Discovery and observation of BY Draconis variables

Details Discovery and observation of BY Draconis variables Discovery and observation of BY Draconis variables

Oct 1981

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1981apj...249..210b&link_type=abstract

Astrophysical Journal, Part 1, vol. 249, Oct. 1, 1981, p. 210-217.

Astronomy and Astrophysics

Astrophysics

65

Binary Stars, H Alpha Line, Stellar Spectra, Stellar Spectrophotometry, Variable Stars, Calcium, Emission Spectra, Late Stars, M Stars, Stellar Rotation

Scientific paper

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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