Kepler Flares III: Stellar Activity on GJ 1245 A and B

TL;DR

This study analyzes nine months of Kepler data to investigate flare rates and starspot evolution on GJ 1245 A and B, revealing differential rotation, flare activity, and orbital effects in a multiple M dwarf system.

Contribution

It introduces a new metric for comparing flare rates and provides detailed analysis of starspot evolution and orbital effects in a multi-star system using Kepler data.

Findings

GJ 1245A and B flare 3.0 and 2.6 times per day on average.

Starspot features evolve over long timescales, with evidence of differential rotation.

Photocenter shifts suggest orbital motion of an unseen companion affecting the system's observed properties.

Abstract

We present the flare occurrence rates and starspot evolution for GJ 1245 A 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 arcseconds, and the stars are not resolved in the Kepler pipeline processing due to Kepler's large plate scale of 4 arcseconds/pixel. 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 non-linear 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, $L_{fl}/L_{\mathrm{Kp}}$, to compare the flare rates between stars, and discuss this in the context of GJ 1245 A and B. Both stars exhibit starspot features that evolve on long time scales, 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 $\sim$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.