609 research outputs found
The Kepler Catalog of Stellar Flares
A homogeneous search for stellar flares has been performed using every
available Kepler light curve. An iterative light curve de-trending approach was
used to filter out both astrophysical and systematic variability to detect
flares. The flare recovery completeness has also been computed throughout each
light curve using artificial flare injection tests, and the tools for this work
have been made publicly available. The final sample contains 851,168 candidate
flare events recovered above the 68% completeness threshold, which were
detected from 4041 stars, or 1.9% of the stars in the Kepler database. The
average flare energy detected is ~ erg. The net fraction of flare
stars increases with color, or decreasing stellar mass. For stars in this
sample with previously measured rotation periods, the total relative flare
luminosity is compared to the Rossby number. A tentative detection of flare
activity saturation for low-mass stars with rapid rotation below a Rossby
number of ~0.03 is found. A power law decay in flare activity with Rossby
number is found with a slope of -1, shallower than typical measurements for
X-ray activity decay with Rossby number.Comment: 15 pages, 8 figures, ApJ accepted. Code is available online:
http://github.com/jradavenport/appaloos
Detecting Differential Rotation and Starspot Evolution on the M dwarf GJ 1243 with Kepler
We present an analysis of the starspots on the active M4 dwarf GJ 1243, using
four years of time series photometry from Kepler. A rapid day rotation period is measured due to the 2.2\%
starspot-induced 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 100-500 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, which
corresponds to a differential rotation rate of
rad day. 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 low mass stars.Comment: 13 pages, 7 figures, ApJ Accepte
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