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Bayesian inference of stellar parameters and interstellar extinction using parallaxes and multiband photometry
Astrometric surveys provide the opportunity to measure the absolutemagnitudes of large numbers of stars, but only if the individualline-of-sight extinctions are known. Unfortunately, extinction is highlydegenerate with stellar effective temperature when estimated frombroad-band optical/infrared photometry. To address this problem, Iintroduce a Bayesian method for estimating the intrinsic parameters of astar and its line-of-sight extinction. It uses both photometry andparallaxes in a self-consistent manner in order to provide anon-parametric posterior probability distribution over the parameters.The method makes explicit use of domain knowledge by employing theHertzsprung-Russell Diagram (HRD) to constrain solutions and to ensurethat they respect stellar physics. I first demonstrate this method byusing it to estimate effective temperature and extinction from BVJHKdata for a set of artificially reddened Hipparcos stars, for whichaccurate effective temperatures have been estimated from high-resolutionspectroscopy. Using just the four colours, we see the expected strongdegeneracy (positive correlation) between the temperature andextinction. Introducing the parallax, apparent magnitude and the HRDreduces this degeneracy and improves both the precision (reduces theerror bars) and the accuracy of the parameter estimates, the latter byabout 35 per cent. The resulting accuracy is about 200 K in temperatureand 0.2 mag in extinction. I then apply the method to estimate theseparameters and absolute magnitudes for some 47 000 F, G, K Hipparcosstars which have been cross-matched with Two-Micron All-Sky Survey(2MASS). The method can easily be extended to incorporate the estimationof other parameters, in particular metallicity and surface gravity,making it particularly suitable for the analysis of the 109stars from Gaia.
| uvby-? photometry of solar twins . The solar colors, model atmospheres, and the Teff and metallicity scales
Aims: Solar colors have been determined on the uvby-?photometric system to test absolute solar fluxes, to examine colorspredicted by model atmospheres as a function of stellar parameters(Teff, log g, [Fe/H]), and to probe zero-points ofTeff and metallicity scales. Methods: New uvby-?photometry is presented for 73 solar-twin candidates. Most stars of oursample have also been observed spectroscopically to obtain accuratestellar parameters. Using the stars that most closely resemble the Sun,and complementing our data with photometry available in the literature,the solar colors on the uvby-? system have been inferred. Our solarcolors are compared with synthetic solar colors computed from absolutesolar spectra and from the latest Kurucz (ATLAS9) and MARCS modelatmospheres. The zero-points of different Teff andmetallicity scales are verified and corrections are proposed. Results: Our solar colors are (b-y)? = 0.4105 ±0.0015, m1, ? = 0.2122 ± 0.0018, c1,? = 0.3319 ± 0.0054, and ?? =2.5915 ± 0.0024. The (b-y)? and m1,? colors obtained from absolute spectrophotometry of the Sunagree within 3-? with the solar colors derived here when thephotometric zero-points are determined from either the STIS HSTobservations of Vega or an ATLAS9 Vega model, but the c1,? and ?? synthetic colors inferred fromabsolute solar spectra agree with our solar colors only when thezero-points based on the ATLAS9 model are adopted. The Kurucz solarmodel provides a better fit to our observations than the MARCS model.For photometric values computed from the Kurucz models,(b-y)? and m1, ? are in excellentagreement with our solar colors independently of the adoptedzero-points, but for c1, ? and ??agreement is found only when adopting the ATLAS9 zero-points. Thec1, ? color computed from both the Kurucz and MARCSmodels is the most discrepant, probably revealing problems either withthe models or observations in the u band. The Teffcalibration of Alonso and collaborators has the poorest performance(~140 K off), while the relation of Casagrande and collaborators is themost accurate (within 10 K). We confirm that the Ramírez &Meléndez uvby metallicity calibration, recommended byÁrnadóttir and collaborators to obtain [Fe/H] in F, G, andK dwarfs, needs a small (~10%) zero-point correction to place the starsand the Sun on the same metallicity scale. Finally, we confirm that thec1 index in solar analogs has a strong metallicitysensitivity.Based on observations collected at the H. L. Johnson 1.5 m telescope atthe Observatorio Astronómico Nacional at San Pedro Mártir,Baja California, México.Tables 1-3 and 5 are only available inelectronic form at http://www.aanda.org
| Lithium depletion in solar-like stars: no planet connection
We have determined precise stellar parameters and lithium abundances ina sample of 117 stars with basic properties very similar to the Sun.This sample selection reduces biasing effects and systematic errors inthe analysis. We estimate the ages of our sample stars mainly fromisochrone fitting but also from measurements of rotation period andX-ray luminosity and test the connection between lithium abundance, age,and stellar parameters. We find strong evidence for increasing lithiumdepletion with age. Our sample includes 14 stars that are known to hostplanets and it does not support recent claims that planet-host starshave experienced more lithium depletion than stars without planets. Wefind the solar lithium abundance normal for a star of its age, mass, andmetallicity. Furthermore, we analyze published data for 82 stars thatwere reported to support an enhanced lithium depletion in planet hosts.We show that those stars in fact follow an age trend very similar tothat found with our sample and that the presence of giant planets is notrelated to low lithium abundances. Finally, we discuss the systematicbiases that led to the incorrect conclusion of an enhanced lithiumdepletion in planet-host stars.
| The PASTEL catalogue of stellar parameters
Aims: The PASTEL catalogue is an update of the [Fe/H] catalogue,published in 1997 and 2001. It is a bibliographical compilation ofstellar atmospheric parameters providing (T_eff, log g, [Fe/H])determinations obtained from the analysis of high resolution, highsignal-to-noise spectra, carried out with model atmospheres. PASTEL alsoprovides determinations of the one parameter T_eff based on variousmethods. It is aimed in the future to provide also homogenizedatmospheric parameters and elemental abundances, radial and rotationalvelocities. A web interface has been created to query the catalogue onelaborated criteria. PASTEL is also distributed through the CDS databaseand VizieR. Methods: To make it as complete as possible, the mainjournals have been surveyed, as well as the CDS database, to findrelevant publications. The catalogue is regularly updated with newdeterminations found in the literature. Results: As of Febuary2010, PASTEL includes 30151 determinations of either T_eff or (T_eff,log g, [Fe/H]) for 16 649 different stars corresponding to 865bibliographical references. Nearly 6000 stars have a determination ofthe three parameters (T_eff, log g, [Fe/H]) with a high qualityspectroscopic metallicity.The catalogue can be queried through a dedicated web interface at http://pastel.obs.u-bordeaux1.fr/.It is also available in electronic form at the Centre de DonnéesStellaires in Strasbourg (http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=B/pastel),at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/515/A111
| Accurate abundance patterns of solar twins and analogs. Does the anomalous solar chemical composition come from planet formation?
We derive the abundance of 19 elements in a sample of 64 stars withfundamental parameters very similar to solar, which minimizes the impactof systematic errors in our spectroscopic 1D-LTE differential analysis,using high-resolution (R?60 000), high signal-to-noise ratio(S/N?200) spectra. The estimated errors in the elemental abundancesrelative to solar are as small as ?0.025 dex. The abundance ratios[X/Fe] as a function of [Fe/H] agree closely with previously establishedpatterns of Galactic thin-disk chemical evolution. Interestingly, themajority of our stars show a significant correlation between [X/Fe] andcondensation temperature (T_C). In the sample of 22 stars withparameters closest to solar, we find that, on average, low TCelements are depleted with respect to high TC elements in thesolar twins relative to the Sun by about 0.08 dex (?20%). Anincreasing trend is observed for the abundances as a function ofTC for 900
| Improved Astrometry and Photometry for the Luyten Catalog. II. Faint Stars and the Revised Catalog
We complete construction of a catalog containing improved astrometry andnew optical/infrared photometry for the vast majority of NLTT starslying in the overlap of regions covered by POSS I and by the secondincremental Two Micron All Sky Survey (2MASS) release, approximately 44%of the sky. The epoch 2000 positions are typically accurate to 130 mas,the proper motions to 5.5 mas yr-1, and the V-J colors to0.25 mag. Relative proper motions of binary components are measured to 3mas yr-1. The false-identification rate is ~1% for11<~V<~18 and substantially less at brighter magnitudes. Theseimprovements permit the construction of a reduced proper-motion diagramthat, for the first time, allows one to classify NLTT stars intomain-sequence (MS) stars, subdwarfs (SDs), and white dwarfs (WDs). We inturn use this diagram to analyze the properties of both our catalog andthe NLTT catalog on which it is based. In sharp contrast to popularbelief, we find that NLTT incompleteness in the plane is almostcompletely concentrated in MS stars, and that SDs and WDs are detectedalmost uniformly over the sky δ>-33deg. Our catalogwill therefore provide a powerful tool to probe these populationsstatistically, as well as to reliably identify individual SDs and WDs.
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