# A Method to Search for Black Hole Candidates with Giant Companions by LAMOST

## TL;DR

This paper introduces a spectroscopic method using LAMOST and Gaia data to identify potential stellar-mass black hole candidates in binary systems with giant companions, focusing on large radial velocity variations.

## Contribution

The study presents a novel approach combining spectroscopic and astrometric data to efficiently find black hole candidates with giant stars, especially in systems with unknown orbital periods.

## Key findings

- Identified seven giant binaries with large radial velocity variations.
- Potential black hole candidates among the selected giants.
- Method suitable for binaries with unknown orbital periods.

## Abstract

We propose a method to search for stellar-mass black hole (BH) candidates with giant companions from spectroscopic observations. Based on the stellar spectra of LAMOST Data Release 6, we obtain a sample of seven giants in binaries with large radial velocity variation $\Delta V_R > 80~{\rm km~s^{-1}}$. With the effective temperature, surface gravity, and metallicity provided by LAMOST, and the parallax given by {\it Gaia}, we can estimate the mass and radius of the giant, and therefore evaluate the possible mass of the optically invisible star in the binary. We show that the sources in our sample are potential BH candidates, and are worthy of dynamical measurement by further spectroscopic observations. Our method may be particularly valid for the selection of BH candidates in binaries with unknown orbital periods.