We present new slit spectral types for 120 O and B stars in the SMC which previously had only objective-prism classification. We discuss the colors of O and B stars in the SMC. As in the LMC, we show that there is no separation in colors between O and early B stars. The lower metallicity of the SMC is particularly evident in the spectra of the B stars. The different composition of the SMC may also be indirectly responsible for apparently redder intrinsic colors, especially in (U - B), compared with LMC stars. We also discuss the distance modulus of the SMC, determined from spectroscopic parallax and ZAMS fitting. The second method depends on a knowledge of the temperature/spectral-type relation in the SMC, which has not yet been addressed in the literature. We adopt DM = 19.0, but note how this might change with better understanding of stellar parameters. The data in this paper are also used to re-examine the Humphreys-Davidson limit, and an analytical relation is presented for this upper luminosity limit.
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Garmany et al. (1987) studied this question.