Far‐Ultraviolet Spectra of B Stars near the Ecliptic

Spectra of B stars in the wavelength range of 911-1100 A have been obtainedwith the EURD spectrograph onboard the Spanish satellite MINISAT-01 with ~5 Aspectral resolution. IUE spectra of the same stars have been used to normalizeKurucz models to the distance, reddening and spectral type of the correspondingstar. The comparison of 8 main-sequence stars studied in detail (alpha Vir,epsilon Tau, lambda Tau, tau Tau, alpha Leo, zeta Lib, theta Oph, and sigmaSgr) shows agreement with Kurucz models, but observed fluxes are 10-40% higherthan the models in most cases. The difference in flux between observations andmodels is higher in the wavelength range between Lyman alpha and Lyman beta. Wesuggest that Kurucz models underestimate the FUV flux of main-sequence B starsbetween these two Lyman lines. Computation of flux distributions ofline-blanketed model atmospheres including non-LTE effects suggests that thisflux underestimate could be due to departures from LTE, although other causescannot be ruled out. We found the common assumption of solar metallicity foryoung disk stars should be made with care, since small deviations can have asignificant impact on FUV model fluxes. Two peculiar stars (rho Leo and epsilonAqr), and two emission line stars (epsilon Cap and pi Aqr) were also studied.Of these, only epsilon Aqr has a flux in agreement with the models. The resthave strong variability in the IUE range and/or uncertain reddening, whichmakes the comparison with models difficult.Comment: 25 pages, 6 figures, to be published in The Astrophysical Journa