Journal Article

<i>J</i>-band variability of M dwarfs in the WFCAM Transit Survey

N. T. Goulding, J. R. Barnes, D. J. Pinfield, G. Kovács, J. Birkby, S. Hodgkin, S. Catalán, B. Sipőcz, H. R. A. Jones, C. del Burgo, S. V. Jeffers, S. Nefs, M.-C. Gálvez-Ortiz and E. L. Martin

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 427, issue 4, pages 3358-3373
Published in print December 2012 | ISSN: 0035-8711
Published online September 2012 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2012.21932.x
J-band variability of M dwarfs in the WFCAM Transit Survey

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We present an analysis of the photometric variability of M dwarfs in the Wide Field Camera (WFCAM) Transit Survey. Although periodic light-curve variability in low mass stars is generally dominated by photospheric star spot activity, M dwarf variability in the J band has not been as thoroughly investigated as at visible wavelengths. Spectral type estimates for a sample of over 200 000 objects are made using spectral type–colour relations, and over 9600 dwarfs (J < 17) with spectral types later than K7 were found. The light curves of the late-type sample are searched for periodicity using a Lomb–Scargle periodogram analysis. A total of 68 periodic variable M dwarfs are found in the sample with periods ranging from 0.16 to 90.33 d, with amplitudes in the range of ∼0.009 to ∼0.115 in the J band. We simulate active M dwarfs with a range of latitude-independent spot coverages and estimate a periodically variable fraction of 1–3 per cent for stars where spots cover more than 10 per cent of the star's surface. Our simulated spot distributions indicate that operating in the J band, where spot contrast ratios are minimized, enables variability in only the most active of stars to be detected. These findings affirm the benefits of using the J band for planetary transit searches compared to visible bands. We also serendipitously find a ΔJ > 0.2 mag flaring event from an M4V star in our sample.

Keywords: stars: activity; stars: late type; stars: starspots; stars: variables: general

Journal Article.  7607 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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