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Discovery and observation of BY Draconis variables
Bopp, B. W.; Noah, P. V.; Klimke, A.; Africano, J.
AA(Toledo, University, Toledo, OH), AB(Toledo, University, Toledo, OH), AC(Cloudcroft Observatory, Cloudcroft, NM), AD(Cloudcroft Observatory, Cloudcroft, NM)
Astrophysical Journal, Part 1, vol. 249, Oct. 1, 1981, p. 210-217. (ApJ Homepage)
Publication Date:
NASA/STI Keywords:
Binary Stars, H Alpha Line, Stellar Spectra, Stellar Spectrophotometry, Variable Stars, Calcium, Emission Spectra, Late Stars, M Stars, Stellar Rotation
A&AA ID. AAA030.122.079
Bibliographic Code:


The discovery of BY Draconis variables was efficiently accomplished by a spectroscopic survey of dK-M stars for weak H-alpha emissions, using 1-2 A resolution. The four BY Dra variables discovered are all spectroscopic binaries with P values lower than about 10 d, in light of which, it is noted that the onset of high surface activity and appearance of H-alpha emission occur sharply at v(equator) of approximately 5 km/sec. At v(equator) of about 3 km/sec, dK-M stars have low levels of surface activity. It is found that while there is a range of Ca II emission strength, and only the strongest emitters of this line are BY Dra and/or flare stars, the H-alpha feature changes abruptly to an emission feature signaling the onset of flaring and/or the BY Dra syndrome. An increase of the rotation rate above v(equator) 5 km/sec does not appear to increase the level of surface activity.

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