Determination of the basic parameters of the dwarf nova EY Cygni

¹ Instituto de Astronomía, Universidad Nacional Autónoma de México, Apartado Postal 70-264, 04510 México, DF, México e-mail: jer,costero@astroscu.unam.mx
² Instituto de Astronomía, Universidad Nacional Autónoma de México, Apartado Postal 877, 22830, Ensenada, Baja California, México e-mail: rmm,zhar@astrosen.unam.mx

Received: 29 March 2006
Accepted: 27 October 2006

Abstract

Context.High-dispersion spectroscopy of EY Cyg obtained from data spanning twelve years show, for the first time, the radial velocity curves from both emission and absorption line systems, yielding semi-amplitudes  ± and  ± . The orbital period of this system is found to be 0.4593249(1) d. The masses of the stars, their mass ratio and their separation are found to be  ± ,  ± , and  ± . We also found that the spectral type of the secondary star is around K0, consistent with an early determination by Kraft (1962).

Aims.From the spectral type of the secondary star and simple comparisons with single main sequence stars, we conclude that the radius of the secondary star is about 30 per cent larger than a main sequence star of the same mass.

Methods.We also present VRI CCD photometric observations, some of them simultaneous with the spectroscopic runs. The photometric data shows several light modulations, including a sinusoidal behaviour with twice the frequency of the orbital period, characteristic of the modulation coming from an elongated, irradiated secondary star. Low and high states during quiescence are also detected and discussed.

Results.From several constrains, we obtain tight limits for the inclination angle of the binary system between 13 and 15 degrees, with a best value of 14 degrees obtained from the sinusoidal light curve analysis.

Conclusions.From the above results we derive masses  ± ,  ± , and a binary separation  ± .