On-line determination of stellar atmospheric parameters Teff, log g, [Fe/H] from ELODIE echelle spectra. II - The library of F5 to K7 stars

A library of 211 echelle spectra taken with ELODIE at the Observatoire de Haute-Provence is presented. It provides a set of spectroscopic standards covering the full range of gravities and metallicities in the effective temperature interval [4000 K, 6300 K]. The spectra are straightened, wavelength calibrated, cleaned of cosmic ray hits, bad pixels and telluric lines. They cover the spectral range [440 nm, 680 nm] with an instrumental resolution of 42000. For each star, basic data were compiled from the Hipparcos catalogue and the Hipparcos Input Catalogue. Radial velocities with a precision better than 100 m/s are given. Atmospheric parameters (Teff, log g, [Fe/H]) from the literature are discussed. Because of scattered determinations in the bibliography, even for the most well-known stars, these parameters were adjusted by an iterative process which takes account of common or different spectral features between the standards, using our homogeneous set of spectra. Revised values of (Teff, log g, [Fe/H]) are proposed. They are still consistent with the literature, and also lead to the self-consistency of the library, in the sense that similar spectra have similar atmospheric parameters. This adjustment was performed by using step by step a method based on the least square comparison of carefully prepared spectra, which was originally developed for the on-line estimation of the atmospheric parameters of faint field stars (companion paper in the main journal). The spectra and corresponding data will only be available in electronic form at the CDS (ftp cdsarc.u-strasbg.fr or http://cdsweb.u-strasbg.fr/Abstract.html).Comment: 7 pages, 7 figures, accepted for publication in A&A Supplement Serie

On the metallicity of open clusters. III. Homogenised sample

Open clusters are known as excellent tools for various topics in Galactic research. For example, they allow accurately tracing the chemical structure of the Galactic disc. However, the metallicity is known only for a rather low percentage of the open cluster population, and these values are based on a variety of methods and data. Therefore, a large and homogeneous sample is highly desirable. In the third part of our series we compile a large sample of homogenised open cluster metallicities using a wide variety of different sources. These data and a sample of Cepheids are used to investigate the radial metallicity gradient, age effects, and to test current models. We used photometric and spectroscopic data to derive cluster metallicities. The different sources were checked and tested for possible offsets and correlations. In total, metallicities for 172 open cluster were derived. We used the spectroscopic data of 100 objects for a study of the radial metallicity distribution and the age-metallicity relation. We found a possible increase of metallicity with age, which, if confirmed, would provide observational evidence for radial migration. Although a statistical significance is given, more studies are certainly needed to exclude selection effects, for example. The comparison of open clusters and Cepheids with recent Galactic models agrees well in general. However, the models do not reproduce the flat gradient of the open clusters in the outer disc. Thus, the effect of radial migration is either underestimated in the models, or an additional mechanism is at work. [abridged]Comment: Accepted for publication in Astronomy and Astrophysics: 18 pages, 10 figures, 4 table

Climbing the cosmic ladder with stellar twins

Distances to stars are key to revealing a three-dimensional view of the Milky Way, yet their determination is a major challenge in astronomy. Whilst the brightest nearby stars benefit from direct parallax measurements, fainter stars are subject of indirect determinations with uncertainties exceeding 30%. We present an alternative approach to measuring distances using spectroscopically-identified twin stars. Given a star with known parallax, the distance to its twin is assumed to be directly related to the difference in their apparent magnitudes. We found 175 twin pairs from the ESO public HARPS archives and report excellent agreement with Hipparcos parallaxes within 7.5%. Most importantly, the accuracy of our results does not degrade with increasing stellar distance. With the ongoing collection of high-resolution stellar spectra, our method is well-suited to complement Gaia.Comment: published online on MNRA

On the correlation of elemental abundances with kinematics among galactic disk stars

We have performed the detailed analysis of 174 high-resolution spectra of FGK dwarfs obtained with the ELODIE echelle spectrograph at the Observatoire de Haute-Provence. Abundances of Fe, Si and Ni have been determined from equivalent widths under LTE approximation, whereas abundances of Mg have been determined under NLTE approximation using equivalent widths of 4 lines and profiles of 5 lines. Spatial velocities with an accuracy better than 1 km/s, as well as orbits, have been computed for all stars. They have been used to define 2 subsamples kinematically representative of the thin disk and the thick disk in order to highlight their respective properties. A transition occurs at [Fe/H]=-0.3. Stars more metal-rich than this value have a flat distribution with Zmax<1 kpc and sigma_W<20 km/s, and a narrow distribution of [alpha/Fe]. There exist stars in this metallicity regime which cannot belong to the thin disk because of their excentric orbits, neither to the thick disk because of their low scale height. Several thin disk stars are identified down to [Fe/H]=-0.80. Their Mg enrichment is lower than thick disk stars with the same metallicity. We confirm from a larger sample the results of Feltzing et al (2003) and Bensby et al (2003) showing a decrease of [alpha/Fe] with [Fe/H] in the thick disk interpreted as the signature of the SNIa which have progressively enriched the ISM with iron. However our data suggest that the star formation in the thick disk stopped when the enrichment was [Fe/H]=-0.30, [Mg/Fe]=+0.20, [Si/Fe]=+0.17. A vertical gradient in [alpha/Fe] may exist in the thick disk but should be confirmed with a larger sample. Finally we have identified 2 new candidates of the HR1614 moving group.Comment: Accepted in A&A, 16 pages, 14 figure

Vertical distribution of Galactic disk stars : II. The surface mass density in the Galactic plane

High resolution spectra data of red clump stars towards the NGP have been obtained with the high resolution spectrograph Elodie at OHP for Tycho-2 selected stars. Combined with Hipparcos local analogues, we determine both the gravitational force law perpendicaular to the Galactic plane, and the total surface mass density and thickness of the Galactic disk. The surface mass density of the Galactic disk within 800 pc derived from this analysis is Sigma(|z|<800pc)=76 Msol.pc-2 and, removing the dark halo contribution, the total disk mass density is Sigma0=67 Msol.pc-2 at solar radius. The thickness of the total disk mass distribution is dynamicaly measured for the first time and is found to be 390pc in relative agreement with the old stellar disk scale height. All dynamical evidences concerning the structure of the disk (its local volume density -i.e. the Oort limit-, its surface density and its thickness) are compatible with our knowledge of the corresponding stellar disk properties.Comment: 11 pages, 9 figures, Accepted for publication in A&

The ELODIE archive

The ELODIE archive contains the complete collection of high-resolution echelle spectra accumulated over the last decade using the ELODIE spectrograph at the Observatoire de Haute-Provence 1.93-m telescope. This article presents the different data products and the facilities available on the web to re-process these data on-the-fly. Users can retrieve the data in FITS format from http://atlas.obs-hp.fr/elodie and apply to them different functions: wavelength resampling and flux calibration in particular.Comment: 8 pages, 3 figures and 1 tabl

The PASTEL catalogue of stellar parameters

The PASTEL catalogue is an update of the [Fe/H] catalogue, published in 1997 and 2001. It is a bibliographical compilation of stellar atmospheric parameters providing (Teff,logg,[Fe/H]) determinations obtained from the analysis of high resolution, high signal-to-noise spectra, carried out with model atmospheres. PASTEL also provides determinations of the one parameter Teff based on various methods. It is aimed in the future to provide also homogenized atmospheric parameters and elemental abundances, radial and rotational velocities. A web interface has been created to query the catalogue on elaborated criteria. PASTEL is also distributed through the CDS database and VizieR. To make it as complete as possible, the main journals have been surveyed, as well as the CDS database, to find relevant publications. The catalogue is regularly updated with new determinations found in the literature. As of Febuary 2010, PASTEL includes 30151 determinations of either Teff or (Teff,logg,[Fe/H]) for 16649 different stars corresponding to 865 bibliographical references. Nearly 6000 stars have a determination of the three parameters (Teff,logg,[Fe/H]) with a high quality spectroscopic metallicity.Comment: 5 pages, accepted for publication in A&A. The PASTEL catalogue can be queried at http://pastel.obs.u-bordeaux1.fr/ or http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=B/paste

Gaia FGK Benchmark Stars: Effective temperatures and surface gravities

Large Galactic stellar surveys and new generations of stellar atmosphere models and spectral line formation computations need to be subjected to careful calibration and validation and to benchmark tests. We focus on cool stars and aim at establishing a sample of 34 Gaia FGK Benchmark Stars with a range of different metallicities. The goal was to determine the effective temperature and the surface gravity independently from spectroscopy and atmospheric models as far as possible. Fundamental determinations of Teff and logg were obtained in a systematic way from a compilation of angular diameter measurements and bolometric fluxes, and from a homogeneous mass determination based on stellar evolution models. The derived parameters were compared to recent spectroscopic and photometric determinations and to gravity estimates based on seismic data. Most of the adopted diameter measurements have formal uncertainties around 1%, which translate into uncertainties in effective temperature of 0.5%. The measurements of bolometric flux seem to be accurate to 5% or better, which contributes about 1% or less to the uncertainties in effective temperature. The comparisons of parameter determinations with the literature show in general good agreements with a few exceptions, most notably for the coolest stars and for metal-poor stars. The sample consists of 29 FGK-type stars and 5 M giants. Among the FGK stars, 21 have reliable parameters suitable for testing, validation, or calibration purposes. For four stars, future adjustments of the fundamental Teff are required, and for five stars the logg determination needs to be improved. Future extensions of the sample of Gaia FGK Benchmark Stars are required to fill gaps in parameter space, and we include a list of suggested candidates.Comment: Accepted by A&A; 34 pages (printer format), 14 tables, 13 figures; language correcte