CCD PHOTOMETRY AND PRELIMINARY ANALYSIS OF V865 CYGNI

Abstract

ABSTRACT CCD images of the thirteenth magnitude variable V865 Cygni were taken on four consecutive nights in the summer of 1990. The 1.1-m Hall reflector telescope at Lowell Observatory was used in conjunction with an RCA CCD camera system. Four times of minimum light were determined and improved linear and quadratic ephemerides were calculated. A period study, spanning over a forty year interval, may indicate that the system is undergoing a continuous period increase of 5.4 X 10-8 d/yr. In a conservative scenario, this would be an indication of a mass accretion by the primary, more massive, component. The V, R, I light curves formed by the first precision photometry to be obtained on V865 Cygni, show that it is an A-type W UMa system. However, the curves are somewhat incomplete since the maximum which follows the secondary eclipse was not covered. The first synthetic light curve solution of V865 Cygni is also presented. This solution reveals that V865 Cygni is a contact binary consisting of two G spectral type components with a fillout of 18% and a mass ratio of 0.45. The component temperature difference is only 110K. A substantial hot spot region of 34 degrees diameter is proposed to model the asymmetry in the light curves following the observed maximum. We suggest that the origins of this region may be attributed to fluid dynamics rather than to the usual magnetic activity which is prevalent in late-type systems like V865 Cygni.