PREDICTED EXTREME-ULTRAVIOLET LINE EMISSION FOR NEARBY MAIN-SEQUENCE B-STARS

The source of the X-ray emission from O and B stars is currently the subject of debate. Shocks propagating through the winds of O and B stars have previously been proposed to explain their observed X-ray luminosities. Strong shocks with velocity jumps of several hundred km s-1 can heat portions of the wind to 10(6)-10(7) K, producing major sources of X-ray and extreme-ultraviolet (EUV) emission lines. Alternatively, a corona at the base of the wind might also be responsible for the X-ray emission. In this paper, we investigate the characteristics of EUV lines produced in high-temperature X-ray emitting regions of early B stars. We present estimates of EUV spectral line fluxes for single- and multitemperature plasma models for three nearby main-sequence B stars (beta-CMa, alpha-Vir, and beta-Cen A). The plasma models are constrained by X-ray spectral data, and are based on insights from previous hydrodynamics calculations of shocks propagating through hot star winds. The purpose of this paper is to demonstrate the importance of EUV emission lines in determining the properties of the X-ray emitting regions of hot stars. We also show that EUV emission lines from B stars with low interstellar medium hydrogen column densities may be detectable with the moderate-resolution (lambda/DELTA-lambda almost-equal-to 300) spectrometers of the Extreme Ultraviolet Explorer (EUVE) satellite. We investigate the effects of Doppler spreading and the time-dependent attenuation of the overlying wind on line profiles, and discuss how spectral observations can be used to determine temperatures, velocities, and locations of the emitting plasma, thereby providing important insights into the physical processes occurring in extended atmospheres of hot stars.