James R. A. Davenport, Andrew C. Becker, Adam F. Kowalski, Suzanne L. Hawley, Sarah J. Schmidt, Eric J. Hilton, Branimir Sesar, Roc Cutri
We present the first rates of flares from M dwarf stars in both red optical
and near infrared (NIR) filters. We have studied ~50,000 M dwarfs from the SDSS
Stripe 82 area, and 1,321 M dwarfs from the 2MASS Calibration Scan Point Source
Working Database that overlap SDSS imaging fields. We assign photometric
spectral types from M0 to M6 using (r-i) and (i-z) colors for every star in our
sample. Stripe 82 stars each have 50-100 epochs of data, while 2MASS
Calibration stars have ~1900 epochs. From these data we estimate the observed
rates and theoretical detection thresholds for flares in eight photometric
bands as a function of spectral type. Optical flare rates are found to be in
agreement with previous studies, while the frequency per hour of NIR flare
detections is found to be more than two orders of magnitude lower. An excess of
small amplitude flux increases in all bands exhibits a power-law distribution,
which we interpret as the result of flares below our detection thresholds. In
order to investigate the recovery efficiency for flares in each filter, we
extend a two-component flare model into the NIR. Quiescent M0-M6 spectral
templates were used with the model to predict the photometric response of
flares from u to Ks. We determine that red optical filters are sensitive to
flares with u-band amplitudes >2 mag, and NIR filters to flares with delta
u>4.5 mag. Our model predicts that M0 stars have the best color-contrast for
J-band detections, but M4-M6 stars should show the highest rate of NIR flares
with amplitudes of delta J ~0.01 mag. Characterizing flare rates and
photometric variations at longer wavelengths is important for predicting the
signatures of M dwarf variability in next-generation surveys, and we discuss
their impact on surveys such as LSST.
View original:
http://arxiv.org/abs/1202.1902
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