Journal Article

The effect of M dwarf starspot activity on low-mass planet detection thresholds

J. R. Barnes, S. V. Jeffers and H. R. A. Jones

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 412, issue 3, pages 1599-1610
Published in print April 2011 | ISSN: 0035-8711
Published online April 2011 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2010.17979.x
The effect of M dwarf starspot activity on low-mass planet detection thresholds

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In light of the growing interest in searching for low mass, rocky planets, we investigate the impact of starspots on radial velocity searches for earth-mass planets in orbit about M dwarf stars. Since new surveys targeting M dwarfs will likely be carried out at infrared wavelengths, a comparison between V and Y band starspot-induced jitter is made, indicating a reduction of up to an order of magnitude when observing in the Y band. The exact reduction in jitter is dependent on the photosphere to spot contrast ratio, with greater improvements at smaller contrasts.

We extrapolate a model used to describe solar spot distributions to simulate the spot patterns that we expect to find on M dwarfs. Under the assumption that M dwarfs are near or fully convective, we randomly place starspots on the stellar surface, simulating different levels of spot coverage. Line profiles distorted by spots are derived and are used to investigate the starspot-induced jitter. By making assumptions about the degree of spot activity, detection limits for earth-mass planets in habitable zones are simulated for between 10 and 500 observation epochs. We find that ≤50 epochs are required to detect 1–2 planets (with <1 per cent false alarm probability) orbiting slowly rotating 0.1 and 0.2 M stars. This sensitivity decreases when typical rotation velocities and activity levels for each stellar mass/spectral type are considered. No detections of below 20 planets are expected for ≤500 observations for the most active stars with v sin i≥ 20 km s−1 and dark spots.

Keywords: techniques: radial velocities; stars: activity; stars: atmospheres; planetary systems; starspots

Journal Article.  9318 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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