SMC: UV Extinction Curves, Gas to Color-Excess Ratios

Abstract

We have made an extensive study of the far-UV extinction in SMC stars using IUE spectra mostly obtained by us. The studied stars are Sk 7, 13, 18, 32, 76, 82, 85, 103, 119, 124, 142, 143, 159, 191 and AV 398. A few other stars have also been observed but are unsuitable for extinction studies. We have obtained at ESO new photometry and spectral classifications for all the studied stars. The far-UV extinction curves derived from IUE spectra of matched star pairs are all similar, except for Sk 143 (Lequeux et al., 1982), Sk 124 and 191. The mean curve, which supersedes that of Rocca-Volmerange et al. (1981) is plotted Fig. 1 with the label SMC “normal”, as well as the curves for the three “anomalous” stars (full lines) For comparison, we also plot the LMC “normal” curve and that for the anomalous star Sk-69°108 (dotted-dashed curves), the “normal” galactic curve and the curves for two stars in Scorpius-Ophiuchus.

Massive star evolution in nearby galaxies

“…IC 1613 has lower metallicity even than the SMC (Davidson and Kinman 1982) while NGC 6822 is intermediate between the LMC and SMC in heavy element abundances (Pagel and Edmonds 1981). IC 1613 also has a different luminosity function (Lequeux et al 1980) from the other dwarf irregulars (SMC and NGC 6822) which means either a low star formation rate or a very different IMF ).…”