White Dwarf in EM Cygni: Beyond the Veil

摘要

Dwarf novae (DNe) are a class of nonmagnetic cataclysmic variables (CVs) in which a white dwarf (WD) accretes matter from a main-sequence star (the secondary) filling its Roche lobe by means of an accretion disk. DN systems are characterized mainly by their brightness variations, due to a periodic change in the accretion rate. Ongoing accretion at a low rate (quiescence) is interrupted every few weeks to months by intense accretion (outburst) of days to weeks which increases the luminosity of the system (Hack & La Dous 1993; Warner 1995). This outburst is believed to be due to an instability in the disk (the disk instability model (DIM; Cannizzo 1998)), and it is known as a dwarf nova accretion event (or dwarf nova outburst).