Gaghik H. Tovmassian

Evidence of Precession of the White Dwarf in Cataclysmic Variables

Cataclysmic variables (CVs) are close binary systems in which the primary, the more massive star, is a white dwarf. CVs usually exhibit a number of periodicities, most of which are now understood. However, recently a new phenomenon was discovered that does not fit the standard picture. Two objects have been found to show periods that are much longer than orbital and have no relation to it, either in light curves or in radial velocity variations measured from spectroscopy. Here we show that the precession of a fast-rotating magnetically accreting white dwarf can successfully explain these phenomena. The theory of compact objects predicts certain relations between the spin and precession periods, and our finding provides a good test for the theory and establishes a qualitative model to be explored both theoretically and observationally. Detection of precession can become a powerful tool in searching for the internal properties of compact stars, which would be otherwise inaccessible to us.

The 2001 superoutburst of WZ Sge: Is there any connection with Nova Outbursts?

We have observed WZ Sge with high resolution echelle spectroscopy during the 2001 superoutburst. The hot‐spot arising near the secondary star is again visible 15 days after its first detection. We have been able to measure its position as a function of orbital phase directly from individual spectra. We derive a a semiamplitude of Khs = 457 ± 16km s−1 and a systemic velocity of γ = 0 ± 14km s−1. We also show that the accretion disc has an ellipsoidal shape with a value around e = 0.75. Based on these facts we derive a phase shift of ΔΦ = −0.12 between the eclipse and the inferior conjuntion ephemeris. If this is the case, then the hot‐spot appears located at the trailing side of the red dwarf and must be the result of in‐falling material back to the donor star.