We describe new optical photometric and spectroscopic observations of the semi-detached 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 H \beta emission line track the orbital motion of the primary star , the primary star has an orbital semiamplitude of K _ { 1 } = K _ { H \beta } = 16.0 \pm 4.6 km s ^ { -1 } .
This result yields a mass ratio , q = 0.22 \pm 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 .