Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1986
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1986apjs...62..899o&link_type=abstract
Astrophysical Journal Supplement Series (ISSN 0067-0049), vol. 62, Dec. 1986, p. 899-938.
Astronomy and Astrophysics
Astronomy
45
Chromosphere, Giant Stars, Helium, Infrared Astronomy, Stellar Spectra, F Stars, G Stars, Hertzsprung-Russell Diagram, K Stars, M Stars, Photoionization, Spectral Line Width, Stellar Activity, Stellar Coronas, Stellar Envelopes, Supergiant Stars, Telluric Lines, Thermodynamic Equilibrium, Variable Stars
Scientific paper
Results of a survey of the chromospheric line He I 10830 A in sixty F, G, and K giants are presented. A weak He line appears in middle and late F supergiants, increases greatly in strength by spectral type G0, appears in all observed K stars, and disappears around type M1. Many of the less luminous K stars show a constant 10830 A line which appears similar in shape to that seen in the sun. Stars showing this profile lie to the left of a well-defined boundary in the H-R diagram. Most of the luminous and cooler K stars to the right of this boundary line show highly variable He I profiles; variations on a time scale of a month are common. Observations suggest episodic ejection of matter and a subsequent return of some fraction of this matter to the photosphere in these stars. The non-LTE radiative transfer problem for helium in a stellar chromosphere is modelled.
Lambert David L.
Obrien George T. Jr.
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