Hot Times in the Hertzsprung Gap

Details Hot Times in the Hertzsprung Gap Hot Times in the Hertzsprung Gap

Jul 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995hst..prop.6067a&link_type=abstract

HST Proposal ID #6067

Physics

Hst Proposal Id #6067 Cool Stars

Scientific paper

I propose to explore the early evolution of magnetic activity in F-G0 giants crossing the Hertzsprung gap. The giant branch evolution of 2-4 solar mass stars provides a vital test of our understanding of magnetic Dynamo action, coronal heating, and winds. The ``X-ray deficiency'' of the F-G0 giants represents a clear distinction compared to cooler Main Sequence stars. Possibly connected with the deficiency is the newly recognized warm wind of the G0 secondary of Capella, as well as indications for a previously unrecognized ``broad component'' in its high excitation emissions like C IV 1548. The mass loss rate of the Capella wind is low, but could be quite important in braking the fast stellar rotation. The broad components might be associated with the wind, but more likely are due to highly dynamic phenomena in the subcoronal atmosphere; perhaps the stellar equivalent of solar ``transition zone explosive events.'' These new aspects of stellar activity warrant detailed consideration. My strategy is to use the HST/GHRS to record key FUV emissions -- spanning the broad temperature range 10,000 K - 200,000 K -- with high S/N in archetype Hertzsprung gap stars. The objective is to measure line widths, profile asymmetries, circumstellar absorptions, systematic Doppler shifts, and density sensitive line ratios. Such diagnostics will be used to constrain existing physical models, and develop new ones. The HST spectra will strongly complement ongoing ROSAT & EUVE work.

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