The eclipsing binary BG Geminorum: Improved constraints on the orbit and the structure of the accretion disk

摘要

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 Hbeta emission-line track the orbital motion of the primary star, the primary star has, an orbital semiamplitude of K-1 = KHbeta = 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. References: 28