The donor star of the long-period dwarf nova DX-Andromedae

Abstract

Spectroscopic observations of the long-period dwarf nova DX Andromedae are reported which show that it has a binary period of 0.44167 d, a secondary radial velocity amplitude of 107 km/s, and a projected rotational velocity of 79 km/s. Photometric observations reveal ellipsoidal variation of 0.08 mag in Z. From all the data, it is found that DX And has a mass ratio of 0.96 and that the accretion disk contributes about 15 percent of the light in the green region of the spectrum. The secondary has a spectral type of K1 V and a radius at least 40 percent larger than the corresponding main sequence stars. It is argued that the companion star mass is less than 0.8 solar. The distance to DX And is 630 pc. The secondary star's absorption spectrum does not exactly match that of a normal main-sequence star: enhanced absorption is seen at some wavelengths.