Detailed chemical composition of Galactic Cepheids

Free access article

Issue		A&A Volume 467, Number 1, May III 2007


Page(s)		283 - 294
Section		Stellar atmospheres
DOI		http://dx.doi.org/10.1051/0004-6361:20066375

A&A 467, 283-294 (2007)
DOI: 10.1051/0004-6361:20066375

A determination of the Galactic abundance gradient in the 8-12 kpc region

B. Lemasle^{1, 2}, P. François^{3, 2}, G. Bono^{4, 5}, M. Mottini⁵, F. Primas⁵, and M. Romaniello⁵

¹ Université de Picardie Jules Verne, Faculté des Sciences, 33 rue Saint-Leu, 80039 Amiens Cedex 1, France
² Observatoire de Paris-Meudon, GEPI, 92195 Meudon Cedex, France
e-mail: Bertrand.Lemasle@etud.u-picardie.fr
³ European Southern Observatory (ESO), 3107 Alonso de Cordova, Vitacura, Casilla 19001, Santiago 19, Chile
⁴ INAF-Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monte Porzio Catone, Italy
⁵ European Southern Observatory (ESO), Karl-Schwarzschild-Strasse 2, 85748 Garching bei Muenchen, Germany

(Received 11 September 2006 / Accepted 10 January 2007)

Abstract
Aims.The recent introduction of high-resolution/large spectral-range spectrographs has provided the opportunity to investigate the chemical composition of classical Cepheids in detail. This paper focusses on new abundance determinations for iron and 6 light metals (O, Na, Mg, Al, Si, Ca) in 30 Galactic Cepheids. We also give a new estimate of the Galactic radial abundance gradient.
Methods.The stellar effective temperatures were determined using the method of line depth ratios, and the surface gravity and the microturbulent velocity $v_{\rm t}$ by imposing the ionization balance between Fe I and Fe II with the help of curves of growth. Abundances were calculated with classical LTE atmosphere models.
Results.Abundances were obtained with rms accuracies of about 0.05-0.10 dex for Fe, and 0.05-0.20 dex for the other elements. Cepheids in our sample have solar-like abundances, and current measurements agree quite well with previous determinations. We computed "single zone" Galactic radial abundance gradients for the 8-12 kpc region and found a slope for iron of -0.061 dex kpc^-1.

Key words: stars: abundances -- stars: supergiants -- Galaxy: abundances -- Galaxy: evolution

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