Rotation and Transition Layer Emission in Cool Giants
Abstract
Gray (1981, 1982) found that field giants with T(eff) less than about 5500 K experience a steep decrease in rotational velocities coupled with a decrease in transition layer emission. This decrease may be attributable to fast magnetic braking or to redistribution of angular momentum for rapidly increasing depths of the convection zones if these rotate with depth independent specific angular momentum. Additional arguments in favor of the latter interpretation are presented. The increase of N/C abundances due to deep mixing occurs at the same point as the decrease in v sin i. On the other hand, the ratios of the C IV to C II emission line fluxes decrease at this point indicating smaller contributions of MHD wave heating. The X-ray fluxes decrease at nearly the same T(eff). Thus, no observations are found which would indicate larger magnetic activity which could lead to fast magnetic braking. Theory predicts a rapid increase in the convection zone depth at the T(eff) where the decrease in v sin i is observed. This can explain the observed phenomena.
- Publication:
-
The Astronomical Journal
- Pub Date:
- February 1992
- DOI:
- 10.1086/116088
- Bibcode:
- 1992AJ....103..608B
- Keywords:
-
- Cool Stars;
- Giant Stars;
- Stellar Rotation;
- Stellar Spectra;
- Stellar Structure;
- Angular Momentum;
- Convective Flow;
- Emission Spectra;
- Stellar Evolution;
- Astrophysics;
- STARS: GIANT;
- STARS: ROTATION