A holistic view of the W UMA type TY BOO

Abstract

New CCD four-color light curves of TY Boo made on eight nights over 2010-2011 were analyzed in comparison with historical light curves obtained from 1969 through 2011. The light curves could all be represented by a unique geometry and by wavelength consistent phototometric parameters of a two-spot model on either stellar component. It is confirmed that TY Boo is a shallow W-type contact binary system with a degree of contact factor of f = 7.6% (±0.8). A period investigation based on all available data shows a long-term decrease (dP/dt = -3.65 × 10 -8daysyr -1) and an oscillation (P 3 = 58.9yr, A = 0.0254days). Without ruling out the presence of a tertiary companion, the weight of evidence points to an active cyclic magnetic activity that causes spot formation rather than an unseen companion. Mass transfer between the components and angular momentum loss are also considered as possible mechanisms. © 2012. The American Astronomical Society. All rights reserved..