Physical Processes in Stellar Atmospheres: Comparative Analysis of the Sun and Alpha Cen A

Details Physical Processes in Stellar Atmospheres: Comparative Analysis of the Sun and Alpha Cen A Physical Processes in Stellar Atmospheres: Comparative Analysis of the Sun and Alpha Cen A

Dec 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997hst..prop.7263l&link_type=abstract

HST Proposal ID #7263

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Hst Proposal Id #7263 Cool Stars

Scientific paper

The quantity and quality of solar data far exceeds what is available for all other stars combined. Nonetheless, solar data alone does not discriminate between competing theories for certain fundamental plasma processes, e.g. magnetic dynamos or heating of the outer atmosphere. By studying stars of different mass, age, composition, and rotation, we can test models of solar phenomena in a broader context. STIS now makes it practical to obtain a high resolution NUV/FUV atlas sufficient to quantitatively understand in detail the photospheres, chromospheres, and transition regions of late-type dwarfs. We propose a detailed study of Alpha Cen A {G2V}, which has small temperature, metallicity, and activity differences, relative to the Sun, allowing a simplified perturbative analysis of atmospheric structure, heating mechanisms, and dynamical processes. We will compare our Alpha Cen A spectrum with existing full-disk atlases of the Sun, using anomalies to guide subsequent analysis. We will then fit the Alpha Cen A spectrum in detail by combining intensity spectra for quiet, network, plage, spot, and flare components. Intensity spectra will be determined using perturbed solar models {e.g. the VAL series} and the NLTE radiative transfer code MULTI, adapted to include line blanketing. The complete inventory of constraints provided by STIS will yield the first model chromosphere approaching solar quality. Using this atmosphere along with observed velocity fields, we will reassess competing theories for various phenomena observed in solar-type stars.

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