ORFEUS Observations of Luminous Cool Stars

Details ORFEUS Observations of Luminous Cool Stars ORFEUS Observations of Luminous Cool Stars

Jun 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998apj...500l..33d&link_type=abstract

Astrophysical Journal Letters v.500, p.L33

Astronomy and Astrophysics

Astronomy

12

Ultraviolet: Stars, Stars: Atmospheres, Stars: Late-Type, Stars: Mass Loss

Scientific paper

The ORFEUS telescope obtained far-ultraviolet spectra ( lambda lambda 912-1218) of three luminous cool stars: beta 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 3x105 K occurs in the hybrid stars with outflows ~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 beta Dra might also result from wind absorption, although the acceleration would have to begin at higher temperatures (T ~ 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 ~ 2x1013 cm-3 K, at T~7x104 K. Wind absorption and interstellar extinction must be considered when applying emission-line diagnostics in this wavelength region.

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