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Introduction

Studies of individual stars and resolved stellar populations are fundamental for a wide variety of astrophysical subjects. In most cases photometric observations, obtained in various systems, represent the main observable. To translate these observables into fundamental stellar parameters (mainly effective temperature, luminosity) one first has to rely on stellar atmosphere models. In a second step the observations can then be compared to stellar evolution models and interpreted in physical terms such as mass, age, composition etc. Only in rare cases (very low mass stars, Baraffe et al. 1995; O stars, Schaerer et al. 1996) stellar evolution and atmosphere models are coupled and predict thus directly observables such as colors, magnitudes etc.

Extensive grids of stellar tracks covering the most important evolutionary phases and a large metallicity range have become available in the nineties (see e.g. compilation in Leitherer et al. 1996). In addition, recent efforts have been undertaken to provide accurate synthetic colours from grids of atmosphere models covering the bulk of the parameter space occupied by observed stars of spectral types from O to M and all luminosity classes (Lejeune et al. 1997, 1998, Bessell et al. 1998). With the availability of such data it now becomes feasible to systematically convert stellar tracks of all stellar masses and derived isochrones to a variety of photometric systems. To provide such a tool is the main goal of our database.

Existing grids, partly fulfilling this aim, include the library of Padova isochrones with UBVRIJHK photometry for ages $\sim$ 4 Myr - 20 Gyr and metallicities $Z$ between 0.0004 and 0.05 (Bertelli et al. 1994, Girardi et al. 1996), the recent $\alpha$-element enhanced tracks and isochrones of Salasnich et al. (2000) with UBVRIJHK and HST-WFPC2 photometry, and various other calculations covering smaller fractions of the parameter space.

For the present work we rely on an updated version of the hybrid library of synthetic stellar spectra compiled by Lejeune et al. (1997, 1998), which is corrected to match empirical colour-temperature relations at solar metallicity and semi-empirically corrected at other metallicities. These atmosphere models are used to derive synthetic photometry of the (UBV)$_J$(RI)$_C$ JHKLL$^\prime$M, WFPC2, Geneva, and Washington systems, using proper reference spectra for the zero points and up-to-date filter curves. This procedure is applied to essentially the full set of Geneva stellar evolution models to yield the photometric data for these systems for 1) individual stellar tracks in the mass range from 0.4-0.8 to 120-150 M_ M$_{\odot}$ and metallicities $Z$=0.0004 (1/50 Z_ Z$_{\odot}$) to 0.1 (5 Z_ Z$_{\odot}$), and 2) corresponding isochrones covering ages from $\sim$ 0 to 16-20 Gyr.

The input tracks, atmosphere models, and the synthetic photometry are described in Sect. 2. The resulting database products (tracks and isochrones) are presented in Sect. 3. Concluding remarks on the use of the various database sets are given in Section 4. The Appendix includes the relevant data for a previously unpublished set of stellar tracks at $Z$=0.0004.


next up previous
Next: Input Up: Database of Geneva stellar Previous: Database of Geneva stellar
Thibault Lejeune
2000-11-23