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

Extract

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.