HST/GHRS Spectroscopy of the Hybrid Star Alpha Aquarii
Session 18 -- Stellar Spectra: Individual Objects
Display presentation, Wednesday, January 12, 9:30-6:45, Salons I/II Room (Crystal Gateway)

## [18.07] HST/GHRS Spectroscopy of the Hybrid Star Alpha Aquarii

A. K. Dupree, D. D. Sasselov, and S. R. Keener (Harvard-Smithsonian Center for Astrophysics)

GHRS observations were made in July 1993 of the luminous hybrid supergiant Alpha Aqr (HD 209750, G2 Ib). This cool supergiant gives evidence for both high temperature emission from N V and C IV ($T= 2 \times 10^5$K) and a massive wind. In addition, the He I $\lambda$10830 transition indicates supersonic wind velocities in the chromosphere. To identify the emitting regions, and determine the profile of wind acceleration, we obtained moderate resolution (G160 M) observations and wavelength calibration exposures at four grating positions centered on He II ($\lambda$ 1640), C II ($\lambda$1335), C IV ($\lambda 1550$), and N V ($\lambda$1240). All four species were detected. The IUE obtained simultaneous ultraviolet spectra including profiles of Mg II ($\lambda$2800). The C IV and N V lines appear blue-shifted ($\approx$~30~$km\ s^{-1}$), and broad, with FWHM ranging from 125 to 180 $km\ s^{-1}$, similar to those found previously in $\alpha$ TrA, another hybrid star, and interpreted as arising from wind expansion. Hydrostatic and dynamic atmospheric models are calculated with and spherical geometry in order to interpret the observed line profiles.