Stellar population synthesis at the resolution of 2003

We present a new model for computing the spectral evolution of stellar populations at ages between 100,000 yr and 20 Gyr at a resolution of 3 A across the whole wavelength range from 3200 to 9500 A for a wide range of metallicities. These predictions are based on a newly available library of observed stellar spectra. We also compute the spectral evolution across a larger wavelength range, from 91 A to 160 micron, at lower resolution. The model incorporates recent progress in stellar evolution theory and an observationally motivated prescription for thermally-pulsing stars on the asymptotic giant branch. The latter is supported by observations of surface brightness fluctuations in nearby stellar populations. We show that this model reproduces well the observed optical and near-infrared colour-magnitude diagrams of Galactic star clusters of various ages and metallicities. Stochastic fluctuations in the numbers of stars in different evolutionary phases can account for the full range of observed integrated colours of star clusters in the Magellanic Clouds. The model reproduces in detail typical galaxy spectra from the Early Data Release (EDR) of the Sloan Digital Sky Survey (SDSS). We exemplify how this type of spectral fit can constrain physical parameters such as the star formation history, metallicity and dust content of galaxies. Our model is the first to enable accurate studies of absorption-line strengths in galaxies containing stars over the full range of ages. Using the highest-quality spectra of the SDSS EDR, we show that this model can reproduce simultaneously the observed strengths of those Lick indices that do not depend strongly on element abundance ratios [abridged].Comment: 35 pages, 22 figures, to appear in MNRAS; version with full resolution figures available at http://www.iap.fr/~charlot/bc2003/pape

High-resolution abundance analysis of two individual stars of the bulge globular cluster NCG 6553

A detailed abundance analysis of 2 giants of the metal-rich bulge globular cluster NGC6553 was carried out using high resolution échelle spectra obtained at the ESO 3.6m telescope. The temperature calibration of metal-rich cool giants needs high quality photometric data.We have obtained JK photometry at ESO and VI photometry with the Hubble Space Telescope for NGC6553. The main purpose of this analysis consists in the determination of elemental abundance ratios for this key bulge cluster, as a basis for the fundamental calibration of metal-rich populations. The present analysis provides a metallicity [Fe/H] = −0.55±0.2 which, combined to overabundances relative to Fe of several elements, results in an overall metallicity Z≈Zʘ

High-resolution abundance analysis of two individual stars of the bulge globular cluster NCG 6553

A detailed abundance analysis of 2 giants of the metal-rich bulge globular cluster NGC6553 was carried out using high resolution échelle spectra obtained at the ESO 3.6m telescope. The temperature calibration of metal-rich cool giants needs high quality photometric data.We have obtained JK photometry at ESO and VI photometry with the Hubble Space Telescope for NGC6553. The main purpose of this analysis consists in the determination of elemental abundance ratios for this key bulge cluster, as a basis for the fundamental calibration of metal-rich populations. The present analysis provides a metallicity [Fe/H] = −0.55±0.2 which, combined to overabundances relative to Fe of several elements, results in an overall metallicity Z≈Zʘ

Infrared array photometry of bulge globular clusters I. Combined ground based JK and HST VI photometry of NGC 6553

JK infrared photometry for the bulge globular cluster NGC 6553, combined with high resolution visual VI observations are presented and discussed in connection with the bulge metal rich population. The infrared data were taken with IRAC2 at ESO 2.2m telescope while the optical counterparts are from Hubble Space Telescope (HST). We nd a mean magnitude for the horizontal branch of VHB = 16.92, and KHB = 12.42 ± 0.01. Assuming a reddening of E(B − V) = 0.7, the mean distance modulus is (m − M)0 = 13.6 giving an heliocentric distance of 5.2 Kpc. This distance is slightly higher than that previously published by Ortolani et al. (1990, hereafter OBB90). The brightest giants have been detected at K ~ 6.5 and (V −K) = 13.10 transforming to MK = −7.34 and (V−K)0 = 11.20, which are exceptionally high values for a globular cluster. The metallicity has been found to be consistent with previous values and an average of [Fe/H] = −0.22±0.05 has been adopted. The helium abundance estimated via the R' method yields Yp ~ 0.28 ± 0.03