Discovery of 15-second oscillations in HST observations of W Sge following the 2001 outburst

摘要

WZ Sge is one of the most extreme CVs known: it has a very short orbital period (82 min), a very low mass ratio (q = 0.05), is one of the faintest CVs (Mv similar or equal to 11.5) and has a 7-8 outburst amplitude recurring on a time scale of roughly 33 yr. Because of its extreme behaviour and characteristics, it is thought that WZ Sge is a highly evolved CV whose secondary is probably a brown dwarf-like object. WZ Sge went into outburst on 2001 July 23, around 10 yr earlier than anticipated. We obtained HST/STIS far-UV spectroscopic observations to cover the immediate aftermath of the outburst. Fig. 1 (left) illustrates the timing of the three observing epochs, each consisting of 4 HST orbits.