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Session 56 - Frontiers of Ultraviolet Astrophysics.
Display session, Wednesday, June 10
ORFEUS spectra of two hybrid stars \alpha Aqr (G2 Ib, HD 209750) and \alpha TrA (K2 II, HD 150798), and \beta Dra (G2 Ib-IIa, HD 159181) cover the far ultraviolet region \lambda\lambda912--1218 with a moderate resolution of \sim 3000. Blue--shifted O VI (\lambda1032) and C III (\lambda977) emission relative to Si III (\lambda1206) is detected in the two hybrid stars, and the markedly narrow resonance line profiles of C III and Si III in the two hybrid objects as compared to the coronal star \beta Dra also suggest wind absorption. The observed Doppler shifts could be caused by a warm wind of at least 3\times 10^5K in the hybrid stars with outflows \sim100--200 km\ s^-1. An asymmetric profile of C III in \beta Dra might also result from wind absorption, although the acceleration would have to begin at higher temperatures (T\sim7000 K) in this coronal star as compared to the hybrids. Electron densities determined from C III multiplets in \beta Dra and \alpha TrA indicate values between 8.3--8.6 dex (cm^-3), giving a pressure of \sim 2 \times 10^13 cm^-3K at T\sim 7\times 10^4 K. Wind absorption and interstellar extinction must be considered when applying emission line diagnostics in this wavelength region. These observations make the connection between hot and cool winds across the color-magnitude diagram, by demonstrating that intermediate warm winds exist among luminous stars.
Program listing for Wednesday