC Source Catalog of the Low-Galactic-latitude Sky (3MAXI) Reviewed

    Hori, T, Shidatsu, M, Ueda, Y, Kawamuro, T, Morii, M, Nakahira, S, Isobe, N, Kawai, N, Mihara, T, Matsuoka, M, Morita, T, Nakajima, M, Negoro, H, Oda, S, Sakamoto, T, Serino, M, Sugizaki, M, Tanimoto, A, Tomida, H, Tsuboi, Y. Tsunemi, H, Ueno, S, Yamaoka, K, Yamada, S, Yoshida, A, Iwakiri, W, Kawakubo, Y, Sugawara, Y, Sugita, S, Tachibana, Y, Yoshii, T

    Astrophysical Journal   235 ( 1 )   40   2018.3

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  • Glimpse of the highly obscured HMXB IGR J16318-4848 with Hitomi Reviewed

    Hitomi Collaboratio

    Publications of the Astronomical Society of Japan   70 ( 2 )   2018.3

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  • Hitomi observations of the LMC SNR N 132 D: Highly redshifted X-ray emission from iron ejecta Reviewed

    Hitomi Collaboratio

    Publications of the Astronomical Society of Japan   70 ( 2 )   2018.3

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  • Hitomi X-ray studies of giant radio pulses from the Crab pulsar Reviewed

    Hitomi Collaboratio

    Publications of the Astronomical Society of Japan   70 ( 2 )   2018.3

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  • Search for thermal X-ray features from the Crab nebula with the Hitomi soft X-ray spectrometer Reviewed

    Hitomi Collaboratio

    Publications of the Astronomical Society of Japan   70 ( 2 )   2018.3

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  • Hitomi observation of radio galaxy NGC 1275: The first X-ray microcalorimeter spectroscopy of Fe-Kα line emission from an active galactic nucleus Reviewed

    Hitomi Collaboratio

    Publications of the Astronomical Society of Japan   70 ( 2 )   2018.3

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  • Atomic data and spectral modeling constraints from high-resolution X-ray observations of the Perseus cluster with Hitomi Reviewed

    Hitomi Collaboratio

    Publications of the Astronomical Society of Japan   70 ( 2 )   2018.3

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  • Measurements of resonant scattering in the Perseus Cluster core with Hitomi SXS Reviewed

    Hitomi Collaboratio

    Publications of the Astronomical Society of Japan   70 ( 2 )   2018.3

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  • Solar abundance ratios of the iron-peak elements in the Perseus cluster Reviewed

    Hitomi Collaboration, 頭著者

    Nature   551 ( 7681 )   478 - 480   2017.11

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:Nature Publishing Group  

    The metal abundance of the hot plasma that permeates galaxy clusters represents the accumulation of heavy elements produced by billions of supernovae(1). Therefore, X-ray spectroscopy of the intracluster medium provides an opportunity to investigate the nature of supernova explosions integrated over cosmic time. In particular, the abundance of the iron-peak elements (chromium, manganese, iron and nickel) is key to understanding how the progenitors of typical type Ia supernovae evolve and explode(2-6). Recent X-ray studies of the intracluster medium found that the abundance ratios of these elements differ substantially from those seen in the Sun(7-11), suggesting differences between the nature of type Ia supernovae in the clusters and in the Milky Way. However, because the K-shell transition lines of chromium and manganese are weak and those of iron and nickel are very close in photon energy, highresolution spectroscopy is required for an accurate determination of the abundances of these elements. Here we report observations of the Perseus cluster, with statistically significant detections of the resonance emission from chromium, manganese and nickel. Our measurements, combined with the latest atomic models, reveal that these elements have near-solar abundance ratios with respect to iron, in contrast to previous claims. Comparison between our results and modern nucleosynthesis calculations(12-14) disfavours the hypothesis that type Ia supernova progenitors are exclusively white dwarfs with masses well below the Chandrasekhar limit (about 1.4 times the mass of the Sun). The observed abundance pattern of the iron-peak elements can be explained by taking into account a combination of near-and sub-Chandrasekhar-mass type Ia supernova systems, adding to the mounting evidence that both progenitor types make a substantial contribution to cosmic chemical enrichment(5,15,16).

    DOI: 10.1038/nature24301

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  • Multi-messenger Observations of a Binary Neutron Star Merger Reviewed

    Abbott, B, 筆頭著者

    Publications of the Astronomical Society of Japan   848 ( 2 )   59   2017.10

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  • Hitomi Constraints on the 3.5 keV Line in the Perseus Galaxy Cluster Reviewed

    Aharonian, F, A

    The Astrophysical Journal Letters   2017.3

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  • A Universal Correlation between the Duration and the X-ray Luminosity in stellar flares Reviewed

    Tsuboi, Y, Sasaki, R, Sugawara, Y, Matsuoka, M

    Acta Polytechnica CTU Proceedings   2017

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  • The quiescent intracluster medium in the core of the Perseus cluster Reviewed

    Hitomi Collaboration, 頭著者

    Nature   535 ( 7610 )   117 - 121   2016.7

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  • The MAXI/GSC Nova-Alert System and results of its first 68 months Reviewed

    H. Negoro

    Publications of the Astronomical Society of Japan   68 ( SP1 )   24   2016.6

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  • uzaku monitoring of the Wolf-Rayet binary WR 140 around periastron passage: An approach for quantifying the wind parameters Reviewed

    Sugawara, Yasuharu, Maeda, Yoshitomo, Tsuboi, Yohko, Hamaguchi, Kenji, Corcoran, Michael, Pollock, Andy M. T, Moffat, Anthony F. J, Williams, Peredur M, Dougherty, Sean, Pittard, Julian

    Publications of the Astronomical Society of Japan   2015.11

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  • MAXI observations of gamma-ray bursts Reviewed

    Serino, Motoko, Sakamoto, Takanori, Kawai, Nobuyuki, Yoshida, Atsumasa, Ohno, Masanori, Ogawa, Yuji, Nishimura, Yasunori, Fukushima, Kosuke, Higa, Masaya, Ishikawa, Kazuto, Ishikawa, Masaki, Kawamuro, Taiki, Kimura, Masashi, Matsuoka, Masaru, Mihara, Tatehiro, Morii, Mikio, Nakagawa, Yujin E, Nakahira, Satoshi, Nakajima, Motoki, Nakano, Yuki, Negoro, Hitoshi, Onodera, Takuya, Sasaki, Masayuki, Shidatsu, Megumi, Sugimoto, Juri, Sugizaki, Mutsumi, Suwa, Fumitoshi, Suzuki, Kazuhiko, Tachibana, Yut

    Publications of the Astronomical Society of Japan   66 ( 5 )   8714   2014.10

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  • Extraordinary Luminous Soft X-Ray Transient MAXI J0158-744 as an Ignition of a Nova on a Very Massive O-Ne White Dwarf Reviewed

    M. Morii, 頭著者名

    2013.12

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  • The 37 Month MAXI/GSC Source Catalog of the High Galactic-Latitude Sky Reviewed

    K. Hiroi

    2013.8

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  • Spectral Evolution of a New X-Ray Transient MAXI J0556-332 Observed by MAXI, Swift, and RXTE Reviewed

    M. Sugizaki, 頭著者名含

    2013.6

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  • Outburst of LS V +44 17 Observed by MAXI and RXTE, and Discovery of a Dip Structure in the Pulse Profile Reviewed

    R. Usui, 筆頭著者名含

    2012.8

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  • A Spectral Study of the Black Hole Candidate XTE J1752-223 in the High/Soft State with MAXI, Suzaku, and Swift Reviewed

    S. Nakahira, 頭著者

    2012.2

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  • The First MAXI/GSC Catalog in the High Galactic-Latitude Sky Reviewed

    K. Hiroi, 筆頭著者名

    2011.11

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  • Peculiarly Narrow SED of GRB 090926B with MAXI and Fermi/GBM Reviewed

    2011.11

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  • Revisit of Local X-Ray Luminosity Function of Active Galactic Nuclei with the MAXI Extragalactic Survey Reviewed

    Y. Ueda, 頭著者名

    2011.11

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  • MAXI GSC Monitoring of the Crab Nebula and Pulsar during the GeV Gamma-Ray Flare in 2010 September Reviewed

    M. Morii, 頭著者名

    2011.11

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  • The variable X-ray spectrum of the Wolf-Rayet binary WR140 with Suzaku Reviewed

    Y. Sugawara, 著

    2011.1

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  • Suzaku Observations of the North Polar Spur: Evidence for Nitrogen Enhancement Reviewed

    E. D. Mille, 頭著者

    2008.2

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  • Measuring the Broad-Band X-Ray Spectrum from 400eV to 40keV in the Southwest Part of the Supernova Remnant RXJ1713.7-3946 Reviewed

    T. Takahashi, 頭著者名

    2008.2

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  • Oxygen line mapping of SN 1006 with Suzaku Reviewed

    A.Bamba|rn, 筆頭著者

    2008

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  • X-Ray Imaging Spectrometer (XIS) on Board Suzaku Reviewed

    K. Koyama, 頭著者

    2007.1

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  • The X-Ray Observatory Suzaku Reviewed

    K. Mitsuda, 頭著者名

    2007.1

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  • A Search for X-Rays from the Long-Duration Microlensing Event MACHO-96-BLG-5 Reviewed

    Y. Maeda

    2005.9

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  • XMM-Newton observations of the Mouse, SLX 1744 299 and SLX 1744 300 Reviewed

    H. Mori, 筆頭著者名含

    2005

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Books

  • X線で探る星の爆発現象

    ( Role: Sole author)

    2010.12 

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MISC

  • A high-resolution very large array observation of a protostar in OMC-3: Shock-induced X-ray emission by a protostellar jet

    M Tsujimoto, K Koyama, N Kobayashi, M Saito, Y Tsuboi, CJ Chandler

    PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN   56 ( 2 )   341 - 345   2004.4

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    Language:English   Publisher:OXFORD UNIV PRESS  

    Using the Very Large Array (VLA) in the A-configuration, we obtained a high-resolution 3.6 cm map of a hard X-ray source detected by the Chandra X-ray Observatory in a protostellar clump in Orion molecular cloud 3. Two radio continuum sources were detected in the vicinity of the X-ray source, both of which have NIR counterparts. We conclude that these VLA sources are free-free emission produced by shocks in protostellar jets from the NIR class I protostars. Using the centimeter data, we determined the power and orientation of the protostellar jets. The center position of the X-ray emission was found to be similar to 1"-2" offset from the exciting sources of the jets, and the displacement is in the direction of the jets and molecular outflows. We discuss the nature of the X-ray emission as the shock-excited plasma at the shock front where the jet propagates through the interstellar medium at a speed of similar to 1000 km s(-1).

    DOI: 10.1093/pasj/56.2.341

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  • X-rays from HH 80, HH 81, and the central region

    SH Pravdo, Y Tsuboi, Y Maeda

    ASTROPHYSICAL JOURNAL   605 ( 1 )   259 - 271   2004.4

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    We report detections of X-rays from HH 80 and HH 81 with the ACIS instrument on the Chandra X-Ray Observatory. These are among the most luminous Herbig-Haro ( HH) sources in the optical, and they are now the most luminous known in X-rays. These X-rays arise from the strong shocks that occur when the southern extension of this bipolar outflow slams into the ambient material. There is a one-to-one correspondence between regions of high X-ray emission and high Halpha emission. The X-ray luminosities of HH 80 and HH 81 are 4.5 and 4.3 x 10(31) ergs s(-1), respectively, assuming that the measured low-energy absorption is not in the sources. The measured temperature of the HH plasma is not as large as that expected from the maximum velocities seen in the extended tails of the optical emission lines. Rather, it is consistent with the similar to 10(6) K temperature of the "narrow'' core of the optical lines. There is no observed emission from HH 80 North, the northern extension of the bipolar flow, based on a measurement of lower sensitivity. We imaged the central region of the bipolar flow revealing a complex of X-ray sources, including one near but not coincident with the putative power source in the radio and infrared. This source, CXOPTM J181912.4 - 204733, has no counterparts at other wavelengths and is consistent in luminosity and spectrum with a massive star with A(V) similar to 90 mag. It may contribute significantly to the power input to the complex. Alternatively, this emission might be extended X-rays from outflows close to the power source. We detect 94 X-ray sources overall in this area of star formation.

    DOI: 10.1086/382220

    Web of Science

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  • X-rays from HH 80, HH 81, and the central region

    SH Pravdo, Y Tsuboi, Y Maeda

    ASTROPHYSICAL JOURNAL   605 ( 1 )   259 - 271   2004.4

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    We report detections of X-rays from HH 80 and HH 81 with the ACIS instrument on the Chandra X-Ray Observatory. These are among the most luminous Herbig-Haro ( HH) sources in the optical, and they are now the most luminous known in X-rays. These X-rays arise from the strong shocks that occur when the southern extension of this bipolar outflow slams into the ambient material. There is a one-to-one correspondence between regions of high X-ray emission and high Halpha emission. The X-ray luminosities of HH 80 and HH 81 are 4.5 and 4.3 x 10(31) ergs s(-1), respectively, assuming that the measured low-energy absorption is not in the sources. The measured temperature of the HH plasma is not as large as that expected from the maximum velocities seen in the extended tails of the optical emission lines. Rather, it is consistent with the similar to 10(6) K temperature of the "narrow'' core of the optical lines. There is no observed emission from HH 80 North, the northern extension of the bipolar flow, based on a measurement of lower sensitivity. We imaged the central region of the bipolar flow revealing a complex of X-ray sources, including one near but not coincident with the putative power source in the radio and infrared. This source, CXOPTM J181912.4 - 204733, has no counterparts at other wavelengths and is consistent in luminosity and spectrum with a massive star with A(V) similar to 90 mag. It may contribute significantly to the power input to the complex. Alternatively, this emission might be extended X-rays from outflows close to the power source. We detect 94 X-ray sources overall in this area of star formation.

    DOI: 10.1086/382220

    Web of Science

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  • A high-resolution very large array observation of a protostar in OMC-3: Shock-induced X-ray emission by a protostellar jet

    M Tsujimoto, K Koyama, N Kobayashi, M Saito, Y Tsuboi, CJ Chandler

    PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN   56 ( 2 )   341 - 345   2004.4

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    Language:English   Publisher:OXFORD UNIV PRESS  

    Using the Very Large Array (VLA) in the A-configuration, we obtained a high-resolution 3.6 cm map of a hard X-ray source detected by the Chandra X-ray Observatory in a protostellar clump in Orion molecular cloud 3. Two radio continuum sources were detected in the vicinity of the X-ray source, both of which have NIR counterparts. We conclude that these VLA sources are free-free emission produced by shocks in protostellar jets from the NIR class I protostars. Using the centimeter data, we determined the power and orientation of the protostellar jets. The center position of the X-ray emission was found to be similar to 1"-2" offset from the exciting sources of the jets, and the displacement is in the direction of the jets and molecular outflows. We discuss the nature of the X-ray emission as the shock-excited plasma at the shock front where the jet propagates through the interstellar medium at a speed of similar to 1000 km s(-1).

    DOI: 10.1093/pasj/56.2.341

    Web of Science

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  • A systematic study of X-ray flares from low-mass young stellar objects in the rho Ophiuchi star-forming region with Chandra

    K Imanishi, H Nakajima, M Tsujimoto, K Koyama, Y Tsuboi

    PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN   55 ( 3 )   653 - 681   2003.6

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    We report on the results of a systematic study of X-ray flares from low-mass young stellar objects, using two deep exposure Chandra observations of the main region of the rho Ophiuchi star-forming cloud. From 195 X-ray sources, including class I-III sources and some young brown dwarfs, we detected a total of 71 X-ray flares. Most of the flares have the typical profile of solar and stellar flares, fast rise and slow decay, while some bright flares show unusually long rise timescales. We derived the time-averaged temperature (<kT>), luminosity (<L-X>), rise and decay timescales (tau(r) and tau(d)) of the flares, finding that (1) class I-II sources tend to have a high <kT>, which sometimes exceeds 5 keV, (2) the distribution of <L-X> during flares is nearly the same for all classes from similar to 10(29.5) to similar to 10(31.5) ergs(-1), although there is a marginal hint of a higher <L-X> distribution for class I than class II-III, and (3) positive and negative log-linear correlations are found between tau(r), and tau(d), and <kT> and tau(r). In order to explain these relations, we used the framework of magnetic reconnection model with heat conduction and chromospheric evaporation to formulate the observational parameters (tau(r), tau(d), and <kT>) as a function of the pre-flare (coronal) electronic density (n(c)), the half-length of the reconnected magnetic loop (L), and magnetic field strength (B). The observed correlations are well reproduced if loop lengths are nearly the same for all classes, regardless of the existence of an accretion disk. The estimated loop length is almost comparable to the typical stellar radius of these objects (10(10)-10(11) cm), which indicates that the observed flares are triggered by solar-type loops, rather than larger ones (similar to 10(12) cm) connecting the star with its inner accretion disk. The higher <kT> observed for class I sources may be explained by a slightly higher magnetic field strength (approximate to 500G) than for class II-III sources (200-300 G).

    DOI: 10.1093/pasj/55.3.653

    Web of Science

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  • A systematic study of X-ray flares from low-mass young stellar objects in the rho Ophiuchi star-forming region with Chandra

    K Imanishi, H Nakajima, M Tsujimoto, K Koyama, Y Tsuboi

    PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN   55 ( 3 )   653 - 681   2003.6

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    We report on the results of a systematic study of X-ray flares from low-mass young stellar objects, using two deep exposure Chandra observations of the main region of the rho Ophiuchi star-forming cloud. From 195 X-ray sources, including class I-III sources and some young brown dwarfs, we detected a total of 71 X-ray flares. Most of the flares have the typical profile of solar and stellar flares, fast rise and slow decay, while some bright flares show unusually long rise timescales. We derived the time-averaged temperature (<kT>), luminosity (<L-X>), rise and decay timescales (tau(r) and tau(d)) of the flares, finding that (1) class I-II sources tend to have a high <kT>, which sometimes exceeds 5 keV, (2) the distribution of <L-X> during flares is nearly the same for all classes from similar to 10(29.5) to similar to 10(31.5) ergs(-1), although there is a marginal hint of a higher <L-X> distribution for class I than class II-III, and (3) positive and negative log-linear correlations are found between tau(r), and tau(d), and <kT> and tau(r). In order to explain these relations, we used the framework of magnetic reconnection model with heat conduction and chromospheric evaporation to formulate the observational parameters (tau(r), tau(d), and <kT>) as a function of the pre-flare (coronal) electronic density (n(c)), the half-length of the reconnected magnetic loop (L), and magnetic field strength (B). The observed correlations are well reproduced if loop lengths are nearly the same for all classes, regardless of the existence of an accretion disk. The estimated loop length is almost comparable to the typical stellar radius of these objects (10(10)-10(11) cm), which indicates that the observed flares are triggered by solar-type loops, rather than larger ones (similar to 10(12) cm) connecting the star with its inner accretion disk. The higher <kT> observed for class I sources may be explained by a slightly higher magnetic field strength (approximate to 500G) than for class II-III sources (200-300 G).

    DOI: 10.1093/pasj/55.3.653

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  • A systematic study of X-ray flares from low-mass young stellar objects in the rho Ophiuchi star-forming region with Chandra

    K Imanishi, H Nakajima, M Tsujimoto, K Koyama, Y Tsuboi

    PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN   55 ( 3 )   653 - 681   2003.6

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    Language:English   Publisher:OXFORD UNIV PRESS  

    We report on the results of a systematic study of X-ray flares from low-mass young stellar objects, using two deep exposure Chandra observations of the main region of the rho Ophiuchi star-forming cloud. From 195 X-ray sources, including class I-III sources and some young brown dwarfs, we detected a total of 71 X-ray flares. Most of the flares have the typical profile of solar and stellar flares, fast rise and slow decay, while some bright flares show unusually long rise timescales. We derived the time-averaged temperature (<kT>), luminosity (<L-X>), rise and decay timescales (tau(r) and tau(d)) of the flares, finding that (1) class I-II sources tend to have a high <kT>, which sometimes exceeds 5 keV, (2) the distribution of <L-X> during flares is nearly the same for all classes from similar to 10(29.5) to similar to 10(31.5) ergs(-1), although there is a marginal hint of a higher <L-X> distribution for class I than class II-III, and (3) positive and negative log-linear correlations are found between tau(r), and tau(d), and <kT> and tau(r). In order to explain these relations, we used the framework of magnetic reconnection model with heat conduction and chromospheric evaporation to formulate the observational parameters (tau(r), tau(d), and <kT>) as a function of the pre-flare (coronal) electronic density (n(c)), the half-length of the reconnected magnetic loop (L), and magnetic field strength (B). The observed correlations are well reproduced if loop lengths are nearly the same for all classes, regardless of the existence of an accretion disk. The estimated loop length is almost comparable to the typical stellar radius of these objects (10(10)-10(11) cm), which indicates that the observed flares are triggered by solar-type loops, rather than larger ones (similar to 10(12) cm) connecting the star with its inner accretion disk. The higher <kT> observed for class I sources may be explained by a slightly higher magnetic field strength (approximate to 500G) than for class II-III sources (200-300 G).

    DOI: 10.1093/pasj/55.3.653

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  • A systematic study of X-ray flares from low-mass young stellar objects in the rho Ophiuchi star-forming region with Chandra

    K Imanishi, H Nakajima, M Tsujimoto, K Koyama, Y Tsuboi

    PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN   55 ( 3 )   653 - 681   2003.6

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    Language:English   Publisher:OXFORD UNIV PRESS  

    We report on the results of a systematic study of X-ray flares from low-mass young stellar objects, using two deep exposure Chandra observations of the main region of the rho Ophiuchi star-forming cloud. From 195 X-ray sources, including class I-III sources and some young brown dwarfs, we detected a total of 71 X-ray flares. Most of the flares have the typical profile of solar and stellar flares, fast rise and slow decay, while some bright flares show unusually long rise timescales. We derived the time-averaged temperature (<kT>), luminosity (<L-X>), rise and decay timescales (tau(r) and tau(d)) of the flares, finding that (1) class I-II sources tend to have a high <kT>, which sometimes exceeds 5 keV, (2) the distribution of <L-X> during flares is nearly the same for all classes from similar to 10(29.5) to similar to 10(31.5) ergs(-1), although there is a marginal hint of a higher <L-X> distribution for class I than class II-III, and (3) positive and negative log-linear correlations are found between tau(r), and tau(d), and <kT> and tau(r). In order to explain these relations, we used the framework of magnetic reconnection model with heat conduction and chromospheric evaporation to formulate the observational parameters (tau(r), tau(d), and <kT>) as a function of the pre-flare (coronal) electronic density (n(c)), the half-length of the reconnected magnetic loop (L), and magnetic field strength (B). The observed correlations are well reproduced if loop lengths are nearly the same for all classes, regardless of the existence of an accretion disk. The estimated loop length is almost comparable to the typical stellar radius of these objects (10(10)-10(11) cm), which indicates that the observed flares are triggered by solar-type loops, rather than larger ones (similar to 10(12) cm) connecting the star with its inner accretion disk. The higher <kT> observed for class I sources may be explained by a slightly higher magnetic field strength (approximate to 500G) than for class II-III sources (200-300 G).

    DOI: 10.1093/pasj/55.3.653

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  • Deep near-infrared observations and identifications of Chandra sources in orion molecular clouds 2 and 3

    M Tsujimoto, K Koyama, N Kobayashi, M Goto, Y Tsuboi, AT Tokunaga

    ASTRONOMICAL JOURNAL   125 ( 3 )   1537 - 1545   2003.3

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    We conducted deep near-infrared (NIR) imaging observations of Orion molecular clouds 2 and 3 using the Quick Infrared Camera on the 88 inch (2.2 m) telescope of the University of Hawaii. Our purposes were (1) to generate a comprehensive NIR source catalog of these star-forming clouds and ( 2) to identify the NIR counterpart of the Chandra X-ray sources that have no counterpart in the Two Micron All Sky Survey (2MASS) catalog. Our J-, H-, and K-band observations are similar to2 mag deeper than those of 2MASS and match the current Chandra observation well. We detected 1448 NIR sources, for which we derived the position, the J-, H-, and K-band magnitude, and the 2MASS counterpart. Using this catalog, we identified the NIR counterpart for similar to42% of the 2MASS unidentified Chandra sources. The nature of these Chandra sources are discussed using their NIR colors and spatial distributions, and a dozen protostar and brown dwarf candidates are identified.

    DOI: 10.1086/346277

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  • Deep near-infrared observations and identifications of Chandra sources in orion molecular clouds 2 and 3

    M Tsujimoto, K Koyama, N Kobayashi, M Goto, Y Tsuboi, AT Tokunaga

    ASTRONOMICAL JOURNAL   125 ( 3 )   1537 - 1545   2003.3

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    We conducted deep near-infrared (NIR) imaging observations of Orion molecular clouds 2 and 3 using the Quick Infrared Camera on the 88 inch (2.2 m) telescope of the University of Hawaii. Our purposes were (1) to generate a comprehensive NIR source catalog of these star-forming clouds and ( 2) to identify the NIR counterpart of the Chandra X-ray sources that have no counterpart in the Two Micron All Sky Survey (2MASS) catalog. Our J-, H-, and K-band observations are similar to2 mag deeper than those of 2MASS and match the current Chandra observation well. We detected 1448 NIR sources, for which we derived the position, the J-, H-, and K-band magnitude, and the 2MASS counterpart. Using this catalog, we identified the NIR counterpart for similar to42% of the 2MASS unidentified Chandra sources. The nature of these Chandra sources are discussed using their NIR colors and spatial distributions, and a dozen protostar and brown dwarf candidates are identified.

    DOI: 10.1086/346277

    Web of Science

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  • Deep near-infrared observations and identifications of Chandra sources in orion molecular clouds 2 and 3

    M Tsujimoto, K Koyama, N Kobayashi, M Goto, Y Tsuboi, AT Tokunaga

    ASTRONOMICAL JOURNAL   125 ( 3 )   1537 - 1545   2003.3

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    Language:English   Publisher:UNIV CHICAGO PRESS  

    We conducted deep near-infrared (NIR) imaging observations of Orion molecular clouds 2 and 3 using the Quick Infrared Camera on the 88 inch (2.2 m) telescope of the University of Hawaii. Our purposes were (1) to generate a comprehensive NIR source catalog of these star-forming clouds and ( 2) to identify the NIR counterpart of the Chandra X-ray sources that have no counterpart in the Two Micron All Sky Survey (2MASS) catalog. Our J-, H-, and K-band observations are similar to2 mag deeper than those of 2MASS and match the current Chandra observation well. We detected 1448 NIR sources, for which we derived the position, the J-, H-, and K-band magnitude, and the 2MASS counterpart. Using this catalog, we identified the NIR counterpart for similar to42% of the 2MASS unidentified Chandra sources. The nature of these Chandra sources are discussed using their NIR colors and spatial distributions, and a dozen protostar and brown dwarf candidates are identified.

    DOI: 10.1086/346277

    Web of Science

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  • Deep near-infrared observations and identifications of Chandra sources in orion molecular clouds 2 and 3

    M Tsujimoto, K Koyama, N Kobayashi, M Goto, Y Tsuboi, AT Tokunaga

    ASTRONOMICAL JOURNAL   125 ( 3 )   1537 - 1545   2003.3

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    Language:English   Publisher:UNIV CHICAGO PRESS  

    We conducted deep near-infrared (NIR) imaging observations of Orion molecular clouds 2 and 3 using the Quick Infrared Camera on the 88 inch (2.2 m) telescope of the University of Hawaii. Our purposes were (1) to generate a comprehensive NIR source catalog of these star-forming clouds and ( 2) to identify the NIR counterpart of the Chandra X-ray sources that have no counterpart in the Two Micron All Sky Survey (2MASS) catalog. Our J-, H-, and K-band observations are similar to2 mag deeper than those of 2MASS and match the current Chandra observation well. We detected 1448 NIR sources, for which we derived the position, the J-, H-, and K-band magnitude, and the 2MASS counterpart. Using this catalog, we identified the NIR counterpart for similar to42% of the 2MASS unidentified Chandra sources. The nature of these Chandra sources are discussed using their NIR colors and spatial distributions, and a dozen protostar and brown dwarf candidates are identified.

    DOI: 10.1086/346277

    Web of Science

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  • Radio Centimeter Emissions at a Protostellar Core in OMC-3 and its Association with X-ray and NIR

    M.Tsujimoto, K.Koyama, K.Imanishi, N.Kobayashi, M.Saitoh, Y.Tsuboi

    The Proceedings of the IAU 8th Asian-Pacific Regional Meeting   289   223 - 224   2003.1

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  • Radio Centimeter Emissions at a Protostellar Core in OMC-3 and its Association with X-ray and NIR

    M.Tsujimoto, K.Koyama, K.Imanishi, N.Kobayashi, M.Saitoh, Y.Tsuboi

    The Proceedings of the IAU 8th Asian-Pacific Regional Meeting   289   223 - 224   2003.1

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  • X-Rays from Class 0/I Protostars

    Abstract of the "Star Formation at High Angular Resolution", International Astronomical Union. Symposium no.221   2003

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  • X-Rays from Class 0/I Protostars

    Abstract of the "Star Formation at High Angular Resolution", International Astronomical Union. Symposium no.221   2003

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  • Coronal X-Ray Emission from an Intermediate-Age Brown Dwarf

    The Astrophysical Journal   587 ( 1 )   L51-L54   2003

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  • Coronal X-Ray Emission from an Intermediate-Age Brown Dwarf

    The Astrophysical Journal Letters   587 ( 1 )   51 - 54   2003

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  • Coronal X-Ray Emission from an Intermediate-Age Brown Dwarf

    The Astrophysical Journal   587 ( 1 )   L51-L54   2003

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  • Coronal X-Ray Emission from an Intermediate-Age Brown Dwarf

    The Astrophysical Journal Letters   587 ( 1 )   51 - 54   2003

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  • Deep near-infrared observations of the X-ray emitting class 0 protostar candidates in the orion molecular cloud 3

    M Tsujimoto, K Koyama, Y Tsuboi, G Chartas, M Goto, N Kobayashi, H Terada, AT Tokunaga

    ASTROPHYSICAL JOURNAL   573 ( 1 )   270 - 274   2002.7

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    Language:English   Publisher:IOP PUBLISHING LTD  

    We obtained near-infrared (NIR) imaging with the Subaru Telescope of the class 0 protostar candidates in the Orion molecular cloud 3, two of which were discovered to have X-ray emission by the Chandra X-Ray Observatory. We found strong evidence for the class 0 nature of the X-ray sources. First, our deep K-band image shows no emission brighter than 19.6 mag from both of these X-ray sources. Since class I protostars or class II T Tauri stars should be easily detected in the NIR with this sensitivity, the lack of K-band detection suggests that they are likely much more obscured than class I protostars. Second, our H-2 v = 1-0 S(1) image shows a bubble-like feature from one of the X-ray class 0 protostar candidates, which reinforces the idea that this is a class 0 protostar. We also discuss the nature of nine NIR sources found in our deep image based on their colors, spatial coincidence with millimeter cores, and the properties of their X-ray counterparts.

    DOI: 10.1086/340559

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  • X-ray emitting young stars in the Orion Nebula

    ED Feigelson, P Broos, JA Gaffney, G Garmire, LA Hillenbrand, SH Pravdo, L Townsley, Y Tsuboi

    ASTROPHYSICAL JOURNAL   574 ( 1 )   258 - 292   2002.7

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    Language:English   Publishing type:Book review, literature introduction, etc.   Publisher:IOP PUBLISHING LTD  

    The Orion Nebula Cluster and the molecular cloud in its vicinity have been observed with the ACIS-I detector on board the Chandra X-ray Observatory with 23 hr exposure in two observations. We detect 1075 X-ray sources, most with subarcsecond positional accuracy. Ninety-one percent of the sources are spatially associated with known stellar members of the cluster, and an additional 7% are newly identified deeply embedded cloud members. This provides the largest X-ray study of a premain-sequence stellar population and covers the initial mass function from brown dwarfs up to a 45 M. O star. Source luminosities span 5 orders of magnitude from log L-X similar or equal to28.0 to 33.3 ergs s(-1) in the 0.5-8 keV band, plasma energies range from 0.2 to >10 keV, and absorption ranges from log N-H < 20.0 to similar to 23.5 cm(-2). Comprehensive tables providing X-ray and stellar characteristics are provided electronically.
    We examine here the X-ray properties of Orion young stars as a function of mass; other studies of astrophysical interest will appear in companion papers. Results include: ( a) the discovery of rapid variability in the 09.5 31 M. star theta(2)A Ori, and several early B stars, inconsistent with the standard model of X-ray production in small shocks distributed throughout the radiatively accelerated wind; (b) support for the hypothesis that intermediate-mass mid-B through A type stars do not themselves produce significant X-ray emission; (c) confirmation that low-mass G through M type T Tauri stars exhibit powerful flaring but typically at luminosities considerably below the saturation level; (d) confirmation that the presence or absence of a circumstellar disk has no discernable effect on X-ray emission; (e) evidence that T Tauri plasma temperatures are often very high with T >= 100 MK, even when luminosities are modest and flaring is not evident; and (f) detection of the largest sample of pre-main-sequence very low-mass objects showing flaring levels similar to those seen in more massive T Tauri stars and a decline in magnetic activity as they evolve into L and T type brown dwarfs.

    DOI: 10.1086/340936

    Web of Science

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  • X-ray emitting young stars in the Orion Nebula

    ED Feigelson, P Broos, JA Gaffney, G Garmire, LA Hillenbrand, SH Pravdo, L Townsley, Y Tsuboi

    ASTROPHYSICAL JOURNAL   574 ( 1 )   258 - 292   2002.7

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    Language:English   Publishing type:Book review, literature introduction, etc.   Publisher:IOP PUBLISHING LTD  

    The Orion Nebula Cluster and the molecular cloud in its vicinity have been observed with the ACIS-I detector on board the Chandra X-ray Observatory with 23 hr exposure in two observations. We detect 1075 X-ray sources, most with subarcsecond positional accuracy. Ninety-one percent of the sources are spatially associated with known stellar members of the cluster, and an additional 7% are newly identified deeply embedded cloud members. This provides the largest X-ray study of a premain-sequence stellar population and covers the initial mass function from brown dwarfs up to a 45 M. O star. Source luminosities span 5 orders of magnitude from log L-X similar or equal to28.0 to 33.3 ergs s(-1) in the 0.5-8 keV band, plasma energies range from 0.2 to >10 keV, and absorption ranges from log N-H < 20.0 to similar to 23.5 cm(-2). Comprehensive tables providing X-ray and stellar characteristics are provided electronically.
    We examine here the X-ray properties of Orion young stars as a function of mass; other studies of astrophysical interest will appear in companion papers. Results include: ( a) the discovery of rapid variability in the 09.5 31 M. star theta(2)A Ori, and several early B stars, inconsistent with the standard model of X-ray production in small shocks distributed throughout the radiatively accelerated wind; (b) support for the hypothesis that intermediate-mass mid-B through A type stars do not themselves produce significant X-ray emission; (c) confirmation that low-mass G through M type T Tauri stars exhibit powerful flaring but typically at luminosities considerably below the saturation level; (d) confirmation that the presence or absence of a circumstellar disk has no discernable effect on X-ray emission; (e) evidence that T Tauri plasma temperatures are often very high with T >= 100 MK, even when luminosities are modest and flaring is not evident; and (f) detection of the largest sample of pre-main-sequence very low-mass objects showing flaring levels similar to those seen in more massive T Tauri stars and a decline in magnetic activity as they evolve into L and T type brown dwarfs.

    DOI: 10.1086/340936

    Web of Science

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  • X-ray emitting young stars in the Orion Nebula

    ED Feigelson, P Broos, JA Gaffney, G Garmire, LA Hillenbrand, SH Pravdo, L Townsley, Y Tsuboi

    ASTROPHYSICAL JOURNAL   574 ( 1 )   258 - 292   2002.7

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    Language:English   Publishing type:Book review, literature introduction, etc.   Publisher:IOP PUBLISHING LTD  

    The Orion Nebula Cluster and the molecular cloud in its vicinity have been observed with the ACIS-I detector on board the Chandra X-ray Observatory with 23 hr exposure in two observations. We detect 1075 X-ray sources, most with subarcsecond positional accuracy. Ninety-one percent of the sources are spatially associated with known stellar members of the cluster, and an additional 7% are newly identified deeply embedded cloud members. This provides the largest X-ray study of a premain-sequence stellar population and covers the initial mass function from brown dwarfs up to a 45 M. O star. Source luminosities span 5 orders of magnitude from log L-X similar or equal to28.0 to 33.3 ergs s(-1) in the 0.5-8 keV band, plasma energies range from 0.2 to >10 keV, and absorption ranges from log N-H < 20.0 to similar to 23.5 cm(-2). Comprehensive tables providing X-ray and stellar characteristics are provided electronically.
    We examine here the X-ray properties of Orion young stars as a function of mass; other studies of astrophysical interest will appear in companion papers. Results include: ( a) the discovery of rapid variability in the 09.5 31 M. star theta(2)A Ori, and several early B stars, inconsistent with the standard model of X-ray production in small shocks distributed throughout the radiatively accelerated wind; (b) support for the hypothesis that intermediate-mass mid-B through A type stars do not themselves produce significant X-ray emission; (c) confirmation that low-mass G through M type T Tauri stars exhibit powerful flaring but typically at luminosities considerably below the saturation level; (d) confirmation that the presence or absence of a circumstellar disk has no discernable effect on X-ray emission; (e) evidence that T Tauri plasma temperatures are often very high with T >= 100 MK, even when luminosities are modest and flaring is not evident; and (f) detection of the largest sample of pre-main-sequence very low-mass objects showing flaring levels similar to those seen in more massive T Tauri stars and a decline in magnetic activity as they evolve into L and T type brown dwarfs.

    DOI: 10.1086/340936

    Web of Science

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  • X-ray emitting young stars in the Orion Nebula

    ED Feigelson, P Broos, JA Gaffney, G Garmire, LA Hillenbrand, SH Pravdo, L Townsley, Y Tsuboi

    ASTROPHYSICAL JOURNAL   574 ( 1 )   258 - 292   2002.7

     More details

    Language:English   Publishing type:Book review, literature introduction, etc.   Publisher:IOP PUBLISHING LTD  

    The Orion Nebula Cluster and the molecular cloud in its vicinity have been observed with the ACIS-I detector on board the Chandra X-ray Observatory with 23 hr exposure in two observations. We detect 1075 X-ray sources, most with subarcsecond positional accuracy. Ninety-one percent of the sources are spatially associated with known stellar members of the cluster, and an additional 7% are newly identified deeply embedded cloud members. This provides the largest X-ray study of a premain-sequence stellar population and covers the initial mass function from brown dwarfs up to a 45 M. O star. Source luminosities span 5 orders of magnitude from log L-X similar or equal to28.0 to 33.3 ergs s(-1) in the 0.5-8 keV band, plasma energies range from 0.2 to >10 keV, and absorption ranges from log N-H < 20.0 to similar to 23.5 cm(-2). Comprehensive tables providing X-ray and stellar characteristics are provided electronically.
    We examine here the X-ray properties of Orion young stars as a function of mass; other studies of astrophysical interest will appear in companion papers. Results include: ( a) the discovery of rapid variability in the 09.5 31 M. star theta(2)A Ori, and several early B stars, inconsistent with the standard model of X-ray production in small shocks distributed throughout the radiatively accelerated wind; (b) support for the hypothesis that intermediate-mass mid-B through A type stars do not themselves produce significant X-ray emission; (c) confirmation that low-mass G through M type T Tauri stars exhibit powerful flaring but typically at luminosities considerably below the saturation level; (d) confirmation that the presence or absence of a circumstellar disk has no discernable effect on X-ray emission; (e) evidence that T Tauri plasma temperatures are often very high with T >= 100 MK, even when luminosities are modest and flaring is not evident; and (f) detection of the largest sample of pre-main-sequence very low-mass objects showing flaring levels similar to those seen in more massive T Tauri stars and a decline in magnetic activity as they evolve into L and T type brown dwarfs.

    DOI: 10.1086/340936

    Web of Science

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  • Deep near-infrared observations of the X-ray emitting class 0 protostar candidates in the orion molecular cloud 3

    M Tsujimoto, K Koyama, Y Tsuboi, G Chartas, M Goto, N Kobayashi, H Terada, AT Tokunaga

    ASTROPHYSICAL JOURNAL   573 ( 1 )   270 - 274   2002.7

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    Language:English   Publisher:IOP PUBLISHING LTD  

    We obtained near-infrared (NIR) imaging with the Subaru Telescope of the class 0 protostar candidates in the Orion molecular cloud 3, two of which were discovered to have X-ray emission by the Chandra X-Ray Observatory. We found strong evidence for the class 0 nature of the X-ray sources. First, our deep K-band image shows no emission brighter than 19.6 mag from both of these X-ray sources. Since class I protostars or class II T Tauri stars should be easily detected in the NIR with this sensitivity, the lack of K-band detection suggests that they are likely much more obscured than class I protostars. Second, our H-2 v = 1-0 S(1) image shows a bubble-like feature from one of the X-ray class 0 protostar candidates, which reinforces the idea that this is a class 0 protostar. We also discuss the nature of nine NIR sources found in our deep image based on their colors, spatial coincidence with millimeter cores, and the properties of their X-ray counterparts.

    DOI: 10.1086/340559

    Web of Science

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  • Deep near-infrared observations of the X-ray emitting class 0 protostar candidates in the orion molecular cloud 3

    M Tsujimoto, K Koyama, Y Tsuboi, G Chartas, M Goto, N Kobayashi, H Terada, AT Tokunaga

    ASTROPHYSICAL JOURNAL   573 ( 1 )   270 - 274   2002.7

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    Language:English   Publisher:IOP PUBLISHING LTD  

    We obtained near-infrared (NIR) imaging with the Subaru Telescope of the class 0 protostar candidates in the Orion molecular cloud 3, two of which were discovered to have X-ray emission by the Chandra X-Ray Observatory. We found strong evidence for the class 0 nature of the X-ray sources. First, our deep K-band image shows no emission brighter than 19.6 mag from both of these X-ray sources. Since class I protostars or class II T Tauri stars should be easily detected in the NIR with this sensitivity, the lack of K-band detection suggests that they are likely much more obscured than class I protostars. Second, our H-2 v = 1-0 S(1) image shows a bubble-like feature from one of the X-ray class 0 protostar candidates, which reinforces the idea that this is a class 0 protostar. We also discuss the nature of nine NIR sources found in our deep image based on their colors, spatial coincidence with millimeter cores, and the properties of their X-ray counterparts.

    DOI: 10.1086/340559

    Web of Science

    researchmap

  • Deep near-infrared observations of the X-ray emitting class 0 protostar candidates in the orion molecular cloud 3

    M Tsujimoto, K Koyama, Y Tsuboi, G Chartas, M Goto, N Kobayashi, H Terada, AT Tokunaga

    ASTROPHYSICAL JOURNAL   573 ( 1 )   270 - 274   2002.7

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    Language:English   Publisher:IOP PUBLISHING LTD  

    We obtained near-infrared (NIR) imaging with the Subaru Telescope of the class 0 protostar candidates in the Orion molecular cloud 3, two of which were discovered to have X-ray emission by the Chandra X-Ray Observatory. We found strong evidence for the class 0 nature of the X-ray sources. First, our deep K-band image shows no emission brighter than 19.6 mag from both of these X-ray sources. Since class I protostars or class II T Tauri stars should be easily detected in the NIR with this sensitivity, the lack of K-band detection suggests that they are likely much more obscured than class I protostars. Second, our H-2 v = 1-0 S(1) image shows a bubble-like feature from one of the X-ray class 0 protostar candidates, which reinforces the idea that this is a class 0 protostar. We also discuss the nature of nine NIR sources found in our deep image based on their colors, spatial coincidence with millimeter cores, and the properties of their X-ray counterparts.

    DOI: 10.1086/340559

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  • 世界の研究室から「アパラチア山麓発最先端の宇宙像」

    坪井陽子

    日経サイエンス   ( 5月号 )   3   2002.5

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    Language:Japanese   Publishing type:Article, review, commentary, editorial, etc. (other)   Publisher:日本経済新聞社  

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  • Skylight「チャンドラで捉えた星の産声」

    坪井陽子

    天文月報   95 ( 2 )   77 - 83   2002.2

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  • X-ray probing for protostars

    Y.Tsuboi

    The Astronomical Herald   95 ( 2 )   77 - 83   2002.2

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  • X-ray properties of young stellar objects in OMC-2 and OMC-3 from the Chandra X-ray observatory

    M Tsujimoto, K Koyama, Y Tsuboi, M Goto, N Kobayashi

    ASTROPHYSICAL JOURNAL   566 ( 2 )   974 - 981   2002.2

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    We report X-ray results of the Chandra observation of OMC-2 and OMC-3. A deep exposure of similar to100 ks detects similar to400 X-ray sources in the field of view of the ACIS array, providing one of the largest X-ray catalogs in a star-forming region. Coherent studies of the source detection, time variability, and energy spectra are performed. We classify the X-ray sources into Class I, Class II, and Class III + MS based on the J-, H-, and K-band colors of their near-infrared counterparts and discuss the X-ray properties (temperature, absorption, and time variability) along these evolutionary phases.

    DOI: 10.1086/338110

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  • X-ray properties of young stellar objects in OMC-2 and OMC-3 from the Chandra X-ray observatory

    M Tsujimoto, K Koyama, Y Tsuboi, M Goto, N Kobayashi

    ASTROPHYSICAL JOURNAL   566 ( 2 )   974 - 981   2002.2

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    We report X-ray results of the Chandra observation of OMC-2 and OMC-3. A deep exposure of similar to100 ks detects similar to400 X-ray sources in the field of view of the ACIS array, providing one of the largest X-ray catalogs in a star-forming region. Coherent studies of the source detection, time variability, and energy spectra are performed. We classify the X-ray sources into Class I, Class II, and Class III + MS based on the J-, H-, and K-band colors of their near-infrared counterparts and discuss the X-ray properties (temperature, absorption, and time variability) along these evolutionary phases.

    DOI: 10.1086/338110

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  • X-ray probing for protostars

    Y.Tsuboi

    The Astronomical Herald   95 ( 2 )   77 - 83   2002.2

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  • Chandra Detection of a Middle Age Brown Dwarf TWA 5B

    Y.Tsuboi, G.Chartas, E.D.Feigelson, G.Garmire, Y.Maeda, K.Mori, L.Townsley, S.Pravdo

    Stellar Coronae in the Chandra and XMM-NEWTON Era, ASP Conference Proceedings   277   255- - 255   2002.1

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  • Chandra/ACIS Observations of the 30 Doradus Star-Forming Complex

    Abstract of the American Physical Society, April Meeting   2002

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  • Chandra Detection of a Middle Age Brown Dwarf TWA 5B

    Stellar Coronae in the Chandra and XMM-NEWTON Era, ASP Conference Proceedings   277   255-   2002

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  • Chandra/ACIS Observations of the 30 Doradus Star-Forming Complex

    Abstract of the American Physical Society, April Meeting   2002

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  • Discovery of X-rays from the protostellar outflow object HH2

    SH Pravdo, ED Feigelson, G Garmire, Y Maeda, Y Tsuboi, J Bally

    NATURE   413 ( 6857 )   708 - 711   2001.10

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    Herbig-Haro (HH) objects have been known(1,2) for 50 years to be luminous condensations of gas in star-forming regions, but their underlying physical nature is still being elucidated. Previously suggested models encompass newborn stars(3), stellar winds clashing with nebular material(4), dense pockets of interstellar gas excited by shocks from outflows(5), and interstellar 'bullets' (ref. 6). Recent progress has been made with the jet-induced shock model(7), in which material streams out of young stellar objects and collides with the surrounding interstellar medium. A clear prediction of this model is that the most energetic Herbig-Haro objects will emit X-rays, although they have not hitherto been detected(8). Here we report the discovery of X-ray emission from one of the brightest and closest Herbig-Haro objects, HH2, at a level consistent with the model predictions. We conclude that this Herbig-Haro object contains shock-heated material located at or near its leading edge with a temperature of about 10(6) K.

    DOI: 10.1038/35099508

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  • Discovery of X-rays from the protostellar outflow object HH2

    SH Pravdo, ED Feigelson, G Garmire, Y Maeda, Y Tsuboi, J Bally

    NATURE   413 ( 6857 )   708 - 711   2001.10

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    Herbig-Haro (HH) objects have been known(1,2) for 50 years to be luminous condensations of gas in star-forming regions, but their underlying physical nature is still being elucidated. Previously suggested models encompass newborn stars(3), stellar winds clashing with nebular material(4), dense pockets of interstellar gas excited by shocks from outflows(5), and interstellar 'bullets' (ref. 6). Recent progress has been made with the jet-induced shock model(7), in which material streams out of young stellar objects and collides with the surrounding interstellar medium. A clear prediction of this model is that the most energetic Herbig-Haro objects will emit X-rays, although they have not hitherto been detected(8). Here we report the discovery of X-ray emission from one of the brightest and closest Herbig-Haro objects, HH2, at a level consistent with the model predictions. We conclude that this Herbig-Haro object contains shock-heated material located at or near its leading edge with a temperature of about 10(6) K.

    DOI: 10.1038/35099508

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  • A Hint of Star-disk Interaction: Quasi-periodic Flares from a Protostar

    Y.Tsuboi, N.Grosso, T.Montmerle, K.Imanishi, K.Koyama

    11th Cambridge Workshop on Cool Stars, Stellar Systems and the Sun, ASP Conference Proceedings   223   1183 - 1188   2001.9

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  • A Hint of Star-disk Interaction: Quasi-periodic Flares from a Protostar

    Y.Tsuboi, N.Grosso, T.Montmerle, K.Imanishi, K.Koyama

    11th Cambridge Workshop on Cool Stars, Stellar Systems and the Sun, ASP Conference Proceedings   223   1183 - 1188   2001.9

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  • Discovery of X-rays from class 0 protostar candidates in OMC-3

    Y Tsuboi, K Koyama, K Hamaguchi, K Tatematsu, Y Sekimoto, J Bally, B Reipurth

    ASTROPHYSICAL JOURNAL   554 ( 2 )   734 - 741   2001.6

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    We have observed the Orion Molecular Clouds 2 and 3 (OMC-2 and OMC-3) with the Chandra X-Ray Observatory (CXO). The northern part of OMC-3 is found to be particularly rich in new X-ray features; four hard X-ray sources are located in and along the filament of cloud cores. Two sources coincide positionally with the submillimeter-millimeter dust condensations of MMS 2 and 3 or an outflow radio source VLA 1, which are in a very early phase of star formation. The X-ray spectra of these sources show an absorption column of (1-3) x 10(23) H cm(-2). Assuming a moderate temperature plasma, the X-ray luminosity in the 0.5-10 keV band is estimated to be similar to 10(30) ergs s(-1) at a distance of 450 pc. From the large absorption, positional coincidence, and moderate luminosity, we infer that the hard X-rays are coming from very young stellar objects embedded in the molecular cloud cores. We found another hard X-ray source near the edge of the dust filament. The extremely high absorption of 3 x 10(23) H cm(-2) indicates that the source must be surrounded by dense gas, suggesting that it is either a young stellar object in an early accretion phase or a Type II AGN (e.g., a Seyfert 2), although no counterpart is found at any other wavelength. In contrast to the hard X-ray sources, soft X-ray sources are found spread around the dust filaments, most of which are identified with IR sources in the T. Tauri phase.

    DOI: 10.1086/321392

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  • Discovery of X-rays from class 0 protostar candidates in OMC-3

    Y Tsuboi, K Koyama, K Hamaguchi, K Tatematsu, Y Sekimoto, J Bally, B Reipurth

    ASTROPHYSICAL JOURNAL   554 ( 2 )   734 - 741   2001.6

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    We have observed the Orion Molecular Clouds 2 and 3 (OMC-2 and OMC-3) with the Chandra X-Ray Observatory (CXO). The northern part of OMC-3 is found to be particularly rich in new X-ray features; four hard X-ray sources are located in and along the filament of cloud cores. Two sources coincide positionally with the submillimeter-millimeter dust condensations of MMS 2 and 3 or an outflow radio source VLA 1, which are in a very early phase of star formation. The X-ray spectra of these sources show an absorption column of (1-3) x 10(23) H cm(-2). Assuming a moderate temperature plasma, the X-ray luminosity in the 0.5-10 keV band is estimated to be similar to 10(30) ergs s(-1) at a distance of 450 pc. From the large absorption, positional coincidence, and moderate luminosity, we infer that the hard X-rays are coming from very young stellar objects embedded in the molecular cloud cores. We found another hard X-ray source near the edge of the dust filament. The extremely high absorption of 3 x 10(23) H cm(-2) indicates that the source must be surrounded by dense gas, suggesting that it is either a young stellar object in an early accretion phase or a Type II AGN (e.g., a Seyfert 2), although no counterpart is found at any other wavelength. In contrast to the hard X-ray sources, soft X-ray sources are found spread around the dust filaments, most of which are identified with IR sources in the T. Tauri phase.

    DOI: 10.1086/321392

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  • Discovery of X-rays from Class 0 Protostar Candidates

    Y.Tsuboi, K.Koyama, K.Hamaguchi, K.tatematsu, Y.Sekimoto, J.Bally, B.Reipurth

    New Century of X-ray Astronomy, ASP Conference Proceedings   251   18- - 18   2001.1

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  • ASCA Observations of Two Molecular Cloud Cores in the Perseus Molecular Cloud Complex

    S.Yamauchi, Y.Tsuboi, K.Koyama

    New Century of X-ray Astronomy, ASP Conference Proceedings   251   286- - 286   2001.1

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  • XMM-Newton EPIC Observations of OMC-2/3 region

    Bulletin of the American Astronomical Society   34   564   2001

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  • Magnetic flaring in the young Sun and implications for solar nebula solids

    Abstract of the Two Years of Science with Chandra   2001

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  • X-rays from the Brown Dwarf BD TWA-5B

    Abstract of the Two Years of Science with Chandra   2001

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  • SUBARU Follow-up Observation of Class 0 Sources Detected by Chandra X-ray Observatory

    New Century of X-ray Astronomy, ASP Conference Proceedings   251   282-   2001

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  • Chandra Observation of the ρ Oph Star-Forming Region

    New Century of X-ray Astronomy, ASP Conference Proceedings   251   246-   2001

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  • Discovery of X-rays from Class 0 Protostar Candidates

    New Century of X-ray Astronomy, ASP Conference Proceedings   251   18-   2001

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  • X-rays From A Protostellar Outflow: HH 2

    Bulletin of the American Astronomical Society   33 ( 2 )   824   2001

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  • Chandra Observation of the ρ Oph Cloud

    The Astrophysical Journal   557 ( 2 )   747 - 760   2001

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  • Magnetic flaring in the young Sun and implications for solar nebula solids

    Abstract of the Two Years of Science with Chandra   2001

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  • X-rays from the Brown Dwarf BD TWA-5B

    Abstract of the Two Years of Science with Chandra   2001

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  • ASCA Observations on Two Molecular Cloud Cores in the Perseus Complex

    Publications of the Astron. Society of Japan   535 ( 5 )   885 - 892   2001

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  • ASCA Observations on Two Molecular Cloud Cores in the Perseus Complex

    Publications of the Astron. Society of Japan   535 ( 5 )   885 - 892   2001

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  • XMM-Newton EPIC Observations of OMC-2/3 region

    Bulletin of the American Astronomical Society   34   564   2001

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  • ASCA Observations of Two Molecular Cloud Cores in the Perseus Molecular Cloud Complex

    New Century of X-ray Astronomy, ASP Conference Proceedings   251   286-   2001

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  • SUBARU Follow-up Observation of Class 0 Sources Detected by Chandra X-ray Observatory

    New Century of X-ray Astronomy, ASP Conference Proceedings   251   282-   2001

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  • Chandra Observation of the ρ Oph Star-Forming Region

    New Century of X-ray Astronomy, ASP Conference Proceedings   251   246-   2001

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  • X-rays From A Protostellar Outflow: HH 2

    Bulletin of the American Astronomical Society   33 ( 2 )   824   2001

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  • Chandra Observation of the ρ Oph Cloud

    The Astrophysical Journal   557 ( 2 )   747 - 760   2001

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  • Chandra X-Ray Observatory study of the Orion Nebula cluster and BN/KL region

    G Garmire, ED Feigelson, P Broos, LA Hillenbrand, SH Pravdo, L Townsley, Y Tsuboi

    ASTRONOMICAL JOURNAL   120 ( 3 )   1426 - 1435   2000.9

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    About 1000 X-ray emitting young pre-main-sequence (PMS) stars distributed in mass from similar to 0.05 M. brown dwarfs to a similar to 50 M. O star are detected in an image of the Orion Nebula obtained with the Advanced CCD Imaging Spectrometer on board the Chandra X-Ray Observatory. This is the richest field of sources ever obtained in X-ray astronomy. Individual X-ray luminosities in the Orion Nebula cluster range from the sensitivity limit of 2 x 10(28) ergs s(-1) to similar to 10(32) ergs s(-1). ACIS sources include 85%-90% of V < 20 stars, plus a lower but substantial fraction of deeply embedded stars with extinctions as high as A(V) similar or equal to 60. The relationships between X-ray and other PMS stellar properties suggest that X-ray luminosity of lower-mass PMS stars depends more on mass, and possibly stellar rotation, than on bolometric luminosity, as widely reported. In a subsample of 17 unabsorbed stars with mass similar or equal to 1 M., X-ray luminosities are constant at a high level around L-x similar or equal to 2 x 10(30) ergs s(-1) for the first similar or equal to 2 Myr while descending the convective Hayashi track, but diverge during the 2-10 Myr phase with X-ray emission plummeting in some stars but remaining high in others. This behavior is consistent with the distribution of X-ray luminosities on the zero-age main sequence and with current theories of their rotational history and magnetic dynamos.
    The sources in the Becklin-Neugebauer/Kleinman-low region of massive star formation are discussed in detail. They include both unabsorbed and embedded low-mass members of the Orion Nebula cluster, the luminous infrared Source n, and a class of sources without optical or infrared counterparts that may be new magnetically active embedded PMS stars. Several X-ray sources are also variable radio emitters, an association often seen in magnetically active PMS stars. Faint X-ray emission is seen close to, but apparently not coincident with, the Becklin-Neugebauer object. Its nature is not clear.

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  • Chandra X-Ray Observatory study of the Orion Nebula cluster and BN/KL region

    G Garmire, ED Feigelson, P Broos, LA Hillenbrand, SH Pravdo, L Townsley, Y Tsuboi

    ASTRONOMICAL JOURNAL   120 ( 3 )   1426 - 1435   2000.9

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    About 1000 X-ray emitting young pre-main-sequence (PMS) stars distributed in mass from similar to 0.05 M. brown dwarfs to a similar to 50 M. O star are detected in an image of the Orion Nebula obtained with the Advanced CCD Imaging Spectrometer on board the Chandra X-Ray Observatory. This is the richest field of sources ever obtained in X-ray astronomy. Individual X-ray luminosities in the Orion Nebula cluster range from the sensitivity limit of 2 x 10(28) ergs s(-1) to similar to 10(32) ergs s(-1). ACIS sources include 85%-90% of V < 20 stars, plus a lower but substantial fraction of deeply embedded stars with extinctions as high as A(V) similar or equal to 60. The relationships between X-ray and other PMS stellar properties suggest that X-ray luminosity of lower-mass PMS stars depends more on mass, and possibly stellar rotation, than on bolometric luminosity, as widely reported. In a subsample of 17 unabsorbed stars with mass similar or equal to 1 M., X-ray luminosities are constant at a high level around L-x similar or equal to 2 x 10(30) ergs s(-1) for the first similar or equal to 2 Myr while descending the convective Hayashi track, but diverge during the 2-10 Myr phase with X-ray emission plummeting in some stars but remaining high in others. This behavior is consistent with the distribution of X-ray luminosities on the zero-age main sequence and with current theories of their rotational history and magnetic dynamos.
    The sources in the Becklin-Neugebauer/Kleinman-low region of massive star formation are discussed in detail. They include both unabsorbed and embedded low-mass members of the Orion Nebula cluster, the luminous infrared Source n, and a class of sources without optical or infrared counterparts that may be new magnetically active embedded PMS stars. Several X-ray sources are also variable radio emitters, an association often seen in magnetically active PMS stars. Faint X-ray emission is seen close to, but apparently not coincident with, the Becklin-Neugebauer object. Its nature is not clear.

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  • 海外研究室事情(7)「米国ペンシルバニア州立大学、天文及び天体物理学科」

    前田良知, 坪井陽子

    天文月報   93 ( 7 )   390 - 931   2000.7

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  • Quasi-periodic X-ray flares from the protostar YLW 15

    Y Tsuboi, K Imanishi, K Koyama, N Grosso, T Montmerle

    ASTROPHYSICAL JOURNAL   532 ( 2 )   1089 - 1096   2000.4

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    With ASCA, we have detected three X-ray flares from the class I protostar YLW 15. The flares occurred every similar to 20 hr and showed an exponential decay with time constant 30-60 ks. The X-ray spectra are explained by a thin thermal plasma emission. The plasma temperature shows a fast rise and slow decay for each flare with kT(peak) similar to 4-6 keV. The emission measure of the plasma shows this time profile only for the first flare, and remains almost constant during the second and third flares, at the level of the tail of the first flare. The peak flare luminosities, L-X,L-peak, were similar to 5-20 x 10(31) ergs s(-1), which are among the brightest X-ray luminosities observed to date for class I protostars. The total energy released in each flare was 3-6 x 10(36) ergs. The first flare is well reproduced by the quasi-static cooling model, which is based on solar flares, and it suggests that the plasma cools mainly radiatively, confined by a semicircular magnetic loop of length similar to 14 R-circle dot with diameter-to-length ratio similar to 0.07. The two subsequent flares were consistent with the reheating of the same magnetic structure and the periodicity of the flares imply that the reheating events of the same magnetic loop originate in an interaction between the star and the disk due to the differential rotation.

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  • Rotation and X-ray emission from protostars

    T Montmerle, N Grosso, Y Tsuboi, K Koyama

    ASTROPHYSICAL JOURNAL   532 ( 2 )   1097 - 1110   2000.4

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    The ASCA satellite has recently detected variable hard X-ray emission from two class I protostars in the rho Oph cloud, YLW 15 (IRS 43) and WL 6, with a characteristic timescale of similar to 20 hr. In YLW 15, the X-ray emission is in the form of quasi-periodic energetic flares, which we explain in terms of strong magnetic shearing and reconnection between the central star and the accretion disk. The flare modeling, based on the solar analogy, gives us access to the size of the magnetic structures, which in turn allows us to calculate the rotation parameters of the star and the disk. In WL 6, X-ray flaring is rotationally modulated and appears to be more like the solar-type magnetic activity ubiquitous on T Tauri stars. On the basis of these observations, we find that YLW 15 is a fast rotator (near break-up), while WL 6 rotates with a significantly longer period. We thus use X-ray flaring as a "clock" to measure the rotation of protostars. With the help of the mass-radius relation on the stellar "birthline," we derive masses of M-* similar to 2 M-circle dot and less than or similar to 0.4 M-circle dot for the central stars of YLW 15 and WL 6, respectively. YLW 15 thus appears to be a future A star. In the long term, the magnetic interactions between the star and the disk result in magnetic braking and angular momentum loss of the star. A comparison of the rotation behavior of YLW 15 and WL 6 confirms that for solar-mass stars magnetic braking takes place on timescales t(br) similar to a few x 10(5) yr, i.e., of the same order as the estimated duration of the class I protostar stage. The main parameter determining t(br) turns out to be the stellar mass, so that close to the birthline there must be a mass-rotation relation, t(br) similar to proportional to M-*, such that stars with M-* greater than or similar to 1-2 M-circle dot are fast rotators, while their lower mass counterparts have had the time to spin down and reach synchronous rotation with the inner surrounding accretion disk. The rapid rotation and strong star-disk magnetic interactions of YLW 15 also naturally explain the observation of "superflares" of X-ray luminosities as high as L-X greater than or similar to 10(33)-10(34) ergs s(-1) during a few hours, while at the WL 6 stage the lower X-ray luminosities are likely to be of purely stellar origin. The mass-rotation relation through magnetic braking may also explain why so few class I protostars have been detected in X-rays to date, and why they all lie in clusters. In the case of YLW 15, and perhaps also in other protostars, a hot coronal wind (T similar to 10(6) K) may be responsible for the VLA thermal radio emission. This paper thus proposes the first clues to the magnetic properties of protostars, which govern their rotation status and evolution.

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  • Quasi-periodic X-ray flares from the protostar YLW 15

    Y Tsuboi, K Imanishi, K Koyama, N Grosso, T Montmerle

    ASTROPHYSICAL JOURNAL   532 ( 2 )   1089 - 1096   2000.4

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    With ASCA, we have detected three X-ray flares from the class I protostar YLW 15. The flares occurred every similar to 20 hr and showed an exponential decay with time constant 30-60 ks. The X-ray spectra are explained by a thin thermal plasma emission. The plasma temperature shows a fast rise and slow decay for each flare with kT(peak) similar to 4-6 keV. The emission measure of the plasma shows this time profile only for the first flare, and remains almost constant during the second and third flares, at the level of the tail of the first flare. The peak flare luminosities, L-X,L-peak, were similar to 5-20 x 10(31) ergs s(-1), which are among the brightest X-ray luminosities observed to date for class I protostars. The total energy released in each flare was 3-6 x 10(36) ergs. The first flare is well reproduced by the quasi-static cooling model, which is based on solar flares, and it suggests that the plasma cools mainly radiatively, confined by a semicircular magnetic loop of length similar to 14 R-circle dot with diameter-to-length ratio similar to 0.07. The two subsequent flares were consistent with the reheating of the same magnetic structure and the periodicity of the flares imply that the reheating events of the same magnetic loop originate in an interaction between the star and the disk due to the differential rotation.

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  • Rotation and X-ray emission from protostars

    T Montmerle, N Grosso, Y Tsuboi, K Koyama

    ASTROPHYSICAL JOURNAL   532 ( 2 )   1097 - 1110   2000.4

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    Language:English   Publisher:IOP PUBLISHING LTD  

    The ASCA satellite has recently detected variable hard X-ray emission from two class I protostars in the rho Oph cloud, YLW 15 (IRS 43) and WL 6, with a characteristic timescale of similar to 20 hr. In YLW 15, the X-ray emission is in the form of quasi-periodic energetic flares, which we explain in terms of strong magnetic shearing and reconnection between the central star and the accretion disk. The flare modeling, based on the solar analogy, gives us access to the size of the magnetic structures, which in turn allows us to calculate the rotation parameters of the star and the disk. In WL 6, X-ray flaring is rotationally modulated and appears to be more like the solar-type magnetic activity ubiquitous on T Tauri stars. On the basis of these observations, we find that YLW 15 is a fast rotator (near break-up), while WL 6 rotates with a significantly longer period. We thus use X-ray flaring as a "clock" to measure the rotation of protostars. With the help of the mass-radius relation on the stellar "birthline," we derive masses of M-* similar to 2 M-circle dot and less than or similar to 0.4 M-circle dot for the central stars of YLW 15 and WL 6, respectively. YLW 15 thus appears to be a future A star. In the long term, the magnetic interactions between the star and the disk result in magnetic braking and angular momentum loss of the star. A comparison of the rotation behavior of YLW 15 and WL 6 confirms that for solar-mass stars magnetic braking takes place on timescales t(br) similar to a few x 10(5) yr, i.e., of the same order as the estimated duration of the class I protostar stage. The main parameter determining t(br) turns out to be the stellar mass, so that close to the birthline there must be a mass-rotation relation, t(br) similar to proportional to M-*, such that stars with M-* greater than or similar to 1-2 M-circle dot are fast rotators, while their lower mass counterparts have had the time to spin down and reach synchronous rotation with the inner surrounding accretion disk. The rapid rotation and strong star-disk magnetic interactions of YLW 15 also naturally explain the observation of "superflares" of X-ray luminosities as high as L-X greater than or similar to 10(33)-10(34) ergs s(-1) during a few hours, while at the WL 6 stage the lower X-ray luminosities are likely to be of purely stellar origin. The mass-rotation relation through magnetic braking may also explain why so few class I protostars have been detected in X-rays to date, and why they all lie in clusters. In the case of YLW 15, and perhaps also in other protostars, a hot coronal wind (T similar to 10(6) K) may be responsible for the VLA thermal radio emission. This paper thus proposes the first clues to the magnetic properties of protostars, which govern their rotation status and evolution.

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  • X-ray spectral study of the most massive HII region NGC3603

    Abstract of the High-mass Star Formation: An Origin in Clusters?   84   2000

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  • X-ray emission from high-mass pre-main-sequence stars

    Abstract of the High-mass Star Formation: An Origin in Clusters?   57   2000

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  • Discovery of Hard X-rays from Class 0 candidates in the Orion Molecular Cloud 2/3 region with Chandra

    Bulletin of the American Astronomical Society   32 ( 3 )   1256   2000

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  • Some Data Analysis Technique for Chandra ACIS

    Bulletin of the American Astronomical Society   32 ( 3 )   1227   2000

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  • Chandra Deep Observation of the rho Ophiuchi Dark Cloud

    Bulletin of the American Astronomical Society   32 ( 3 )   1256   2000

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  • Chandra/ACIS Observations of Protostars

    Bulletin of the American Astronomical Society   32 ( 4 )   1597   2000

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  • Hard X-ray Detection from the Core of the Monoceros R2 Star Forming Region

    Advances in Space Research   25 ( 3-4 )   531 - 534   2000

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  • Chandra/ACIS Spectra of the 30 Doradus Star Forming Region

    Bulletin of the American Astronomical Society   32 ( 4 )   1594   2000

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  • Quasi-periodic X-Ray Flares on Protostar YLW15

    Advances in Space Research   25 ( 3-4 )   535 - 538   2000

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  • Hard X-ray Detection from the Core of the Monoceros R2 Star Forming Region

    Advances in Space Research   25 ( 3-4 )   531 - 534   2000

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  • チャンドラ衛星によるOMC 2-3領域のX線観測

    2000年度春季天文学会予稿集   2000

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  • オリオン ネビュラ クラスターのチャンドラX線観

    2000年度春季天文学会予稿集   2000

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  • X-ray spectral study of the most massive HII region NGC3603

    Abstract of the High-mass Star Formation: An Origin in Clusters?   84   2000

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  • X-ray emission from high-mass pre-main-sequence stars

    Abstract of the High-mass Star Formation: An Origin in Clusters?   57   2000

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  • Chandra衛星によるRhoOph星形成領域のX線観測

    2000年度秋季天文学会予稿集   2000

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  • Discovery of Hard X-rays from Class 0 candidates in the Orion Molecular Cloud 2/3 region with Chandra

    Bulletin of the American Astronomical Society   32 ( 3 )   1256   2000

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  • Some Data Analysis Technique for Chandra ACIS

    Bulletin of the American Astronomical Society   32 ( 3 )   1227   2000

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  • Chandra Deep Observation of the rho Ophiuchi Dark Cloud

    Bulletin of the American Astronomical Society   32 ( 3 )   1256   2000

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  • X-ray Emitting Class 0 Sources の近赤外詳細観測

    2001年度春季天文学会予稿集   2000

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  • Chandra衛星によるRhoOph星形成領域のX線観測II-X線フレアの詳細解析

    2001年度春季天文学会予稿集   2000

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  • Chandra/ACIS Observations of Protostars

    Bulletin of the American Astronomical Society   32 ( 4 )   1597   2000

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  • Chandra/ACIS Spectra of the 30 Doradus Star Forming Region

    Bulletin of the American Astronomical Society   32 ( 4 )   1594   2000

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  • Quasi-periodic X-Ray Flares on Protostar YLW15

    Advances in Space Research   25 ( 3-4 )   535 - 538   2000

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  • Eta Carinae

    Corcoran, M.F

    IAU Circ.   ( 7177 )   2   1999.5

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  • Eta Carinae

    Corcoran, M.F

    IAU Circ.   ( 7177 )   2   1999.5

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  • Hard X-Ray Activities in Yound Stellar Objects

    Y.Tsuboi, K.Koyama

    Proc. of Star Formation 1999   187 - 188   1999.4

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  • Hard X-rays from Giant Molecular Cloud Core

    K.Hamaguchi, Y.Tsuboi, K.Koyama

    Proc. of the Japanese-German Workshop on high energy astrophysics   52 - 55   1999.4

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  • X-ray Study of Class I Protostars with ASCA

    Y.Tsuboi, K.Koyama

    Proc. of the Japanese-German Workshop on high energy astrophysics   3 - 5   1999.4

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  • Quasi-Periodic X-Ray Flares from the Class I Protostar YLW15

    K.Imanishi, Y.Tsuboi, K.Koyama, N.Grosso, T.Montmerle

    Proc. of Star Formation 1999   312 - 313   1999.4

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  • Hard X-Ray Activities in Yound Stellar Objects

    Y.Tsuboi, K.Koyama

    Proc. of Star Formation 1999   187 - 188   1999.4

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  • Hard X-rays from Giant Molecular Cloud Core

    K.Hamaguchi, Y.Tsuboi, K.Koyama

    Proc. of the Japanese-German Workshop on high energy astrophysics   52 - 55   1999.4

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  • X-ray Study of Class I Protostars with ASCA

    Y.Tsuboi, K.Koyama

    Proc. of the Japanese-German Workshop on high energy astrophysics   3 - 5   1999.4

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  • Quasi-Periodic X-Ray Flares from the Class I Protostar YLW15

    K.Imanishi, Y.Tsuboi, K.Koyama, N.Grosso, T.Montmerle

    Proc. of Star Formation 1999   312 - 313   1999.4

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  • X-Ray Study of the Bright W-R Star HD 93162 with Chandra

    Bulletin of the American Astronomical Society   31 ( 5 )   1541   1999

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  • ASCA Spectra of the Central Star of the Orion Nebula: a Magnetic O Star

    Bulletin of the American Astronomical Society   32 ( 2 )   705   1999

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  • Magnetic activities in Young Stellar Objects

    Y. Tsuboi, K. Hamaguchi, K. Koyama, S. Yamauchi

    Astronomische Nachrichten   320 ( 4-5 )   175 - 176   1999

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    With ASCA, we detected hard X-rays from low-mass and high-mass Young Stellar Objects (YSOs), deeply embedded in dense molecular cloud cores. The X-rays from YSOs possessed line emissions from highly ionized ions of heavy elements, and were well fitted with thin-thermal plasma model. Some of them exhibited time valiabilities like solar flares, while their luminosities were at least 3-5 orders of magnitude larger than those from the Sun. These results support a scenario that stars in very young stage always emit magnetic-powered X-rays independently of the mass.

    DOI: 10.1002/1521-3994(199908)320:4/5<175::AID-ASNA175>3.0.CO;2-O

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  • Chandra ACIS observation of the Orion Nebula Cluster

    Bulletin of the American Astronomical Society   31 ( 5 )   1491   1999

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  • Chandra/ACIS Observations of 30 Doradus

    Bulletin of the American Astronomical Society   31 ( 5 )   1453   1999

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  • X-ray activities in a Young Open Cluster: Chandra Observations of NGC2516

    Bulletin of the American Astronomical Society   31 ( 5 )   1442   1999

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  • X-Ray Study of the Bright W-R Star HD 93162 with Chandra

    Bulletin of the American Astronomical Society   31 ( 5 )   1541   1999

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  • ASCA Spectra of the Central Star of the Orion Nebula: a Magnetic O Star

    Bulletin of the American Astronomical Society   32 ( 2 )   705   1999

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  • Magnetic activities in Young Stellar Objects

    Y Tsuboi, K Hamaguchi, K Koyama, S Yamauchi

    ASTRONOMISCHE NACHRICHTEN   320 ( 4-5 )   175 - 176   1999

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    With ASCA, we detected hard X-rays from low-mass and high-mass Young Stellar Objects (YSOs), deeply embedded in dense molecular cloud cores. The X-rays from YSOs possessed line emissions from highly ionized ions of heavy elements, and were well fitted with thin-thermal plasma model. Some of them exhibited time valiabilities like solar flares, while their luminosities were at least 3-5 orders of magnitude larger than those from the Sun. These results support a scenario that stars in very young stage always emit magnetic-powered X-rays independently of the mass.

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  • Chandra ACIS observation of the Orion Nebula Cluster

    Bulletin of the American Astronomical Society   31 ( 5 )   1491   1999

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  • Chandra/ACIS Observations of 30 Doradus

    Bulletin of the American Astronomical Society   31 ( 5 )   1453   1999

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  • X-ray activities in a Young Open Cluster: Chandra Observations of NGC2516

    Bulletin of the American Astronomical Society   31 ( 5 )   1442   1999

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  • ASCA detection of a superhot 100 million K X-ray flare on the weak-lined T Tauri star V773 Tauri

    Y Tsuboi, K Koyama, H Murakami, M Hayashi, S Skinner, S Ueno

    ASTROPHYSICAL JOURNAL   503 ( 2 )   894 - 901   1998.8

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    We present results of a approximate to 40 ks ASCA observation of the active weak-lined T Tauri star V773 Tau (HD 283447) and the surrounding Barnard 209 dark cloud, obtained in 1995 February. During this observation, V773 Tau exhibited a dramatic X-ray flare, with the X-ray count rate increasing rapidly by a factor of similar to 20, then decreasing exponentially with an e-folding timescale of approximate to 2.3 hr. The peak flare luminosity was at least similar to 10(33) ergs s(-1) (0.7-10 keV; distance = 150 pc), which is among the highest X-ray luminosities observed to date for T Tauri stars. The total energy release was similar to 10(37) ergs. However, the most spectacular aspect of this hare was its temperature, which reached a maximum value of at least 100 million K. Spectral fits near flare maximum give a temperature of similar to 10 keV, which slowly declined to a value similar to 6 keV at the end of the observation. These temperature measurements are based on high signal-to-noise ratio spectra, and provide the first unambiguous evidence for superhot flaring plasma at temperatures of similar to 10(8) K in T Tauri stars. A simple cooling-loop model gives electron densities that are similar to those of solar flares, but requires loop sizes that are comparable to or larger than the star itself. The flare showed other interesting behavior, including a high (and possibly variable) absorption column density, N-H = 4 x 10(22) cm(-2), and an apparent increase in the global metal abundance during the flare.

    DOI: 10.1086/306024

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  • ASCA detection of a superhot 100 million K X-ray flare on the weak-lined T Tauri star V773 Tauri

    Y Tsuboi, K Koyama, H Murakami, M Hayashi, S Skinner, S Ueno

    ASTROPHYSICAL JOURNAL   503 ( 2 )   894 - 901   1998.8

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    We present results of a approximate to 40 ks ASCA observation of the active weak-lined T Tauri star V773 Tau (HD 283447) and the surrounding Barnard 209 dark cloud, obtained in 1995 February. During this observation, V773 Tau exhibited a dramatic X-ray flare, with the X-ray count rate increasing rapidly by a factor of similar to 20, then decreasing exponentially with an e-folding timescale of approximate to 2.3 hr. The peak flare luminosity was at least similar to 10(33) ergs s(-1) (0.7-10 keV; distance = 150 pc), which is among the highest X-ray luminosities observed to date for T Tauri stars. The total energy release was similar to 10(37) ergs. However, the most spectacular aspect of this hare was its temperature, which reached a maximum value of at least 100 million K. Spectral fits near flare maximum give a temperature of similar to 10 keV, which slowly declined to a value similar to 6 keV at the end of the observation. These temperature measurements are based on high signal-to-noise ratio spectra, and provide the first unambiguous evidence for superhot flaring plasma at temperatures of similar to 10(8) K in T Tauri stars. A simple cooling-loop model gives electron densities that are similar to those of solar flares, but requires loop sizes that are comparable to or larger than the star itself. The flare showed other interesting behavior, including a high (and possibly variable) absorption column density, N-H = 4 x 10(22) cm(-2), and an apparent increase in the global metal abundance during the flare.

    DOI: 10.1086/306024

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  • X-ray Emission from the Orion Nebula Region Reviewed

    M.Gagne, Y.Tsuboi

    Proc. of the ASP Conf. Series The Orion Complex Revisited   1998.4

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  • X-ray Emission from the Orion Nebula Region Reviewed

    M.Gagne, Y.Tsuboi

    Proc. of the ASP Conf. Series The Orion Complex Revisited   1998.4

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  • The ASCA X-ray spectrum of eta Carinae

    MF Corcoran, R Petre, JH Swank, SA Drake, K Koyama, Y Tsuboi, R Viotti, A Damineli, K Davidson, K Ishibashi, S White, D Currie

    ASTROPHYSICAL JOURNAL   494 ( 1 )   381 - 395   1998.2

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    We have obtained high signal-to-noise ratio 0.5-10 keV band X-ray spectra of the peculiar, extremely luminous star eta Carinae with the Advanced Satellite for Cosmology and Astrophysics (ASCA) X-ray observatory during Cycle 4 observations in mid-1996. These data comprise the best X-ray spectra to date of the cool source (kT similar to 0.3 keV) surrounding the homunculus and of the hot source (kT similar to 5 keV) associated with eta Car itself. We identify line emission from ions of N, Mg, Si, and S and numerous strong transitions of Fe in a variety of ionization stages, including the first clear identification of a fluorescent Fe line produced by photoionization of cool material by the X-ray continuum from the hot source. The line strengths are consistent with thermal equilibrium models, though abundances of some important elements are nonsolar. Our analysis suggests that Fe is slightly underabundant and S and Si somewhat overabundant. Most importantly, we confirm the high N enrichment derived by Tsuboi et al. from their analysis of a shorter ASCA observation obtained during the performance verification (PV) phase in 1993 August. The O/N abundance ratio derived from the ASCA spectra is consistent with an upper limit from optical/UV spectral analysis (Davidson et al.) and with predictions of evolutionary models for extremely massive stars. Comparison of the Cycle 4 and PV-phase spectra shows that the X-ray luminosity increased by similar to 50% during this 3 year interval. Using the ASCA spectral model as a template, we reevaluate the spectrum of II Car obtained by the Rontgen Satelite (ROSAT) in late 1992 and construct an X-ray light curve for the 1992.4-1996.6 interval. We present spectra from the Intel national Ultraviolet Explorer (IUE) satellite obtained at nearly the same time as the Cycle 4 ASCA spectra and show that the observed X-ray variability is reflected in changes of some important UV spectral features. Our data suggest that the X-ray emission and state of the stellar wind are intimately connected, though the exact mechanism of coupling is not known. We suggest two alternatives: an underlying photospheric change of undetermined origin in eta Car itself, or a collision between a dense stellar wind from eta Car and the wind or photosphere of a companion.

    DOI: 10.1086/305190

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  • The ASCA X-ray spectrum of eta Carinae

    MF Corcoran, R Petre, JH Swank, SA Drake, K Koyama, Y Tsuboi, R Viotti, A Damineli, K Davidson, K Ishibashi, S White, D Currie

    ASTROPHYSICAL JOURNAL   494 ( 1 )   381 - 395   1998.2

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    We have obtained high signal-to-noise ratio 0.5-10 keV band X-ray spectra of the peculiar, extremely luminous star eta Carinae with the Advanced Satellite for Cosmology and Astrophysics (ASCA) X-ray observatory during Cycle 4 observations in mid-1996. These data comprise the best X-ray spectra to date of the cool source (kT similar to 0.3 keV) surrounding the homunculus and of the hot source (kT similar to 5 keV) associated with eta Car itself. We identify line emission from ions of N, Mg, Si, and S and numerous strong transitions of Fe in a variety of ionization stages, including the first clear identification of a fluorescent Fe line produced by photoionization of cool material by the X-ray continuum from the hot source. The line strengths are consistent with thermal equilibrium models, though abundances of some important elements are nonsolar. Our analysis suggests that Fe is slightly underabundant and S and Si somewhat overabundant. Most importantly, we confirm the high N enrichment derived by Tsuboi et al. from their analysis of a shorter ASCA observation obtained during the performance verification (PV) phase in 1993 August. The O/N abundance ratio derived from the ASCA spectra is consistent with an upper limit from optical/UV spectral analysis (Davidson et al.) and with predictions of evolutionary models for extremely massive stars. Comparison of the Cycle 4 and PV-phase spectra shows that the X-ray luminosity increased by similar to 50% during this 3 year interval. Using the ASCA spectral model as a template, we reevaluate the spectrum of II Car obtained by the Rontgen Satelite (ROSAT) in late 1992 and construct an X-ray light curve for the 1992.4-1996.6 interval. We present spectra from the Intel national Ultraviolet Explorer (IUE) satellite obtained at nearly the same time as the Cycle 4 ASCA spectra and show that the observed X-ray variability is reflected in changes of some important UV spectral features. Our data suggest that the X-ray emission and state of the stellar wind are intimately connected, though the exact mechanism of coupling is not known. We suggest two alternatives: an underlying photospheric change of undetermined origin in eta Car itself, or a collision between a dense stellar wind from eta Car and the wind or photosphere of a companion.

    DOI: 10.1086/305190

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  • ASCA observation of NGC1333 star forming region

    M Itoh, H Fukunaga, K Koyama, Y Tsuboi, S Yamauchi, N Kobayashi, M Hayashi, S Ueno

    HOT UNIVERSE   ( 188 )   228 - 229   1998

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  • ASCA observations of Class I protostars in the Rho Oph dark cloud

    Y Tsuboi, K Koyama, Y Kamata, S Yamauchi

    HOT UNIVERSE   ( 188 )   236 - 237   1998

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  • ASCA observation of NGC1333 star forming region

    M Itoh, H Fukunaga, K Koyama, Y Tsuboi, S Yamauchi, N Kobayashi, M Hayashi, S Ueno

    HOT UNIVERSE   ( 188 )   228 - 229   1998

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  • ASCA observations of Class I protostars in the Rho Oph dark cloud

    Y Tsuboi, K Koyama, Y Kamata, S Yamauchi

    HOT UNIVERSE   ( 188 )   236 - 237   1998

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  • ASCA Observations of Embedded Sources in Dark Clouds Reviewed

    K.Koyama, K.Hamaguchi, H.Murakami, Y.Tsuboi

    Memorie della Societa Astromia Italiana   68   1033 - 1037   1997.12

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  • ASCA Observations of X-Rays from YSOs Reviewed

    Y.Tsuboi

    Memorie della Societa Astronomia Italiana   68   1039 - 1042   1997.12

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  • ASCA Observations of Embedded Sources in Dark Clouds Reviewed

    K.Koyama, K.Hamaguchi, H.Murakami, Y.Tsuboi

    Memorie della Societa Astromia Italiana   68   1033 - 1037   1997.12

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  • ASCA Observations of X-Rays from YSOs Reviewed

    Y.Tsuboi

    Memorie della Societa Astronomia Italiana   68   1039 - 1042   1997.12

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  • X-ray analysis of the rho Ophiuchi dark cloud with ASCA: Source identification, X-ray spectra, and temporal variability

    Y Kamata, K Koyama, Y Tsuboi, S Yamauchi

    PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN   49 ( 4 )   461 - 470   1997.8

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    This paper presents a comprehensive study with the Japanese X-ray astronomical satellite ASCA on X-rays from the main body of the rho Ophiuchi dark cloud. We have constructed separate X-ray images using 3 energy bands and 12 time-sliced data, and thereby detected 19 X-ray sources, doubling the previous ASCA results of II X-ray sources. Three of the sources are associated with class-I infrared sources, which precede the T Tauri phase. Half of the 19 sources were found to be time variable, and 5 flare-like events with an averaged energy of &gt; 3 x 10(35) erg were observed. With the analogy of solar flares, we estimated the flare loop height and plasma density to be 3 x 10(11) cm and 3 x 10(11) cm(-3), respectively. Among these sources, a flare from the class-I source EL 29 exhibited an order-of-magnitude larger absorption (N-H) than in quiescence states, which may indicate the exsistence of a dense protostellar disk.

    DOI: 10.1093/pasj/49.4.461

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  • X-ray analysis of the rho Ophiuchi dark cloud with ASCA: Source identification, X-ray spectra, and temporal variability

    Y Kamata, K Koyama, Y Tsuboi, S Yamauchi

    PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN   49 ( 4 )   461 - 470   1997.8

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    This paper presents a comprehensive study with the Japanese X-ray astronomical satellite ASCA on X-rays from the main body of the rho Ophiuchi dark cloud. We have constructed separate X-ray images using 3 energy bands and 12 time-sliced data, and thereby detected 19 X-ray sources, doubling the previous ASCA results of II X-ray sources. Three of the sources are associated with class-I infrared sources, which precede the T Tauri phase. Half of the 19 sources were found to be time variable, and 5 flare-like events with an averaged energy of &gt; 3 x 10(35) erg were observed. With the analogy of solar flares, we estimated the flare loop height and plasma density to be 3 x 10(11) cm and 3 x 10(11) cm(-3), respectively. Among these sources, a flare from the class-I source EL 29 exhibited an order-of-magnitude larger absorption (N-H) than in quiescence states, which may indicate the exsistence of a dense protostellar disk.

    DOI: 10.1093/pasj/49.4.461

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  • X-Rays from Young Stars - a Giant X-Ray Flare from V773 Tan -

    Y.Tsuboi, S.Ueno, K.Koyama

    Proc. of the X-Ray Imaging and Spectroscopy of Hot Plasmas   583 - 584   1997.4

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  • X-Rays from Young Stars - a Giant X-Ray Flare from V773 Tan -

    Y.Tsuboi, S.Ueno, K.Koyama

    Proc. of the X-Ray Imaging and Spectroscopy of Hot Plasmas   583 - 584   1997.4

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  • ASCA observations of Eta Carinae

    Y Tsuboi, K Koyama, M Sakano, R Petre

    PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN   49 ( 1 )   85 - 92   1997.2

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    We present ASCA results on the peculiar star eta Car in the center of the Carina Nebula. The X-ray emission from eta Car was found to be attributable to two thermal components: the high-temperature component (kT similar to 5 keV) is consistent with a point source, and is highly absorbed, while the low-temperature plasma (kT similar to 0.7 keV) is extended, and shows no significant circumstellar absorption. We found a line-like structure around 0.5 keV, which is probably due to the Ly alpha line of nitrogen. Using a variable-abundance coronal plasma model, we found that the relative abundance of nitrogen to oxygen is extremely large in comparison with the solar value. This may be the first X-ray evidence of the enrichment of CNO-processed material in an evolved massive star.

    DOI: 10.1093/pasj/49.1.85

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  • ASCA observations of Eta Carinae

    Y Tsuboi, K Koyama, M Sakano, R Petre

    PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN   49 ( 1 )   85 - 92   1997.2

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    We present ASCA results on the peculiar star eta Car in the center of the Carina Nebula. The X-ray emission from eta Car was found to be attributable to two thermal components: the high-temperature component (kT similar to 5 keV) is consistent with a point source, and is highly absorbed, while the low-temperature plasma (kT similar to 0.7 keV) is extended, and shows no significant circumstellar absorption. We found a line-like structure around 0.5 keV, which is probably due to the Ly alpha line of nitrogen. Using a variable-abundance coronal plasma model, we found that the relative abundance of nitrogen to oxygen is extremely large in comparison with the solar value. This may be the first X-ray evidence of the enrichment of CNO-processed material in an evolved massive star.

    DOI: 10.1093/pasj/49.1.85

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  • Skylight「X線でさぐる原始星」

    坪井陽子, 小山勝二

    天文月報   90 ( 1 )   8   1997.1

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  • Molecular Outflows from X-Ray- Emitting Protostars in the rho Ophiuchi Dark Cloud

    Astrophysical Journal Letters   489 ( 1 )   63 - 66   1997

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  • Molecular Outflows from X-Ray- Emitting Protostars in the rho Ophiuchi Dark Cloud

    Astrophysical Journal Letters   489 ( 1 )   63 - 66   1997

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  • X-ray Spectral Variability of Eta Carinae

    Bulletin of the American Astronomical Society   29 ( 5 )   1261   1997

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  • Hard X-ray emissions from star forming regions

    Y Tsuboi, K Koyama, S Ueno

    STAR FORMATION NEAR AND FAR - SEVENTH ASTROPHYSICS CONFERENCE   393 ( 393 )   175 - 178   1997

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    ASCA is the first satellite which has an imaging capability in high energies up to 10 keV, hence can peer deeply into the molecular cloud where protostar candidates may reside. We have carried out a systematic survey of hard X-rays from the core of molecular clouds, and discovered hard X-rays from protostar candidates (Class I objects) in the core of Rho Oph dark cloud. Two of them showed clear time variability; one (EL29) is flare-like and the other (WL6) is sinusoidal flux variation.
    On the other hand, in Taurus dark cloud, we have detected a giant flare of a weak-lined TTS, V773 Tau in hard X-ray band. The plasma temperature was extremely high, about 8 keV, at the maximum flux, then it decreased as the flux decreased. The decay time and estimated electron density were found to be comparable to those of the sun, but the geometrical flare size was equal or even larger than the stellar size. The absorption column during the flare was large, about 3.6 x 10(22) H cm(-3), and it makes impossible to detect the flare in soft X-ray band. Interestingly, in the decay phase, we found the apparent change of the metal abundance.

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  • X-ray Spectral Variability of Eta Carinae

    Bulletin of the American Astronomical Society   29 ( 5 )   1261   1997

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  • Hard X-ray emissions from star forming regions

    Y Tsuboi, K Koyama, S Ueno

    STAR FORMATION NEAR AND FAR - SEVENTH ASTROPHYSICS CONFERENCE   393 ( 393 )   175 - 178   1997

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    ASCA is the first satellite which has an imaging capability in high energies up to 10 keV, hence can peer deeply into the molecular cloud where protostar candidates may reside. We have carried out a systematic survey of hard X-rays from the core of molecular clouds, and discovered hard X-rays from protostar candidates (Class I objects) in the core of Rho Oph dark cloud. Two of them showed clear time variability; one (EL29) is flare-like and the other (WL6) is sinusoidal flux variation.
    On the other hand, in Taurus dark cloud, we have detected a giant flare of a weak-lined TTS, V773 Tau in hard X-ray band. The plasma temperature was extremely high, about 8 keV, at the maximum flux, then it decreased as the flux decreased. The decay time and estimated electron density were found to be comparable to those of the sun, but the geometrical flare size was equal or even larger than the stellar size. The absorption column during the flare was large, about 3.6 x 10(22) H cm(-3), and it makes impossible to detect the flare in soft X-ray band. Interestingly, in the decay phase, we found the apparent change of the metal abundance.

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  • 原始星からのX線~rho Oph分子雲~

    ラインX線・ガンマ線による天体物理(V)収録   146 - 150   1997

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  • CCD Cal装置の開発装置(I)

    ラインX線・ガンマ線による天体物理(V)収録   167 - 169   1997

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  • 衛星搭載用X線CCDの評価システムの開発

    1997年春季物理学会予稿集   1997

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  • rho-Oph分子雲のX線描像

    LMSA Science Workshop『LMSA計画と高エネルギー天文学』収録   1997

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  • X-Ray Spectra from Star Forming Regions

    K.Koyama, Y.Tsuboi, S.Ueno

    Proc. of the UV and X-Ray Spectroscopy of Astrophysical and Laboratory Plasmas   105 - 110   1996.4

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  • Hard X-Ray Emissions from Protostar Candidates

    K.Koyama, Y.Tsuboi, S.Ueno

    Proc. of the Magetodynamic phenomena in the solar atmosphere - Prototypes of Stellar Magnetic Activity   243- - 243   1996.4

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  • Spatial and Spectral Structure of η Carinae

    Y.Tsuboi, K.Koyama

    Proc. of the UV and X-ray Spectroscopy of Astrophysical and Laboratory Plasmas   271 - 274   1996.4

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  • X-Ray Spectra from Star Forming Regions

    K.Koyama, Y.Tsuboi, S.Ueno

    Proc. of the UV and X-Ray Spectroscopy of Astrophysical and Laboratory Plasmas   105 - 110   1996.4

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  • Spatial and Spectral Structure of η Carinae

    Y.Tsuboi, K.Koyama

    Proc. of the UV and X-ray Spectroscopy of Astrophysical and Laboratory Plasmas   271 - 274   1996.4

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  • Spectral and spatial structure of eta Carinae

    Y Tsuboi, K Koyama, R Petre

    MAGNETODYNAMIC PHENOMENA IN THE SOLAR ATMOSPHERE   481 - 482   1996

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  • Spectral and spatial structure of eta Carinae

    Y Tsuboi, K Koyama, R Petre

    MAGNETODYNAMIC PHENOMENA IN THE SOLAR ATMOSPHERE   481 - 482   1996

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    Web of Science

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  • 前主系列星巨大フレアのプラズマ診断~V773 TauのX線フレア~

    1996年度秋季天文学会予稿集   1996

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  • 原始星のX線と双極分子流構造

    重点領域"高エネルギー天体”葉山研究会収録   1996

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  • ASCAによる星生成領域の観測

    1996年科学衛星・宇宙観測シンポジウム収録   1996

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  • Hard X-Ray Emissions from Protostar Candidates

    Proc. of the Magetodynamic phenomena in the solar atmosphere - Prototypes of Stellar Magnetic Activity   243-   1996

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  • V773 TauからのX線フレア観測

    1996年度日本天文学会春季年会予稿集   1996

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  • ASCA X-RAY OBSERVATIONS OF THE WOLF-RAYET STARS HD-193793 AND HD-93162

    S SKINNER, F NAGASE, K KOYAMA, Y MAEDA, Y TSUBOI

    WOLF-RAYET STARS: BINARIES, COLLIDING WINDS, EVOLUTION   ( 163 )   471 - 475   1995

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    The Japan-U.S. satellite ASCA was launched in February 1993 and provides a new capability to obtain high-resolution X-ray spectra of Wolf-Rayet stars in the 0.5 - 10 keV band. We present spectra of the wide binary HD 193793 (WC7+O4-5) obtained three months after periastron with the WC7 star in front, and of the WN7 star HD 93162 in Carina. The spectrum of HD 193793 is heavily absorbed below 2 keV by the WC7 wind and shows a prominent emission line from He-like iron at 6.7 keV. Acceptable fits were obtained using a Raymond-Smith model with kT approximate to 3 keV and non-solar abundances. In contrast, the spectrum of HD 93162 is softer and shows very little emission above approximate to 2 keV. The relatively low signal-to-noise precludes emission line analysis, and an acceptable spectral fit was obtained using a simple Bremsstrahlung model with kT approximate to 1.6 keV. No significant variability was detected in the X-ray light-curves of either star.

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  • Carina Nebulaに拡がるX線起源の考察

    原始惑星系円盤ワークショップ収録   1995

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  • New Transient X-Ray Source in the Scutum Region Discovered with ASCA

    Publications of the Astron, Society of Japan   47 ( 2 )   187 - 194   1995

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  • X線で探る恒星の生成過程~Herbig Ae/Be starの観測~

    重点領域研究「星間物質とその進化」大研究会収録   1995

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  • 硬X線による星生成領域の観測

    1995年日本天文学会秋季年会予稿集   1995

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  • 星生成領域からのX線放射~V773 Tauからの巨大X線フレア観測~

    ラインX線・ガンマ線による天体物理(IV)収録   170 - 174   1995

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  • Spatial and Spectral structure of eta Car

    1995年度日本天文学会春季年会予稿集   1995

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  • ASCA X-RAY OBSERVATIONS OF THE WOLF-RAYET STARS HD-193793 AND HD-93162

    S SKINNER, F NAGASE, K KOYAMA, Y MAEDA, Y TSUBOI

    WOLF-RAYET STARS: BINARIES, COLLIDING WINDS, EVOLUTION   ( 163 )   471 - 475   1995

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    The Japan-U.S. satellite ASCA was launched in February 1993 and provides a new capability to obtain high-resolution X-ray spectra of Wolf-Rayet stars in the 0.5 - 10 keV band. We present spectra of the wide binary HD 193793 (WC7+O4-5) obtained three months after periastron with the WC7 star in front, and of the WN7 star HD 93162 in Carina. The spectrum of HD 193793 is heavily absorbed below 2 keV by the WC7 wind and shows a prominent emission line from He-like iron at 6.7 keV. Acceptable fits were obtained using a Raymond-Smith model with kT approximate to 3 keV and non-solar abundances. In contrast, the spectrum of HD 93162 is softer and shows very little emission above approximate to 2 keV. The relatively low signal-to-noise precludes emission line analysis, and an acceptable spectral fit was obtained using a simple Bremsstrahlung model with kT approximate to 1.6 keV. No significant variability was detected in the X-ray light-curves of either star.

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  • eta Carの空間及びスペクトル構造

    太陽および恒星の超高温、高エネルギー現象研究会収録   1995

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  • Spatial and Spectral structure of eta Car

    1995年度日本天文学会春季年会予稿集   1995

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  • New Transient X-Ray Source in the Scutum Region Discovered with ASCA

    Publications of the Astron, Society of Japan   47 ( 2 )   187 - 194   1995

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  • ASCA Observation of η Car

    Y.Tsuboi, K.Koyama

    Proc. of the New Horizon of X-Ray Astronomy   403 - 404   1994.4

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  • ASCA Observation of η Car

    Y.Tsuboi, K.Koyama

    Proc. of the New Horizon of X-Ray Astronomy   403 - 404   1994.4

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  • X線放射と原始星の進化2;大質量星

    重点領域研究「星間物質とその進化」大研究会収録   1994

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  • eta Carの空間及びスペクトル構造

    ラインX線・ガンマ線による天体物理(III)収録   55 - 59   1994

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Presentations

  • 可視光測光;分光自動追観測システム PHAST による巨大恒星フレア観測

    甲原潤也, 坪井陽子, 浦部蒼太, 那波咲良, 根本登, 後藤絵美, 金子陽, 猶木皓太, 河合広樹, 岩切渉, 他 MAXI チーム

    日本天文学会2023年春季年会  2023.3 

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  • M29a おひつじ座 UX 星で起こった巨大フレアのせいめい及び MAXI による同時観測

    那波咲良, 坪井陽子, 岩切渉, 浦部蒼太, 根本登, 甲原潤也, 前原裕之, 行方宏介, 野津湧太, 他 MAXI チーム

    日本天文学会2022年秋季年会  2022.9 

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    Event date: 2022.9    

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  • 恒星フレア自動観測のための中央大学 40cm 可視光望遠鏡

    甲原潤也, 坪井陽子, 岩切渉, 河合広樹, 浦部蒼太, 那波咲良, 根本登

    日本天文学会2022年春季年会  2022.3 

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    Event date: 2022.3    

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  • 湾曲 Si 結晶を用いたブラッグ反射型偏光計の分光性能評価 (2)

    井上諒大, 坪井陽子, 岩切渉, 中島七海, 前田良知

    日本天文学会2022年春季年会  2022.3 

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  • 多波長同時観測で迫るおひつじ座UX星で生じた巨大フレアの特徴 (2)

    北古賀智紀, 坪井陽子, 岩切渉, 河合広樹, 佐々木亮, 米倉覚則, 岳藤一宏, 新沼浩太郎, 元木業人, 藤 沢健太, 青木貴弘, 下条圭美, 梅本智文

    日本天文学会2022年春季年会  2022.3 

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  • 巨大フレア同時観測で得た軟X線とHα線のフレア減衰時間の相関

    河合広樹, 坪井陽子, 岩切渉, 佐々木亮, 前田良知, 菅原泰晴, AXA, ISAS, 勝田哲, 他 MAXI チーム

    日本天文学会2021年秋季年会  2021.9 

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  • TESSで観測したけんびきょう座AT星のフレア検出方法およびフレア発生頻度分布について

    岡本豊, 坪井陽子, 岩切渉, 佐々木亮, 河合広樹, 行方宏介, 野津湧太, 河合 誠之, 河原創, 他 MAXI チーム

    日本天文学会2021年秋季年会  2021.9 

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  • X-Rays from Class 0/I Protostars

    Y.Tsuboi

    Abstract of the Star Formation at High Angular Resolution, International Astronomical Union. Symposium no.221/IAU  2003.7 

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  • Chandra/ACIS Observations of the 30 Doradus Star-Forming Complex

    L.Townsley

    Abstract of the American Physical Society, April Meeting  2002.4 

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  • XMM-Newton EPIC Observations of OMC-2/3 region

    Y.Tsuboi, E.D.Feigelson, K.Koyama, M.Tsujimoto, J.Bally, B.Reipurth

    Bulletin of the American Astronomical Society  2001.12 

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  • Magnetic flaring in the young Sun and implications for solar nebula solids

    E.Feigelson, G.Garmire, Y.Tsuboi, S.Pravdp

    Abstract of the Two Years of Science with Chandra/CXC  2001.9 

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  • X-rays from the Brown Dwarf BD TWA-5B

    Y.Tsuboi, G.Chartas, E.Feigelson, G.Garmire, Y.Maeda, K.Mori, L.Townsley

    Abstract of the Two Years of Science with Chandra/CXC  2001.9 

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  • X-rays From A Protostellar Outflow: HH 2

    Pravdo.S, other

    Bulletin of the American Astronomical Society  2001.5 

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  • Chandra/ACIS Observations of Protostars

    Tsuboi.Y

    Bulletin of the American Astronomical Society  2000.12 

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  • Chandra/ACIS Spectra of the 30 Doradus Star Forming Region

    Townsley.L, others

    Bulletin of the American Astronomical Society  2000.12 

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  • Chandra衛星によるRhoOph星形成領域のX線観測

    今西健介, 濱口健二, 小山勝二, 坪井陽子

    2000年度秋季天文学会予稿集,日本天文学会  2000.10 

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  • Discovery of Hard X-rays from Class 0 candidates in the Orion Molecular Cloud 2/3 region with Chandra

    Tsuboi.Y

    Bulletin of the American Astronomical Society  2000.10 

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  • Some Data Analysis Technique for Chandra ACIS

    Feigelson, E.D, o

    Bulletin of the American Astronomical Society  2000.10 

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  • Chandra Deep Observation of the rho Ophiuchi Dark Cloud

    Tsuboi.Y, Hamaguchi.K, Imanishi.K, Koyama.K

    Bulletin of the American Astronomical Society  2000.10 

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  • X-ray Emitting Class 0 Sources の近赤外詳細観測

    辻本匡弘

    2001年度春季天文学会予稿集,日本天文学会  2000.10 

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  • Chandra衛星によるRhoOph星形成領域のX線観測II-X線フレアの詳細解析

    今西健介, 小山勝二, 坪井陽子

    2001年度春季天文学会予稿集,日本天文学会  2000.10 

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  • X-ray spectral study of the most massive HII region NGC3603

    Y.Tsuboi, Y.Maeda

    Abstract of the High-mass Star Formation: An Origin in Clusters?/Arcetri Observastory  2000.5 

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  • X-ray emission from high-mass pre-main-sequence stars

    K.Hamaguchi, H.Terada, A.Bamba, Y.Tsuboi, K.Koyama

    Abstract of the High-mass Star Formation: An Origin in Clusters?/Arcetri Observastory  2000.5 

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  • チャンドラ衛星によるOMC 2-3領域のX線観測

    Y.Tsuboi, ABC

    2000年度春季天文学会予稿集,日本天文学会  2000.4 

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  • オリオン ネビュラ クラスターのチャンドラX線観

    Y.Tsuboi, ABC

    2000年度春季天文学会予稿集,日本天文学会  2000.4 

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  • Chandra ACIS observation of the Orion Nebula Cluster

    Feigelson, E.D, o

    Bulletin of the American Astronomical Society  1999.12 

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  • Chandra/ACIS Observations of 30 Doradus

    Townsley, L

    Bulletin of the American Astronomical Society  1999.12 

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  • X-ray activities in a Young Open Cluster: Chandra Observations of NGC2516

    Tsuboi.Y, Feigelson, E.D, Maeda.Y

    Bulletin of the American Astronomical Society  1999.12 

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  • X-Ray Study of the Bright W-R Star HD 93162 with Chandra

    Maeda.Y, Tsuboi.Y

    Bulletin of the American Astronomical Society  1999.12 

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  • ASCA Spectra of the Central Star of the Orion Nebula: a Magnetic O Star

    Gagne, M

    Bulletin of the American Astronomical Society  1999.4 

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  • X-ray Spectral Variability of Eta Carinae

    Corcoran, M.F

    Bulletin of the American Astronomical Society  1997.12 

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  • rho-Oph分子雲のX線描像

    坪井陽子

    LMSA Science Workshop『LMSA計画と高エネルギー天文学』収録,野辺山電波観測所  1997.9 

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  • 衛星搭載用X線CCDの評価システムの開発

    前田良知

    1997年春季物理学会予稿集,日本物理学会  1997.3 

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  • 原始星からのX線~rho Oph分子雲~

    坪井陽子, 鎌田祐一, 小山勝二, 関本裕太郎

    ラインX線・ガンマ線による天体物理(V)収録,宇宙科学研究所  1997.1 

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  • CCD Cal装置の開発装置(I)

    前田良知

    ラインX線・ガンマ線による天体物理(V)収録,宇宙科学研究所  1997.1 

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  • 原始星のX線と双極分子流構造

    坪井陽子, 小山勝二, 鎌田祐一, 関本裕太郎

    重点領域高エネルギー天体”葉山研究会収録,宇宙線研究所  1996.12 

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  • 前主系列星巨大フレアのプラズマ診断~V773 TauのX線フレア~

    坪井陽子, 上野史郎, 小山勝二

    1996年度秋季天文学会予稿集,日本天文学会  1996.10 

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  • ASCAによる星生成領域の観測

    坪井陽子

    1996年科学衛星・宇宙観測シンポジウム収録,宇宙科学研究所  1996.7 

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  • V773 TauからのX線フレア観測

    坪井陽子, 上野史郎, 小山勝二

    1996年度日本天文学会春季年会予稿集,日本天文学会  1996.3 

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  • 星生成領域からのX線放射~V773 Tauからの巨大X線フレア観測~

    坪井陽子, 上野史郎, 小山勝二

    ラインX線・ガンマ線による天体物理(IV)収録,宇宙科学研究所  1995.11 

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  • 硬X線による星生成領域の観測

    坪井陽子, 小山勝二

    1995年日本天文学会秋季年会予稿集,日本天文学会  1995.10 

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  • X線で探る恒星の生成過程~Herbig Ae/Be starの観測~

    坪井陽子, 小山勝二, 冨田和学

    重点領域研究「星間物質とその進化」大研究会収録,宇宙科学研究所  1995.8 

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  • Spatial and Spectral structure of eta Car

    坪井陽子, 小山勝二

    1995年度日本天文学会春季年会予稿集,日本天文学会  1995.3 

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  • Carina Nebulaに拡がるX線起源の考察

    坪井陽子

    原始惑星系円盤ワークショップ収録,国立天文台  1995.3 

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  • eta Carの空間及びスペクトル構造

    坪井陽子, 小山勝二

    太陽および恒星の超高温、高エネルギー現象研究会収録,国立天文台  1995.2 

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  • X線放射と原始星の進化2;大質量星

    坪井陽子

    重点領域研究「星間物質とその進化」大研究会収録,宇宙科学研究所  1994.12 

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  • eta Carの空間及びスペクトル構造

    坪井陽子, 小山勝二

    ラインX線・ガンマ線による天体物理(III)収録,宇宙科学研究所  1994.11 

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Works

  • 硬X線撮像分光による原始星の構造と進化の研究

    2005 - 2006

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  • 硬X線撮像分光による原始星の高空間分解能探査

    2003 - 2005

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Research Projects

  • 大型国際X線天文衛星計画Athenaの科学成果最大化

    2020.4 - 2022.3

    文部科学省  科学研究費補助金(日本学術振興会・文部科学省)-基盤研究(B) 

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    Grant type:Competitive

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  • 分光・偏光・撮像の3大観測能力を高いレベルで備えた新しいX線望遠鏡の開発

    2019.4 - 2021.3

    文部科学省  科学研究費補助金(日本学術振興会・文部科学省)-基盤研究(B) 

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    Grant type:Competitive

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  • 恒星ハイパーフレアの発生環境の解明

    2017.4 - 2020.3

    文部科学省  科学研究費補助金(日本学術振興会・文部科学省)-基盤研究(C) 

    坪井陽子

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    Grant type:Competitive

    近年、太陽フレアのさらに10-10000 倍ものエネルギーを放出するフレア(スーパーフレアと呼ばれる)が恒星の可視光観測で発見されている(例えば Maehara et al. 2012 Nature など)。このスーパーフレアが太陽でもし起これば、地球規模の大停電やオゾン層破壊など、我々の社会に多大な打撃が加わると考えられている。本研究では、発生頻度の少ない巨大フレアをキャッチする能力の高い全天X 線監視装置MAXI を用いて、(1)全天方向に対してスーパーフレアサーチをX 線帯域で行い、(2)星の若さや生成環境と、スーパーフレアの頻度との関係を明らかにする。また(3)フレアループの幾何、位置に新たな情報を与える偏光に高い感度を持つ光学系の開発を行う。

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  • 科学衛星観測データベースの宇宙科学教育への活用

    2007.4 - 2009.3

    文部科学省  科学研究費補助金(日本学術振興会・文部科学省)-基盤研究(B) 

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    Grant type:Competitive

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  • 硬X線撮像分光による原始星の高空間分解能探査

    2003.4 - 2005.3

    文部科学省  科学研究費補助金(若手研究B) 

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    Grant type:Competitive

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Intellectual property rights

  • X線分光偏光計

    飯塚 亮

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    Application no:特願2016-048851  Date applied:2016.3.11

    Announcement no:特開2017-161480  Date announced:2017.9.14

    Registration no:特許第6650301号  Date registered:2020.1.22 

    Applicant (Organization):学校法人中央大学、国立研究開発法人宇宙航空研究開発機構

  • 湾曲結晶の製造方法および湾曲結晶

    飯塚 亮

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    Application no:特願2012-147355  Date applied:2012.6.29

    Announcement no:特開2014-009131  Date announced:2014.1.20

    Applicant (Organization):学校法人中央大学

Committee Memberships

  • 2003 - 2005

    日本天文学会   天文教育委員会