Bf eridani: a cataclysmic variable with a massive white dwarf and an evolved secondary

Abstract

We present high- and medium-resolution spectroscopic observations of the cataclysmic variable BF Eridani (BF Eri) during its low and bright states. The orbital period of this system was found to be 0.270881(3) d. The secondary star is clearly visible in the spectra through the absorption lines of the neutral metals MgI, FeI and CaI. Its spectral type was found to be K(3) +/- 0.5. A radial velocity study of the secondary yielded a semi-amplitude of K(2) = 182.5 +/- 0.9 km s(-1). The radial velocity semi-amplitude of the white dwarf was found to be K(1) = 74 +/- 3 km s(-1) from the motion of the wings of the H alpha and H beta emission lines. From these parameters, we have obtained that the secondary in BF Eri is an evolved star with a mass of 0.50 - 0.59 M(circle dot), whose size is about 30 per cent larger than a zero-age main-sequence single star of the same mass. We also show that BF Eri contains a massive white dwarf (M(1) >= 1.2M(circle dot)), which allows us to consider the system as a Type Ia supernova progenitor. BF Eri also shows a high. - velocity (gamma = -94 km s(-1)) and substantial proper motion. With our estimation of the distance to the system (d approximate to 700 +/- 200 pc), this corresponds to a space velocity of similar to 350 km s(-1) with respect to the dynamical local standard of rest. The cumulative effect of repeated nova eruptions with asymmetric envelope ejection might explain the high space velocity of the system. We analyse the outburst behaviour of BF Eri and question the current classification of the system as a dwarf nova. We propose that BF Eri might be an old nova exhibiting 'stunted' outbursts.