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The Juno mission has provided measurements of Jupiter s gravity field with an outstanding level of accuracy, leading to better constraints on the interior of the planet. Improving our knowledge of the internal structure of Jupiter is key to understanding its formation and evolution but is also important in the framework of exoplanet exploration. In this study, we investigated the differences between the state-of-the-art equations of state and their impact on the properties of interior models. Accounting for uncertainty on the hydrogen and helium equation of state, we assessed the span of the interior features of Jupiter. We carried out an extensive exploration of the parameter space and studied a wide range of interior models using Markov chain Monte Carlo (MCMC) simulations. To consider the uncertainty on the equation of state, we allowed for modifications of the equation of state in our calculations. Our models harbour a dilute core and indicate that Jupiter s internal entropy is higher than what is usually assumed from the Galileo probe measurements. We obtain solutions with extended dilute cores, but contrary to other recent interior models of Jupiter, we also obtain models with small dilute cores. The dilute cores in such solutions extend to 20% of Jupiter s mass, leading to better agreement with formation evolution models. We conclude that the equations of state used in Jupiter models have a crucial effect on the inferred structure and composition. Further explorations of the behaviour of hydrogen helium mixtures at the pressure and temperature conditions in Jupiter will help to constrain the interior of the planet, and therefore its origin.

While Jupiter's massive gas envelope consists mainly of hydrogen and helium, the key to understanding Jupiter's formation and evolution lies in the distribution of the remaining (heavy) elements. Before the Juno mission, the lack of high-precision gravity harmonics precluded the use of statistical analyses in a robust determination of the heavy-elements distribution in Jupiter's envelope. In this paper, we assemble the most comprehensive and diverse collection of Jupiter interior models to date and use it to study the distribution of heavy elements in the planet's envelope. We apply a Bayesian statistical approach to our interior model calculations, reproducing the Juno gravitational and atmospheric measurements and constraints from the deep zonal flows. Our results show that the gravity constraints lead to a deep entropy of Jupiter corresponding to a 1 bar temperature 5-15 K higher than traditionally assumed. We also find that uncertainties in the equation of state are crucial when determining the amount of heavy elements in Jupiter's interior. Our models put an upper limit to the inner compact core of Jupiter of 7 Earth masses, independently on the structure model (with or without dilute core) and the equation of state considered. Furthermore, we robustly demonstrate that Jupiter's envelope is inhomogenous, with a heavy-element enrichment in the interior relative to the outer envelope. This implies that heavy element enrichment continued through the gas accretion phase, with important implications for the formation of giant planets in our solar system and beyond., Comment: Accepted for publication in A&A

In this study I assess how existing data for the solar analogues 16 Cyg A and B, in particular the asteroseismic measurements obtained from \emph{Kepler}, constrain theoretical stellar models. The goal is two-fold: first to use these stars as benchmarks to discuss which precisions can realistically be expected on the inferred stellar quantities; and second to determine how well 'non-standard' prescriptions, such as microscopic diffusion and overshoot, are constrained. I used a Bayesian statistical model to infer the values of the stellar parameters of 16 Cyg A and B. I sampled the posterior density of the stellar parameters via a Markov chain Monte Carlo (MCMC) algorithm, tested different physical prescription, and examined the impact of using different seismic diagnostics. General good agreement is found with several recent modelling studies on these stars, even though some discrepancies subsist regarding the precise estimates of the uncertainties on the parameters. An age of $6.88\pm0.12$ Gyr is estimated for the binary system. The inferred masses, $1.07\pm0.02$ M$_{\odot}$ for Cyg A and $1.05\pm0.02$ M$_{\odot}$ for Cyg B, are shown to be stable with respect to changes in the physical prescriptions considered for the modelling. For both stars, microscopic diffusion has a significant effect on the estimates of the initial metallicity. Overshoot is confined to very small regions below the convective zone. I show that a proper treatment of the seismic constraints is necessary to avoid biases in the estimate of the mass., Comment: 13 pages, 7 figures, to appear in A & A

Asteroseismology has undergone a profound transformation as a scientific field following the CoRoT and Kepler space missions. The latter is now yielding the first measurements of latitudinal differential rotation obtained directly from oscillation frequencies. Differential rotation is a fundamental mechanism of the stellar dynamo effect. Our goal is to measure the amount of differential rotation in the solar analogues 16 Cyg A and B, which are the components of a binary system. These stars are the brightest observed by Kepler and have therefore been extensively observed, with exquisite precision on their oscillation frequencies. We modelled the acoustic power spectrum of 16 Cyg A and B using a model that takes into account the contribution of differential rotation to the rotational frequency splitting. The estimation was carried out in a Bayesian setting. We then inverted these results to obtain the rotation profile of both stars under the assumption of a solar-like functional form. We observe that the magnitude of latitudinal differential rotation has a strong chance of being solar-like for both stars, their rotation rates being higher at the equator than at the pole. The measured latitudinal differential rotation, defined as the difference of rotation rate between the equator and the pole, is $320\pm269$ nHz and $440^{+363}_{-383}$ nHz for 16 Cyg A and B, respectively, confirming that the rotation rates of these stars are almost solar-like. Their equatorial rotation rates are $535\pm75$ nHz and $565_{-129}^{+150}$ nHz. Our results are in good agreement with measurements obtained from spectropolarimetry, spectroscopy, and photometry. We present the first conclusive measurement of latitudinal differential rotation for solar analogues. Their rotational profiles are very close to those of the Sun. These results depend weakly on the uncertainties of the stellar parameters., Comment: Accepted in A&A

Stellar magnetic fields are poorly understood but are known to be important for stellar evolution and exoplanet habitability. They drive stellar activity, which is the main observational constraint on theoretical models for magnetic field generation and evolution. Starspots are the main manifestation of the magnetic fields at the stellar surface. In this study we measure the variation of their latitude with time, called a butterfly diagram in the solar case, for the solar analogue HD 173701 (KIC 8006161). To that effect, we use Kepler data, to combine starspot rotation rates at different epochs and the asteroseismically determined latitudinal variation of the stellar rotation rates. We observe a clear variation of the latitude of the starspots. It is the first time such a diagram is constructed using asteroseismic data., Comment: 8 pages, 4 figures, accepted in A&A Letters

Solar twins are objects of great interest in that they allow us to understand better how stellar evolution and structure are affected by variations of the stellar mass, age and chemical composition in the vicinity of the commonly accepted solar values. We aim to use the existing spectrophotometric, interferometric and asteroseismic data for the solar twin 18 Sco to constrain stellar evolution models. 18 Sco is the brightest solar twin and is a good benchmark for the study of solar twins. The goal is to obtain realistic estimates of its physical characteristics (mass, age, initial chemical composition, mixing-length parameter) and realistic associated uncertainties using stellar models. We set up a Bayesian model that relates the statistical properties of the data to the probability density of the stellar parameters. Special care is given to the modelling of the likelihood for the seismic data, using Gaussian mixture models. The probability densities of the stellar parameters are approximated numerically using an adaptive MCMC algorithm. From these approximate distributions we proceeded to a statistical analysis. We also performed the same exercise using local optimisation. The precision on the mass is approximately 6%. The precision reached on X0 and Z0 and the mixing-length parameter are respectively 6%, 9%, and 35%. The posterior density for the age is bimodal, with modes at 4.67 Gyr and 6.95 Gyr, the first one being slightly more likely. We show that this bimodality is directly related to the structure of the seismic data. When asteroseismic data or interferometric data are excluded, we find significant losses of precision for the mass and the initial hydrogen-mass fraction. Our final estimates of the uncertainties from the Bayesian analysis are significantly larger than values inferred from local optimization.

The differentially rotating outer layers of stars are thought to play a role in driving their magnetic activity, but the underlying mechanisms that generate and sustain differential rotation are poorly understood. We report the measurement of latitudinal differential rotation in the convection zones of 40 Sun-like stars using asteroseismology. For the most significant detections, the stars' equators rotate approximately twice as fast as their mid-latitudes. The latitudinal shear inferred from asteroseismology is much larger than predictions from numerical simulations., Comment: 45 pages, 11 figures, 4 tables, published in Science

Oscillation properties are usually measured by fitting symmetric Lorentzian profiles to the power spectra of Sun-like stars. However the line profiles of solar oscillations have been observed to be asymmetrical for the Sun. The physical origin of this line asymmetry is not fully understood, although it should depend on the depth dependence of the source of wave excitation (convective turbulence) and details of the observable (velocity or intensity). For oscillations of the Sun, it has been shown that neglecting the asymmetry leads to systematic errors in the frequency determination. This could subsequently affects the results of seismic inferences of the solar internal structure. Using light curves from the {\it Kepler} spacecraft we have measured mode asymmetries in 43 stars. We confirm that neglecting the asymmetry leads to systematic errors that can exceed the $1\sigma$ confidence intervals for seismic observations longer than one year. Therefore, the application of an asymmetric Lorentzian profile is to be favoured to improve the accuracy of the internal stellar structure and stellar fundamental parameters. We also show that the asymmetry changes sign between cool Sun-like stars and hotter stars. This provides the best constraints to date on the location of the excitation sources across the Hertzsprung-Russel diagram., Comment: 8 pages, 7 Figures, 1 Table, Accepted to ApJ

Binary star systems are important for understanding stellar structure and evolution, and are especially useful when oscillations can be detected and analysed with asteroseismology. However, only four systems are known in which solar-like oscillations are detected in both components. Here, we analyse the fifth such system, HD 176465, which was observed by Kepler. We carefully analysed the system's power spectrum to measure individual mode frequencies, adapting our methods where necessary to accommodate the fact that both stars oscillate in a similar frequency range. We also modelled the two stars independently by fitting stellar models to the frequencies and complementary parameters. We are able to cleanly separate the oscillation modes in both systems. The stellar models produce compatible ages and initial compositions for the stars, as is expected from their common and contemporaneous origin. Combining the individual ages, the system is about 3.0$\pm$0.5 Gyr old. The two components of HD 176465 are young physically-similar oscillating solar analogues, the first such system to be found, and provide important constraints for stellar evolution and asteroseismology., Comment: Accepted for publication in Astronomy and Astrophysics. 16 pages, 10 figures and 8 tables

High-quality astrometric, spectroscopic, interferometric and, importantly, asteroseismic observations are available for $\alpha$ Cen A, which is the closest binary star system to earth. Taking all these constraints into account, we study the internal structure of the star by means of theoretical modelling. Using the Aarhus STellar Evolution Code (ASTEC) and the tools of Computational Bayesian Statistics, in particular a Markov chain Monte Carlo algorithm, we perform statistical inferences for the physical characteristics of the star. We find that $\alpha$ Cen A has a probability of approximately 40% of having a convective core. This probability drops to few percents if one considers reduced rates for the $^{14}$N(p,$\gamma$)$^{15}$O reaction. These convective cores have fractional radii less than 8% when overshoot is neglected. Including overshooting also leads to the possibility of a convective core mostly sustained by the ppII chain energy output. We finally show that roughly 30% of the stellar models describing $\alpha$ Cen A are in the subgiant regime., Comment: 17 pages, 7 figures, accepted for publication in MNRAS

We study with unprecedented detail the chemical composition and stellar parameters of the solar twin 18 Sco in a strictly differential sense relative to the Sun. Our study is mainly based on high resolution (R ~ 110 000) high S/N (800-1000) VLT UVES spectra, which allow us to achieve a precision of about 0.005 dex in differential abundances. The effective temperature and surface gravity of 18 Sco are Teff = 5823+/-6 K and log g = 4.45+/-0.02 dex, i.e., 18 Sco is 46+/-6 K hotter than the Sun and log g is 0.01+/-0.02 dex higher. Its metallicity is [Fe/H] = 0.054+/-0.005 dex and its microturbulence velocity is +0.02+/-0.01 km/s higher than solar. Our precise stellar parameters and differential isochrone analysis show that 18 Sco has a mass of 1.04+/-0.02M_Sun and that it is ~1.6 Gyr younger than the Sun. We use precise HARPS radial velocities to search for planets, but none were detected. The chemical abundance pattern of 18 Sco displays a clear trend with condensation temperature, showing thus higher abundances of refractories in 18 Sco than in the Sun. Intriguingly, there are enhancements in the neutron-capture elements relative to the Sun. Despite the small element-to-element abundance differences among nearby n-capture elements (~0.02 dex), we successfully reproduce the r-process pattern in the solar system. This is independent evidence for the universality of the r-process. Our results have important implications for chemical tagging in our Galaxy and nucleosynthesis in general., Comment: ApJ, in press

Determining the physical characteristics of a star is an inverse problem consisting in estimating the parameters of models for the stellar structure and evolution, knowing certain observable quantities. We use a Bayesian approach to solve this problem for alpha Cen A, which allows us to incorporate prior information on the parameters to be estimated, in order to better constrain the problem. Our strategy is based on the use of a Markov Chain Monte Carlo (MCMC) algorithm to estimate the posterior probability densities of the stellar parameters: mass, age, initial chemical composition,... We use the stellar evolutionary code ASTEC to model the star. To constrain this model both seismic and non-seismic observations were considered. Several different strategies were tested to fit these values, either using two or five free parameters in ASTEC. We are thus able to show evidence that MCMC methods become efficient with respect to more classical grid-based strategies when the number of parameters increases. The results of our MCMC algorithm allow us to derive estimates for the stellar parameters and robust uncertainties thanks to the statistical analysis of the posterior probability densities. We are also able to compute odds for the presence of a convective core in alpha Cen A. When using core-sensitive seismic observational constraints, these can raise above ~40%. The comparison of results to previous studies also indicates that these seismic constraints are of critical importance for our knowledge of the structure of this star., Comment: 21 pages, 6 figures, to be published in MNRAS

The growing interest in solar twins is motivated by the possibility of comparing them directly to the Sun. To carry on this kind of analysis, we need to know their physical characteristics with precision. Our first objective is to use asteroseismology and interferometry on the brightest of them: 18 Sco. We observed the star during 12 nights with HARPS for seismology and used the PAVO beam-combiner at CHARA for interferometry. An average large frequency separation $134.4\pm0.3$ $\mu$Hz and angular and linear radiuses of $0.6759 \pm 0.0062$ mas and $1.010\pm0.009$ R$_{\odot}$ were estimated. We used these values to derive the mass of the star, $1.02\pm0.03$ M$_{\odot}$., Comment: 5 pages, 5 figures

Solar twins have been a focus of attention for more than a decade, because their structure is extremely close to that of the Sun. Today, thanks to high-precision spectrometers, it is possible to use asteroseismology to probe their interiors. Our goal is to use time series obtained from the HARPS spectrometer to extract the oscillation frequencies of 18 Sco, the brightest solar twin. We used the tools of spectral analysis to estimate these quantities. We estimate 52 frequencies using an MCMC algorithm. After examination of their probability densities and comparison with results from direct MAP optimization, we obtain a minimal set of 21 reliable modes. The identification of each pulsation mode is straightforwardly accomplished by comparing to the well-established solar pulsation modes. We also derived some basic seismic indicators using these values. These results offer a good basis to start a detailed seismic analysis of 18 Sco using stellar models., Comment: 12 pages, 6 figures, to be published in A&A

Having started science operations in May 2009, the Kepler photometer has been able to provide exquisite data of solar-like stars. Five out of the 42 stars observed continuously during the survey phase show evidence of oscillations, even though they are rather faint (magnitudes from 10.5 to 12). In this paper, we present an overview of the results of the seismic analysis of 4 of these stars observed during more than eight months., Comment: 5 pages, 1 figure. To appear in the ASP proceedings of "The 61st Fujihara seminar: Progress in solar/stellar physics with helio- and asteroseismology", 13th-17th March 2011, Hakone, Japan

The evolved main-sequence Sun-like stars KIC 10273246 (F-type) and KIC 10920273 (G-type) were observed with the NASA Kepler satellite for approximately ten months with a duty cycle in excess of 90%. Such continuous and long observations are unprecedented for solar-type stars other than the Sun. We aimed mainly at extracting estimates of p-mode frequencies - as well as of other individual mode parameters - from the power spectra of the light curves of both stars, thus providing scope for a full seismic characterization. The light curves were corrected for instrumental effects in a manner independent of the Kepler Science Pipeline. Estimation of individual mode parameters was based both on the maximization of the likelihood of a model describing the power spectrum and on a classic prewhitening method. Finally, we employed a procedure for selecting frequency lists to be used in stellar modeling. A total of 30 and 21 modes of degree l=0,1,2 - spanning at least eight radial orders - have been identified for KIC 10273246 and KIC 10920273, respectively. Two avoided crossings (l=1 ridge) have been identified for KIC 10273246, whereas one avoided crossing plus another likely one have been identified for KIC 10920273. Good agreement is found between observed and predicted mode amplitudes for the F-type star KIC 10273246, based on a revised scaling relation. Estimates are given of the rotational periods, the parameters describing stellar granulation and the global asteroseismic parameters $\Delta\nu$ and $\nu_{\rm{max}}$., Comment: 15 pages, 15 figures, to be published in Astronomy & Astrophysics

The star HD 52265 is a G0V metal-rich exoplanet-host star observed in the seismology field of the CoRoT space telescope from November 2008 to March 2009. The satellite collected 117 days of high-precision photometric data on this star, showing that it presents solar-like oscillations. HD 52265 was also observed in spectroscopy with the Narval spectrograph at the same epoch. We characterise HD 52265 using both spectroscopic and seismic data. The fundamental stellar parameters of HD 52265 were derived with the semi-automatic software VWA, and the projected rotational velocity was estimated by fitting synthetic profiles to isolated lines in the observed spectrum. The parameters of the observed p modes were determined with a maximum-likelihood estimation. We performed a global fit of the oscillation spectrum, over about ten radial orders, for degrees l=0 to 2. We also derived the properties of the granulation, and analysed a signature of the rotation induced by the photospheric magnetic activity. Precise determinations of fundamental parameters have been obtained: Teff = 6100 +- 60 K, log g = 4.35 +- 0.09, [M/H] = 0.19 +- 0.05, as well as vsini = 3.6 +0.3 -1.0 km/s. We have measured a mean rotation period P_rot = 12.3 +- 0.15 days, and find a signature of differential rotation. The frequencies of 31 modes are reported in the range 1500-2550 micro-Hz. The large separation exhibits a clear modulation around the mean value = 98.3 +- 0.1 micro-Hz. Mode widths vary with frequency along an S-shape with a clear local maximum around 1800 micro-Hz. We deduce lifetimes ranging between 0.5 and 3 days for these modes. Finally, we find a maximal bolometric amplitude of about 3.96 +- 0.24 ppm for radial modes., Comment: published in A&A, 11 pages, 14 figures, 6 tables

We present two independent methods for studying the global stellar parameter space (mass M, age, initial chemical composition X_0, Z_0) of HD 49933 with seismic data. Using a local minimization and an MCMC algorithm, we obtain consistent results for the determination of the stellar properties: M = 1.1 - 1.2 M_solar, Age ~ 3.0 Gyr, Z_0 ~ 0.008. A description of the error ellipses can be defined using Singular Value Decomposition techniques, and this is validated by comparing the errors with those from the MCMC method., Comment: to be published in JPCS

The primary science goal of the Kepler Mission is to provide a census of exoplanets in the solar neighborhood, including the identification and characterization of habitable Earth-like planets. The asteroseismic capabilities of the mission are being used to determine precise radii and ages for the target stars from their solar-like oscillations. Chaplin et al. (2010) published observations of three bright G-type stars, which were monitored during the first 33.5 days of science operations. One of these stars, the subgiant KIC 11026764, exhibits a characteristic pattern of oscillation frequencies suggesting that it has evolved significantly. We have derived asteroseismic estimates of the properties of KIC 11026764 from Kepler photometry combined with ground-based spectroscopic data. We present the results of detailed modeling for this star, employing a variety of independent codes and analyses that attempt to match the asteroseismic and spectroscopic constraints simultaneously. We determine both the radius and the age of KIC 11026764 with a precision near 1%, and an accuracy near 2% for the radius and 15% for the age. Continued observations of this star promise to reveal additional oscillation frequencies that will further improve the determination of its fundamental properties., Comment: 16 pages, 6 figures, 4 tables, ApJ in press

We have analyzed data from a multi-site campaign to observe oscillations in the F5 star Procyon. The data consist of high-precision velocities that we obtained over more than three weeks with eleven telescopes. A new method for adjusting the data weights allows us to suppress the sidelobes in the power spectrum. Stacking the power spectrum in a so-called echelle diagram reveals two clear ridges that we identify with even and odd values of the angular degree (l=0 and 2, and l=1 and 3, respectively). We interpret a strong, narrow peak at 446 muHz that lies close to the l=1 ridge as a mode with mixed character. We show that the frequencies of the ridge centroids and their separations are useful diagnostics for asteroseismology. In particular, variations in the large separation appear to indicate a glitch in the sound-speed profile at an acoustic depth of about 1000 s. We list frequencies for 55 modes extracted from the data spanning 20 radial orders, a range comparable to the best solar data, which will provide valuable constraints for theoretical models. A preliminary comparison with published models shows that the offset between observed and calculated frequencies for the radial modes is very different for Procyon than for the Sun and other cool stars. We find the mean lifetime of the modes in Procyon to be 1.29 +0.55/-0.49 days, which is significantly shorter than the 2-4 days seen in the Sun., Comment: accepted for publication in ApJ

We combine results from interferometry, asteroseismology and spectroscopy to determine accurate fundamental parameters of 23 bright solar-type stars, from spectral type F5 to K2 and luminosity classes III to V. For some stars we can use direct techniques to determine the mass, radius, luminosity and effective temperature, and we compare with indirect methods that rely on photometric calibrations or spectroscopic analyses. We use the asteroseismic information available in the literature to infer an indirect mass with an accuracy of 4-15 percent. From indirect methods we determine luminosity and radius to 3 percent. For Teff we find a slight offset of -40+-20 K between the spectroscopic method and the direct method, meaning the spectroscopic temperatures are too high. From the spectroscopic analysis we determine the detailed chemical composition for 13 elements, including Li, C and O. We find no significant offset between the spectroscopic surface gravity and the value from combining asteroseismology with radius estimates. From the spectroscopy we also determine vsini and we present a new calibration of macro- and microturbulence. From the comparison between the results from the direct and spectroscopic methods we claim that we can determine Teff, log g, and [Fe/H] with absolute accuracies of 80 K, 0.08 dex, and 0.07 dex. The indirect methods are important to obtain reliable estimates of the fundamental parameters of relatively faint stars when interferometry cannot be used. Our study is the first to compare direct and indirect methods for a large sample of stars, and we conclude that indirect methods are valid, although slight corrections may be needed., Comment: Accepted by MNRAS. Abstract abridged

We present preliminary asteroseismic results from Kepler on three G-type stars. The observations, made at one-minute cadence during the first 33.5d of science operations, reveal high signal-to-noise solar-like oscillation spectra in all three stars: About 20 modes of oscillation may be clearly distinguished in each star. We discuss the appearance of the oscillation spectra, use the frequencies and frequency separations to provide first results on the radii, masses and ages of the stars, and comment in the light of these results on prospects for inference on other solar-type stars that Kepler will observe., Comment: 16 pages, 3 figures, 1 table; now accepted for publication in ApJ Letters

We review three Li problems. First, the Li problem in the Sun, for which some previous studies have argued that it may be Li-poor compared to other Suns. Second, we discuss the Li problem in planet hosting stars, which are claimed to be Li-poor when compared to field stars. Third, we discuss the cosmological Li problem, i.e. the discrepancy between the Li abundance in metal-poor stars (Spite plateau stars) and the predictions from standard Big Bang Nucleosynthesis. In all three cases we find that the "problems" are naturally explained by non-standard mixing in stars., Comment: Astrophysics and Space Science, in press. New version has one reference corrected

We analyze the non-standard mixing history of the solar twins HIP 55459, HIP 79672, HIP 56948, HIP 73815, and HIP 100963, to determine as precisely as possible their mass and age. We computed a grid of evolutionary models with non-standard mixing at several metallicities with the Toulouse-Geneva code for a range of stellar masses assuming an error bar of +-50K in Teff. We choose the evolutionary model that reproduces accurately the observed low lithium abundances observed in the solar twins. Our best-fit model for each solar twin provides a mass and age solution constrained by their Li content and Teff determination. HIP 56948 is the most likely solar-twin candidate at the present time and our analysis infers a mass of 0.994 +- 0.004 Msun and an age of 4.71 +-1.39 Gyr. Non-standard mixing is required to explain the low Li abundances observed in solar twins. Li depletion due to additional mixing in solar twins is strongly mass dependent. An accurate lithium abundance measurement and non-standard models provide more precise information about the age and mass more robustly than determined by classical methods alone., Comment: 10 pages, 5 figures, Accepted for publication in Astronomy and Astrophysics

We apply Monte Carlo Markov Chain methods to the stellar parameter estimation problem. This technique is useful when dealing with non-linear models and allows to derive realistic error bars on the inferred parameters. We give the first results obtained for alpha Cen A., Comment: 3 pages, 1 figures, to appear in "Memorie della Societa' Astronomica Italiana", Vol. 79 No. 2, eds. S. Cassisi & M. Salaris. Proceedings of the Cefalu' 2007 Workshop "XXI Century challenges for stellar evolution", Cefalu' (Sicily, Italy), August 29 - September 2, 2007

We show that the exoplanet-host star iota Horologii, alias HD17051, which belongs to the so-called Hyades stream, was formed within the primordial Hyades stellar cluster and has evaporated towards its present location, 40 pc away. This result has been obtained unambiguously by studying the acoustic oscillations of this star, using the HARPS spectrometer in La Silla Observatory (ESO, Chili). Besides the fact that $\iota$ Hor belongs to the Hyades stream, we give evidence that it has the same metallicity, helium abundance, and age as the other stars of the Hyades cluster. They were formed together, at the same time, in the same primordial cloud. This result has strong implications for theories of stellar formation. It also indicates that the observed overmetallicity of this exoplanet-host star, about twice that of the Sun, is original and not caused by planet accretion during the formation of the planetary system., Comment: to be published in A&A letters

Procyon A is a bright F5IV star in a binary system. Although the distance, mass and angular diameter of this star are all known with high precision, the exact evolutionary state is still unclear. Evolutionary tracks with different ages and different mass fractions of hydrogen in the core pass, within the errors, through the observed position of Procyon A in the Hertzsprung-Russell diagram. For more than 15 years several different groups have studied the solar-like oscillations in Procyon A to determine its evolutionary state. Although several studies independently detected power excess in the periodogram, there is no agreement on the actual oscillation frequencies yet. This is probably due to either insufficient high-quality data (i.e., aliasing) or due to intrinsic properties of the star (i.e., short mode lifetimes). Now a spectroscopic multi-site campaign using 10 telescopes world-wide (minimizing aliasing effects) with a total time span of nearly 4 weeks (increase the frequency resolution) is performed to identify frequencies in this star and finally determine its properties and evolutionary state., Comment: 7 pages, 4 figures to be published in the proceedings of HELAS II International Conference: Helioseismology, Asteroseismology and MHD Connections published in the Journal of Physics: Conference Series. High resolution colour figures can be provided on request

Asteroseismology provides a unique tool for studying stellar interiors. Recently p modes have been detected on the bright solar-like star alpha Cen A thanks to high-precision radial-velocity measurements. However a better characterisation of these p modes is clearly needed to constrain theoretical models. We observed alpha Cen A during five nights using the HARPS spectrograph in order to improve our knowledge of the seismic properties of this star. We performed high-precision radial-velocity sequences and computed the acoustic spectrum of alpha Cen A. We identify 34 p modes with angular degree l=0-3 in the frequency range 1.8-2.9 mHz and amplitude range 13-48 cm/s, in agreement with previous seismic studies. We find an enhancement of the frequency scatter with the angular degree l that indicates, considering the high inclination axis of alpha Cen A, rotational splitting and explains the low values of previously suggested mode lifetimes. We also derive new values for the small separations that take the effect of rotational splitting into account . Our seismic study of alpha Cen A leads to a list of now well identified p-mode frequencies and shows the importance of taking the rotation into account in order to properly characterise the p modes even in quite short campaigns., Comment: 10 pages, 9 figures. To be published in A&A

As most exoplanets host stars, HD 160691 (alias mu Ara) presents a metallicity excess in its spectrum compared to stars without detected planets. This excess may be primordial, in which case the star would be completely overmetallic, or it may be due to accretion in the early phases of planetary formation, in which case it would be overmetallic only in its outer layers. As discussed in a previous paper (Bazot and Vauclair 2004), seismology can help choosing between the two scenarios. This star was observed during eight nights with the spectrograph HARPS at La Silla Observatory. Forty three p-modes have been identified (Bouchy et al. 2005). In the present paper, we discuss the modelisation of this star. We computed stellar models iterated to present the same observable parameters (luminosity, effective temperature, outer chemical composition) while the internal structure was different according to the two extreme assumptions : original overmetallicity or accretion. We show that in any case the seismic constraints lead to models in complete agreement with the external parameters deduced from spectroscopy and from the Hipparcos parallax (L and Teff). We discuss the tests which may lead to a choice between the two typical scenarios. We show that the ``small separation'' seem to give a better fit for the accretion case than for the overmetallic case, but in spite of the very good data the uncertainties are still too large to conclude. We discuss the observations which would be needed to go further and solve this question., Comment: 16 pages, 8 figures, accepted in A&A

In this letter we present the discovery of a very light planetary companion to the star mu Ara (HD160691). The planet orbits its host once every 9.5days, and induces a sinusoidal radial velocity signal with a semi-amplitude of 4.1 m/s, the smallest Doppler amplitude detected so far. These values imply a mass of m2 sini = 14 earth-masses. This detection represents the discovery of a planet with a mass slightly smaller than that of Uranus, the smallest ``ice giant" in our Solar System. Whether this planet can be considered an ice giant or a super-earth planet is discussed in the context of the core-accretion and migration models., Comment: Replaced on 2004-09-10 by final version, accepted for publication in A&A Letters

Exoplanets host stars present a clear metallicity excess compared to stars without detected planets, with an average overabundance of 0.2 dex. This excess may be primordial, in which case the stars should be overmetallic down to their center, or it may be due to accretion in the early phases of planetary formation, in which case the stars would be overmetallic only in their outer layers. In the present paper, we show the differences in the internal structure of stars, according to the chosen scenario. Namely two stars with the same observable parameters (luminosity, effective temperature, outer chemical composition) are completely different in their interiors according to their past histories, which we reconstitute through the computations of their evolutionary tracks. It may happen that stars with an initial overmetallicity have a convective core while the stars which suffered accretion do not. We claim that asteroseismic studies of these exoplanets host stars can give clues about their internal structures and metallicities, which may help in understanding planetary formation., Comment: 24 pages, 18 figures, accepted by A&A