Showing papers by "Alejandra Recio-Blanco published in 2012"

The Gaia-ESO Public Spectroscopic Survey

Abstract: The Gaia-ESO Public Spectroscopic Survey has begun and will obtain high quality spectroscopy of some 100000 Milky Way stars, in the field and in open clusters, down to magnitude 19, systematically ...

The AMBRE project: A new synthetic grid of high-resolution FGKM stellar spectra

Abstract: Context. Large grids of synthetic spectra covering a wide range of stellar parameters are essential tools for different stellar and (extra-) Galactic physical applications. They can be used for the automatic parametrisation of stellar spectra such as that performed by the AMBRE project whose main goal is to determine the stellar atmospheric parameters of a few hundred thousands of archived spectra of four ESO spectrographs.Aims. To fulfil the needs of AMBRE and similar future projects, we computed a grid of synthetic spectra over the whole optical domain for cool to very cool stars of any luminosity (from dwarfs to supergiants) with metallicities varying from 10-5 to 10 times the solar metallicity, and considering large variations in the chemical composition of the α -elements.Methods. In these spectrum computations, we used new generation MARCS model atmospheres and the Turbospectrum code for radiative transfer. We also took into account atomic and molecular linelists that were as complete as possible and adopted, in the spectral synthesis, the same physical assumptions and input data as in the MARCS models. This allowed us to present a grid in which there is a high consistency between the atmosphere models and the synthetic spectra.Results. We present a new grid of 16 783 high resolution spectra over the wavelength range 3000 A to 12 000 A computed at a spectral resolution higher than 150 000. Normalised and absolute flux versions are available over a wide range of stellar atmospheric parameters for stars of FGKM spectral types. The parameters covered are 2500 K ≤ T eff ≤ 8000 K, −0.5 ≤ log(g ) ≤ 5.5 dex, and −5.0 ≤ [M/H] ≤ + 1.0 dex. Moreover, for each combination of these stellar parameters, five different values of the enrichment in α -elements were considered (0.0, ± 0.2 dex and ± 0.4 dex around the standard values). This library is thus relevant to any stellar type and luminosity class, present in old and intermediate-age stellar populations with chemical composition varying from extremely metal-poor to metal-rich. This grid is made publicly available through the POLLUX database (about 50% of the spectra have been included in this database) and in FITS format upon request to the authors.

The AMBRE project: A new synthetic grid of high-resolution FGKM stellar spectra

Abstract: Large grids of synthetic spectra covering a widespread range of stellar parameters are mandatory for different stellar and (extra-)Galactic physics applications. Such large grids can be used for the automatic parametrisation of stellar spectra such as that performed within the AMBRE project for which the main goal is the stellar atmospheric parameters determination for the few hundreds of thousands of archived spectra of four ESO spectrographs. To fulfil the needs of AMBRE and future similar projects, we have computed a grid of synthetic spectra over the whole optical domain for cool to very cool stars of any luminosity with metallicities varying from 10-5 to 10 times the solar metallicity, and considering large variations in the chemical content of the {\alpha}-elements. New generation MARCS model atmospheres and the Turbospectrum code for radiative transfer have been used. We have also taken into account as complete as possible atomic and molecular linelists. A new grid of 16783 high resolution spectra over the wavelength range 3000 to 12000 A has been computed with a spectral resolution always larger than 150000. Normalised and absolute flux versions are available over a wide range of stellar atmospheric parameters for stars of FGKM spectral types. The covered parameters are 2500K\leqTeff\leq8000K, -0.5\leqlog(g)\leq5.5dex, -5.0\leq[M/H]\leq+1.0 dex and five different values of the enrichment in {\alpha}-elements have been considered (0.0, \pm0.2 dex and \pm0.4 dex around the standard values). This grid is made publicly available through the POLLUX database (about 50% of the spectra are already included in this database) and in FITS format upon request to the authors.

The AMBRE Project: Stellar parameterisation of the ESO:FEROS archived spectra

Abstract: Context. The AMBRE Project is a collaboration between the European Southern Observatory (ESO) and the Observatoire de la Cote d’Azur (OCA) that has been established to determine the stellar atmospheric parameters for the archived spectra of four ESO spectrographs.Aims. The analysis of the UVES archived spectra for their stellar parameters was completed in the third phase of the AMBRE Project. From the complete ESO:UVES archive dataset that was received covering the period 2000 to 2010, 51 921 spectra for the six standard setups were analysed. These correspond to approximately 8014 distinct targets (that comprise stellar and non-stellar objects) by radial coordinate search.Methods. The AMBRE analysis pipeline integrates spectral normalisation, cleaning and radial velocity correction procedures in order that the UVES spectra can then be analysed automatically with the stellar parameterisation algorithm MATISSE to obtain the stellar atmospheric parameters. The synthetic grid against which the MATISSE analysis is carried out is currently constrained to parameters of FGKM stars only.Results. Stellar atmospheric parameters are reported for 12 403 of the 51 921 UVES archived spectra analysed in AMBRE:UVES. This equates to ~23.9% of the sample and ~3708 stars. Effective temperature, surface gravity, metallicity, and alpha element to iron ratio abundances are provided for 10 212 spectra (~19.7%), while effective temperature at least is provided for the remaining 2191 spectra. Radial velocities are reported for 36 881 (~71.0%) of the analysed archive spectra. While parameters were determined for 32 306 (62.2%) spectra these parameters were not considered reliable (and thus not reported to ESO) for reasons such as very low S/N, too poor radial velocity determination, spectral features too broad for analysis, and technical issues from the reduction. Similarly the parameters of a further 7212 spectra (13.9%) were also not reported to ESO based on quality criteria and error analysis which were determined within the automated parameterisation process. Those tests lead us to expect that multi-component stellar systems will return high errors in radial velocity and fitting to the synthetic spectra and therefore will not have parameters reported to ESO. Typical external errors of σ T eff ~ 110 dex, σ log g ~ 0.18 dex, σ [ M/H ] ~ 0.13 dex, and σ [ α / Fe ] ~ 0.05 dex with some variation between giants and dwarfs and between setups are reported.Conclusions. UVES is used to observe an extensive collection of stellar and non-stellar objects all of which have been included in the archived dataset provided to OCA by ESO. The AMBRE analysis extracts those objects that lie within the FGKM parameter space of the AMBRE slow-rotating synthetic spectra grid. Thus by homogeneous blind analysis AMBRE has successfully extracted and parameterised the targeted FGK stars (23.9% of the analysed sample) from within the ESO:UVES archive.

Comparative modelling of the spectra of cool giants

Abstract: Context. Our ability to extract information from the spectra of stars depends on reliable models of stellar atmospheres and appropriate techniques for spectral synthesis. Various model codes and strategies for the analysis of stellar spectra are available today. Aims. We aim to compare the results of deriving stellar parameters using different atmosphere models and different analysis strategies. The focus is set on high-resolution spectroscopy of cool giant stars. Methods. Spectra representing four cool giant stars were made available to various groups and individuals working in the area of spectral synthesis, asking them to derive stellar parameters from the data provided. The results were discussed at a workshop in Vienna in 2010. Most of the major codes currently used in the astronomical community for analyses of stellar spectra were included in this experiment. Results. We present the results from the different groups, as well as an additional experiment comparing the synthetic spectra produced by various codes for a given set of stellar parameters. Similarities and differences of the results are discussed. Conclusions. Several valid approaches to analyze a given spectrum of a star result in quite a wide range of solutions. The main causes for the differences in parameters derived by different groups seem to lie in the physical input data and in the details of the analysis method. This clearly shows how far from a definitive abundance analysis we still are.

Fluorine abundances in dwarf stars of the solar neighbourhood

Abstract: Aims. In spite of many observational efforts aiming to characterize the chemical evolution of our Galaxy, not much is known about the origin of fluorine (F). Models suggest that the F found in t he Galaxy might have been produced mainly in three different ways, namely, Type II Supernovae, asymptotic giant branch nucleosynthesis, or in the core of Wolf-Rayet stars. Only a few observational measurements of F abundances are available in the literature and mostly for objects whose characteristics might hamper an accurate determination of fluorine abundance (e.g.,complex mixing a nd nucleosynthesis processes, external/internal contamination). Methods. We derive the F abundances for a set of nine cool main-sequence dwarfs in the solar neighbourhood, based on an unblended line of the HF molecule at 2.3 microns. In addition, we study the s-process elements of five of these stars. Results. We acquire data using the high-resolution IR-spectrograph CRIRES and gather FEROS data from the European Southern Observatory archive. The classical method of spectral synthesis in local thermodynamic equilibrium has been used for the abundance analysis. Conclusions. Several of the analysed stars seem to be slightly fluorine enh anced with respect to the Sun, although no correlation is found between the F abundance and the iron content. In addition, the most fluorine enriched stars are also yttrium and zi rconium enriched, which suggests that AGB fluorine nucleosynthesis is the dominant source of fluorine production for the observe d stars. Nevertheless, the correlation between [F/Fe] and the s-elements is rather weak and possibly masked by the uncertainties in the F abundance measurements. Finally, we compare our derived F abundances to previous measurements of alpha-element and iron-peak element abundances. Type II core collapse Supernovae do not appear to be the main site of F production for our targets, as no correlation seems to exist between the [F/Fe] and the [α/Fe] ratios.

Comparative Modelling of the Spectra of Cool Giants

Abstract: Our ability to extract information from the spectra of stars depends on reliable models of stellar atmospheres and appropriate techniques for spectral synthesis. Various model codes and strategies for the analysis of stellar spectra are available today. We aim to compare the results of deriving stellar parameters using different atmosphere models and different analysis strategies. The focus is set on high-resolution spectroscopy of cool giant stars. Spectra representing four cool giant stars were made available to various groups and individuals working in the area of spectral synthesis, asking them to derive stellar parameters from the data provided. The results were discussed at a workshop in Vienna in 2010. Most of the major codes currently used in the astronomical community for analyses of stellar spectra were included in this experiment. We present the results from the different groups, as well as an additional experiment comparing the synthetic spectra produced by various codes for a given set of stellar parameters. Similarities and differences of the results are discussed. Several valid approaches to analyze a given spectrum of a star result in quite a wide range of solutions. The main causes for the differences in parameters derived by different groups seem to lie in the physical input data and in the details of the analysis method. This clearly shows how far from a definitive abundance analysis we still are.

Fluorine abundances in dwarf stars of the solar neighbourhood

Abstract: In spite of many observational efforts aiming to characterize the chemical evolution of our Galaxy, not much is known about the origin of fluorine (F). Models suggest that the F found in the Galaxy might have been produced mainly in three different ways, namely, Type II supernovae, asymptotic giant branch nucleosynthesis, or in the core of Wolf-Rayet stars. Only a few observational measurements of F abundances are available in the literature and mostly for objects whose characteristics might hamper an accurate determination of fluorine abundance (e.g.,complex mixing and nucleosynthesis processes, external/internal contamination). We derive the F abundances for a set of nine cool main-sequence dwarfs in the solar neighbourhood, based on an unblended line of the HF molecule at 2.3 microns. In addition, we study the s-process elements of five of these stars. We acquire data using the high-resolution IR-spectrograph CRIRES and gather FEROS data from the European Southern Observatory archive. Several of the analysed stars seem to be slightly fluorine enhanced with respect to the Sun, although no correlation is found between the F abundance and the iron content. In addition, the most fluorine enriched stars are also yttrium and zirconium enriched, which suggests that AGB fluorine nucleosynthesis is the dominant source of fluorine production for the observed stars. Nevertheless, the correlation between [F/Fe] and the s-elements is rather weak and possibly masked by the uncertainties in the F abundance measurements. Finally, we compare our derived F abundances to previous measurements of alpha-element and iron-peak element abundances. Type II core collapse Supernovae do not appear to be the main site of F production for our targets, as no correlation seems to exist between the [F/Fe] and the [alpha/Fe] ratios.