Han Zhanwen | Searcharxiv

arXiv2022

Detection of 2460 SB2 candidates in the LAMOST-MRS, using projected rotational velocities and a binary spectral model

We present a new method for the detection of double-lined spectroscopic binaries (SB2) using $v\sin{i}$ values from spectral fits. The method is tested on synthetic and real spectra from LAMOST-MRS. It can reliably detect SB2 candidates for double-lined binaries with $v\sin{i}_1+v\sin{i}_2<300\,km\,s^{-1}$ if the radial velocity separation is large enough. Using this method, we detect 2460 SB2 candidates, 1410 of which are new discoveries. We confirm the correlation between the radial velocity separation estimated by the binary model and $v\sin{i}_0$ estimated by the single star model using the selected sample. Additionally, our method finds one new SB2 candidate in open cluster M~11.

astro-ph.SR↗

arXiv2017

The Formation of EL CVn-type Binaries

EL CVn-type binaries contain an A-type dwarf star and a very low mass ($\sim 0.2M_\odot$) helium white dwarf precursor (pre-He WD). Recent surveys and observations have discovered dozens of them, and showed that some pre-He WDs have multi-periodic pulsations, opening up the possibility of using asteroseismology to study the interior structure of these stars. We have studied the formation of EL CVn-type binaries to understand the physics of their formation and give the properties and the space density of this population of stars in the Galaxy. We use a simple analysis to show that EL CVn binaries cannot be produced by rapid common envelope evolution because this process leads to merging of the components when a giant has such a low-mass core. We find that EL CVn-type binaries can be produced by long-term stable mass transfer between low-mass stars in close binary systems. We have comprehensively studied this formation channel and the characteristics of the resulting population of EL CVn-type binaries from more than 65,000 runs of binary evolution with primary star masses between 0.9 and $2.0M_\odot$ and assuming composition appropriate for Population I stars. The theoretical evolutionary tracks, mass ratios and the WD mass-period ($M_{\rm WD}-P$) relation are generally in agreement with observations. We conclude that many more EL CVn-type binaries remain to be discovered and that these binaries will be predominantly low-mass systems in old stellar populations.

astro-ph.SR↗