Radial velocity variations of the del SCT variable BET Cas.

Precision radial velocities with a time resolution of 15 min (P/10) are measured for Beta Cas (P = 2h30m) over almost two cycles using the HF absorption-cell technique. The precision of + or - 0.2 km/s is limited by line-profile variations not by the technique. The Ca II 8662 A line exhibits the largest amplitude (+ or - 2.3 km/s) in comparison with the HI, P12 line and weak metallic lines of S I, Si I, Mg I and Fe I, which have amplitudes of + or - 2 km/s and + or - 1.6 km/s, respectively. The period of 0.0976 day derived from the Ca II velocity curve agrees with the photometric period of 0.104 day. The H I velocity minima lag by some 2% in phase compared with the Ca II and metallic-line velocity curves; this is similar to the van Hoof effect in Beta CMa variables. The Ca II line shows broad and narrow phases that coincide with the phases of minimum and maximum velocity, respectively. Details are given of the HF reference line technique.