Effective temperature derived from isochrone analysis as a function of spectral type. Colors and symbols have the same meaning as in Fig. 1 except for the magenta symbols. The latter represent the results on SMC stars by Mokiem et al. (2007) and Massey et al. (2009), and the calibration of Trundle et al. (2007) for B stars in this galaxy (lines; thick = supergiants, thin = dwarfs), derived from quantitative spectral analysis. The WO and the Be stars have been arbitrarily located in the X-axis. Dotted lines represent the revision of spectral types by Garcia et al. (2010, in prep.). T_eff  derived from isochrones for our IC 1613 sample increases with earlier spectral type as expected, but flattens at O stars, hinting that color degeneracy is still a problem for these types. The T_eff  we derived for the IC 1613 stars roughly agrees with the trend observed in the SMC.