Identification of a deep contact binary in the field of the globular cluster 47 Tuc

Abstract

Three light curves of the eclipsing binary V95–47 Tuc were obtained in serval nights from December, 2010 to November, 2011. By analyzing the light curves with the 2010 version of the W-D code, the mass-ratio and the fill-out factor of V95 are determined as 0.164 and 53.8%, respectively. It is sure that this contact binary is a foreground object of the globular cluster 47 Tuc. By comparing to the Dartmouth model isochrones, the masses and the radii of the component stars are estimated, as well as the age and the distance. They are, M1 ¼ 0:97M; M2 ¼ 0:16M; R1 ¼ 1:05R; R2 ¼ 0:49R, Age = 7.0 Gyr and Dist = 1570 pc. The cool spots model is introduced in the BV-band photometric solutions because of the observed O’Connell effect. We compare the two modeling cool spots in size, temperature and position, thinking that they could be the same one. It can be explained as that a cool spot, which is on the surface of the more massive component, shifted 126 degrees along the latitude line from west to east in a year. This phenomenon may be called as starspot migration.