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A statistical study of the relation between soft X-ray excess and accretion disk

Science China(Physics,Mechanics & Astronomy) 2010年第S1期53卷 102-105页

作者： LIU JieYing1,2,3 & QIAO ErLin1,2 1 National Astronomical Observatories/Yunnan Observatory,Chinese Academy of Science,Kunming 650011,China 2 Key laboratory for the structure and evolution of celestial objects,Chinese Academy of Sciences,Kunming 650011,China 3 Graduate University of Chinese Academy of Sciences,Beijing 100049,China 1. National Astronomical Observatories/Yunnan Observatory Chinese Academy of Science Kunming 650011 China 2. Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming 650011 China 3. Graduate University of Chinese Academy of Sciences Beijing 100049 China

To study the origin of the soft X-ray excess,we compile a sample of 94 unobscured,radio-quiet QSOs and Seyfert galaxies with available data from GALEX and *** find that 50 sources show strong soft X-ray excess and the other 44 show weak/no soft X-ray *** analyses of the data indicate that the difference in soft X-rays is mainly but not only resulting from different accretion rates(in units of Eddington rate).The statistical study of the sources with soft X-ray excess shows that the strength of soft X-ray excess weakly and positively correlates with the Eddington ratio and increases with the increase of the strength of UV radiations relative to the *** that the UV emissions are from the thin disk,the correlations imply that the origin of soft X-ray excess is associated with the thin disk,either by means of Comptonization of the disk photons or in some other ways.

关键词： accretion:accretion disks ultraviolet:galaxies X-rays:galaxies

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The Helium Star Donor Channel for the Progenitors of Type Ia Supernovae and their Surviving Companion Stars

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AIP Conference Proceedings 2010年第1期1314卷 244-249页

作者： Bo Wang Zhanwen Han aNational Astronomical Observatories/Yunnan Observatory CAS Kunming 650011 China bKey Laboratory for the Structure and Evolution of Celestial Objects CAS Kunming 650011 China

The nature of type Ia supernovae (SNe Ia) is still unclear. Employing Eggleton’s stellar evolution code with the optically thick wind assumption, we systematically studied the He star donor channel of SNe Ia, in which a carbon‐oxygen white dwarf accretes material from a He main‐sequence star or a He subgiant to increase its mass to the Chandrasekhar mass. We mapped out the initial parameters for producing SNe Ia in the orbital period‐secondary mass plane for various WD masses from this channel. According to a detailed binary population synthesis approach, we find that this channel can produce SNe Ia with short delay times (∼100 Myr) implied by recent observations. We obtained many properties of the surviving companions of this channel after SN explosion, which can be verified by future observations. We also find that the surviving companions from the SN explosion scenario have a high spatial velocity (>400 km/s), which could be an alternative origin for hypervelocity stars (HVSs), especially for HVSs such as US 708.

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New Formation Channels of Hot Subdwarf Stars

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AIP Conference Proceedings 2010年第1期1314卷 85-90页

作者： Zhanwen Han Xuefei Chen Zhenxin Lei aNational Astronomical Observatories/Yunnan Observatory the Chinese Academy of Sciences Kunming 650011 China bKey Laboratory for the Structure and Evolution of Celestial Objects the Chinese Academy of Sciences

Hot subdwarf stars, known as extreme horizontal branch stars in globular clusters, are important objects in many aspects, e.g., stellar evolution, distance indicators, Galactic structure, and the long‐standing problem of far‐ultraviolet (far‐UV) excess in early‐type galaxies. In this talk, we review the current formation scenarios for hot subdwarf stars and discuss related problems, and then propose two new formation channels. The first channel is tidally enhanced stellar wind channel, in which a first giant branch (FGB) star experiences an enhanced stellar wind mass loss due to the proximity of its companion star and becomes a hot subdwarf if most of the envelope is lost. Such a channel can produce extreme horizontal branch stars, blue horizontal branch stars and red horizontal branch stars. The second channel is envelope ejection channel, in which a star ejects its envelope near the tip of FGB if the binding energy of the envelope becomes positive, and the remnant star becomes a hot subdwarf. Hot subdwarf stars may form in metal‐rich old stellar populations from the envelope ejection channel and contribute to the far‐UV excess in early‐type galaxies.

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Mass transfer and loss of the massive semi-detached binary AI Crucis

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Research in Astronomy and Astrophysics 2010年第5期10卷 438-444页

作者： Er-Gang Zhao Sheng-Bang Qian E. Femanindez Lajus Carolina von Essen Li-Ying Zhu National Astronomical Observatories / Yunnan Observatory Chinese Academy of SciencesKunming 650011 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy ofSciences Kunming 650011 China Graduate University of Chinese Academy of Sciences Beijing 100049 China Facultad de Ciencias Astron6micas y Geoffsicas Universidad Nacional de La Plata 1900 LaPlata Buenos Aires Argentina

AI Crucis is a short-period semi-detached massive close binary （P = 1.41771d, Sp.=B1.5） in the open cluster NGC 4103. It is a good astrophysical laboratory for investigating the formation and evolution of massive close binary stars via case A mass transfer. Orbital period variations of the system were analyzed based on one newly determined eclipse time and the others compiled from the literature. It is discovered that the orbital period of the binary is continuously increasing at a rate of dP/dt = ＋1.00（±0.04） × 10-7 d yr-1. After the long-term increase is subtracted from the O - C diagram, weak evidence indicates the presence of a cyclic oscillation with a period of 30.1yr, which may reveal a very cool stellar companion in the system. The long-term period increase can be explained by mass transfer from the less massive component to the more massive one. This is in agreement with the semidetached configuration of the binary, indicating that the system is undergoing a slow mass-transfer stage on the nuclear time scale of the secondary. However, it is found that the slow mass transfer is insufficient to cause the observed period increase, which suggests that the stellar wind from the hot component should contribute to the amount of period increase dP/dt = ＋0.54× 10-7 d yr-1 that corresponds to a mass loss rate of M˙1 = 2.72 × 10-7 M yr-1. It is estimated that the hot component lost a total mass of 4.1M during the slow mass-transfer stage and, thus, the evolution of the binary system should be changed greatly by the mass loss.

关键词： stars： binaries： close — stars： binaries： eclipsing — stars： individual （AI Crucis） — stars： early-type — stars： evolution

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structure and evolution of W UMa‐type Systems

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AIP Conference Proceedings 2010年第1期1314卷 37-38页

作者： Lifang Li Fenghui Zhang Zhanwen Han aNational Astronomical Observatories/Yunnan Observatory CAS Kunming 650011 P.R. China bKey Laboratory for the Structure and Evolution of Celestial Objects CAS Kunming 650011 P.R. China

we summarized and discussed our works on the structure and evolution of low‐mass W UMa‐type systems. Our works predict that the convection is by no means essential to the energy transfer in common envelope (CE) and the energy transfer probably occurs in the radiative zone of CE, and that W UMa‐type systems undergo cyclic evolution and would merge into the fast‐rotating single stars owing to Darwin’s instability at last, and during their merging process they would lose a large amount of mass and angular momentum.

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Revision of the photometric parameters of BS Cassiopeiae

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Research in Astronomy and Astrophysics 2010年第6期10卷 569-576页

作者： Jia-Jia He Sheng-Bang Qian Miloslav Zejda Zdenek Mikulasek National Astronomical Observatories / Yunnan Observatory Chinese Academy of Sciences Kunming 650011 China Graduate University of the Chinese Academy of Sciences Beijing 100049 China Key Laboratory for the Structure and Evolution of Celestial Objects National Astronomical Observatories/Yunnan Observatory Chinese Academy of Sciences Kunming 650011 China Institute of Theoretical Physics and Astrophysics Masaryk University Kotlarska 2 611 37 Brno Czech Republic Observatory and Planetarium of J. Palisa VSB- Technical University Ostrava Czech Republic

Seven charge-coupled device （CCD） photometric times of light minimum of the overcontact binary BS Cas which were obtained from 2007 August to November and one CCD light curve in the R band which was observed on 2007 September 24 and October 15, are presented. It is found that the light curve ofBS Cas has characteristics like a typical EW-type light variation. The light curve obtained by us is symmetric and shows total eclipses, which is very useful for determining photometric parameters with high precision. Photometric solutions were derived by using the 2003 version of the Wilson-Devinney code. It shows that BS Cas is a W-subtype overcontact binary （f = 27.5% ± 0.4%） with a mass ratio of q = 2.7188± 0.0040. The temperature difference between the two components is 190 K. Analysis of the 042 curve suggests that the period of AE Phe shows a long-term continuous decrease at a rate of dP/dt = - 2.45 × 10^-7 d yr^- 1 The long-time period decrease can be explained by mass transfer from the primary to the secondary.

关键词： stars binaries close -- stars binaries eclipsing -- stars individual BS Cas

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Properties of Swift‘s intermediate bursts

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AIP Conference Proceedings 2011年第1期1358卷 251-254页

作者： P. Veres A. de Ugarte Postigo I. Horvath Z. Bagoly D. A. Kann C. C. Thöne L. G. Balazs P. D’Avanzo M. A. Aloy S. Foley S. Campana J. Mao P. Jakobsson S. Covino J. P. U. Fynbo J. Gorosabel A. J. Castro‐Tirado M. Nardini L. Amati aDept. of Physics of Complex Systems Eötvös Univ. Pázmány P. s. 1/A 1117 Budapest Hungary bDept. of Physics Bolyai Military University POB 15 1581 Budapest Hungary jYunnan Observatory Chinese Academy of Sciences Kunming Yunnan 650011 China cDark Cosmology Centre Niels Bohr Institute Juliane Maries Vej 30 Copenhage O/ 2100 Denmark dThüringer Landessternwarte Tautenburg Sternwarte 5 D‐07778 Tautenburg Germany eINAF ‐ Osservatorio Astronomico di Brera via E. Bianchi 46 23807 Merate LC Italy fKonkoly Observatory 1525 Budapest POB 67 Hungary gDepartamento de Astronomía y Astrofísica Universidad de Valencia 46100 Burjassot Spain hUCD School of Physics University College Dublin Dublin 4 Ireland iMax‐Planck‐Institut für extraterrestrische Physik 85748 Garching Germany kKey Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Yunnan 650011 China lCentre for Astrophysics and Cosmology Science Institute University of Iceland Dunhagi 5 107 Reykjavik Iceland mDark Cosmology Centre Niels Bohr Institute University of Copenhagen Juliane Maries Vej 30 2100 Copenhagen O/ Denmark nInstituto de Astrofísica de Andalucía (IAA‐CSIC) 18008 Granada Spain oINAF ‐ IASF Bologna via P. Gobetti 101 40129 Bologna Italy

Based on their prompt, high‐energy emission, gamma‐ray bursts are usually classified into short‐duration and long‐duration classes. A third intermediate group has been identified on statistical grounds but its individual properties have not yet been studied in detail. Using the large sample of follow‐up observations of GRBs produced during the Swift era we analyze the individual characteristics of this group. We find that intermediate bursts are significantly different from short GRBs but share many properties with long bursts, probably pointing to a common progenitor type. However, we find that intermediate bursts are significantly dimmer and have on average lower redshifts.

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Multi-epoch X-ray observations of the narrow-line Seyfert 1 galaxy SDSS J160508.87+323921.4 with XMM-Newton

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Science China(Physics,Mechanics & Astronomy) 2010年第S1期53卷 207-211页

作者： AI YanLi1,2,3,YUAN WeiMin1,2,ZHOU HongYan4,5 & WANG JianGuo1,2,3 1 National Astronomical Observatories/Yunnan Observatory,Chinese Academy of Sciences,Kunming 650011,China 2 Key laboratory for the structure and evolution of celestial objects,Chinese Academy of Sciences,Kunming 650011,China 3 Graduate University of the Chinese Academy of Sciences,Beijing 100049,China 4 Center for Astrophysics,University of Science and Technology of China,Hefei 230026,China 5 Joint Institute of Galaxies and Cosmology,SHAO and USTC,Shanghai 200030,China 1. National Astronomical Observatories/Yunnan Observatory Chinese Academy of Sciences Kunming 650011 China 2. Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming 650011 China 3. Graduate University of the Chinese Academy of Sciences Beijing 100049 China 4. Center for Astrophysics University of Science and Technology of China Hefei 230026 China 5. Joint Institute of Galaxies and Cosmology SHAO and USTC Shanghai 200030 China

We present results of multi-epoch XMM-Newton observations separated by several years of the narrow-line Seyfert 1(NLS1) galaxy,SDSS J160508.87+*** NLS1 showed X-ray flux variations on timescales of years as well as low amplitude variations on timescales as short as hours,while the X-ray spectral shape remained essentially *** spectrum shows a significant soft X-ray *** model of reflection from an ionized disc,that is dominant in the whole XMM-Newton bandpass,provides the best description of the observed spectra for all the observations,though alternatives such as Compton scattering(T-0.25 keV) cannot be ruled out in a statistical *** the disc reflection model,the observed variations may originate either from the change in the reflection fraction,or from the variability of the intrinsic X-ray luminosity.

关键词： galaxies:active Seyfert X-rays individual

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Stellar Adiabatic Mass Loss in Binary Stars

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AIP Conference Proceedings 2010年第1期1314卷 53-54页

作者： Hongwei Ge Ronald F. Webbink Xuefei Chen Zhanwen Han aNational Astronomical Observatories/Yunnan Observatory CAS Kunming 650011 P.R. China bKey Laboratory for the Structure and Evolution of Celestial Objects CAS Kunming 650011 P.R. China cDepartment of Astronomy University of Illinois 1002 W. Green St. Urbana IL 61801 USA

Stellar adiabatic mass loss model show us the approximate responses of the donor stars suffering rapid mass loss. According to the radius response and the change of total energy during adiabatic mass loss, we present our results on the criteria of dynamical mass transfer instability and the limits on common envelope evolution.

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Properties of Swift’s intermediate bursts

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AIP Conference Proceedings 2010年第1期1279卷 283-286页

作者： A. de Ugarte Postigo I. Horváth P. Veres Z. Bagoly D. A. Kann C. C. Thöne L. G. Balazs P. D’Avanzo M. A. Aloy S. Foley S. Campana J. Mao P. Jakobsson S. Covino J. P. U. Fynbo J. Gorosabel A. J. Castro‐Tirado L. Amati M. Nardini aINAF‐Osservatorio Astronomico di Brera via E. Bianchi 46 23807 Merate LC Italy bEuropean Southern Observatory Casilla 19001 Santiago 19 Chile jYunnan Observatory Chinese Academy of Sciences Kunming Yunnan 650011 China cDept. of Physics Bolyai Military University POB 15 1581 Budapest Hungary dDept. of Physics of Complex Systems Eötvös Univ. Pázmány P. s. 1/A 1117 Budapest Hungary eThüringer Landessternwarte Tautenburg Sternwarte 5 D‐07778 Tautenburg Germany fKonkoly Observatory 1525 Budapest POB 67 Hungary gDepartamento de Astronomía y Astrofísica Universidad de Valencia 46100 Burjassot Spain hUCD School of Physics University College Dublin Dublin 4 Ireland iMax‐Planck‐Institut für extraterrestrische Physik 85748 Garching Germany kKey Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Yunnan 650011 China lCentre for Astrophysics and Cosmology Science Institute University of Iceland Dunhagi 5 107 Reykjavik Iceland mDark Cosmology Centre Niels Bohr Institute University of Copenhagen Juliane Maries Vej 30 2100 Copenhagen O/ Denmark nInstituto de Astrofísica de Andalucía (IAA‐CSIC) 18008 Granada Spain oINAF‐IASF Bologna via P. Gobetti 101 40129 Bologna Italy

Gamma‐ray bursts are usually classified through their high‐energy emission into short‐duration and long‐duration bursts. A third intermediate group has been identified on statistical grounds but its individual properties have not yet been studied in detail. Using the large sample of follow‐up observations of GRBs produced during the Swift era we analyze the individual characteristics of this group. We find that intermediate bursts are significantly different from short GRBs but share many properties with long bursts, probably pointing to a common progenitor type. However, we find that intermediate bursts are significantly dimmer and have on average lower redshifts.

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