Many stellar models present difficulties in reproducing basic observational relations of very low mass stars (VLMS), including the mass-radius relation and the optical colour-magnitudes of cool dwarfs. Here, we improve PARSEC models on these points. We implement the T -τ relations from PHOENIX BT-Settl model atmospheres as the outer boundary conditions in the PARSEC code, finding that this change alone reduces the discrepancy in the mass-radius relation from 8 to 5 per cent. We compare the models with multi-band photometry of clusters Praesepe and M 67, showing that the use of T -τ relations clearly improves the description of the optical colours and magnitudes. But anyway, using both Kurucz and PHOENIX model spectra, model colours are still systematically fainter and bluer than the observations. We then apply a shift to the above T -τ relations, increasing from 0 at T eff = 4730 K to ∼14% at T eff = 3160 K, to reproduce the observed mass-radius radius relation of dwarf stars. Taking this experiment as a calibration of the T -τ relations, we can reproduce the optical and near infrared CMDs of low mass stars in the old metal-poor globular clusters NGC 6397 and 47 Tuc, and in the intermediate-age and young solar-metallicity open clusters M 67 and Praesepe. Thus, we extend PARSEC models using this calibration, providing VLMS models more suitable for the lower main sequence stars over a wide range of metallicities and wavelengths. Both sets of models are available on PARSEC webpage.

Abstract. We present element-to-element abundance ratios measured from high dispersion spectra for 150 field subdwarfs and early subgiants with accurate Hipparcos parallaxes (errors <20%). For 50 stars new spectra were obtained with the UVES on Kueyen (VLT UT2), the McDonald 2.7 m telescope, and SARG at TNG. Additionally, literature equivalent widths were taken from the works by Nissen & Schuster, Fulbright, and Prochaska et al. to complement our data. The whole sample includes both thick disk and halo stars (and a few thin disk stars); most stars have metallicities in the range −2 < [Fe/H] < −0.6. We found our data, that of Nissen & Schuster, and that of Prochaska to be of comparable quality; results from Fulbright scatter a bit more, but they are still of very good quality and are extremely useful due to the large size of his sample. The results of the present analysis will be used in forthcoming papers to discuss the chemical properties of the dissipational collapse and accretion components of our Galaxy.

Aims. We report the discovery of very shallow (ΔF/F ≈ 3.4× 10 −4 ), periodic dips in the light curve of an active V = 11.7 G9V star observed by the CoRoT satellite, which we interpret as caused by a transiting companion. We describe the 3-colour CoRoT data and complementary ground-based observations that support the planetary nature of the companion. Methods. We used CoRoT colours information, good angular resolution ground-based photometric observations in-and out-of transit, adaptive optics imaging, near-infrared spectroscopy, and preliminary results from radial velocity measurements, to test the diluted eclipsing binary scenarios. The parameters of the host star were derived from optical spectra, which were then combined with the CoRoT light curve to derive parameters of the companion. Results. We examined all conceivable cases of false positives carefully, and all the tests support the planetary hypothesis. Blends with separation >0.40 or triple systems are almost excluded with a 8 × 10 −4 risk left. We conclude that, inasmuch we have been exhaustive, we have discovered a planetary companion, named CoRoT-7b, for which we derive a period of 0.853 59 ± 3 × 10 −5 day and a radius of R p = 1.68 ± 0.09 R Earth . Analysis of preliminary radial velocity data yields an upper limit of 21 M Earth for the companion mass, supporting the finding. Conclusions. CoRoT-7b is very likely the first Super-Earth with a measured radius. This object illustrates what will probably become a common situation with missions such as Kepler, namely the need to establish the planetary origin of transits in the absence of a firm radial velocity detection and mass measurement. The composition of CoRoT-7b remains loosely constrained without a precise mass. A very high surface temperature on its irradiated face, ≈1800-2600 K at the substellar point, and a very low one, ≈50 K, on its dark face assuming no atmosphere, have been derived.

The Kepler space telescope detects exoplanets by measuring periodic dimmings of light as a planet passes in front of its host star (1). The majority of the ∼ 150,000 targets observed by Kepler are unevolved stars near the main sequence, because those stars provide the best prospect for detecting habitable planets similar to Earth (2). In contrast, the temperature and surface gravity of indicate that it is an evolved star with exhausted hydrogen in its core, and that it started burning hydrogen in a shell surrounding an inert Helium core. Stellar evolutionary theory predicts that our Sun will evolve into a low-luminosity red giant similar in size to Kepler-56 in roughly 7 billion years.The Kepler planet search pipeline detected two planet candidates orbiting (designated as KOI-1241) (3) with periods of 10.50 and 21.41 days, a nearly 2:1 commensurability. The observation of transit time variations caused by gravitational interactions 2 showed that the two candidates represent objects orbiting the same star, and modeling of these variations led to upper limits on their masses that place them firmly in the planetary regime (4). Kepler-56 is the most evolved star observed by Kepler with more than one detected planet.Transit observations lead to measurements of planet properties relative to stellar properties, and hence accurate knowledge of the host star is required to characterize the system. Asteroseismology enables inference of stellar properties through the measurement of oscillations excited by near-surface convection (5). The power spectrum of the Kepler-56 data after removing the planetary transits shows a regular series of peaks ( Fig. 1), which are characteristic of stellar oscillations. By combining the measured oscillation frequencies with the effective temperature and chemical composition obtained from spectroscopy, we were able to precisely determine the properties of the host star (6). Kepler-56 is more than four times as large as the Sun and its mass is 30% greater (Table 1).Non-radial oscillations in evolved stars are mixed modes, behaving like pressure modes in the envelope and like gravity modes in the core (7,8). Unlike pressure-dominated mixed modes, gravity-dominated mixed modes have frequencies that are shifted from the regular asymptotic spacing. Mixed modes are also approximately equally spaced in period (9). We measured the average period spacing between dipole (l = 1) modes in Kepler-56 to be 50 seconds, consistent with a first ascent red giant (10).Individual mixed dipole modes are further split into multiplets as a result of stellar rotation. Because the modes in each multiplet are on average expected to be excited to very nearly equal amplitudes, the observed relative amplitudes depend only on viewing angle relative to the stellar rotation axis (11). For Kepler-56 several mixed dipole modes show triplets (Fig. 1). A rotation axis perpendicular to the line of sight (inclination i = 90 • for pressure-dominated modes. Simulations confirmed that the inclination measurements are not strongly...

We report on an intensive observational campaign carried out with HARPS at the 3.6 m telescope at La Silla on the star CoRoT-7. Additional simultaneous photometric measurements carried out with the Euler Swiss telescope have demonstrated that the observed radial velocity variations are dominated by rotational modulation from cool spots on the stellar surface. Several approaches were used to extract the radial velocity signal of the planet(s) from the stellar activity signal. First, a simple pre-whitening procedure was employed to find and subsequently remove periodic signals from the complex frequency structure of the radial velocity data. The dominant frequency in the power spectrum was found at 23 days, which corresponds to the rotation period of CoRoT-7. The 0.8535 day period of CoRoT-7b planetary candidate was detected with an amplitude of 3.3 m s −1 . Most other frequencies, some with amplitudes larger than the CoRoT-7b signal, are most likely associated with activity. A second approach used harmonic decomposition of the rotational period and up to the first three harmonics to filter out the activity signal from radial velocity variations caused by orbiting planets. After correcting the radial velocity data for activity, two periodic signals are detected: the CoRoT-7b transit period and a second one with a period of 3.69 days and an amplitude of 4 m s −1 . This second signal was also found in the pre-whitening analysis. We attribute the second signal to a second, more remote planet CoRoT-7c . The orbital solution of both planets is compatible with circular orbits. The mass of CoRoT-7b is 4.8 ± 0.8 (M ⊕ ) and that of CoRoT-7c is 8.4 ± 0.9 (M ⊕ ), assuming both planets are on coplanar orbits. We also investigated the false positive scenario of a blend by a faint stellar binary, and this may be rejected by the stability of the bisector on a nightly scale. According to their masses both planets belong to the super-Earth planet category. The average density of CoRoT-7b is ρ = 5.6 ± 1.3 g cm −3 , similar to the Earth. The CoRoT-7 planetary system provides us with the first insight into the physical nature of short period super-Earth planets recently detected by radial velocity surveys. These planets may be denser than Neptune and therefore likely made of rocks like the Earth, or a mix of water ice and rocks.

Context. The CoRoT mission, a pioneer in exoplanet searches from space, has completed its first 150 days of continuous observations of ∼12 000 stars in the galactic plane. An analysis of the raw data identifies the most promising candidates and triggers the ground-based follow-up. Aims. We report on the discovery of the transiting planet CoRoT-Exo-2b, with a period of 1.743 days, and characterize its main parameters. Methods. We filter the CoRoT raw light curve of cosmic impacts, orbital residuals, and low frequency signals from the star. The folded light curve of 78 transits is fitted to a model to obtain the main parameters. Radial velocity data obtained with the SOPHIE, CORALIE and HARPS spectrographs are combined to characterize the system. The 2.5 min binned phase-folded light curve is affected by the effect of sucessive occultations of stellar active regions by the planet, and the dispersion in the out of transit part reaches a level of 1.09 × 10 −4 in flux units. Results. We derive a radius for the planet of 1.465 ± 0.029 R Jup and a mass of 3.31 ± 0.16 M Jup , corresponding to a density of 1.31 ± 0.04 g/cm 3 . The large radius of CoRoT-Exo-2b cannot be explained by current models of evolution of irradiated planets.

Aims. The statistical properties of planets in binaries were investigated. Any difference to planets orbiting single stars can shed light on the formation and evolution of planetary systems. As planets were found around components of binaries with very different separation and mass ratio, it is particularly important to study the characteristics of planets as a function of the effective gravitational influence of the companion. Methods. A compilation of planets in binary systems was made; a search for companions orbiting stars recently shown to host planets was performed, resulting in the addition of two further binary planet hosts (HD 20782 and HD 109749). The probable original properties of the three binary planet hosts with white dwarfs companions were also investigated. Using this updated sample of planets in binaries we performed a statistical analysis of the distributions of planet mass, period, and eccentricity, fraction of multiplanet systems, and stellar metallicity for planets orbiting components of tight and wide binaries and single stars. Results. The only highly significant difference revealed by our analysis concerns the mass distribution of short-period planets. Massive planets in short period orbits are found in most cases around the components of rather tight binaries. The properties of exoplanets orbiting the components of wide binaries are compatible with those of planets orbiting single stars, except for a possible greater abundance of high-eccentricity planets. The previously suggested lack of massive planets with P > 100 days in binaries is not confirmed. Conclusions. We conclude that the presence of a stellar companion with separation smaller than 100-300 AU is able to modify the formation and/or migration and/or the dynamical evolution history of giant planets while wide companions play a more limited role.

Our understanding of how the Galaxy was formed and evolves is severely hampered by the lack of precise constraints on basic stellar properties such as distances, masses, and ages. Here, we show that solar-like pulsating red giants represent a well-populated class of accurate distance indicators, spanning a large age range, which can be used to map and date the Galactic disc in the regions probed by observations made by the CoRoT † and Kepler space telescopes. When combined with photometric constraints, the pulsation spectra of such evolved stars not only reveal their radii, and hence distances, but also provide well-constrained estimates of their masses, which are reliable proxies for the ages of the stars. As a first application we consider red giants observed by CoRoT in two different parts of the Milky Way, and determine precise distances for ∼2000 stars spread across nearly 15,000 pc of the Galactic disc, exploring regions which are a long way from the solar neighbourhood. We find significant differences in the mass distributions of these two samples which, by comparison with predictions of synthetic models of the Milky Way, we interpret as mainly due to the vertical gradient in the distribution of stellar masses (hence ages) in the disc. In the future, the availability of spectroscopic constraints for this sample of stars will not only improve the age determination, but also provide crucial constraints on age-velocity and age-metallicity relations at different Galactocentric radii and heights from the plane.