SURFACE ACTIVITY AND OSCILLATION AMPLITUDES OF RED GIANTS IN ECLIPSING BINARIES

Abstract

Among 19 red-giant stars belonging to eclipsing binary systems that have been\nidentified in Kepler data, 15 display solar-like oscillations. We study whether\nthe absence of mode detection in the remaining 4 is an observational bias or\npossibly evidence of mode damping that originates from tidal interactions. A\ncareful analysis of the corresponding Kepler light curves shows that modes with\namplitudes that are usually observed in red giants would have been detected if\nthey were present. We observe that mode depletion is strongly associated with\nshort-period systems, in which stellar radii account for 16-24 % of the\nsemi-major axis, and where red-giant surface activity is detected. We suggest\nthat when the rotational and orbital periods synchronize in close binaries, the\nred-giant component is spun up, so that a dynamo mechanism starts and generates\na magnetic field, leading to observable stellar activity. Pressure modes would\nthen be damped as acoustic waves dissipate in these fields.\n