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Session 67 - Stars: Evolution, Atmospheres, Intrinsic.
Display session, Thursday, June 11
Atlas Ballroom,
We report on a rich set of observations of the K0 III star \beta Geminorum (Pollux) with the Goddard High-Resolution Spectrograph (GHRS). The dataset consists of low-dispersion spectra (\lambda/\Delta \lambda = 2,000) of the 1169 - 1671 Å\ region, moderate dispersion spectra (\lambda/\Delta \lambda = 20,000) of selected spectral intervals, and echelle observations (\lambda/\Delta \lambda = 90,000) of the O I resonance lines and Mg II h and k lines. We perform an analysis of intersystem lines and determine the emission measure distribution, from which we infer properties of the stellar transition region. The line profile shapes do not reveal evidence of broad components, similar to what is observed in the atmosphere of the inactive star Procyon and unlike what is observed in active stars. We find a trend of increasing redshift with line formation temperature up to a maximum log T of 5.2, and a decrease for temperatures greater than log T of 5.2, similar to what is seen on the Sun and dissimilar to what is seen on Procyon. We interpret these findings in light of differences in activity and atmospheric structure.
