Discovery and observation of BY DRA variables.
Abstract
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.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- October 1981
- DOI:
- 10.1086/159277
- Bibcode:
- 1981ApJ...249..210B
- Keywords:
-
- Binary Stars;
- H Alpha Line;
- Stellar Spectra;
- Stellar Spectrophotometry;
- Variable Stars;
- Calcium;
- Emission Spectra;
- Late Stars;
- M Stars;
- Stellar Rotation;
- Astronomy