The Active Contact Binary FU Draconis: Four Color Light Curves and Period Changes

Abstract

Abstract Secured four color light curves of FU Dra were analyzed with the 2003 version of the Wilson and Devinney (WD) code. It was shown that FU Dra is still a W-type contact binary system, but might have a high fill-out factor ($f$$=$ 26.7% $\pm$ 1.0%). A dark spot was introduced on the massive cool component. A period investigation based on all available data shows that the period of the system may include a long-term increase ($dP/dt$$=$ 8.8 $\pm$ 2.9 $\times$ 10$^{-8}$ d yr$^{-1}$) and an oscillation (semi-amplitude of 0.0024 d, $P_3$$=$ 7.8 yr). The long-term period decrease may be caused by mass transfer, though the periodic oscillation may be rooted in cyclic magnetic activity.