Activity in late-type dwarfs. III. Chromospheric and transition region line fluxes for two dM stars.
Abstract
Weak upper-chromospheric and transition-region emission from two dM stars (Gl 784 and Gl 825) has been observed using deep UV spectroscopy. Ly-alpha fluxes for the two stars were also determined for the first time. Using these results it is shown that the transition from weakly active dM to active dMe star is probably due to increasing surface coverage by solarlike active regions. Also discussed are the relative importance of Ly-alpha and Mg II as chromospheric coolants in the M dwarfs and how this changes between dM and dMe stars. The interrelationship between X-ray, He II (1640-A) and C IV (1550-A) fluxes is discussed in the light of these results, and it is shown that all three are tightly related over three orders of magnitude in each. Several flux-period relationships are used to predict the rotation periods of the two stars.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- January 1989
- Bibcode:
- 1989A&A...208..159B
- Keywords:
-
- Dwarf Stars;
- Flare Stars;
- Late Stars;
- M Stars;
- Stellar Activity;
- Stellar Spectra;
- Chromosphere;
- Helium;
- Iue;
- Lyman Alpha Radiation;
- Stellar Rotation;
- Astrophysics