記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：American Astronomical Society  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：American Astronomical Society  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：American Astronomical Society  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：American Astronomical Society  

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：American Astronomical Society  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：American Astronomical Society  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：American Astronomical Society  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：American Astronomical Society  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：American Astronomical Society  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：American Astronomical Society  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：American Astronomical Society  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：American Astronomical Society  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Nature Publishing Group  

DOI： 10.1038/nature24301

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：American Astronomical Society  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：American Astronomical Society  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Czech Technical University in Prague  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Nature Publishing Group  

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：日本語   掲載種別：研究論文（学術雑誌）  

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記述言語：日本語   掲載種別：研究論文（学術雑誌）  

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記述言語：日本語   掲載種別：研究論文（学術雑誌）  

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記述言語：日本語   掲載種別：研究論文（学術雑誌）  

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記述言語：日本語   掲載種別：研究論文（学術雑誌）  

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記述言語：日本語   掲載種別：研究論文（学術雑誌）  

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記述言語：日本語   掲載種別：研究論文（学術雑誌）  

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記述言語：日本語   掲載種別：研究論文（学術雑誌）  

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記述言語：日本語   掲載種別：研究論文（学術雑誌）  

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記述言語：日本語   掲載種別：研究論文（学術雑誌）  

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記述言語：日本語   掲載種別：研究論文（学術雑誌）  

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記述言語：日本語   掲載種別：研究論文（学術雑誌）  

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記述言語：日本語   掲載種別：研究論文（学術雑誌）  

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記述言語：日本語   掲載種別：研究論文（学術雑誌）  

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記述言語：日本語   掲載種別：研究論文（学術雑誌）  

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記述言語：日本語   掲載種別：研究論文（学術雑誌）  

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記述言語：日本語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   出版者・発行元：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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記述言語：英語   出版者・発行元：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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記述言語：英語   出版者・発行元：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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記述言語：英語   出版者・発行元：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

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記述言語：英語   出版者・発行元：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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記述言語：英語   出版者・発行元：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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記述言語：英語   出版者・発行元：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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記述言語：英語   出版者・発行元：ASP Conference Series  

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記述言語：英語   出版者・発行元：ASP Conference Series  

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DOI： 10.1086/375017

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DOI： 10.1086/375017

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DOI： 10.1086/375017

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DOI： 10.1086/375017

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記述言語：英語   出版者・発行元：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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記述言語：英語   掲載種別：書評論文，書評，文献紹介等   出版者・発行元：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

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記述言語：英語   掲載種別：書評論文，書評，文献紹介等   出版者・発行元：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

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記述言語：英語   掲載種別：書評論文，書評，文献紹介等   出版者・発行元：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

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記述言語：英語   掲載種別：書評論文，書評，文献紹介等   出版者・発行元：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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記述言語：英語   出版者・発行元：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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記述言語：英語   出版者・発行元：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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記述言語：英語   出版者・発行元：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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記述言語：日本語   掲載種別：記事・総説・解説・論説等（その他）   出版者・発行元：日本経済新聞社  

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記述言語：日本語   掲載種別：記事・総説・解説・論説等（その他）   出版者・発行元：日本天文学会  

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記述言語：英語   出版者・発行元：ARI  

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記述言語：英語   出版者・発行元：UNIV CHICAGO PRESS  

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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記述言語：英語   出版者・発行元：UNIV CHICAGO PRESS  

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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記述言語：英語   出版者・発行元：ARI  

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記述言語：英語   出版者・発行元：Astronomical Society of the Pacific  

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記述言語：英語   出版者・発行元：MACMILLAN PUBLISHERS LTD  

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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記述言語：英語   出版者・発行元：MACMILLAN PUBLISHERS LTD  

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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記述言語：英語   出版者・発行元：Astronomical Society of the Pacific  

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記述言語：英語   出版者・発行元：Astronomical Society of the Pacific  

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記述言語：英語   出版者・発行元：UNIV CHICAGO PRESS  

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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記述言語：英語   出版者・発行元：UNIV CHICAGO PRESS  

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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記述言語：英語   出版者・発行元：Astronomical Society of the Pacific  

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記述言語：英語   出版者・発行元：Astronomical Society of the Pacific  

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記述言語：英語   出版者・発行元：UNIV CHICAGO PRESS  

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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記述言語：英語   出版者・発行元：UNIV CHICAGO PRESS  

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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記述言語：日本語   掲載種別：記事・総説・解説・論説等（その他）   出版者・発行元：日本天文学会  

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記述言語：英語   出版者・発行元：IOP PUBLISHING LTD  

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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記述言語：英語   出版者・発行元：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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記述言語：英語   出版者・発行元：IOP PUBLISHING LTD  

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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記述言語：英語   出版者・発行元：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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記述言語：英語   掲載種別：記事・総説・解説・論説等（その他）   出版者・発行元：Central Bureau for Astronomical telegrams  

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記述言語：英語   掲載種別：記事・総説・解説・論説等（その他）   出版者・発行元：Central Bureau for Astronomical telegrams  

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記述言語：英語   出版者・発行元：野辺山電波観測所  

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記述言語：英語   出版者・発行元：MAX-Planck 研究所  

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記述言語：英語   出版者・発行元：Max-Planck 研究所  

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記述言語：英語   出版者・発行元：野辺山電波観測所  

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記述言語：英語   出版者・発行元：野辺山電波観測所  

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記述言語：英語   出版者・発行元：MAX-Planck 研究所  

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記述言語：英語   出版者・発行元：Max-Planck 研究所  

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記述言語：英語   出版者・発行元：野辺山電波観測所  

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記述言語：英語   出版者・発行元：Wiley-VCH Verlag  

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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記述言語：英語   出版者・発行元：WILEY-V C H VERLAG GMBH  

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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記述言語：英語   出版者・発行元：IOP PUBLISHING LTD  

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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記述言語：英語   出版者・発行元：IOP PUBLISHING LTD  

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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記述言語：英語   出版者・発行元：The Astronomical Society of the Pacific  

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記述言語：英語   出版者・発行元：The Astronomical Society of the Pacific  

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記述言語：英語   出版者・発行元：IOP PUBLISHING LTD  

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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記述言語：英語   出版者・発行元：IOP PUBLISHING LTD  

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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記述言語：英語   出版者・発行元：KLUWER ACADEMIC PUBL  

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記述言語：英語   出版者・発行元：KLUWER ACADEMIC PUBL  

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記述言語：英語   出版者・発行元：KLUWER ACADEMIC PUBL  

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記述言語：英語   出版者・発行元：KLUWER ACADEMIC PUBL  

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記述言語：英語   出版者・発行元：イタリア天文学会  

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記述言語：英語   出版者・発行元：イタリア天文学会  

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記述言語：英語   出版者・発行元：イタリア天文学会  

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記述言語：英語   出版者・発行元：イタリア天文学会  

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記述言語：英語   出版者・発行元：OXFORD UNIV PRESS  

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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記述言語：英語   出版者・発行元：OXFORD UNIV PRESS  

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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記述言語：英語   出版者・発行元：Universal Academy 出版社  

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記述言語：英語   出版者・発行元：Universal Academy 出版社  

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記述言語：英語   出版者・発行元：OXFORD UNIV PRESS  

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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記述言語：英語   出版者・発行元：OXFORD UNIV PRESS  

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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記述言語：日本語   掲載種別：記事・総説・解説・論説等（その他）   出版者・発行元：日本天文学会  

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記述言語：英語   出版者・発行元：AIP PRESS  

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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記述言語：英語   出版者・発行元：AIP PRESS  

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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記述言語：英語   出版者・発行元：Universal Academy 出版社  

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記述言語：英語   出版者・発行元：Kluwer Academic 出版社  

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記述言語：英語   出版者・発行元：Universal Academy 出版社  

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記述言語：英語   出版者・発行元：Universal Academy 出版社  

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記述言語：英語   出版者・発行元：Universal Academy 出版社  

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記述言語：英語   出版者・発行元：KLUWER ACADEMIC PUBL  

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記述言語：英語   出版者・発行元：KLUWER ACADEMIC PUBL  

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記述言語：英語   出版者・発行元：KLUWER ACADEMIC PUBL  

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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記述言語：英語   出版者・発行元：KLUWER ACADEMIC PUBL  

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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記述言語：英語   出版者・発行元：Universal Academy Press  

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記述言語：英語   出版者・発行元：Universal Academy Press  

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記述言語：日本語   会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

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記述言語：日本語   会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

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記述言語：英語   会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

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記述言語：英語   会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

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記述言語：英語   会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

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記述言語：英語   会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

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記述言語：英語   会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

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記述言語：英語   会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

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記述言語：英語   会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

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記述言語：英語   会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

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記述言語：日本語   会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

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記述言語：英語   会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

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記述言語：英語   会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

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記述言語：英語   会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

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記述言語：日本語   会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

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記述言語：日本語   会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

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記述言語：英語   会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

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記述言語：英語   会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

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記述言語：日本語   会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

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記述言語：日本語   会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

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記述言語：英語   会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

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記述言語：英語   会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

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記述言語：英語   会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

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記述言語：英語   会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

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記述言語：英語   会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

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記述言語：英語   会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

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記述言語：日本語   会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

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記述言語：日本語   会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

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記述言語：日本語   会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

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記述言語：日本語   会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

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記述言語：日本語   会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

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記述言語：日本語   会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

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記述言語：日本語   会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

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記述言語：日本語   会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

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記述言語：日本語   会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

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記述言語：日本語   会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

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記述言語：日本語   会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

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記述言語：日本語   会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

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記述言語：日本語   会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

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記述言語：日本語   会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

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記述言語：日本語   会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

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