The Atmospheric Dynamics of α Tau (K5 III)-Clues to Understanding the Magnetic Dynamo in Late-Type Giant Stars
Abstract
Using HST/GHRS, HST/STIS and FUSE archival data for α Tau and the CHIANTI spectroscopic code, we have derived line shifts, volumetric emission measures, and plasma density estimates, and calculated filling factors for a number of UV lines forming between 10,000 K and 300,000 K in the outer atmosphere of this red giant star. The data suggest the presence of low-temperature extended regions and high-temperature compact regions, associated with magnetically open and closed structures in the stellar atmosphere, respectively. The signatures of UV lines from α Tau can be consistently understood via a model of upward-traveling Alfvén waves in a gravitationally stratified atmosphere. These waves cause nonthermal broadening in UV lines due to unresolved wave motions and downward plasma motions in compact magnetic loops heated by resonant Alfvén wave heating.
- Publication:
-
15th Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun
- Pub Date:
- February 2009
- DOI:
- 10.1063/1.3099213
- Bibcode:
- 2009AIPC.1094..712C
- Keywords:
-
- 97.20.Li;
- 52.35.Bj;
- 97.10.Ex;
- Giant and subgiant stars;
- Magnetohydrodynamic waves;
- Stellar atmospheres;
- radiative transfer;
- opacity and line formation;
- giant stars;
- magnetohydrodynamic waves;
- stellar atmospheres