Determination of QW Ser and QZ Lib parameters from optical spectra

Abstract

The paper investigates a new technique for determining dwarf nova parameters based on the analysis of their optical spectra with a signal-to-noise ratio S/N ≈ 80. We have determined parameters for the QW Ser and QZ Lib systems related to the SU UMa and WZ Sge dwarf novae. Moderate resolution spectra of both systems were obtained at BTA SAO during their low state with an optically thin accretion disk and the dominance of white dwarf radiation. As a result of the model analysis of the spectra, the parameters of the accretor atmosphere of QW Ser (Teff = 23500 ± 400 K and log g = 8.36 ± 0.05 dex) and constraints on the parameters for QZ Lib (Teff = 9500 ± 300 K and log g > 8.55 dex) were found. The presence of moderate noise in the studied spectra is not shown to affect the accuracy of determining parameters. The low temperature of the white dwarf does not allow to obtain a correct estimate of its surface gravity. Based on the determined parameters of the accretor atmospheres, a complete set of QW Ser parameters and estimates of QZ Lib parameters were found. The secondary components of both systems are defined to be red dwarfs of spectral type M.