A radial velocity study of the companion to the central star of Abell 35

Abstract

We report the results of a radial velocity study of BD - 22.3467 deg (LW Hya), the cool companion to the subdwarf central star of the planetary nebula Abell 35. Estimates for its radial velocity have been obtained by cross correlation with radial velocity standards for five epochs of observations sampling periods of the order of days and decades. We find that any radial velocity variation of BD - 22.3467 deg on periods shorter than 30 d cannot possess a semi-amplitude greater than 5 km/s. Also, with the exception of a limited number of possible periods not covered by our sampling frequency, we can exclude radial velocity variations of semi-amplitude larger than about 8 km/s up to periods of approximately 30 yr. On the other hand, short-period, small-semi-amplitude about 5 km/s) radial velocity variations have been observed in the blue spectral region and possibly, with a smaller semi-amplitude (about 2 km/s), in the red. The photometric period of 0.766 +/- 0.001 d, which has been associated with the rotation of the star, is consistent with them, although other periods cannot yet be ruled out.