Searching for Black Hole Candidates by LAMOST and ASAS-SN

TL;DR

This study searches for black hole candidates by analyzing LAMOST spectra and ASAS-SN photometry, focusing on binary systems with giant stars and long orbital periods to estimate the mass of unseen companions.

Contribution

It introduces a method combining spectroscopic radial velocity data with photometric periods to identify potential black hole candidates in binary systems.

Findings

Identified 9 binary systems with giant stars and long periods.

Provided lower limits on the masses of unseen companions, suggesting possible black holes.

Demonstrated the effectiveness of combining LAMOST and ASAS-SN data for black hole searches.

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 ($\Delta V_{\rm R} > 70~{\rm km~s^{-1}}$) and periods known from light curves. We focus on the 9 sources with long periods ($T_{\rm ph} > 5$ days) and evaluate the mass $M_2$ of the optically invisible companion. Since the observed $\Delta V_{\rm R}$ 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 $\Delta V_{\rm R}$ from LAMOST and $T_{\rm ph}$ from ASAS-SN, particularly by the ongoing LAMOST Medium Resolution Survey.