NEW CMOS PHOTOMETRY AND ARCHIVAL PHOTOGRAPHIC OBSERVATIONS OF THE W UMA STAR V752 CEN: EXTENDING THE O-C RECORD OF PERIOD CHANGES

Abstract

We present new CMOS Bayer g-band photometry of the southern W UMa star V752 Cen, presenting two new times of primary minimum, and use archival photographic photometry from the Bamberg Sky Survey (mid 1960s) and the Harvard plate collection (∼1890 to 1990) to extend the O-C diagram back in time to ∼1900. Earlier authors have reported a constant period from the earliest published photometry in 1970 to about the year 2000, when a sudden change occurred to an increasing period. The archival photographic record presented here indicates the period was effectively constant back to 1900. Our 2020 data are also consistent with reported period increase. The V752 Cen system is known from earlier work to be a W UMa binary orbiting a lower mass spectroscopic binary. Our preliminary calculations, based on the reported centre-of-mass velocity change of the W UMa binary, suggest the wide orbit may have a period near 245 d, and could give rise to a light-travel time-effect of order 0.02 d. This does not however appear to be consistent with the SuperWASP photometric O-C results. Hence we suggest that considerable uncertainty exists concerning the properties of the wide orbit.