Other
Scientific paper
May 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993aas...182.4619r&link_type=abstract
American Astronomical Society, 182nd AAS Meeting, #46.19; Bulletin of the American Astronomical Society, Vol. 25, p.877
Other
Scientific paper
As part of an investigation of the velocity fields in the atmospheres of cool, luminous stars we used the Goddard High Resolution Spectrograph (GHRS) aboard the Hubble Space Telescope to obtain a high resolution spectrum of the Mg II h and k lines in the M supergiant alpha Ori. These strong, centrally reversed emission lines have been well studied by the IUE. While the h line in alpha Ori has nearly equal intensity in the red and blue peaks, the blue peak of the k line is always much weaker than the red peak. This asymmetry is normally explained as resulting from absorption by Fe I and Mn I in the circumstellar shell. An examination of the GHRS spectrum, however, reveals that the asymmetry results from a velocity shift between the emission wings and the central absorption core of the line. Further, while the central absorption profiles for the h and k lines agree very well when plotted on a velocity scale, the centroid of the k line emission wings was observed to be redshifted by approximately 23 km/s with respect to that of the h line. Examination of other high resolution GHRS observations of Mg II showed a similar, though less pronounced, relative redshift of the k line centroid on the normal M giant gamma Cru and the hybrid K giant gamma Dra. To date, no concrete model has been proposed to explain these shifts. Examining well exposed, high resolution IUE observations of alpha Ori shows a close agreement with the GHRS results. This gives us confidence that we can use IUE spectra to study the relative shapes and velocities of the Mg II h and k lines and we are currently involved in a program to use the IUE archive to quantify the behavior of the Mg II h and k profiles as a function of luminosity and spectral type for luminous, cool stars. The results of this program will be presented.
Carpenter Kenneth G.
Robinson Richard D.
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