AAS 196th Meeting, June 2000
Session 40. High Resolution Spectroscopy at Visible and Ultraviolet Wavelengths
Topical Contributed Display, Wednesday, June 7, 2000, 10:00am-7:00pm, Empire Hall South

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[40.13] Stellar Activity and Outer Atmospheric Structure of Yellow Supergiants from HST STIS and GHRS Spectroscopy

A. Brown, T. R. Ayres, G. M. Harper, R. A. Osten (CASA, U. of Colorado), J. L. Linsky (JILA, U. of Colorado), A. K. Dupree (Harvard-Smithsonian CfA), C. Jordan (U. of Oxford)

Yellow supergiants with spectral types F-G show a complex pattern of outer atmospheric structure with stellar wind and activity indicators varying significantly for stars with similar positions in the H-R diagram. The efficiency of the processes driving their stellar winds and heating their atmospheres is critically dependent on the evolutionary position and surface gravity of each star. We present high-resolution ultraviolet HST/STIS and HST/GHRS spectra for a range of intermediate mass F and G supergiants, including Alpha Car (F0 Ib), Beta Cam (G0 Ib), Beta Dra (G2 Ib), and Epsilon Gem (G8 Ib), and compare the atmospheric properties of these stars with lower luminosity giants and bright giants. We provide a systematic overview of the supergiant atmospheric properties dealing particularly with activity levels, the presence of hot ``transition region'' plasma, signatures of wind outflow, and the role of overlying cool absorbing plasma that becomes increasingly prominent for the cooler stars like Epsilon Gem.

This work is supported by HST grants for program GO-08280 and by NASA grant NAG5-3226.

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