M. L. Malagnini

Lick Spectral Indices for Super–Metal‐rich Stars*

We present Lick spectral indices for a complete sample of 139 candidate super-metal-rich stars of different luminosity classes (MK type from I to V). For 91 of these stars we were able to identify, in an accompanying paper, the fundamental atmosphere parameters. This confirms that at least 2/3 of the sample consists of stars with [Fe/H] in excess of +0.1 dex. Optical indices for both observations and fiducial synthetic spectra have been calibrated to the Lick system according to Worthey et al. and include the Fe i indices of Fe5015, Fe5270, and Fe5335 and the Mg i and MgH indices of Mg2 and Mg b at 5180 A. The internal accuracy of the observations is found to be σ(Fe5015) = ±0.32 A, σ(Fe5270) = ±0.19 A, σ(Fe5335) = ±0.22 A, σ(Mg2) = ±0.004 mag, and σ(Mg b) = ±0.19 A. This is about a factor of 2 better than the corresponding theoretical indices from the synthetic spectra, the latter being a consequence of the intrinsic limitations in the input physics, as discussed by Chavez et al.By comparing models and observations, we find no evidence for nonstandard Mg versus Fe relative abundance, so [Mg/Fe] =0, on the average, for our sample. Both the Worthey et al. and Buzzoni et al. fitting functions are found to suitably match the data and can therefore confidently be extended for population synthesis application also to supersolar metallicity regimes. A somewhat different behavior of the two fitting sets appears, however, beyond the temperature constraints of our stellar sample. Its impact on the theoretical output is discussed, as far as the integrated Mg2 index is derived from synthesis models of stellar aggregates. A two-index plot, such as Mg2 versus Fe5270, is found to provide a simple and powerful tool for probing distinctive properties of single stars and stellar aggregates as a whole. The major advantage, over a classical CM diagram, is that it is both reddening free and distance independent.

Observations and Atmospheric Parameters of Super-Metal-rich Candidates*

ABSTRACT The spectroscopic properties of a sample of 92 Population I bright stars ( \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape

Synthetic mid-UV spectroscopic indices of stars

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Synthetic Lick Indices and Detection of α-Enhanced Stars

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Metallicity Determinations from Ultraviolet-Visual Spectrophotometry. I. The Test Sample

Using the UVBLUE library of synthetic stellar spectra we have computed a set of mid-UV line and continuum spectroscopic indices. We explore their behavior in terms of the leading stellar parameters (Teff, log g). The overall result is that synthetic indices follow the general trends depicted by those computed from empirical databases. Separately we also examine the index sensitivity to changes in chemical composition, an analysis only feasible under a theoretical approach. In this respect, lines indices Fe I 3000, BL 3096, and Mg I 2852 and the continuum index 2828/2921 are the least sensitive features, an important characteristic to be taken into account for the analyses of integrated spectra of stellar systems. We also quantify the effects of instrumental resolution on the indices and find that indices display variations up to 0.1 mag in the resolution interval between 6 and 10 A of FWHM. We discuss the extent to which synthetic indices are compatible with indices measured in spectra collected by the International Ultraviolet Explorer (IUE). Five line and continuum indices (Fe I 3000, 2110/2570, 2828/2921, S2850, and S2850L) display a remarkably good correlation with observations. The rest of the indices are either underestimated or overestimated; however, two of them, Mg Wide and BL 3096, display only marginal discrepancies. For 11 indices we give the coefficients to convert synthetic indices to the IUE system. This work represents the first attempt to synthesize mid-UV indices from high-resolution theoretical spectra and foresees important applications for the study of the ultraviolet morphology of old stellar aggregates.

Far-Ultraviolet Continuum of G-Type Stars: A Signature of the Temperature Minimum Region

Synthetic Lick indices computed with solar scaled abundances and with α-element enhancement are presented and compared with predictions from both theoretical computations (Tripicco & Bell; Thomas, Maraston, & Bender; Barbuy et al.) and empirical fitting functions (de Freitas Pacheco). We propose selected combinations of indices capable of singling out α-enhanced stars without requiring previous knowledge of their main atmospheric parameters. By applying this approach to the 460 stars in the Worthey et al. catalog, we detected a list of 82 candidate α-enhanced stars. The confirmation of α-enhancement was obtained by searching the literature for individual element abundance determinations from high-resolution spectroscopy for a subsample of 34 stars. Preliminary discussion of the properties of the detected α-enhanced stars with respect to their [Fe/H] values and kinematics is presented.

Synthetic Lick Indices and Detection of α-enhanced Stars. III. F, G, and K Stars with [Fe/H] > 0.00

New visual spectrophotometric observations of non-supergiant solar neighborhood stars are combined with IUE Newly Extracted Spectra (INES) energy distributions in order to derive their overall metallicities, [M/H]. This fundamental parameter, together with effective temperature and apparent angular diameter, is obtained by applying the flux-fitting method while surface gravity is derived from the comparison with evolutionary tracks in the theoretical H-R diagram. Trigonometric parallaxes for the stars of the sample are taken from the Hipparcos Catalogue. The quality of the flux calibration is discussed by analyzing a test sample via comparison with external photometry. The validity of the method in providing accurate metallicities is tested on a selected sample of G-type stars with well-determined atmospheric parameters from recent high-resolution spectral analysis. The extension of the overall procedure to the determination of the chemical composition of all the INES non-supergiant G-type stars with accurate parallaxes is planned in order to investigate their atmospheric temperature structure.

Search for α‐enhanced stars in the spectroscopic SDSS stellar database

The main results of a program of systematic comparison between observed and computed UV spectral energy distributions of field G-type stars are illustrated. We constructed the UV observed energy distributions for 53 G stars, starting from the IUE Uniform Low Dispersion Archive (ULDA) and computed the corresponding theoretical fluxes by using the atmospheric parameters from the Catalogue of [Fe/H] Determinations (1996 edition) and a Kurucz grid of model fluxes. From the comparison between observations and classical models, a UV excess shortward of 2000 A is evident for all the program stars. The UV continuum in the region 1600-2000 A can be described by synthetic fluxes computed from semiempirical models based on the temperature minimum concept. Values for the Tmin/Teff ratio on the order of 0.80 are suitable for the interpretation of the observed fluxes. The residual discrepancies shortward of 1600 A are suggested to be effects of the chromosphere, on the basis of a comparison with the Maltby et al. semiempirical model of the Sun.

Alpha-enhancement in the MW: results from the SDSS spectroscopic stellar database

A sample of 119 F, G, and K solar neighborhood stars, selected under the condition [Fe/H] > 0.00, is investigated in order to detect which of them, if any, present α-enhanced characteristics. According to the kinematics, the sample represents stars of the thin-disk component of the Galaxy. The search of α-enhanced characteristics is performed by adopting an already tested procedure that does not require previous knowledge of the stellar main atmospheric parameters. The analysis is based on the comparison of spectral indices in the Lick IDS system, coming from different observational data sets, with synthetic ones computed with solar-scaled abundances and with α-element enhancement. The main result of the analysis is the extreme paucity (likely just one in 119) of α-enhanced stars in our sample, thus suggesting [α/Fe] = 0.0 for thin-disk stars with [Fe/H] > 0.00. This result, which is in agreement with the standard evolutionary picture of the disk of the Galaxy, is compared with recent results from high-resolution analysis reported in the literature. The role of the atmospheric parameter assumptions in the analysis of high-resolution spectroscopic data is discussed, and a possible explanation of discrepant results about α-enhancement for stars with [Fe/H] > 0.00 is presented.

Calibration of Lick indices from SDSS spectra

We analyze a sample of about 8000 stars extracted from the Sloan Digital Sky Survey with Teff in the range 4500–7000 K and log g greater than 2.0 dex as estimated by comparing measured and synthetic Lick indices. We present preliminary results on the dependence of the α‐enhancement phenomenon on the stellar metallicity and on the galactic position.