Abstract

The spectral predictions of stellar population models are not as accurate in the ultra-violet (UV) as in the optical wavelength domain. One of the reasons is the lack of high-quality stellar libraries. The New Generation Stellar Library (NGSL), recently released, represents a significant step towards the improvement of this situation. To prepare NGSL for population synthesis, we determined the atmospheric parameters of its stars, we assessed the precision of the wavelength calibration and characterised its intrinsic resolution. We also measured the Galactic extinction for each of the NGSL stars. For our analyses we used ULySS, a full spectrum fitting package, fitting the NGSL spectra against the MILES interpolator. As a second step we build preliminary single stellar population models using Vazdekis (2003) synthesis code.

We find that the wavelength calibration is precise up to 0.1 px, after correcting a systematic effect in the optical range. The spectral resolution varies from 3Å in the UV to 10Å in the near-infrared (NIR), corresponding to a roughly constant reciprocal resolution R = λ/δλ ≈ 1000 and an instrumental velocity dispersion σ_ins ≈ 130 kms^-1. We derived the atmospheric parameters homogeneously. The precision for the FGK stars is 42 K, 0.24 and 0.09 dex for T_eff, logg and [Fe/H], respectively. The corresponding mean errors are 150 K, 0.50 and 0.48 dex for the M stars, and for the OBA stars they are 4.5 percent, 0.44 and 0.18 dex. The comparison with the literature shows that our results are not biased. Our first version of models compares well with models based on optical libraries, having the advantages to be free from artifacts due to the atmosphere. In future we will fine-tune our models by comparing to different models and observations of globular clusters.