Other
Scientific paper
Feb 1987
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1987mnras.224..821c&link_type=abstract
Monthly Notices of the Royal Astronomical Society (ISSN 0035-8711), vol. 224, Feb. 15, 1987, p. 821-845.
Other
21
Binary Stars, Giant Stars, H Lines, K Lines, Star Clusters, Subgiant Stars, Emission Spectra, Radial Velocity, Stellar Models, Stellar Spectrophotometry
Scientific paper
The authors present the results of a search for chromospheric Ca II H and K emission in a sample of 195 subgiant and lower giant-branch stars in the old disc clusters NGC 2204, 2243, 2420, 2506 and Melotte 66. They argue that in subgiant stars belonging to old (3 - 8×109yr) clusters such as these, the presence of Ca II emission comparable to that seen in the RS CVn binaries of the solar neighbourhood should be a reliable indicator of abnormally rapid axial rotation brought about by tidal locking in a binary system with an orbital period between 1 and 50 day. Four stars have Ca II H and K fluxes which are significantly higher than those of the other cluster members and are comparable with those observed in RS CVn systems in the solar neighbourhood. The observations are compared with theoretical estimates of (1) the ratio of blue stragglers to RS CVn systems which would be expected if blue stragglers were formed through Algol-type mass exchange in evolved binary systems with initial periods less than 100 day; and (2) the expected total number of RS CVn systems in a coeval population of stars with a binary fraction and orbital period distribution similar to those determined empirically for the solar neighbourhood by Abt & Levy (1976).
Collier Cameron Andrew
Reid Neill
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