  A 10.24 days Neptune-mass planet was recently announced to orbit the nearby
M2 dwarf Gl 176, based on 28 radial velocities measured with the HRS
spectrograph on the Hobby-Heberly Telescope (HET). We obtained 57 radial
velocities of Gl 176 with the ESO 3.6m telescope and the HARPS spectrograph,
which is known for its sub-m/s stability. The median photon-noise standard
error of our measurements is 1.1 m/s, significantly lower than the 4.7 m/s of
the HET velocities, and the 4 years period over which they were obtained has
much overlap with the epochs of the HET measurements. The HARPS measurements
show no evidence for a signal at the period of the putative HET planet,
suggesting that its detection was spurious. We do find, on the other hand,
strong evidence for a lower mass 8.4 Mearth planet, in a quasi-circular orbit
and at the different period of 8.78 days. The host star has moderate magnetic
activity and rotates on a 39-days period, which we confirm through modulation
of both contemporaneous photometry and chromospheric indices. We detect that
period as well in the radial velocities, but it is well removed from the
orbital period and no cause for confusion. This new detection of a super-Earth
(2 Mearth < M sin(i) < 10 Mearth) around an M dwarf adds to the growing
evidence that such planets are common around very low mass stars: a third of
the 20 known planets with M sin(i) < 0.1 Mjup and 3 of the 7 known planets with
M sin(i) < 10 Mearth orbit an M dwarf, in contrast to just 4 of the ~300 known
Jupiter-mass planets.
