Astron. Astrophys. 324, 435-448 (1997)

1. Introduction

The Magellanic Clouds have often been used as laboratories to test the validity of theories built up in our own Galaxy. In particular, the understanding of the chemical evolution of these two galaxies is of great interest as a probe of evolution of extragalactic systems. From numerous metallicity indicators, the present day metallicity of the Clouds have been determined to be around half solar ([M/H] -0.25 dex) and one fifth of solar ([M/H] -0.7 dex) respectively in the Large and Small Magellanic Cloud, implying that the Magellanic Clouds have not evolved at the same rate as our own Galaxy.

In the last years, modern detectors have made it possible to observe high resolution spectra of luminous young stars, providing information on the chemical content of these stars (abundances of numerous elements). The latest studies concerned F supergiant stars (Russell and Bessell 1989, hereafter RB89; Spite et al. 1989, hereafter SSF89; Luck and Lambert 1992, hereafter LL92; Hill et al. 1995). Studies of H II  regions (Pagel 1978, Dufour 1984, Russell & Dopita 1992 and references therein) also give information on the abundance of the lighter elements (C,N,O, S, etc.). The general findings from these studies is that the abundance pattern of the elements do not always follow the solar pattern, in particular concerning the light elements and the neutron capture elements, which are not yet fully understood. Moreover, in the Small Magellanic Cloud (SMC), from the F stars studies, it is not very clear whether the abundances are homogeneous across the whole galaxy or if a dispersion, exists. Confusing also, was the finding that the young cluster NGC330 appeared to be noticeably more metal poor than its surroundings (Spite et al. 1991).
Since deriving abundances in very luminous stars is always questionable because of the extreme atmospheres that are concerned (non-LTE effects are almost surely present), it appeared useful to study also a slightly different kind of cooler stars: the K supergiants, in particular to be used as field "reference stars" for a future analysis of a more complete sample of stars in NGC 330. Furthermore, state of the art models specifically developed for cool giants stars were made available by B. Plez (1992 and 1995) and made it possible to derive precise abundances from these metal-poor K supergiants.
In this paper, we present the analysis of six K supergiant stars of the SMC. The abundances of 16 elements from sodium to europium are derived and discussed in terms of chemical evolution of the galaxy. The scatter around the mean value for our sample is also discussed in terms of homogeneity of the SMC. The abundance of C, N and O will be discussed in a forthcoming paper by Hill & Barbuy (1996).

© European Southern Observatory (ESO) 1997

Online publication: May 26, 1998

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