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Title:
The enigmatic H alpha line of FK Comae - Last stages of a coalescing binary
Authors:
Walter, F. M.; Basri, G. S.
Affiliation:
AA(California, University, Berkeley, CA), AB(California, University, Berkeley, CA)
Publication:
Astrophysical Journal, Part 1, vol. 260, Sept. 15, 1982, p. 735-743. (ApJ Homepage)
Publication Date:
09/1982
Category:
Astrophysics
Origin:
STI
NASA/STI Keywords:
Binary Stars, Emission Spectra, G Stars, H Alpha Line, Stellar Evolution, Stellar Spectra, Stellar Spectrophotometry, High Resolution, Photosphere, Radial Velocity, Radiant Flux Density, Spectral Line Width, Spectral Resolution, Stellar Mass Accretion, Stellar Models, Stellar Rotation, Visual Photometry
DOI:
10.1086/160293
Bibliographic Code:
1982ApJ...260..735W

Abstract

The apparently single, rapidly rotating G giant FK Comae displays an unusual hydrogen alpha emission line which is very broad, strong, and variable. Extensive high-resolution studies of this line with complete phase coverage are presented. The alpha hydrogen emission centroid shows a radial velocity modulation on the 2.4 days stellar rotation period with a semiamplitude identical to the photospheric rotational velocity. These data, when phased with optical photometry, indicate that the star has a bright, rather than dark, region on its surface and that the phase may have been stable for seven years. A qualitative model wherein the bright spot is caused by accretion from a low mass unseen companion onto the surface of the G giant is considered. Such a model explains many of the observed characteristics of the stellar spectrum and hydrogen alpha feature, and it is concluded that FK Comae is not yet a single star, but is still evolving toward coalescence of the system.

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