Kepler flares III: Stellar activity on GJ 1245A and B

Abstract

We present the flare occurrence rates and starspot evolution for GJ 1245A and B, two active M5 stars, based on nine months of Kepler short cadence observations, and four years of nearly continuous long cadence observations. The A component is separated from the B component by 7″, and the stars are not resolved in the Kepler pipeline processing due to Kepler's large plate scale of 4″ pixel-1. Analyzing the target pixel data, we have generated separate light curves for components A and B using the PyKE pixel response function modeling procedures, and note the effects of CCD saturation and nonlinear response to high-energy flares. In our sample, GJ 1245A and B exhibit an average of 3.0 and 2.6 flares per day, respectively. We introduce a new metric, Lfl /L Kp, to compare the flare rates between stars, and discuss this in the context of GJ 1245A and B. Both stars exhibit starspot features that evolve on long timescales, with the slower rotating B component showing evidence of differential rotation. Intriguingly, the angular separation between the A and B component photocenters decreases during the four years of observations in a manner consistent with a shift in the position of the A photocenter due to the orbit of its unseen M8 companion (GJ 1245C), which is 94% less bright. Among the most detailed photometric studies of fully convective M dwarfs in a multiple system, these results provide an important constraint on stellar age-rotation-activity models.