Outer atmospheres of cool stars. IX - A survey of ultraviolet emission from F-K dwarfs and giants with IUE

Details Outer atmospheres of cool stars. IX - A survey of ultraviolet emission from F-K dwarfs and giants with IUE Outer atmospheres of cool stars. IX - A survey of ultraviolet emission from F-K dwarfs and giants with IUE

Jul 1981

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1981apj...247..545a&link_type=abstract

Astrophysical Journal, Part 1, vol. 247, July 15, 1981, p. 545-559.

Astronomy and Astrophysics

Astronomy

223

Chromosphere, Cool Stars, Dwarf Stars, F Stars, G Stars, Giant Stars, K Stars, Stellar Atmospheres, Ultraviolet Astronomy, Ultraviolet Spectra, Emission Spectra, Iue, Line Spectra, Protostars, Solar Wind, Stellar Coronas, Stellar Spectra

Scientific paper

Low-dispersion ultraviolet spectra (1150-2000 A) of a representative sample of cool stars, including dwarfs and giants of spectral types F-K, obtained with the IUE, are examined. The observation and the absolute calibration procedures are described. Correlation diagrams are constructed that compare chromospheric and transition-region emission line strengths and broadband coronal soft X-ray fluxes. The transition-region and coronal emission in the G-K dwarfs and G giants is well correlated with the Mg II (wavelength 2800) doublet emission strength, which is symptomatic of chromospheric energy losses. The power-law slopes are steeper than unity, particularly for soft X-rays. The implications of the correlations are discussed with respect to the weakening or disappearance of transition regions and hot coronae in the cool half of the red-giant branch and possible chromospheric and coronal heating mechanisms. It is proposed that the weakness of outer atmospheres in the red giants compared with the yellow giants can be understood as a consequence of stellar evolution, since it is possible that stars of slightly different spectral type in the giant branch have very different main-sequence progenitors.

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