EDP Sciences
Free Access
Issue
A&A
Volume 488, Number 1, September II 2008
Page(s) 25 - 35
Section Astrophysical processes
DOI https://doi.org/10.1051/0004-6361:200809859
Published online 09 July 2008


A&A 488, 25-35 (2008)
DOI: 10.1051/0004-6361:200809859

Baade-Wesselink distances and the effect of metallicity in classical cepheids

M. A. T. Groenewegen1, 2

1  Koninklijke Sterrenwacht van België, Ringlaan 3, 1180 Brussels, Belgium
    e-mail: marting@oma.be
2  Instituut voor Sterrenkunde, Celestijnenlaan 200 D, 3001 Leuven, Belgium

Received 27 March 2008 / Accepted 3 June 2008

Abstract
Context. The metallicity dependence of the Cepheid PL-relation is of importance in establishing the extra-galactic distance scale.
Aims. The aim of this paper is to investigate the metallicity dependence of the PL-relation in V and K based on a sample of 68 Galactic Cepheids with individual Baade-Wesselink distances (some of the stars also have an HST-based parallax) and individually determined metallicities from high-resolution spectroscopy.
Methods. Literature values of the V-band, K-band and radial velocity data have been collected for a sample of 68 classical cepheids that have their metallicity determined in the literature from high-resolution spectroscopy. Based on a (V-K) surface-brightness relation and a projection factor derived in a previous paper, distances have been derived from a Baade-Wesselink analysis. PL- and PLZ-relations in V and K are derived.
Results. The effect of the adopted dependence of the projection factor on period is investigated. The change from a constant p-factor to one recently suggested in the literature with a mild dependence on $\log P$ results in a less steep slope by 0.1 unit, which is about the 1-sigma error bar in the slope itself. The observed slope in the PL-relation in V in the LMC agrees with both hypotheses. In K the difference between the Galactic and LMC slope is larger and would favour a mild period dependence of the p-factor. The dependence on metallicity in V and K is found to be marginal, and independent of the choice of p-factor on period. This result is severely limited by the small range in metallicity covered by the Galactic Cepheids.


Key words: stars: distances -- stars: variables: cepheids -- cosmology: distance scale -- stars: oscillations including pulsations



© ESO 2008

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