ORFEUS observations of luminous cool stars

The ORFEUS telescope obtained far-ultraviolet spectra (lambda lambda 912-1218) of three luminous cool stars: P Draconis (HD 159181) and two hybrid stars, alpha Aquarii (HD 209750) and alpha Trianguli Australis (HD 150798). Most striking is the detection of blueshifted O VI lambda 1032, and C III lambda 977 emission relative to Si III lambda 1206, indicating outward motion, and the markedly narrow resonance line profiles of C III and Si III in the two hybrid objects as compared with the coronal star beta Dra. The observed Doppler shifts suggest that a warm wind of at least 3 x 10(5) K occurs in the hybrid stars with outflows similar to 100-200 km s(-1); narrow lines of C III and Si III are consistent with signatures of wind absorption. The asymmetric profile of C III in P Dra might also result from wind absorption, although the acceleration would have to begin at higher temperatures (T similar to 70,000 K) in this coronal star as compared with the hybrids, since its chromospheric Mg II profiles show no asymmetry due to wind absorption. Electron densities determined from C III multiplets in beta Dra and alpha TrA indicate values between 8.3 and 8.6 dex (cm(-3)), giving a pressure of similar to 2 x 10(13) cm(-3) K, at T similar to 7 x 10(4) K. Wind absorption and interstellar extinction must be considered when applying emission-line diagnostics in this wavelength region.