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A&A Supplement Series, Vol. 125, October II, 229-246

Received September 23, 1996; accepted January 2, 1997

A standard stellar library for evolutionary synthesis

I. Calibration of theoretical spectra

Th. Lejeune tex2html_wrap1979 - F. Cuisinier tex2html_wrap1981 - R. Buser tex2html_wrap1983

Send offprint request: R. Buser
tex2html_wrap557  Astronomisches Institut der Universität Basel, Venusstr. 7, CH-4102 Binningen, Switzerland
tex2html_wrap557  Observatoire de Strasbourg, 11, rue de l'Université, F-67000 Strasbourg, France
tex2html_wrap557  Instituto Astronomico e Geofisico da Universidade Sao Paulo, Departamento de Astronomia, Caixa Postal 9638, 01065-970 Sao Paulo SP, Brasil


We present a comprehensive hybrid library of synthetic stellar spectra based on three original grids of model atmosphere spectra by Kurucz (1995), Fluks et al. (1994), and Bessell et al. (1989, 1991), respectively. The combined library has been intended for multiple-purpose synthetic photometry applications and was constructed according to the precepts adopted by Buser & Kurucz (1992): (i) to cover the largest possible ranges in stellar parameters (tex2html_wrap_inline1949, tex2html_wrap_inline1951, and [M/H]); (ii) to provide flux spectra with useful resolution on the uniform grid of wavelengths adopted by Kurucz (1995); and (iii) to provide synthetic broad-band colors which are highly realistic for the largest possible parameter and wavelength ranges.

Because the most astrophysically relevant step consists in establishing a realistic library, the corresponding color calibration is described in some detail. Basically, for each value of the effective temperature and for each wavelength, we calculate the correction function that must be applied to a (theoretical) solar-abundance model flux spectrum in order for this to yield synthetic UBVRIJHKL colors matching the (empirical) color-temperature calibrations derived from observations. In this way, the most important systematic differences existing between the original model spectra and the observations can indeed be eliminated. On the other hand, synthetic UBV and Washington ultraviolet excesses tex2html_wrap_inline1959 and tex2html_wrap_inline1961 and tex2html_wrap_inline1963 obtained from the original giant and dwarf model spectra are in excellent accord with empirical metal-abundance calibrations (Lejeune & Buser 1996). Therefore, the calibration algorithm is designed in such a way as to preserve the original differential grid properties implied by metallicity and/or luminosity changes in the new library, if the above correction function for a solar-abundance model of a given effective temperature is also applied to models of the same temperature but different chemical compositions [M/H] and/or surface gravities tex2html_wrap_inline1951.

While the new library constitutes a first-order approximation to the program set out above, it will be allowed to develop toward the more ambitious goal of matching the full requirements imposed on a standard library. Major input for refinement and completion is expected from the extensive tests now being made in population and evolutionary synthesis studies of the integrated light of globular clusters (Lejeune 1997) and galaxies (Bruzual et al. 1997).

keywords: atlases -- stars: fundamental parameters

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