OPTICAL AND ULTRAVIOLET SPECTROSCOPY OF VW HYDRI

Abstract

ABSTRACT Spectra of the SU UMa type dwarf nova VW Hydri obtained in the visual (lambda-lambda 3400-7200A) and ultraviolet (lambda-lambda 1150-3200A) spectral regions are presented. During the quiescent phase, visual spectra of VW Hydri present strong double-peaked Balmer emission lines. In addition, He I lambda 5876, Fe II lambda-lambda 4233, 5196 He I lambda 5015, Fe II lambda 5018, He I lambda 4922, Fe II lambda 4293, He II lambda 4686, and He I lambda-lambda 4471, 6678 appear in emission. The S-wave behavior of the hot spot is well defined. The amplitude of the radial velocity curve for H-alpha is 39 (±11) km/s and for H-beta is 85 (±23) km/s. From the radial velocity amplitude and the total line width we derived the primary mass in the range of 0.91 solar mass to 1.28 solar mass and the mass ratio q = M1/M2 = 4.4 to 6.4. We applied the method given by Schoembs and Vogt (1981), which is a modified version of the method described earlier by Warner (1973). We compared and discussed the fundamental physical and spectral parameters with those in the literature. In the ultraviolet region we obtained disk temperatures in the range of 14500-48000 K, using continuum fluxes. The continuum energy distributions were compared with optically thick accretion disk models. In the IUE SWP region the best-fit spectrum is of the form Flambda proportional to lambda -2.4. In this region the effective disk radius is between 0.69Rodot and 0.75Rodot. The mass accretion rate (M) was computed with a relation given by Faulkner (1971), and is about 0-10 Modot yr-1. From the P Cygni profile of the C IV doublet, terminal velocities of about 2250 km/s for a normal outburst and 2500 km/s for superoutburst were derived. Mass loss rates were derived using these velocities as about 0.8 to 6 x 10-13 Modot yr-1 for normal outbursts and about 0.8 to 7 x 10-13 Modot yr-1 for superoutburst.