The CoRoT primary target HD 52265: models and seismic tests

HD 52265 is the only known exoplanet-host star selected as a main target for the seismology programme of the CoRoT satellite. As such, it will be observed continuously during five months, which is of particular interest in the framework of planetary systems studies. This star was misclassified as a giant in the Bright Star Catalog, while it is more probably on the main-sequence or at the beginning of the subgiant branch. We performed an extensive analysis of this star, showing how asteroseismology may lead to a precise determination of its external parameters and internal structure. We first reviewed the observational constraints on the metallicity, the gravity and the effective temperature derived from the spectroscopic observations of HD 52265. We also derived its luminosity using the Hipparcos parallax. We computed the evolutionary tracks for models of various metallicities which cross the relevant observational error boxes in the gravity-effective temperature plane. We selected eight different stellar models which satisfy the observational constraints, computed their p-modes frequencies and analysed specific seismic tests. The possible models for HD 52265, which satisfy the constraints derived from the spectroscopic observations, are different in both their external and internal parameters. They lie either on the main sequence or at the beginning of the subgiant branch. The differences in the models lead to quite different properties of their oscillation frequencies. We give evidences of an interesting specific behaviour of these frequencies in case of helium-rich cores: the ``small separations'' may become negative and give constraints on the size of the core. We expect that the observations of this star by the CoRoT satellite wi ll allow choosing between these possible models.Comment: 11 pages, 7 figures, to be published in Astronomy and Astrophysic

Asteroseismology of alpha Cen A. Evidence of rotational splitting

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&

Asteroseismology of exoplanets host stars: the special case of ι\iota Horologii (HD17051)

{This paper presents detailed analysis and modelisation of the star HD17051 (alias $\iota$ Hor), which appears as a specially interesting case among exoplanet host stars. As most of these stars, $\iota$ Hor presents a metallicity excess which has been measured by various observers who give different results, ranging from [Fe/H] = 0.11 to 0.26, associated with different atmospheric parameters. Meanwhile the luminosity of the star may be determined owing to Hipparcos parallax. Although in the southern hemisphere, this star belongs to the Hyades stream and its external parameters show that it could even be one of the Hyades stars ejected during cluster formation. The aim of this work was to gather and analyse our present knowledge on this star and to prepare seismic tests for future observations with the HARPS spectrometer (planned for November 2006).} {We have computed evolutionary tracks with various metallicities, in the two frameworks of primordial overmetallicity and accretion. We have concentrated on models inside the error boxes given by the various observers in the log g - log T$_{eff}$ diagram. We then computed the adiabatic oscillation frequencies of these models to prepare future observations.} {The detailed analysis of $\iota$ Hor presented in this paper already allowed to constrain its external parameters, mass and age. Some values given in the literature could be rejected as inconsistent with the overall analysis. We found that a model computed with the Hyades parameters (age, metallicity) was clearly acceptable, but other ones were possible too. We are confident that observations with HARPS will allow for a clear conclusion about this star and that it will bring important new light on the physics of exoplanet host stars.}Comment: to be published in Astronomy and Astrophysic

Seismic predictions for the CoRoT main target HD 52265

International audienceHD 52265 is the only exoplanet-host star selected as a main target for the seismology programme of the CoRoT mission, and so it will be observed continuously during five months. This is of great interest in the framework of asteroseismology of exoplanet-host stars, in order to better understand the planetary formation and migration. We performed and extensive analysis of this star, computed models and analysed their frequencies. CoRoT observations should enable us to discriminate between the various models allowed from spectroscopic observations

Asteroseismology of α Cen A

Asteroseismology, which consists in measuring properties of p-mode oscillations, provides a unique tool for studying stellar interiors . Recently p modes have been detected on the bright solar-like star α Cen A thanks to high- precision radial- velocity measurements. However a better characterization of p modes is clearly needed to constrain theoretical models. We observed α Cen A during five nights using the high precision spectrograph HARPS in order to improve our knowledge of the seismic properties of this star and to investigate its mode lifetimes and rotational splitting. We obtained high- precision radial- velocity sequences and computed the acoustic spectrum of α Cen A . We estimate the scatter in the frequencies for each angular degree ( ℓ) and analyse it to constrain the rotational splitting and mode lifetimes. We identify 34 p modes with angular degree ℓ = 0 - 3 in the frequency range 1.8 - 2 .9 mHz and amplitude range 13 - 4 8 cms, in agreement with the previous seismic studies. We find a clear enhancement of the frequency scatter with the angular degree ( ℓ) , which indicates rotational splitting and explains the low value of mode lifetimes previously suggested by Kjeldsen et al. (2005). Combining all of the existing seismic measurements, we determine a mode lifetime of days and a rotational rate. We also derive new values for the small separations that take into account the effect of rotational splitting. Our seismic study of α Cen A leads to a list of now well- identified p-mode frequencies and shows the importance of taking into account the rotation in order to properly characterize the p modes even for quite short campaigns

Rotation and small separations of ? Cen A

We observed ? Cen A during five nights using HARPS. We identified 34 p modes. We observed multiple frequencies for some value of radial order n and degree ?. We analyse the scatter of these frequencies relative to the asymptotic relation and argue that they result from rotational splitting. We derive new values for the small separations taking in account this effect

Synthesis of β-Hydroxy and β-Amino Ketones from Allylic Alcohols Catalyzed by Ru(η5-C5Ph5)(CO)2Cl

An efficient method for the synthesis of beta-hydroxy and beta-amino ketones from allylic alcohols catalyzed by Ru(5-C5Ph5)(CO)2Cl is described. The influence of the stereoelectronic properties of the catalyst on the reaction outcome has been studied. Optimization of the reaction conditions supressed the formation of undesired side products such as saturated ketones, benzyl alcohols, and a,beta-unsaturated ketones. Several aromatic and aliphatic allylic alcohols have been reacted with a large variety of aldehydes or imines to produce beta-hydroxy ketones or beta-amino ketones, respectively, in yields up to 99%. Based on experimental data, a mechanism via ruthenium alkoxides and ruthenium aldoxides is proposed. In addition, a C-bound ruthenium enolate has been characterized.5</p

ASTEROSEISMOLOGY OF EXOPLANETS-HOST STARS: A LINK BETWEEN THE TWO SCIENTIFIC PROGRAMMES OF COROT

Studying the internal structure of exoplanets-host stars compared to that of similar stars without detected planets is particularly important for the understanding of planetary formation. The observed overmetallicity of stars with planets may be a hint in that respect. Although it is obviously related to the physical processes which occur during the early phases of planetary formation, the origin of this overmetallicity is unclear. It may be either primordial or related to accretion processes or both. In this framework, asteroseismic studies represent an excellent tool to determine the structural differences between stars with and without detected planets. The two different missions of COROT are linked in this programme: the detection of new planets and the seismic studies of their host stars share the same goal of a better understanding of planetary formation and evolution. The COROT main target HD52265, which is known to host at least one giant planet, will be observed continuously during five months: many interesting results are expected from this long run. Meanwhile, stellar oscillations will be searched for in all stars around which new planets will be discovered. Key words: asteroseismology, exoplanets, chemical composition. 1

The exoplanet-host star

Aims. We show that the exoplanet-host star iota Horologii, alias HD 17051, 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. Methods. This result has been obtained unambiguously by studying the acoustic oscillations of this star, using the HARPS spectrometer in La Silla Observatory (ESO, Chili). Results. Besides the fact that ι 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. Conclusions. 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

Ancient and Modern Geochemical Signatures in the 13,500-Year Sedimentary Record of Lake Cadagno

Although lake sediments are globally important organic carbon sinks and therefore important habitats for deep microbial life, the deep lacustrine biosphere has thus far been little studied compared to its marine counterpart. To investigate the impact of the underexplored deep lacustrine biosphere on the sediment geochemical environment and vice versa, we performed a comprehensive microbiological and geochemical characterization of a sedimentary sequence from Lake Cadagno covering its entire environmental history since formation following glacial retreat. We found that both geochemical gradients and microbial community shifts across the ∼13.5 kyr subsurface sedimentary record reflect redox changes in the lake, going from oxic to anoxic and sulfidic. Most microbial activity occurs within the top 20 cm of sediment, where millimolar sulfate concentrations diffusing in from the bottom water are almost completely consumed. In deeper sediment layers, organic carbon remineralization is much slower but microorganisms nonetheless subsist on fermentation, sulfur cycling, metal reduction, and methanogenesis. The most surprising finding was the presence of a deep, oxidizing groundwater source. This water source generates an inverse redox gradient at the bottom of the sedimentary sequence and could contribute to the remineralization of organic matter sequestered in the energy-limited deep subsurface.ISSN:2296-646