FS Aurigae: A New Class of Cataclysmic Variables or the Missing Link between Intermediate Polars and SW Sextantis Objects?

Abstract

ABSTRACT FS Aur is a known dwarf nova with an orbital period of about 85.7 minutes. It has been assumed to be a member of the SU UMa subclass of cataclysmic variables, but previous searches for superhumps and superoutbursts have been unsuccessful. We conducted a series of photometric and spectroscopic observations of FS Aur during quiescence. We confirmed its short orbital period from radial velocity measurements. However, the long‐term photometry revealed an unexpected result: the system also shows a distinct 0.24 mag modulation in the BVR photometric bands with a period of 205.5 minutes, which is 2.4 times longer than the orbital period. We discuss various possible causes for such a peculiar behavior.