Chromospherically Active Stars in the Galactic Bulge

Abstract

We present the results from the discovery and study of ∼3000 chromospherically active giant and subgiant stars toward the Galactic bulge. We find that these stars are predominantly RS CVn binaries with rotation periods between 10 and 100 days. We discover that the average rotational period of these stars decreases with their distance from the Galactic plane. We find that the primary stars in the RS CVn systems are predominantly first-ascent giants. Our research also suggests that if these stars have spot cycles like the Sun, then the cycle period must be longer than 10 yr on average. We confirm that the amplitude of the spot-induced modulations observed in the light curves of these objects is generally larger at minimum light than at maximum. Furthermore, we confirm that the amplitudes of the modulations due to stellar spots generally increase as the observed change in average brightness increases. We find no evidence for a relationship between a chromospherically active star's brightness and its rotational period. However, the average period does increase with color for stars with periods ≲30 days.