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Title:
ULySS: a full spectrum fitting package
Authors:
Koleva, M.; Prugniel, Ph.; Bouchard, A.; Wu, Y.
Affiliation:
AA(Université de Lyon, Lyon, 69000; Université Lyon 1, Villeurbanne, 69622; Centre de Recherche Astronomique de Lyon, Observatoire de Lyon, St. Genis Laval, 69561; CNRS, UMR 5574; École Normale Supérieure de Lyon, Lyon, France ; Department of Astronomy, St. Kliment Ohridski University of Sofia, 5 James Bourchier Blvd., 1164 Sofia, Bulgaria), AB(Université de Lyon, Lyon, 69000; Université Lyon 1, Villeurbanne, 69622; Centre de Recherche Astronomique de Lyon, Observatoire de Lyon, St. Genis Laval, 69561; CNRS, UMR 5574; École Normale Supérieure de Lyon, Lyon, France), AC(Université de Lyon, Lyon, 69000; Université Lyon 1, Villeurbanne, 69622; Centre de Recherche Astronomique de Lyon, Observatoire de Lyon, St. Genis Laval, 69561; CNRS, UMR 5574; École Normale Supérieure de Lyon, Lyon, France; Department of Astronomy, University of Cape Town, Private Bag X3, Rondebosch 7701, South Africa), AD(Université de Lyon, Lyon, 69000; Université Lyon 1, Villeurbanne, 69622; Centre de Recherche Astronomique de Lyon, Observatoire de Lyon, St. Genis Laval, 69561; CNRS, UMR 5574; École Normale Supérieure de Lyon, Lyon, France; National Astronomical Observatories, Chinese Academy of Sciences, 20A Datun Road, Chaoyang District, 100012, Beijing, PR China)
Publication:
Astronomy and Astrophysics, Volume 501, Issue 3, 2009, pp.1269-1279 (A&A Homepage)
Publication Date:
07/2009
Origin:
EDP Sciences
Keywords:
techniques: spectroscopic, methods: data analysis, galaxies: stellar content, stars: fundamental parameters
DOI:
10.1051/0004-6361/200811467
Bibliographic Code:
2009A&A...501.1269K

Abstract

Aims: We provide an easy-to-use full-spectrum fitting package and explore its applications to (i) the determination of the stellar atmospheric parameters and (ii) the study of the history of stellar populations.
Methods: We developed ULySS, a package to fit spectroscopic observations against a linear combination of non-linear model components convolved with a parametric line-of-sight velocity distribution. The minimization can be either local or global, and determines all the parameters in a single fit. We use χ2 maps, convergence maps and Monte-Carlo simulations to study the degeneracies, local minima and to estimate the errors.
Results: We show the importance of determining the shape of the continuum simultaneously to the other parameters by including a multiplicative polynomial in the model (without prior pseudo-continuum determination, or rectification of the spectrum). We also stress the usefulness of using an accurate line-spread function, depending on the wavelength, so that the line-shape of the models properly matches the observation. For simple models, i.e., to measure the atmospheric parameters or the age/metallicity of a single-age stellar population, there is often a unique minimum, or when local minima exist they can be recognized unambiguously. For more complex models, Monte-Carlo simulations are required to assess the validity of the solution.
Conclusions: The ULySS package is public, simple to use and flexible. The full spectrum fitting makes optimal use of the signal.
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