SIMBAD references

We describe new optical photometric and spectroscopic observations of the semidetached eclipsing binary BG Geminorum. A large change in the amount of Mg I absorption at secondary maximum indicates the presence of cool material in the outer edge of the disk surrounding the unseen primary star. Detection of weak He I emission implies a hot radiation source at the inner edge of the disk. If the velocity variations in the Hβ emission-line track the orbital motion of the primary star, the primary star has an orbital semiamplitude of K₁=K_Hβ=16.0±4.6 km.s^–1. This result yields a mass ratio q=0.22±0.07, consistent with the q=0.1 derived from the large ellipsoidal variation. Despite this progress, the nature of the primary star–B type star or black hole–remains uncertain.