Population synthesis of high mass X-ray binaries

By simulating the evolution of spin periods of magnetized neutron stars which interact with their environment in binary systems,we investigate the Galactic population of high mass X-ray binaries（HMXBs） .The number of HMXBs in the Galaxy is between 190 and 240,and their birthrate is from 5.9×10-5 yr-1 to 6.3× 10-5 yr-1.Comparing the Corbet diagram（the positions of the spin periods vs.the orbital periods of HMXBs） in our model with the associated observations,we find that the stellar wind structure and the process of matter transfer are very important for understanding HMXBs.

Case Study on the γ-algorithm: Possible Tests from the Luminosity versus Displacement Correlation of High Mass X-Ray Binaries

Using the apparent correlation of luminosity(L;) versus displacement(R) of high mass X-ray binaries(HMXBs),we aim to constrain the common envelope(CE) mechanism, which is vital in the formation and evolution of compact binaries. We find that under the assumption of the γ-algorithm, the apparent correlation can also be reconstructed generally within a reasonable range of key parameters adopted, though the population of HMXBs is distinct with that in the canonical αCE-formalism. We compare the spatial distribution of HMXBs under the two CE mechanisms, and suggest the difference in L;versus R distribution may provide an additional clue for the study of the CE phase and to discriminate between CE models.

Absolute parameters of young stars:PU Pup

We present combined photometric and spectroscopic analyses of the southern binary star PU Pup.High-resolution spectra of this system were taken at the University of Canterbury Mt.John Observatory in the years 2008 and again in 2014-2015.We find the light contribution of the secondary component to be only 2%of the total light of the system in optical wavelengths,resulting in a single-lined spectroscopic binary.Recent TESS data revealed grazing eclipses within the light minima,though the tidal distortion,examined also from Hipparcos data,remains the predominating light curve effect.Our model shows PU Pup to have the more massive primary relatively close to filling its Roche lobe.PU Pup is thus approaching the rare‘fast phase’of interactive(Case B)evolution.Our adopted absolute parameters are as follows:M_(1)=4.10(±0.20)M_(⊙),M_(2)=0.65(±0.05)M_(⊙),R_(1)=6.60(±0.30)R_(⊙),R_(2)=0.90(±0.10)R_(⊙);T_(1)=11500(±500)K,T_(2)=5000(±350)K;photometric distance=186(±20)pc,age=170(±20)Myr.The less-massive secondary component is found to be significantly oversized and overluminous compared to standard main sequence models.We discuss this discrepancy referring to heating from the reflection effect.

Mira Symbiotic Stars

We have carried out a detailed study of Mira symbiotic stars by means of a population synthesis code. We estimate the number of Mira symbiotic stars in the Galaxy as 1700 - 3100 and the Galactic occurrence rate of Mira symbiotic novae as from -0.9 to 6.0 yr^-1, depending on the model assumptions. The distributions of the orbital periods, the masses of the components, mass-loss rates of cool components, mass-accretion rates of hot components and Mira pulsation periods in Mira symbiotic stars are simulated. By a comparison of the number ratio of Mira symbiotic stars to all symbiotic stars, we find the model with the stellar wind model of Winters et al. to be reasonable.

Binary Star Fractions from the LAMOST DR4

Stellar systems composed of single, double, triple or higher-order systems are rightfully regarded as the fundamental building blocks of the Milky Way. Binary stars play an important role in formation and evolution of the Galaxy. Through comparing the radial velocity variations from multiepoch observations, we analyze the binary fraction of dwarf stars observed with LAMOST. Effects of different model assumptions, such as orbital period distributions on the estimate of binary fractions,are investigated. The results based on log-normal distribution of orbital periods reproduce the previous complete analyses better than the power-law distribution. We find that the binary fraction increases with Teff and decreases with [Fe/H]. We first investigate the relation between α-elements and binary fraction in such a large sample as provided by LAMOST. The old stars with high [α/Fe] dominate with a higher binary fraction than young stars with low [α/Fe]. At the same mass, earlier forming stars possess a higher binary fraction than newly forming ones, which may be related with evolution of the Galaxy.

The Effect of Method of Constructing the Mass Distribution on Single Stellar Populations

We use two methods of constructing the initial mass distribution, the traditional way and Monte Carlo simulation, to obtain integrated U - B, B - V,V-R and V-I colours and absorption-line indices defined by the Lick Observatory image dissector scanner （referred to as Lick/IDS）, for instantaneous burst solarmetallicity single stellar populations with ages in the range 1-15Gyr. We find that the evolutionary curves of all colours obtained by the traditional method are smoother than those by Monte Carlo simulation, that the U- B and B- V colours obtained by the two methods agree with one another, while the V - R and V - I colours by the traditional method are bluer than those by Monte Carlo simulation.A comparison of the Lick/IDS absorption-line indices shows that the variations in all the indices by the traditional method are smoother than that for the Monte Carlo simulation, and that all the indices except for TiO1 and TiO2 are consistent with those for the Monte Carlo simulation.

恒星物理研究与发展

文章介绍了恒星物理的研究现状和发展趋势,包括恒星形成、恒星结构与演化、双星演化与应用、恒星振动、恒星化学丰度、系外行星系统、Ia型超新星与伽马射线暴、星族合成等等,并对国内恒星学科的发展进行了展望。