This Letter reports on the detection of two super-Earth planets in the Gl 581 system, which is already known to harbour a hot Neptune. One of the planets has a mass of 5 M ⊕ and resides at the "warm" edge of the habitable zone of the star. It is thus the known exoplanet that most resembles our own Earth. The other planet has a 7.7 M ⊕ mass and orbits at 0.25 AU from the star, close to the "cold" edge of the habitable zone. These two new light planets around an M3 dwarf further confirm the formerly tentative statistical trend toward (i) many more very low-mass planets being found around M dwarfs than around solar-type stars and (ii) low-mass planets outnumbering Jovian planets around M dwarfs.

We performed a uniform and detailed abundance analysis of 12 refractory elements (Na, Mg, Al, Si, Ca, Ti, Cr, Ni, Co, Sc, Mn, and V) for a sample of 257 G-and K-type evolved stars from the CORALIE planet search program. To date, only one of these stars is known to harbor a planetary companion. We aimed to characterize this large sample of evolved stars in terms of chemical abundances and kinematics, thus setting a solid base for further analysis of planetary properties around giant stars. This sample, being homogeneously analyzed, can be used as a comparison sample for other planet-related studies, as well as for different type of studies related to stellar and Galaxy astrophysics. The abundances of the chemical elements were determined using an LTE abundance analysis relative to the Sun, with the spectral synthesis code MOOG and a grid of Kurucz ATLAS9 atmospheres. To separate the Galactic stellar populations both a purely kinematical approach and a chemical method were applied. We confirm the overabundance of Na in giant stars compared to the field FGK dwarfs. This enhancement might have a stellar evolutionary character, but departures from LTE may also produce a similar enhancement. Our chemical separation of stellar populations also suggests a "gap" in metallicity between the thick-disk and high-α metal-rich stars, as previously observed in dwarfs sample from HARPS. The present sample, as most of the giant star samples, also suffers from the B -V colour cut-off, which excludes low-log g stars with high metallicities, and high-log g star with low-[Fe/H]. For future studies of planet occurrence dependence on stellar metallicity around these evolved stars we suggest to use a sub-sample of stars in a "cut-rectangle" in the log g -[Fe/H] diagram to overcome the aforementioned issue.

In the context of the programme Global Architecture of Planetary Systems (GAPS), we have performed radial velocity monitoring of the metal-poor star HIP 11952 on 35 nights during about 150 days using the newly installed high-resolution spectrograph HARPS-N at the TNG and HARPS at the ESO 3.6 m telescope. The radial velocities show a scatter of 7 m s −1 , compatible with the measurement errors for such a moderately warm metal-poor star (T eff = 6040 ± 120 K; [Fe/H] = −1.9 ± 0.1). We exclude the presence of the two giant planets with periods of 6.95 ± 0.01 d and 290.0 ± 16.2 d and radial velocity semi-amplitudes of 100.3 ± 19.4 m s −1 and 105.2 ± 14.7 m s −1 , respectively, which have recently been announced. This result is important because HIP 11952 was thought to be the most metal-poor star hosting a planetary system with giant planets, which challenged some models of planet formation.

Context. The presence of a small-mass planet (M p < 0.1 M Jup) seems, to date, not to depend on metallicity, however, theoretical simulations have shown that stars with subsolar metallicities may be favoured for harbouring smaller planets. A large, dedicated survey of metal-poor stars with the HARPS spectrograph has thus been carried out to search for Neptunes and super-Earths. Aims. In this paper, we present the analysis of HD 175607, an old G6 star with metallicity [Fe/H] = −0.62. We gathered 119 radial velocity measurements in 110 nights over a time span of more than nine years. Methods. The radial velocities were analysed using Lomb-Scargle periodograms, a genetic algorithm, a Markov chain Monte Carlo analysis, and a Gaussian processes analysis. The spectra were also used to derive stellar properties. Several activity indicators were analysed to study the effect of stellar activity on the radial velocities. Results. We find evidence for the presence of a small Neptune-mass planet (M p sin i = 8.98 ± 1.10 M ⊕) orbiting this star with an orbital period P = 29.01 ± 0.02 days in a slightly eccentric orbit (e = 0.11 ± 0.08). The period of this Neptune is close to the estimated rotational period of the star. However, from a detailed analysis of the radial velocities together with the stellar activity, we conclude that the best explanation of the signal is indeed the presence of a planetary companion rather than stellar related. An additional longer period signal (P ∼ 1400 d) is present in the data, for which more measurements are needed to constrain its nature and its properties. Conclusions. HD 175607 is the most metal-poor FGK dwarf with a detected low-mass planet amongst the currently known planet hosts. This discovery may thus have important consequences for planet formation and evolution theories.

Since the discovery of the transiting Super-Earth CoRoT-7b, several investigations have been made of the number and precise masses of planets present in the system, but they all yield different results, owing to the star's high level of activity. Radial velocity (RV) variations induced by stellar activity therefore need to be modelled and removed to allow a reliable detection of all planets in the system. We re-observed CoRoT-7 in January 2012 with both HARPS and the CoRoT satellite, so that we now have the benefit of simultaneous RV and photometric data. We fitted the off-transit variations in the CoRoT lightcurve using a harmonic decomposition similar to that implemented in Queloz et al. (2009). This fit was then used to model the stellar RV contribution, according to the methods described by Aigrain et al. (2011). This model was incorporated into a Monte Carlo Markov Chain in order to make a precise determination of the orbits of CoRoT-7b and CoRoT-7c. We also assess the evidence for the presence of one or two additional planetary companions.