A Critical Test for Radiatively Driven Hot Winds in Cool Stars

Details A Critical Test for Radiatively Driven Hot Winds in Cool Stars A Critical Test for Radiatively Driven Hot Winds in Cool Stars

Jul 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004hst..prop10212l&link_type=abstract

HST Proposal ID #10212

Physics

Hst Proposal Id #10212 Cool Stars

Scientific paper

We propose STIS observations of the C IV resonance emission line profiles for the two brightest short-period classical Cepheid variables Delta Cep and Beta Dor, to critically test if P Cygni-type profiles form in the hot transition region plasmas of their pulsating upper atmospheres. Recent FUSE observations of the cool {non-variable} G-supergiant Alpha Aqr {and Beta Aqr} show a distinct P Cygni-type profile in warm transition region emission lines of C III. The observations reveal supersonic wind outflow velocities that exceed 140 km/s, based on our semi-empiric radiative transfer models. The models demonstrate that optically thick supersonic winds occur in the outer atmospheres of cool giant and supergiant stars, at kinetic gas temperatures well above 80 kK. STIS observations of cool regular pulsating Cepheid variables will confirm or reject our present hypothesis that these peculiar P Cygni-type line shapes form in a supersonic accelerating wind structure that is {partly} driven by a radiative atmospheric acceleration mechanism, generally adopted for driving the much faster winds of hot luminous stars. STIS observations of the detailed line shapes of hot transition region emission lines in Cepheids can establish an important physical link between the radiation-driven wind theory of hot stars, and the acoustic/magnetic wave-driven wind theory of cool stars. The proposed high-resolution far-UV spectra of these important pulsating cool stars will be an invaluable contribution to the HST Archive.

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