  BG Gem is an eclipsing binary with a 91.6-day orbital period. The more
massive primary component does not seem to show absorption lines in the
spectrum, while the less massive secondary is thought to be a K-type star,
possibly a supergiant. These results were obtained with optical low-resolution
spectroscopy and photometry. The primary was suggested to be a black hole,
although with a low confidence. We present a high-resolution optical spectrum
of the system along with new BVR-photometry. Analysis of the spectrum shows
that the K-type star rotates rapidly at v sin i = 18 km/s compared to most
evolved stars of this temperature range. We also discuss constraints on the
secondary's luminosity using spectroscopic criteria and on the entire system
parameters using both the spectrum and photometry.
