The puzzling case of 56 Pegasi: A fast rotator seen nearly face-on?

Abstract

A spectroscopic orbit has been recently found by R. Griffin for the long known barium star 56 Peg, which is also a strong X-ray source. This short-period, low mass-function orbit raises several questions regarding the history of the system. In the present paper, we show that it is not easy to find an evolutionary history for 56 Peg which is consistent with the current component's masses, unless one assumes that the giant is a relatively fast rotator (a few times 10 km/s). The hypothesis of fast rotation allows us to explain some other peculiarities of this object as well.