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Abstract: Masses are a fundamental parameter, but they are not well known for most hotsubdwarfs. In general, the mass of a hot subdwarf is derived withasteroseismology or dynamical methods, for which it is often difficult toobtain the necessary data from observations. We intend to find an approach toderiving the masses of hot subdwarfs from observational data in the literature.We presented full evolutionary calculations for hot subdwarfs in a wide massrange 0.33 $M \odot$ to 1.4 $M \odot$ for a Population I metallicity of$Z$=0.02, and obtained a relation between $M { m p}$ and $\log \frac{T { meff}^4}{g}$, where $M { m p}$, $T { m eff}$, and $g$ are the most probablemass, effective temperature, and gravity. This relation is used to study themasses of some observed hot subdwarfs. We proposed a method of determining themasses of hot subdwarfs. Using this method, we studied the masses of hotsubdwarfs from the ESO supernova Ia progenitor survey and Hamburg quasarsurvey. The study shows that most of subdwarf B stars have masses between 0.42and 0.54 $M \odot$, whilst most sdO stars are in the range 0.40 $\sim$ 0.55$M \odot$. Comparing our study to the theoretical mass distributions of Han etal. 2003, we found that sdO stars with mass less than $\sim$ 0.5 $M \odot$may evolve from sdB stars, whilst most high-mass$>$ 0.5 $M \odot$ sdO starsresult from mergers directly.

Author: X. Zhang, X. Chen, Z. Han


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