THE CHEMICAL-COMPOSITION OF MAGELLANIC CLOUD CEPHEIDS AND NONVARIABLE SUPERGIANTS

Abundance analyses of 14 Cepheids and nonvariable supergiants in the Magellanic Clouds (seven stars in each Cloud) are presented along with comparison data on four Galactic objects. Elemental abundances derived include Li, C, N, O, the alpha-elements, the Fe peak, and limited data on the heavy elements. Only HV 5497 in the LMC shows any detectable Li [log epsilon(Li) = 2.5] among the Cloud objects. It is also unique (among LMC objects analyzed) in that it is metal-rich ([Fe/H] approximately +0.2) which may explain its Li-rich nature. Our CNO data when combined with previous results suggest a disparity between the LMC and the SMC supergiants in that the SMC stars have an essentially constant [O/Fe] ratio, while the LMC stars do not. The [O/Fe] ratios within both Clouds are lower than the ratio found in Galactic stars of similar metallicity, but are comparable to the [O/Fe] ratios found in Galactic supergiants. Both Clouds show a range of CNO abundances larger than that of Galactic supergiants, but this could be a result of analysis deficiencies and small sample sizes. The [Fe/H] ratios are consistent with the analysis errors dominating the abundance dispersion in the SMC, while within the LMC a real dispersion in [Fe/H] is possible. For the heavier elements, we confirm previous results which indicate the light s- and r-process elements (Sr, Y, Zr) show Galactic ratios with respect to Fe, but that the heavy s- and r-process elements (Ba-Sm) are enhanced in the Clouds.