Closed coronal structures. VI - Far-ultraviolet and X-ray emission from active late-type stars and the applicability of coronal loop models

Details Closed coronal structures. VI - Far-ultraviolet and X-ray emission from active late-type stars and the applicability of coronal loop models Closed coronal structures. VI - Far-ultraviolet and X-ray emission from active late-type stars and the applicability of coronal loop models

Feb 1985

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1985apj...289..203g&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 289, Feb. 1, 1985, p. 203-212. Research supported by the Ministero della Pu

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Coronal Loops, Late Stars, Stellar Coronas, Ultraviolet Astronomy, X Ray Astronomy, Computational Astrophysics, Far Ultraviolet Radiation, Stellar Models, Stellar Spectra

Scientific paper

We present far-ultraviolet line fluxes of prominent transition region emission lines, as obtained with the International Ultraviolet Explorer satellite, for a sample of solar-type stars. We combine the ultraviolet observations with existing soft X-ray measurements obtained by the Einstein Observatory (HEAO 2). We utilize the resulting data set and a new coronal loop model numerical code developed at the Harvard-Smithsonian Center for Astrophysics to perform a preliminary investigation of the applicability of coronal loop models to solar-type stars. In a few cases, reasonable agreement between the predictions of single-component, coronal loop model atmospheres and the observational data is achieved for a relatively well-defined, plausible range of values in the pressure-filling factor (p, f) plane. In general, however, we find that the addition of non- simultaneous ultraviolet observations to a previously acquired soft X-ray data set does not provide a sufficient constraint on the range of possible loop filling factors and pressures for loop model atmospheres that may be producing the observed X-ray and transition region emissions. We discuss the origins of the discrepancies between the model results and the observations within the context of (1) stellar variability, (2) multiple coronal components, and (3) the presence of relatively low temperature loops that give rise to far-ultraviolet emission but not to coronal X-ray emission. We suggest on the basis of the results presented in this investigation that in order to verify the applicability of coronal loop models to solar-type stars, simultaneous far-ultraviolet and moderate spectral resolution X-ray observations will eventually have to be obtained.

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