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| Paper: |
Non-Radiative Heating in ``Flat Activity'' Stars |
| Volume: |
154, Cool Stars, Stellar Systems and the Sun: Tenth Cambridge Workshop |
| Page: |
211 |
| Authors: |
Saar, S. H. |
| Abstract: |
The Mount Wilson Ca ii program has identified a group of stars with very low level, non-variable chromospheric emission over the ~25 year survey. Many of these stars are very likely in the stellar analog of the solar Maunder minimum --- a period when the normal cyclic (alpha Omega) dynamo was in temporary quiescence. I study UV and X-ray emission for a sample of these ``flat activity'' stars. While their chromospheric Ca ii and C ii emission is consistent with ``basal'' (possibly acoustic) flux levels, and increase with T_eff, their transition region (TR) and coronal fluxes 1) are lower than in normal cyclic stars, 2) increase towards cooler T_eff, and 3) are independent of rotation. The TR and coronal fluxes thus appear to be formed by a largely non-acoustic process which is weak, non-variable, and depends on mass (convection zone depth) rather than rotation. These properties are consistent with magnetic heating due to a turbulent, distributed, convection zone dynamo. Turbulent dynamos thus likely operate at some level in all cool stars. I discuss implications of these results for dynamos and magnetic activity in late-type stars. |
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