Comparative modelling of the spectra of cool giants^{⋆,⋆⋆,⋆⋆⋆}

¹ University of Vienna, Türkenschanzstrasse 17, 1180 Vienna, Austria
e-mail: thomas.lebzelter@univie.ac.at
² Department of Physics and Astronomy, Uppsala University, Box 516, 75120 Uppsala, Sweden
³ Depto. Física Teórica y del Cosmos, Universidad de Granada, 18071 Granada, Spain
⁴ Department of Physics and Astronomy, Macquarie University, NSW 2109, Australia
⁵ Argelander Institute for Astronomy, University of Bonn, Auf dem Huegel 71, 53121 Bonn, Germany
⁶ Universidad Autónoma de Madrid, Dpto. Física Teórica, Módulo 15, Facultad de Ciencias, Campus de Cantoblanco, 28049 Madrid, Spain
⁷ Université de Nice Sophia Antipolis, CNRS (UMR 6202), Observatoire de la Côte d’Azur, Cassiopée, BP 4229, 06304 Nice Cedex 04, France
⁸ Astrophysical Advances/UCOLick, 607 Marion Pl, Palo Alto, CA 94301, USA
⁹ Laboratoire Univers et Particules de Montpellier, Université Montpellier 2, CNRS, 34095 Montpellier, France
¹⁰ Department of Astronomy & Physics, Saint Mary’s University, 923 Robie Street Halifax, Nova Scotia, B3H 3C3, Canada
¹¹ Goddard Space Flight Center, NASA, Greenbelt MD 20771, USA
¹² INAF – OAPD, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
¹³ Indian Institute of Astrophysics, Koramangala, Bangalore, India
¹⁴ ESA – ESAC Gaia SOC, PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain
¹⁵ Department of Physics, Catholic University of America, 620 Michigan Ave, NE, Washington, DC 20064, USA
¹⁶ Zentrum für Astronomie der Universität Heidelberg (ZAH), Institut für Theoretische Astrophysik, Albert Ueberle-Str. 2, 69120 Heidelberg, Germany
¹⁷ Institute of Astronomy, The University of Tokyo, 2-21-1 Osawa, Mitaka, 181-0015 Tokyo, Japan
¹⁸ Centro de Astrobiología (INTA-CSIC), LAEFF Campus, European Space Astronomy Center (ESAC), PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain
¹⁹ Astronomy Department, Ohio State University, 140 West 18th Avenue, Columbus, OH 43210, USA
²⁰ Australian Astronomical Observatory, PO Box 296, Epping, NSW 1710, Australia
²¹ SIfA, School of Physics, University of Sydney, NSW 2006, Australia

Received: 1 March 2012
Accepted: 29 August 2012

Abstract

Context. Our ability to extract information from the spectra of stars depends on reliable models of stellar atmospheres and appropriate techniques for spectral synthesis. Various model codes and strategies for the analysis of stellar spectra are available today.

Aims. We aim to compare the results of deriving stellar parameters using different atmosphere models and different analysis strategies. The focus is set on high-resolution spectroscopy of cool giant stars.

Methods. Spectra representing four cool giant stars were made available to various groups and individuals working in the area of spectral synthesis, asking them to derive stellar parameters from the data provided. The results were discussed at a workshop in Vienna in 2010. Most of the major codes currently used in the astronomical community for analyses of stellar spectra were included in this experiment.

Results. We present the results from the different groups, as well as an additional experiment comparing the synthetic spectra produced by various codes for a given set of stellar parameters. Similarities and differences of the results are discussed.

Conclusions. Several valid approaches to analyze a given spectrum of a star result in quite a wide range of solutions. The main causes for the differences in parameters derived by different groups seem to lie in the physical input data and in the details of the analysis method. This clearly shows how far from a definitive abundance analysis we still are.