Lick Spectral Indices for Super Metal-rich Stars

The Lick Fe5015, Fe5270, Fe5335, Mgb and Mg2 indices are presented for 139 candidate SMR stars of different luminosity class studied in Malagnini et al. (2000). Evidence is found for a standard (i.e. [Mg/Fe]~0) Mg vs. Fe relative abundance. Both the Worthey et al. (1994) and Buzzoni et al. (1992, 1994) fitting functions are found to suitably match the data at super-solar metallicity regimes. See http://www.merate.mi.astro.it/~eps/home.html for further details.Comment: 16 pages with 11 figures (Aastex format). To appear in the Nov. '01 issue of the PAS

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

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

SYNTHESIS OF STELLAR Mg AND Fe ABSORPTION INDICES FOR STELLAR POPULATION STUDIES. II. THE EXTENDED AND UP-TO-DATE COLLECTION

This paper is mainly concerned with the prediction of absorption-line spectral features in cool stars, to be used as input in stellar population synthesis projects. From a detailed comparison with the solar intensity spectrum, we have re-ned the main parameters of atomic and molecular absorption lines that are prominent in the 4850E5400 wavelength interval. This line list was used to compute an extensive Ae library of synthetic stellar spectra at high resolution in the temperature range K, T eff \ 4000E8000 surface gravity interval log g \ 1.0E5.0 dex, metallicities ((M/H)) from (1.0 to )0.5 dex, and micro- turbulent velocity m \ 2k m s~1. The computations were performed by using the latest release of KuruczIs model atmospheres and numerical codes. The library contains a total of 693 synthetic spectra, from which iron and magnesium indices were obtained, together with the corresponding "" pseudocontinuum II Nuxes. We illustrate the behavior of -ve "" Lick-like II spectral indices, namely, Mg b, Fe5270, and Mg 1 ,M g 2 , Fe5335, in terms of the main atmospheric parameters, namely, e†ective temperature, surface gravity, and metallicity. The trend of the indices with microturbulent velocity is also illustrated by means of an addi- tional set of spectra computed at di†erent microturbulent velocities. Transformation equations of the theoretical grid into the Lick/IDS observational database are presented, showing the full consistency of our grid with the empirical database. Subject heading: galaxies: stellar content E stars: atmospheres E stars: late-typ

Uncertainties of Synthetic Integrated Colors as Age Indicators

We investigate the uncertainties in the synthetic integrated colors of simple stellar populations. Three types of uncertainties are from the stellar models, the population synthesis techniques, and from the spectral libraries. Despite some skepticism, synthetic colors appear to be reliable age indicators when used for select age ranges. Rest-frame optical colors are good age indicators at ages 2 -- 7Gyr. At ages sufficiently large to produce hot HB stars, the UV-to-optical colors provide an alternative means for measuring ages. This UV technique may break the age-metallicity degeneracy because it separates old populations from young ones even in the lack of metallicity information. One can use such techniques on extragalactic globular clusters and perhaps even for high redshift galaxies that are passively evolving to study galaxy evolution history.Comment: 38 pages, 21 figures, LaTex, 2003, ApJ, 582 (Jan 1), in pres

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

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

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

Observations and Atmospheric Parameters of Super-Metal-rich Candidates

The spectroscopic properties of a sample of 92 Population I bright stars (V=+0.1 are reviewed in order to study the metallicity scale at supersolar regimes. For 73 of these candidate super-metal-rich (SMR) stars we identified the photospheric fiducial parameters (Teff, logg, [M/H]) from among published parameter sets via a comparison of new observations in the wavelength range 5034-5398 Å with synthetic spectra derived from the 1997 database of Chavez et al. As a main issue in our analysis, we find that a ``genuine'' SMR stellar component in the Galactic disk exists with more than one-fourth of the stars in our sample fulfilling the criterion [Fe/H]>=0.2 dex, and three of them as rich as [Fe/H]>+0.4 dex. Based on observations collected at the INAOE ``G. Haro'' Observatory, Cananea (Mexico)

Synthetic Lick Indices and Detection of α-enhanced Stars. II. F, G, and K Stars in the –1.0 < [Fe/H] < +0.50 Range

We present an analysis of 402 F, G, and K solar neighborhood stars, with accurate estimates of [Fe/H] in the range -1.0 to +0.5 dex, aimed at the detection of α-enhanced stars and at the investigation of their kinematical properties. The analysis is based on the comparison of 571 sets of spectral indices in the Lick/IDS system, coming from four different observational data sets, with synthetic indices computed with solar-scaled abundances and with α-element enhancement. We use selected combinations of indices to single out α-enhanced stars without requiring previous knowledge of their main atmospheric parameters. By applying this approach to the total data set, we obtain a list of 60 bona fide α-enhanced stars and of 146 stars with solar-scaled abundances. The properties of the detected α-enhanced and solar-scaled abundance stars with respect to their [Fe/H] values and kinematics are presented. A clear kinematic distinction between solar-scaled and α-enhanced stars was found, although a one-to-one correspondence to "thin disk" and "thick disk" components cannot be supported with the present data

The Super Metal Rich Component of the Galaxyx

We present the results obtained by comparing mid-resolution stellar spectra of super metal rich candidates with synthetic spectra computed in the wavelength range 4850-5400 Å. Atmospheric parameters, derived by using the flux fitting method, are illustrated for a sample of representative stars. The final aim of the project is the definition of a fully consistent metallicity scale for SMR stars