The long-period orbit of the dwarf nova V630 Cassiopeiae

Abstract

We present extensive spectroscopy and photometry of the dwarf nova V630 Cassiopeiae. A late-type (K4-5) absorption spectrum is easily detectable, from which we derive the orbital parameters. We find a spectroscopic period of P=2.56387 +/- (4 times 10^{-5}) days and a semiamplitude of K_2=132.9 +/- 4.0 km/s. The resulting mass function, which is a firm lower limit on the mass of the white dwarf, is then f(M)=0.624 +/- 0.056 solar masses. The secondary star is a ``stripped giant'', and using relations between the core mass and the luminosity and the core mass and the radius we derive a lower limit of M_2 > 0.165 solar masses for the secondary star. The rotational velocity of the secondary star is not resolved in our spectra and we place a limit of V_rot*sin(i) 0.165 solar masses and V_rot*sin(i) < 40 km/s yields a white dwarf mass of M_1=0.977^{+0.168}_{-0.098} solar masses and a secondary star mass of M_2=0.172^{+0.029}_{-0.012} solar masses (90 per cent confidence limits). Our findings confirm the suggestion of Warner (1994), namely that V630 Cas is rare example of a dwarf nova with a long orbital period.