The Precataclysmic Binary RR Caeli Revisited: Spectroscopy and Light-Curve Synthesis

Abstract

Time-resolved spectroscopic observations of the precataclysmic binary RR Cae in the red make it possible to measure the radial velocity (RV) curve of this late-type secondary star and its Hα emission component. The latter is not caused by the illumination of the secondary star by the white dwarf, as in other precataclysmic binaries, but is intrinsic to the late-type star. The phasing of the RV curve allows for an improved measurement of the orbital period. Although still lacking RV measurements of the white dwarf primary, the present observations, together with a reanalysis of previous photometric measurements with the Wilson-Devinney light curve synthesis routine, permit improved determinations of many system parameters. Component masses are found to be 0.467 M⊙ and 0.095 M⊙ for the primary and the secondary stars, respectively. The radius of the secondary star, at 0.189 R⊙, is considerably larger than expected for such a low-mass star, possibly as a consequence of a previous common envelope phase. An orbital eccentricity, although strongly suggested by the shape of the light curve, is not supported by the RV curve. RR Cae is an eclipsing binary with two spectral line systems, which makes it possible to measure the component masses directly. This is of particular importance for the red dwarf secondary, which is of a later spectral type and probably of lower mass than any other known star for which such measurements are possible.