Atmospheric Dynamics and Mass Loss in Gappers, Clumpers, and Hybrids CYC4 - Medium

Details Atmospheric Dynamics and Mass Loss in Gappers, Clumpers, and Hybrids CYC4 - Medium Atmospheric Dynamics and Mass Loss in Gappers, Clumpers, and Hybrids CYC4 - Medium

Jul 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994hst..prop.5323a&link_type=abstract

HST Proposal ID #5323

Physics

Hst Proposal Id #5323 Cool Stars Atmospheres &Amp, Winds

Scientific paper

The giant branch evolution of moderate-mass stars provides a vital test of our understanding of magnetic dynamo action, coronal energization, and winds. The blatant``X-ray deficiency'' of the Hertzsprung-gap giants appears to be genuine, while that of many ``hybrid-chromosphere'' supergiants appears to be due to absorption by a previously unrecognized warm or hot component of their winds; not apparent in the Mg II circumstellar features but quite evident in the H I Lyman-alpha profile (of at least one case). There also is new evidence for a warm wind on the G0 secondary of Capella -- a ``gap'' star. The mass-loss rate is low, but dynamically quite significant in braking the fast stellar rotation. Outflows of some kind probably exist on post-helium-flash Clump giants, as well, although ``antiwinds'' are the hallmark of the archetype, Beta Ceti. I propose to clarify the subcoronal properties of the Hertzsprung-gap, active Clump, and Hybrid stars through a spectral dissection of one representative of each class. My strategy is to use the HST/GHRS to record key FUV emissions -- spanning the broad temperature range 10,000-250,000 K -- with high S/N 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 X-ray work with ROSAT and recent EUVE spectroscopy.

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