J. Gomes da Silva, N. C. Santos, X. Bonfils, X. Delfosse, T. Forveille, S. Udry, X. Dumusque, C. Lovis
Due to their low mass and luminosity, M dwarfs are ideal targets if one hopes
to find low-mass planets similar to Earth by using the radial velocity (RV)
method. However, stellar magnetic cycles could add noise or even mimic the RV
signal of a long-period companion. Following our previous work that studied the
correlation between activity cycles and long-term RV variations for K dwarfs we
now expand that research to the lower-end of the main sequence. Our objective
is to detect any correlations between long-term activity variations and the
observed RV of a sample of M dwarfs. We used a sample of 27 M-dwarfs with a
median observational timespan of 5.9 years. The cross-correlation function
(CCF) with its parameters RV, bisector inverse slope (BIS), full-width-at-half-
maximum (FWHM) and contrast have been computed from the HARPS spectrum. The
activity index have been derived using the Na I D doublet. These parameters
were compared with the activity level of the stars to search for correlations.
We detected RV variations up to ~5 m/s that we can attribute to activity cycle
effects. However, only 36% of the stars with long-term activity variability
appear to have their RV affected by magnetic cycles, on the typical timescale
of ~6 years. Therefore, we suggest a careful analysis of activity data when
searching for extrasolar planets using long-timespan RV data.
View original:
http://arxiv.org/abs/1202.1564
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