Radial velocity curves of alpha Lib A

Here, we report on a bright textbook example of this kind with the nearby A-type star {alpha} Lib A. Although discovered as a spectroscopic binary already in the year 1904, a radial velocity curve has never been published up to a point where the existence of the secondary became even suspicious.

However, in this work, we demonstrate that {alpha} Lib A is indeed a double-lined spectroscopic binary with a rapidly rotating - and hence almost invisible - A-type primary, accompanied and predominated by a more slowly rotating late-A or early F-type secondary in an eccentric P=70.34d orbit. On account of the shallow absorption lines of the primary, uncertainties remain with its semi-amplitude and hence the exact mass ratio.