Polarimetric and photometric variability of Wolf-Rayet （WR） stars as caused by clumps in the winds is revisited. In our model, which is improved from Li et al., radial expansion of the thickness is accounted for, bu...Polarimetric and photometric variability of Wolf-Rayet （WR） stars as caused by clumps in the winds is revisited. In our model, which is improved from Li et al., radial expansion of the thickness is accounted for, but we retain dependence on the β velocity law and stellar occultation effects. We again search for parameters that can yield results consistent with observations in regards to the mean polarization p, the ratio R = σp/σphot of polarimetric to photometric variability and the volume filling factor fV. Clump generation and spatial distribution are randomized by the Monte Carlo method so as to produce clumps which are, in the mean, distributed uniformly in space and have time intervals that obey a Gaussian distribution. The generated clumps move radially outward with a velocity law determined by a β index, and the angular size of clumps is assumed to be fixed. By fitting the observed σp/σphot and the volume filling factor fv, clump velocity taw index β （- 2） and clump ejection rate .N （- 1） are inferred, and are found to be well constrained. In addition, the subpeak features of broad emission lines seem to support the clump ejection rate. Meanwhile, the fraction of total mass loss rate that is contained in clumps is obtained by fitting observed polarization. We conclude that this picture of the clumps＇ properties produces a valuable diagnostic of WR wind structure.展开更多
We have analysed, for the first time, the clustering properties of Wolf-Rayet （W-R） galaxies, using a large sample of 846 W-R galaxies selected from the Data Release 4 （DR4） of the Sloan Digital Sky Survey （SDSS...We have analysed, for the first time, the clustering properties of Wolf-Rayet （W-R） galaxies, using a large sample of 846 W-R galaxies selected from the Data Release 4 （DR4） of the Sloan Digital Sky Survey （SDSS）. We compute the cross-correlation function between W- R galaxies and a reference sample of galaxies drawn from the DR4. We compare the function to the results for control samples of non-W-R star-forming galaxies that are matched closely in redshift, luminosity, concentration, 4000-A break strength and specific star formation rate （SSFR）. On scales larger than a few Mpc, W-R galaxies have almost the same clustering amplitude as the control samples, indicating that W-R galaxies and non-W-R control galaxies populate dark matter haloes of similar masses. On scales between 0.1-1 h^-1 Mpc, W-R galaxies are less clustered than the control samples, and the size of the difference depends on the SSFR. Based on both observational and theoretical considerations, we speculate that this negative bias can be interpreted by W-R galaxies residing preferentially at the centers of their dark matter haloes. We examine the distribution of W-R galaxies more closely using the SDSS galaxy group catalogue of Yang et al., and find that -82% of our W-R galaxies are the central galaxies of groups, compared to -74% for the corresponding control galaxies. We find that W-R galaxies are hosted, on average, by dark matter haloes of masses of 10^12.3M⊙, compared to 10^12.1M⊙ for centrally-located W-R galaxies and 10^12.7M⊙ for satellite ones. We would like to point out that this finding, which provides a direct observational support to our conjecture, is really very crude due to the small number of W-R galaxies and the incompleteness of the group catalogue, and needs more work in future with larger samples.展开更多
We study Luminous Blue Variable(LBV)candidate J004341.84+411112.0 in the Andromeda galaxy.We present optical spectra of the object obtained with the 6 m telescope of BTA SAO RAS.The candidate shows typical LBV feature...We study Luminous Blue Variable(LBV)candidate J004341.84+411112.0 in the Andromeda galaxy.We present optical spectra of the object obtained with the 6 m telescope of BTA SAO RAS.The candidate shows typical LBV features in its spectra:broad and strong hydrogen lines and the He I lines with P Cygni profiles.Its remarkable spectral resemblance to the well known LBV P Cygni suggests a common nature of the objects and supports LBV classification of J004341.84+411112.0.We estimate the temperature,reddening,radius and luminosity of the star using its spectral energy distribution.Obtained bolometric luminosity of the candidate(M_(bol)=-10.41±0.12 mag)is quite similar to those of known LBV stars in the Andromeda galaxy.We analyzed a ten year light curve of the object in R filter.The candidate demonstrates photometric variations of the order of 0.4 mag,with an overall brightness increasing trendΔR>0.1 mag.Therewith,the corresponding color variations of the object are fully consistent with LBV behavior when a star become cooler and brighter in the optical spectral range with a nearly constant bolometric luminosity.LBV-type variability of the object,similarity of its spectrum and estimated luminosity to those of known LBVs allow us to classify J004341.84+411112.0 as an LBV.展开更多
Planetary nebulae are the progenetors of white dwarfs in the final evolution stage of stars with intermediate initial mass ( 1M_⊙【M_*【9M_⊙). The planetary nebulae can be devided into different groups according to ...Planetary nebulae are the progenetors of white dwarfs in the final evolution stage of stars with intermediate initial mass ( 1M_⊙【M_*【9M_⊙). The planetary nebulae can be devided into different groups according to the spectral type of their core stars. One of these groups, in which the spectrum is dominated by the carbon lines of different levels of ionization, is similar to the carbon-rich Wolf-Rayet stars. According to Van der Hucht展开更多
基金the National NaturalScience Foundation of China (grant Nos. 10273002, 10573022 and 10778601 (QL))the NSF Center forMagnetic Self Organization in Laboratory and Astrophysics Plasmas (JPC)UK STFC Rolling Grant(JCB). JPC and RI have been supported in part by award TM3-4001 issued by the Chandra X-rayObservatory Center.
文摘Polarimetric and photometric variability of Wolf-Rayet （WR） stars as caused by clumps in the winds is revisited. In our model, which is improved from Li et al., radial expansion of the thickness is accounted for, but we retain dependence on the β velocity law and stellar occultation effects. We again search for parameters that can yield results consistent with observations in regards to the mean polarization p, the ratio R = σp/σphot of polarimetric to photometric variability and the volume filling factor fV. Clump generation and spatial distribution are randomized by the Monte Carlo method so as to produce clumps which are, in the mean, distributed uniformly in space and have time intervals that obey a Gaussian distribution. The generated clumps move radially outward with a velocity law determined by a β index, and the angular size of clumps is assumed to be fixed. By fitting the observed σp/σphot and the volume filling factor fv, clump velocity taw index β （- 2） and clump ejection rate .N （- 1） are inferred, and are found to be well constrained. In addition, the subpeak features of broad emission lines seem to support the clump ejection rate. Meanwhile, the fraction of total mass loss rate that is contained in clumps is obtained by fitting observed polarization. We conclude that this picture of the clumps＇ properties produces a valuable diagnostic of WR wind structure.
基金the National Natural Science Foundation of China
文摘We have analysed, for the first time, the clustering properties of Wolf-Rayet （W-R） galaxies, using a large sample of 846 W-R galaxies selected from the Data Release 4 （DR4） of the Sloan Digital Sky Survey （SDSS）. We compute the cross-correlation function between W- R galaxies and a reference sample of galaxies drawn from the DR4. We compare the function to the results for control samples of non-W-R star-forming galaxies that are matched closely in redshift, luminosity, concentration, 4000-A break strength and specific star formation rate （SSFR）. On scales larger than a few Mpc, W-R galaxies have almost the same clustering amplitude as the control samples, indicating that W-R galaxies and non-W-R control galaxies populate dark matter haloes of similar masses. On scales between 0.1-1 h^-1 Mpc, W-R galaxies are less clustered than the control samples, and the size of the difference depends on the SSFR. Based on both observational and theoretical considerations, we speculate that this negative bias can be interpreted by W-R galaxies residing preferentially at the centers of their dark matter haloes. We examine the distribution of W-R galaxies more closely using the SDSS galaxy group catalogue of Yang et al., and find that -82% of our W-R galaxies are the central galaxies of groups, compared to -74% for the corresponding control galaxies. We find that W-R galaxies are hosted, on average, by dark matter haloes of masses of 10^12.3M⊙, compared to 10^12.1M⊙ for centrally-located W-R galaxies and 10^12.7M⊙ for satellite ones. We would like to point out that this finding, which provides a direct observational support to our conjecture, is really very crude due to the small number of W-R galaxies and the incompleteness of the group catalogue, and needs more work in future with larger samples.
基金funded by RFBR and NSFB according to the research project N 19-52-18007supported by the Ministry of Science and Higher Education of the Russian Federation (including agreement No05.619.21.0016,project ID RFMEFI61919X0016)support from the DN18-10/2017 grant from the NSF of Bulgaria performed with the equipment purchased from the funds of the Program of Development of Moscow University。
文摘We study Luminous Blue Variable(LBV)candidate J004341.84+411112.0 in the Andromeda galaxy.We present optical spectra of the object obtained with the 6 m telescope of BTA SAO RAS.The candidate shows typical LBV features in its spectra:broad and strong hydrogen lines and the He I lines with P Cygni profiles.Its remarkable spectral resemblance to the well known LBV P Cygni suggests a common nature of the objects and supports LBV classification of J004341.84+411112.0.We estimate the temperature,reddening,radius and luminosity of the star using its spectral energy distribution.Obtained bolometric luminosity of the candidate(M_(bol)=-10.41±0.12 mag)is quite similar to those of known LBV stars in the Andromeda galaxy.We analyzed a ten year light curve of the object in R filter.The candidate demonstrates photometric variations of the order of 0.4 mag,with an overall brightness increasing trendΔR>0.1 mag.Therewith,the corresponding color variations of the object are fully consistent with LBV behavior when a star become cooler and brighter in the optical spectral range with a nearly constant bolometric luminosity.LBV-type variability of the object,similarity of its spectrum and estimated luminosity to those of known LBVs allow us to classify J004341.84+411112.0 as an LBV.
文摘Planetary nebulae are the progenetors of white dwarfs in the final evolution stage of stars with intermediate initial mass ( 1M_⊙【M_*【9M_⊙). The planetary nebulae can be devided into different groups according to the spectral type of their core stars. One of these groups, in which the spectrum is dominated by the carbon lines of different levels of ionization, is similar to the carbon-rich Wolf-Rayet stars. According to Van der Hucht
