A PHOTOMETRIC STUDY OF THE SHORT-PERIOD CLOSE BINARY V432 PERSEI AND ITS IMPLICATIONS FOR THE STAR'S EVOLUTION

Abstract

We present new multicolor charge-coupled device (CCD) photometry for the short-period close binary V432 Per, made on six nights between 2006 February and December. A period study of the system, based on all published and newly observed times of minimum light, reveals that the orbital period has varied as a beat effect due to the combination of a secular period increase and a sinusoidal variation, with a period of 35.3 yr and semi-amplitude of 0.0104 d. The continuous period increase can be interpreted as mass transfer from the less massive secondary star to the more massive primary component in the system with a rate of about 1.16 × 10–7 M ☉ yr–1. The sinusoidal component of the period variability could, in principle, be produced by either a light-time effect due to a third body or a magnetic modulation seated in at least one component star, but light variations do not conform to a prediction of the second mechanism. New light curves, showing a total eclipse at secondary minimum and a variable O'Connell effect, are best modeled by including a third light source and a cool spot on the primary star. The model also represents Agerer's light curves. Our results indicate V432 Per, at present, to be in a broken or a marginal contact stage, investing a hotter, more massive primary star with a spectral type of G4 and a cooler, less massive secondary star with a spectral type of G8–G9. We suggest that the most likely explanation of the sinusoidal variation is the existence of a gravitationally bound M-type tertiary companion. When all of this is verified and understood more comprehensively, the formation and evolution of this binary system should be greatly advanced.