Fewer giants planets are found around M dwarfs than around more massive stars , and this dependence of planetary characteristics on the mass of the central star is an important observational diagnostic of planetary formation theories .
In part to improve on those statistics , we are monitoring the radial velocities of nearby M dwarfs with the HARPS spectrograph on the ESO 3.6 m telescope .
We present here the detection of giant planets around two nearby M0 dwarfs : planets , with minimum masses of respectively 5 Jupiter masses and 1 Saturn mass , orbit around Gl 676A and HIP 12961 .
The latter is , by over a factor of two , the most massive planet found by radial velocity monitoring of an M dwarf , but its being found around an early M-dwarf is in approximate line with the upper envelope of the planetary vs stellar mass diagram .
HIP 12961 ( [ Fe/H ] =-0.07 ) is slightly more metal-rich than the average solar neighborhood ( [ Fe/H ] =-0.17 ) , and Gl 676A ( [ Fe/H=0.18 ) significantly so .
The two stars together therefore reinforce the growing trend for giant planets being more frequent around more metal-rich M dwarfs , and the 5 Jupiter mass Gl 676Ab being found around a metal-rich star is consistent with the expectation that the most massive planets preferentially form in disks with large condensate masses .