Detecting Differential Rotation and Starspot Evolution on the M Dwarf GJ 1243 with Kepler
Abstract
We present an analysis of the starspots on the active M4 dwarf GJ 1243, using 4 years of time series photometry from Kepler. A rapid P = 0.592596 ± 0.00021 days rotation period is measured due to the ∼2.2% starspotinduced flux modulations in the light curve. We first use a light curve modeling approach, using a Monte Carlo Markov Chain sampler to solve for the longitudes and radii of the two spots within 5 day windows of data. Within each window of time the starspots are assumed to be unchanging. Only a weak constraint on the starspot latitudes can be implied from our modeling. The primary spot is found to be very stable over many years. A secondary spot feature is present in three portions of the light curve, decays on 100500 day timescales, and moves in longitude over time. We interpret this longitude shearing as the signature of differential rotation. Using our models we measure an average shear between the starspots of 0.0047 rad day^{1}, which corresponds to a differential rotation rate of ∆{Ω } = 0.012 ± 0.002 rad day^{1}. We also fit this starspot phase evolution using a series of bivariate Gaussian functions, which provides a consistent shear measurement. This is among the slowest differential rotation shear measurements yet measured for a star in this temperature regime, and provides an important constraint for dynamo models of lowmass stars.
 Publication:

The Astrophysical Journal
 Pub Date:
 June 2015
 DOI:
 10.1088/0004637X/806/2/212
 arXiv:
 arXiv:1505.01524
 Bibcode:
 2015ApJ...806..212D
 Keywords:

 starspots;
 stars: activity;
 stars: lowmass;
 Astrophysics  Solar and Stellar Astrophysics
 EPrint:
 13 pages, 7 figures, ApJ Accepted