THE BRIGHT SOUTHERN CEPHEID BETA-DORADUS - THE RADIAL-VELOCITY CURVE,DISTANCE AND SIZE

A new high-accuracy velocity curve is presented for the bright souther n Cepheid beta Doradus (HR 1922), and an investigation into the long-t erm stability of the velocity curve is made. An upper Limit of 0.57 km s(-1) is placed on cycle-to-cycle variations, This work is compared w ith a similar analysis previously applied to the long-period Cepheid l Carinae (HR 3884). Using a near-infrared variant of the Barnes-Evans method, the mean radius of and distance to beta Dor are found to be R = 67.8 +/- 0.7 R. and d = 349 +/- 4 pc. The systematic errors in these parameters are less than 3 per cent. If these systematics can be reso lved, through the development of advanced theoretical models and/or th e direct measurement of angular diameters, a calibration of the cosmic distance scale to better than 1 per cent can be achieved.