Cool luminous stars
Abstract
A broad theme emerging from IUE and Einstein observations of cool stars is that magnetic fields control the structure and energy balance of the outer atmospheres of these stars. I summarize the phenomena associated with magnetic fields in the Sun and show that similar phenomena occur in cool luminous stars. High dispersion spectra are providing unique information concerning densities, atmospheric extension, and emission line widths. A recent unanticipated discovery is that the transition lines are redshifted (an antiwind) in β Dra (G2 Ib) and perhaps other stars, which I interpret as indicating downflows in closed magnetic flux tubes as are seen in the solar flux tubes above sunspots. Finally, I classify the G and K giants and supergiants into three groups - active stars, quiet stars, and hybrid stars - depending on whether their atmospheres are dominated by closed magnetic flux tubes, open field geometries, or a predominately open geometry with a few closed flux tubes embedded.
Staff Member, Quantum Physics Division, National Bureau of Standards.- Publication:
-
Advances in Space Research
- Pub Date:
- 1982
- DOI:
- 10.1016/0273-1177(82)90275-7
- Bibcode:
- 1982AdSpR...2i.249L
- Keywords:
-
- Stellar Atmospheres;
- Stellar Magnetic Fields;
- Stellar Temperature;
- Ultraviolet Astronomy;
- Cool Stars;
- Giant Stars;
- High Dispersion Spectrographs;
- Iue;
- Spaceborne Astronomy;
- Supergiant Stars;
- Astrophysics