X. Bonfils, X. Delfosse, S. Udry, T. Forveille, M. Mayor, C. Perrier, F. Bouchy, M. Gillon, C. Lovis, F. Pepe, D. Queloz, N. C. Santos, D. Ségransan, J. -L. Bertaux
(Abridged) Searching for planets around stars with different masses probes
the outcome of planetary formation for different initial conditions. This
drives observations of a sample of 102 southern nearby M dwarfs, using a
fraction of our guaranteed time on the ESO/HARPS spectrograph (Feb. 11th, 2003
to Apr. 1st 2009). This paper makes available the sample's time series,
presents their precision and variability. We apply systematic searches and
diagnostics to discriminate whether the observed Doppler shifts are caused by
stellar surface inhomogeneities or by the radial pull of orbiting planets. We
recover the planetary signals corresponding to 9 planets already announced by
our group (Gl176b, Gl581b, c, d & e, Gl674b, Gl433b, Gl 667Cb and c). We
present radial velocities that confirm GJ 849 hosts a Jupiter-mass planet, plus
a long-term radial-velocity variation. We also present RVs that precise the
planetary mass and period of Gl 832b. We detect long-term RV changes for Gl
367, Gl 680 and Gl 880 betraying yet unknown long-period companions. We
identify candidate signals in the radial-velocity time series and demonstrate
they are most probably caused by stellar surface inhomogeneities. Finally, we
derive a first estimate of the occurrence of M-dwarf planets as a function of
their minimum mass and orbital period. In particular, we find that giant
planets (m sin i = 100-1,000 Mearth) have a low frequency (e.g. f<1% for P=1-10
d and f=0.02^{+0.03}_{-0.01} for P=10-100 d), whereas super-Earths (m sin i =
1-10 Mearth) are likely very abundant (f=0.36^{+0.25}_{-0.10} for P=1-10 d and
f=0.35^{+0.45}_{-0.11} for P=10-100 d). We also obtained
eta_earth=0.41^{+0.54}_{-0.13}, the frequency of habitable planets orbiting M
dwarfs (1View original: http://arxiv.org/abs/1111.5019
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