Magellanic Clouds elemental abundances from F supergiants: Revisited results for the Large Magellanic Cloud

With an improved method of the LTE abundance analysis for most elements (Kovtyukh & Andrievsky 1999), the abundances hare been re-investigated in nine F supergiants of the Large Magellanic Cloud. The NLTE calculations for carbon, oxygen and sodium, based on Kurucz's atmospheric models with an over-all metal deficiency, were carried out. The most important results are the following: - carbon abundance in supergiants is in much better agreement with the carbon abundance of the LMC HII regions, oxygen remaining in fair agreement with HII regions. The (C/O) ratio is low, lower than solar and the HII ratios (a possible sign of the first dredge-up, or another large-scale mixing event in the supergiant atmospheres); - the NLTE computations: do not show remarkable sodium overabundances in the LMC supergiants, in contrast with the Galactic supergiants; - the mean abundance of iron is found to be [Fe/H] = -0.40, slightly lower than the results of some previous determinations for the LMC. but in agreement with the recent result obtained bq Kern ct al. (2000), who give [Fe/H] = -0.41. The relative to iron abundance of oxygen [O/Fe] = +0.01 derived from nine F supergiants appears to be in excellent accordance with predictions based on the smooth model of the LMC evolution; - the (alpha /Fe) ratios are comparable to those found in previous analyses. The surprisingly low abundance of Mg is even lower in the new analysis, but it is in good agreement with the relative magnesium abundance in LMC B-stars [Mg/H] = -0.62 determined by Kern et al, (2000). Sulphur in the program supergiants shows the same abundance within an error bar as in H II regions; - the iron-group elements follow the solar distribution of the (M/Fe) ratios; - the heavy elements show enhanced abundances; - significantly larger log g values were obtained than in a previous study, resulting in supergiant masses of about 10-20 M. which are in excellent agreement with evolutionary calculations.