EDP Sciences
Free access
Issue
A&A
Volume 409, Number 2, October II 2003
Page(s) 511 - 522
Section Stellar clusters and associations
DOI http://dx.doi.org/10.1051/0004-6361:20031096


A&A 409, 511-522 (2003)
DOI: 10.1051/0004-6361:20031096

Using spectroscopic data to disentangle stellar population properties

N. Cardiel1, 2, J. Gorgas2, P. Sánchez-Blázquez2, A. J. Cenarro2, S. Pedraz1, 2, G. Bruzual3 and J. Klement4

1  Calar Alto Observatory, CAHA, Apdo. 511, 04004, Almería, Spain
2  Departamento de Astrofísica, Facultad de Físicas, Universidad Complutense de Madrid, 28040 Madrid, Spain
3  Centro de Investigaciones de Astronomía (CIDA), Apartado Postal 264, Mérida 5101-A, Venezuela
4  Institut für Astronomie, ETH Zentrum, SEC E3, Scheuchzerstrasse 7, 8092 Zürich, Switzerland

(Received 11 February 2003 / Accepted 18 June 2003 )

Abstract
It is well known that, when analyzed in the light of current synthesis model predictions, variations in the physical properties of single stellar populations (e.g. age, metallicity, initial mass function, element abundance ratios) may have a similar effect in their integrated spectral energy distributions. The confusion is even worsened when more realistic scenarios, i.e. composite star formation histories, are considered. This is, in fact, one of the major problems when facing the study of stellar populations in star clusters and galaxies. Typically, the observational efforts have aimed to find the most appropriate spectroscopic indicators in order to avoid, as far as possible, degeneracies in the parameter space. However, from a practical point of view, the most suited observables are not, necessarily, those that provide more orthogonality in that parameter space, but those that give the best balance between parameter degeneracy and sensitivity to signal-to-noise ratio per Å, ${\mbox{\rm
{\it S/N}({\rm\AA})}}$ . In order to achieve the minimum combined total error in the derived physical parameters, this work discusses how the functional dependence of typical line-strength indices and colors on ${\mbox{\rm
{\it S/N}({\rm\AA})}}$ allows to define a suitability parameter which helps to obtain more realistic combinations of spectroscopic data. As an example, we discuss in more detail the problem of breaking the well known age-metallicity degeneracy in relatively old stellar populations, comparing the suitability of different spectroscopic diagrams for a simple stellar population of solar metallicity and of 12 Gyr in age.


Key words: methods: data analysis -- techniques: spectroscopic -- galaxies: stellar content

Offprint request: N. Cardiel, ncl@astrax.fis.ucm.es




© ESO 2003