The formation of emission lines in the expanding chromospheres of luminous cool stars. I - The importance of atmospheric extension and partial redistribution effects

Details The formation of emission lines in the expanding chromospheres of luminous cool stars. I - The importance of atmospheric extension and partial redistribution effects The formation of emission lines in the expanding chromospheres of luminous cool stars. I - The importance of atmospheric extension and partial redistribution effects

Oct 1983

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1983apj...273..299d&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 273, Oct. 1, 1983, p. 299-308.

Astronomy and Astrophysics

Astrophysics

28

Chromosphere, Cool Stars, Late Stars, Line Spectra, Stellar Spectra, Emission Spectra, Radiative Transfer, Resonance Lines, Stellar Mass Ejection

Scientific paper

Most late-type luminous stars are losing mass in cool stellar winds, although the mass-loss rates and mechanisms of these outflows remain uncertain. In many red giants the only evidence for mass loss is the presence of a characteristic asymmetry in the strongest ultraviolet resonance lines, such as the Mg II k line. In this paper, we discuss the available methods for treating radiative transfer in such chromospheric lines in an expanding, extended medium and select the comoving frame method (including partial redistribution) as the most suitable. We briefly outline this technique in the context of a two-level atom. Prior to applying this technique to deriving atmospheric properties from observed line profiles, we present some schematic examples to illustrate the sensitivity of the calculated line profiles to the outflow velocity, chromospheric temperature gradient, physical extent of the atmosphere, line-to-continuum strength, and the incoherence fraction. In this paper, we illustrate the difference in the computed line profiles between assuming partial and complete redistribution for a wide range of atmospheric and wind parameters.

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