Parameters of SU UMa and WZ Sge-Type Dwarf Novae in Quiescent State. I. FL Psc, TY Psc and V455 And

We present the results of model analysis of the optical spectra of SU UMa and WZ Sge-type dwarf novae TY Psc, FL Psc, and V455 And. Spectroscopic observations were carried out at the SAO RAS 6-m BTA telescope in 2013. The selection criterion for the systems under study is their existence in a quiescent state with an optically thin accretion disk and dominance of white dwarf radiation. The fulfillment of the criterion was verified by observing the H I Balmer series broad absorption lines simultaneously with two-peak H I, He I, and Fe II emissions. A technique for automated fitting of model spectra of white dwarfs and observed spectra of dwarf novae based on quantitative criteria for their matching is proposed and implemented. The atmospheric parameters (effective temperature T-eff and surface gravity log g) of accretors in TY Psc, FL Psc, and V455 And were determined applying it and used further to obtain their masses and radii. Due to the technique proposed here we obtained the estimates of the fundamental parameters of the secondaries using the theoretical "mass-radius" relationships for brown and red main-sequence dwarfs. As a result, we demonstrate the possibility in principle of determining all the main parameters of the SU UMa and WZ Sge dwarf novae based on modeling and the analysis of a small number of their spectra in the quiescent state.