Results of a Search for Bright Cephei Variables in the Southern Sky

The radial velocities of seven bright southern early B-type stars, known to have variable velocity, have been systematically examined at the Radcliffe Observatory in an effort to detect the presence of short periods (3 to 7 hours) characteristic of β Cephei variables. Positive results were obtained for three stars: β Cru $$(0\lt2K\lt14\,\text{km/sec})$$, τ¹ Lup (2K=11 km/sec), and α Lup (2K=15 km/sec). Definitive periods have been derived for τ¹ Lup and α Lup, while a provisional period is suggested for β Cru. β Cru and τ¹ Lup have been observed photoelectrically by the staff of the Cape Observatory and found to have short-period variations in light with a range of about 0^m.04. In the case of τ¹ Lup, the light variation shows the same period as the velocity variation, with the phase relationship typical of β Cephei variables. In the case of β Cru, all that can be said is that the light variation has approximately the period of the velocity variation. α Lup was observed photoelectrically by A. B. Muller at the Leiden Observatory Southern Station; no variation in excess of 0^m.01 has so far been detected. τ¹ Lup fits closely the period–luminosity relations derived for β Cephei variables by Blaauw and Savedoff and by Petrie. It is clearly a typical member of the group with constant velocity amplitude. α Lup comes tolerably near to the period-luminosity relation, but, until some variation in light can be established, one cannot quite exclude the possibility that it is a single-lined spectroscopic binary. β Cru, in spite of its early spectral type (B0), would seem to be related to the β Cephei group, though it is anomalous in a number of ways.