EDP Sciences
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Volume 401, Number 3, April III 2003
Page(s) 939 - 949
Section Stellar clusters and associations
DOI http://dx.doi.org/10.1051/0004-6361:20030155

A&A 401, 939-949 (2003)
DOI: 10.1051/0004-6361:20030155

The galactic abundance gradient from Cepheids

IV. New results for the outer disc
R. E. Luck1, W. P. Gieren2, S. M. Andrievsky3, 4, V. V. Kovtyukh3, 4, P. Fouqué5, F. Pont6 and F. Kienzle6

1  Department of Astronomy, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106-7215, USA
    e-mail: luck@fafnir.astr.cwru.edu
2  Departamento de Fisica, Grupo de Astronomia, Universidad de Concepción, Casilla 160-C, Concepción, Chile
    e-mail: wgieren@coma.cfm.udec.cl
3  Department of Astronomy, Odessa State University, Shevchenko Park, 65014 Odessa, Ukraine
    e-mail: val@deneb.odessa.ua
4  Odessa Astronomical Observatory and Isaac Newton Institute of Chile, Odessa Branch, Ukraine
5  European Southern Observatory, Casilla 19001, 19 Santiago, Chile
    e-mail: pfouque@eso.org
6  Geneva Observatory, 1290 Sauverny, Switzerland
    e-mail: Frederic.Pont@obs.unige.ch; Francesco.Kienzle@obs.unige.ch

(Received 8 October 2002 / Accepted 22 January 2003 )

As a continuation of our previous work on the abundance gradient in the outer part of the galactic disc, this paper presents results on the metallicicty distribution over galactocentric distances up to 15 kpc. The outer disc is clearly separated from the middle part by the existence of a step in the metallicity distribution at about 10 kpc. Taking the region of galactocentric distances from 10 kpc to 15 kpc, one can derive an iron gradient $-0.03 \pm 0.01$ dex kpc -1 (25 stars). The existence of a discontinuity can be caused by the effective suppression of mixing processes near the corotation circle where the radial component of the gas velocity should be very small.

Key words: stars: abundances -- stars: variables: Cepheids -- Galaxy: abundances -- Galaxy: evolution

Offprint request: S. M. Andrievsky, scan@deneb.odessa.ua

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