FS Aurigae: a Triple Cataclysmic Variable System containing Precessing, Magnetic White Dwarf

AbstractWe present here results of numerical calculations demonstrating that the verylong periodic variability detected in the Cataclysmic Variable FS Aur can be theresult of eccentricity modulation of a close binary (CB) orbit induced by the pres-ence of a third body on a circumbinary orbit. A third component with a substellarmass on a circular, relatively close orbit, modulates the mass transfer rate of thebinary on much longer time scales than periods within the triple system.We also report here preliminary results of X-ray observations of FS Aur, provid-ing further evidence that it contains magnetic and freely precessing white dwarf.These two findings allow us to incorporate the new and previously stressed hy-pothesis on the nature of FS Aur into one consistent model.1. IntroductionFS Aur is a short period Dwarf Nova (DN) renown for the presence of a varietyof uncommon and largely incomprehensible periodic variabilities of brightness andradial velocity. The orbital period (OP) is determined from the radial velocity(RV) variation of the central peak of emission lines, also referred to as S-wave.The widely used method of making RV measurements using the double-gaussianmethod reveals a different picture in the case of FS Aur because the wings of thelines are dominated by a periodicity that is longer than the OP, which we call thelong spectroscopic period (LSP). The light curve (LC) is even more complicated.The most persistent and dominant LC modulation is the so-called long photomet-ric period (LPP). There is, however, a definite relation between OP, LSP & LPP:1/P