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Astron. Astrophys. 318, L47-L50 (1997)

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Letter to the Editor

The effect of metallicity on the Cepheid distance scale and its implications for the Hubble constant (H0) determination

J.P. Beaulieu 1, D.D. Sasselov 1, 2, C. Renault 3, P. Grison 1, R.Ferlet 1, A. Vidal-Madjar 1, E. Maurice 4, L. Prévot 4, E. Aubourg 3, P. Bareyre 3, S. Brehin 3, C. Coutures 3, N. Delabrouille 3, J. de Kat 3, M. Gros 3, B. Laurent 3, M. Lachièze-Rey 3, E. Lesquoy 3, C. Magneville 3, A. Milsztajn 3, L. Moscoso 3, F. Queinnec 3, J. Rich 3, M. Spiro 3, L. Vigroux 3, S. Zylberajch 3, R. Ansari 5, F. Cavalier 5, M. Moniez 5, C. Gry 6, J. Guibert 7, O. Moreau 7 and F. Tajhmady(The EROS collaboration). 7

1 Institut d'Astrophysique de Paris, CNRS, 98bis Boulevard. Arago, 75014 Paris, France
2 Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138, USA.
3 CEA, DSM/DAPNIA, Centre d'études de Saclay, 91191 Gif-sur-Yvette, France.
4 Observatoire de Marseille, 2 place Le Verrier, 13238 Marseille 03, France.
5 Laboratoire de l'Accélérateur Linéaire IN2P3, Centre d'Orsay, 91405 Orsay, France.
6 Laboratoire d'Astronomie Spatiale CNRS, Traversée du siphon, les trois lucs, 13120 Marseille, France.
7 Centre d'Analyse des Images de l'Institut National des Sciences de l'Univers, CNRS Observatoire de Paris, 61 Avenue de l'Observatoire, 75014 Paris, France.

Received 19 July 1996 / Accepted 5 November 1996


Recent HST determinations of the expansion's rate of the Universe (the Hubble constant, [FORMULA]) assumed that the Cepheid Period-Luminosity relation at V and I are independent of metallicity (Freedman, et al., 1996, Saha et al., 1996, Tanvir et al., 1995). The three groups obtain different vales for [FORMULA]. We note that most of this discrepancy stems from the asumption (by both groups) that the Period-Luminosity relation is independent of metallicity. We come to this conclusion as a result of our study of the Period-Luminosity relation of 481 Cepheids with 3 millions two colour measurements in the Large Magellanic Cloud and the Small Magellanic Cloud obtained as a by-product of the EROS microlensing survey. We find that the derived interstellar absorption corrections are particularly sensitive to the metallicity and when our result is applied to recent estimates based on HST Cepheids observations it makes the low- [FORMULA] values higher and the high- [FORMULA] value lower, bringing those discrepant estimates into agrement around [FORMULA] kms-1 Mpc-1.

Key words: Stars : cepheids - Stars : fundamental parameters - galaxies : distances

Send offprint requests to: JP. Beaulieu

© European Southern Observatory (ESO) 1997

Online publication: July 8, 1998