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 proble...
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.
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 cl...
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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.
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 ...
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.
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...
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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.
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 ind...
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.
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 lo...
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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.
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 ...
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.
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 pro...
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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