Pulsational constraints to the metallicity gradient in the Galactic disk

¹ Osservatorio Astronomico di Roma, Via di Frascati 33, 00040 Monteporzio Catone, Italy
² Osservatorio Astronomico di Capodimonte, Via Moiariello 16, 80131 Napoli, Italy
³ Observatoire de Genève, Switzerland e-mail: caputo@coma.mporzio.astro.it; marcella@na.astro.it; ilaria@na.astro.it;

Corresponding author: M. Marconi, marcella@na.astro.it

Received: 11 December 2000
Accepted: 26 March 2001

Abstract

BVI data of Galactic Cepheids observed in the solar neighborhood and in the outer disk are analyzed on the basis of nonlinear, non-local and time-dependent convective pulsating models computed for different assumptions on the chemical composition. We show that the theoretical color-color, period-luminosity, and period-luminosity-color relations, as predicted by the models with varying metal content, provide the way to simultaneously estimate the true distance modulus and the metal content Z of each individual variable. On this basis, we estimate that the metallicity distribution of Cepheids with Galactocentric distances d from ~6 to ~19 kpc can be represented by a linear gradient of dex kpc^-1, which is close to previous empirical determinations based on Cepheids, Planetary Nebulae and HII regions. However, our results are not excluding a different scenario, such as a two-zone model with a discontinuity in metallicity near kpc (see Twarog et al. 1997).