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

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 Large sky Area Multi-Object fiber Spectroscopic Telescope (LAMOST) Data Release 6, we obtain a sample of seven giants in binaries with large radial velocity variation ΔVR > 80 km s−1. With the effective temperature, surface gravity, and metallicity provided by LAMOST, and the parallax given by 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.