Optical Polarization of X Per

Abstract

IT has been suggested that the variable star X Per may be the X-ray source 2ASE 0352 + 30 (refs. 1 and 2, and R. J. Brucato and J. Kristian, personal communication). Nikulin et al.3 report strong and variable circular polarization of Sco X-1 and HD 226868 (the possible optical counterpart of Cyg X-1), so the polarization of X Per (and its variation) is of interest. One of us (J. T., unpublished thesis) has recently developed a wideband polarization modulator of the Dollfus type4,5. A prototype using plastic retarders was used on a 30-cm Cassegrain reflector to observe the polarization of nearby bright stars, and of ζ Per and X Per. The observations on bright stars and on ζ Per show that instrumental polarization (linear or circular) is certainly less than 0.02% of the total intensity, even in the presence of several % of total intensity in polarization forms other than that being measured. Our bandwidth of approximately 1000 A is centred between 5000 A and 5500 A.