Starspot distributions on fully convective M dwarfs: Implications for radial velocity planet searches
- Department of Physical Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA (United Kingdom)
- Institut für Astrophysik, Georg-August-Universität, Friedrich-Hund-Platz 1, D-37077 Gttingen (Germany)
- Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield AL10 9AB (United Kingdom)
Since M4.5–M9 dwarfs exhibit equatorial rotation velocities of the order of 10 km s{sup −1} on average, radial velocity surveys targeting this stellar population will likely need to find methods to effectively remove starspot jitter. We present the first high resolution Doppler images of the M4.5 dwarf, GJ 791.2A, and the M9 dwarf, LP 944-20. The time series spectra of both objects reveal numerous line profile distortions over the rotation period of each star, which we interpret as starspots. The transient distortions are modeled with spot/photosphere contrast ratios that correspond to model atmosphere temperature differences of T{sub phot}−T{sub spot} = 300 and 200 K. GJ 791.2A is a fully convective star with v sin i = 35.1 km s{sup −1}. Although we find more starspot structure at high latitudes, we reconstruct spots at a range of phases and latitudes with a mean spot filling of ∼3%. LP 944-20 is one of the brightest known late-M dwarfs, with spectral type M9V and v sin i = 30.8 km s{sup −1}. Its spectral time series exhibits two dominant transient line distortions that are reconstructed as high latitude spots, while a mean spot filling factor of only 1.5% is found. The occurrence of low-contrast spots at predominantly high latitudes, which we see in both targets here, is, in general, likely to be responsible for the low amplitude photometric variability seen in late-M dwarfs. For GJ 791.2A, the radial velocities induced by the starspot features yield an rms velocity variability of 138 m s{sup −1}, which can be reduced by a factor of 1.9 using our reconstructed surface brightness distributions.
- OSTI ID:
- 22882499
- Journal Information:
- Astrophysical Journal, Vol. 812, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); Since 2009, the country of publication for this journal is the UK.; ISSN 0004-637X
- Country of Publication:
- United Kingdom
- Language:
- English
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