Unusual State in V Sagittae

Abstract

It has been recently demonstrated that the recurring high/low states in the peculiar binary V Sge can be explained by considering the limit-cycle oscillation involving negative feedback by the wind on the mass-transfer from the secondary star. We noticed, from the recent observations reported to the VSNET (http://www.kusastro.kyoto-u.ac.jp/vsnet/), the presence of a different state of recurring variations (recurrence time ~30 d) showing a gradual rise and a sudden drop in brightness. The observed features of this light variation are unlikely to be reproduced by the limit-cycle oscillation mechanism involving a mass-transfer variation from the secondary star (Hachisu, Kato 2003, astro-ph/0308065). We suggest that the phenomenon originates from an unidentified intrinsic instability in the disk or in the wind of a high luminosity object as in V Sge.

2 pages, 1 figure, to appear in PASJ (special issue on VSNET)