Searching for Black Hole Candidates by LAMOST and ASAS-SN

Abstract

Most dynamically confirmed stellar-mass black holes and the candidates were originally selected from X-ray outbursts. In the present work, we search for black hole candidates in the LAMOST survey by using the spectra along with photometry from the ASAS-SN survey, where the orbital period of the binary may be revealed by the periodic light curve, such as the ellipsoidal modulation type. Our sample consists of 9 binaries, where each source contains a giant star with large radial velocity variation ($\hat{I}”V_{\mathrm{R}}>70\mathrm{km}{\mathrm{s}}^{-1}$) and periods known from light curves. We focus on the 9 sources with long periods ($T_{\mathrm{ph}}>5$ days) and evaluate the mass $M_2$ of the optically invisible companion. Since the observed $\hat{I}”V_{\mathrm{R}}$ from only a few repeating spectroscopic observations is a lower limit of the real amplitude, the real mass $M_2$ can be significantly higher than the current evaluation. It is likely an efficient method to place constraints on $M_2$ by combining $\hat{I}”V_{\mathrm{R}}$ from LAMOST and $T_{\mathrm{ph}}$ from ASAS-SN, particularly by the ongoing LAMOST Medium Resolution Survey.

12 pages, 3 figures, accepted for publication in Astronomical Journal