SV Centauri: An Unusual Example of Mass Transfer

We have analysed the recent Irwin–Landolt observations of the eclipsing binary SV Centauri for photometric parameters, by differential corrections. We find that the photometric secondary component (lower temperature star) is the more massive but less luminous star, that the system is an ‘ early-type ’ contact binary, and that the amount of overcontact is large (≃ 0·7). However, the main point of this paper is to argue that the large rate of period change in SV Cen (one of the largest known, in terms of dP/P) is almost certainly due to mass transfer, with the flow from the more to the less massive star. SV Cen thus becomes the second such case known. Mass transfer was given only scant attention in earlier discussions of the period change. We calculate a mass transfer rate of about $$4 \times 10^{-4} M_{\odot}/\text{yr}.,$$ which is approximately 30 times that of β Lyrae. The secondary component is underluminous for its mass, and the primary component overluminous, as expected for stars which are rapidly losing and gaining mass, respectively.