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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.
| 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
| Integral-field spectroscopy of the Galactic cluster [DBS2003]8. Discovery of an ultra-compact HII region and its ionizing star in the bright rimmed cloud SFO49
Context: We have started a program of infrared (IR) studies of thestellar clusters associated with HII regions in order to understand thestructure of the spiral arms and their interaction with the central barof the Galaxy better. Aims: This is accomplished by determiningthe distance to the OB stars embedded in the clusters. We want to use IRstellar spectro-photometric measurements to complement the kinematicdistances from the radial velocity of the gas. Methods: SINFONI,the infrared integral-field spectrograph of the VLT, enabled us to imagethe clusters and to resolve them into individual stars, to get thespectra of the brightest stars, and to analyze the possible nebularemission. We performed pilot observations of [DBS2003]8, an embeddedGalactic stellar cluster in the bright rimmed cloud SFO49, during theSINFONI science verification. The results are presented in this paper.Results: The center of the cluster is resolved for the first timeand four stars are detected, the brightest being a late O type or earlyB star. A spectro-photometric distance to the cluster of 2.65±0.4kpc is derived. We discovered that the O type star is located in thecenter of a nebula, which is quite circular in shape with an observedradius of 0.03-0.06 pc, a value typical of an ultra-compact HII region.We measured the nebula's Br ? emission, which is generated byphoto-ionization of the central star; and from the hydrogen molecularline ratio, we have proved that the ionized nebula is surrounded by aphoto-dissociated region (PDR). We also detected [FeII] line emission at1.664 ?m. The ratio of the iron flux to that of the {Br} ? lineis found 15 times higher than in a classical HII region. This suggeststhat at least part of the [FeII] line emission emanates from shockedstellar wind material.The acronym was given by Simbad, the CDS Database.Based on observations collected at the European Southern Observatory,ParanalChile.
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