SIMBAD references

Using a previously developed technique, a study of moderate-resolution optical spectra was carried out, and sets of parameters for the dwarf novae V355 UMa, V521 Peg, VY Aqr, and PQ And were obtained. Observations of the systems in late relaxation state after a burst or in a quiescent state were carried out in 2020 and 2021 with the 6-m BTA telescope of SAO RAS. Their analysis took into account the requirement for an optimum description of the observed absorption profiles of the Balmer series lines with the model spectra of white dwarfs with radiative and convective transfer. As a result, the atmospheric parameters of the primaries were determined for all the systems, and when they were subsequently compared with models of the internal structure of white dwarf and main-sequence stars, sets of fundamental parameters of the objects were also determined. It has been established that analysis of the spectra of dwarf novae containing moderately cool white dwarfs with Teff=12000 - 15000 K provides better accuracy of their parameters than systems with hotter primaries. A simultaneous condition to be fulfilled for increasing accuracy is to carry out observations after the objects relax to a quiescent state, since the emission lines of the accretion disk significantly narrow the region of the analyzed spectrum. It has been found that the primary components of V355 UMa, V521 Peg, VY Aqr, and PQ And have masses within th Nizhnii Arkhyze range of M1=0.59-0.87 M_solar, and their cool companions are red dwarfs with M2=0.11-0.13 M_solar