Far-Ultraviolet (912--1900 Angstrom ) Energy Distribution in Early-Type Main-Sequence Stars

Abstract

We present the comparison between observed far-ultraviolet (FUV) fluxes of early-type stars and those predicted by the most recent classical LTE, line-blanketed models of Kurucz. High-quality lUE spectra from the Uniform Low Dispersion Archive (ULDA) of more than 100 stars are selected. The averages of the observed fluxes, normalized to the visual flux, for each spectral class are calculated in three narrow bands centered at 1300, 1500, and 1750 Å and compared with model atmosphere predictions. We found that our results agree better with the models if we use the effective temperature scale of Lesh. lUE fluxes indicate a much lower temperature for B3 stars than reported in several spectral type T_eff relationships found in the literature, while for B9 stars our results point to a higher temperature. Using lUE mean fluxes, we derived a new T_eff scale for B-type stars. The normalized fluxes obtained using this new scale as input in model atmospheres are compared to the normalized fluxes at 1050 Å of 15 low-reddening early-type stars observed by the Voyager UVS. Voyager fluxes are within a factor of 2 in agreement with the models. Four of these stars match very well the predictions or have slightly lower flux than the models.