We have constructed a new set of isochrones, called the Y 2 Isochrones, that represent an update of the Revised Yale Isochrones (RYI), using improved opacities and equations of state. Helium diffusion and convective core overshoot have also been taken into consideration. This first set of isochrones is for the scaled solar mixture. A subsequent paper will consider the effects of α-element enhancement, believed to be relevant in many stellar systems. Two additionally significant features of these isochrones are that (1) the stellar models start their evolution from the pre-main sequence birthline instead of from the zero-age main sequence, and (2) the color transformation has been performed using both the latest table of Lejeune et al., and

Abstract. 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 (T eff , log g, 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 UBV RIJHKL 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 δ (U−B) and δ (C−M) and δ (C−T1) 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 log g. Send offprint requests to: R. BuserWhile 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).

Abstract.We have used an updated version of the empirically and semi-empirically calibrated BaSeL library of synthetic stellar spectra of Lejeune et al. (1997Lejeune et al. ( , 1998 and Westera et al. (1999) to calculate synthetic photometry in the (UBV)J(RI)C JHKLL M, HST-WFPC2, Geneva, and Washington systems for the entire set of non-rotating Geneva stellar evolution models covering masses from 0.4-0.8 to 120-150 M and metallicities Z = 0.0004 (1/50 Z ) to 0.1 (5 Z ). The results are provided in a database which includes all individual stellar tracks and the corresponding isochrones covering ages from 10 3 yr to 16-20 Gyr in time steps of ∆ log t = 0.05 dex. The database also includes a new grid of stellar tracks of very metal-poor stars (Z = 0.0004) from 0.8−150 M calculated with the Geneva stellar evolution code.

Abstract. A standard library of theoretical stellar spectra intended for multiple synthetic photometry applications including spectral evolutionary synthesis is presented. The grid includes M dwarf model spectra, hence complementing the first library version established in Paper I . It covers wide ranges of fundamental parameters: T eff : 50 000 K ∼ 2000 K, log g: 5.5 ∼ −1.02, and [M/H]: +1.0 ∼ −5.0. A correction procedure is also applied to the theoretical spectra in order to provide color-calibrated flux distributions over a large domain of effective temperatures. For this purpose, empirical T eff -color calibrations are constructed between 11500 K and 2000 K, and semi-empirical calibrations for non-solar abundances ([M/H] = −3.5 to +1.0) are established. Model colors and bolometric corrections for both the original and the corrected spectra, synthesized in the (UBV ) J (RI) C JHKLL M system, are given for the full range of stellar parameters. We find that the corrected spectra provide a more realistic representation of empirical stellar colors, though the method employed is not completely adapted to the lowest temperature models. In particular the original differential colors of the grid implied by metallicity and/or luminosity changes are not preserved below 2500 K. Limitations of the correction method used are also discussed.