Analysis of medium resolution spectra by automated methods – Application to M 55 and ω Centauri
Sternwarte der Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany e-mail: firstname.lastname@example.org
2 Astronomisches Institut der Universität Basel, Venusstrasse 7, 4102 Binningen, Switzerland
3 Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
Accepted: 8 February 2005
We have employed feedforward neural networks trained on synthetic spectra in the range 3800 to 5600 Å with resolutions of ~2–3 Å to determine metallicities from spectra of about 1000 main-sequence turn-off, subgiant and red giant stars in the globular clusters M 55 and ω Cen. The overall metallicity accuracies are of the order of 0.15 to 0.2 dex. In addition, we tested how well the stellar parameters and Teff can be retrieved from such data without additional colour or photometric information. We find overall uncertainties of 0.3 to 0.4 dex for and 140 to 190 K for Teff. In order to obtain some measure of uncertainty for the determined values of [Fe/H], and Teff, we applied the bootstrap method for the first time to neural networks for this kind of parametrization problem. The distribution of metallicities for stars in ω Cen clearly shows a large spread in agreement with the well known multiple stellar populations in this cluster.
Key words: globular clusters: individual: ω Centauri / globular clusters: individual: M 55 / stars: fundamental parameters / methods: data analysis / techniques: spectroscopic / stars: abundances
© ESO, 2005