EDP Sciences
Free access
Issue A&A
Volume 501, Number 3, July III 2009
Page(s) 1269 - 1279
Section Numerical methods and codes
DOI http://dx.doi.org/10.1051/0004-6361/200811467
Published online 13 May 2009

A&A 501, 1269-1279 (2009)
DOI: 10.1051/0004-6361/200811467

ULySS: a full spectrum fitting package

M. Koleva1, 2, Ph. Prugniel1, A. Bouchard1, 3, and Y. Wu1, 4

1  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
    e-mail: prugniel@obs.univ-lyon1.fr
2  Department of Astronomy, St. Kliment Ohridski University of Sofia, 5 James Bourchier Blvd., 1164 Sofia, Bulgaria
3  Department of Astronomy, University of Cape Town, Private Bag X3, Rondebosch 7701, South Africa
4  National Astronomical Observatories, Chinese Academy of Sciences, 20A Datun Road, Chaoyang District, 100012, Beijing, PR China

Received 3 December 2008 / Accepted 15 March 2009

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 $\chi^2$ 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.


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



© ESO 2009

What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.
  • If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
  • You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
  • You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.

Editor-in-Chief: T. Forveille
Letters Editor-in-Chief: J. Alves
Managing Editor: C. Bertout

ISSN: 0004-6361 ; e-ISSN: 1432-0746
Frequency: 12 volumes per year
Published by: EDP Sciences

Mirror sites: CDS | EDP Sciences
  RSS feeds
© The European Southern Observatory (ESO)