  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.
