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 whic...
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.
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.
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.
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.
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.
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.
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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