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A. K. Dupree, P. R. Young, A. Lobel (Harvard-Smithsonian CfA), T. R. Ake (JHU/CSC), J. L. Linsky, S. Redfield (JILA/CU), FUSE Cool Star Team
The FUSE telescope has been used to survey spectroscopically eight cool luminous stars (\beta Cet, \alpha Ori,\alpha Tau, \alpha Car, \beta Gem, 31 Com, \beta Dra, \alpha Aqr) in the spectral region \lambda\lambda910--1180. Emission from O VI has been detected in all stars with the exception of \alpha Ori, decreasing in surface flux across the giant branch. This demonstrates the pervasive extent of high temperature plasma (~ 3\times 105K) to stars as late as K5 III (\alpha Tau). Densities in the lower transition region (~ 70000K), as determined from C III line ratios, are on the order of 109 cm-3, with densities in the active stars 31 Com and \beta Cet perhaps as much as an order of magnitude higher. Emission from coronal plasma represented by Fe XVIII occurs in \beta Cet. Line profiles of individual species can be used to infer atmospheric heating and dynamics. Extended atmospheres are signaled by the presence of narrow Fe II emission that is fluoresced by H-Lyman \alpha in the coolest stars including \alpha Ori. These rich spectra document the energetics and dynamics of giant and supergiant atmospheres.
Based on Guaranteed Team observations made with the NASA-CNES-CSA Far Ultraviolet Explorer which is operated for NASA by The Johns Hopkins University under NASA contract NAS5-32985.