AAS Meeting #193 - Austin, Texas, January 1999
Session 44. Modeling Stellar Characteristics
Display, Thursday, January 7, 1999, 9:20am-6:30pm, Exhibits Hall 1

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[44.02] Two-Component Chromosphere Models for K Dwarf Stars: The Chromospheric Emission --- Stellar Rotation Relationship

M. Cuntz (UAH), Z.E. Musielak (UTA,UAH), P. Ulmschneider, W. Rammacher (Univ. Heidelberg), S.H. Saar (CfA)

We present two-component theoretical chromosphere models for K dwarf stars with different levels of magnetic activity. The two components are: a nonmagnetic component heated by acoustic waves, and a magnetic component heated by longitudinal tube waves. The filling factor for the magnetic component is determined from an observational relationship between the stellar rotation rate and the measured coverage of stellar surface by magnetic fields. The chromosphere models are constructed by performing state-of-the-art calculations of the generation of acoustic and magnetic energy in stellar convection zones, the propagation and dissipation of this energy at the different atmospheric heights, and the formation of specific chromospheric emission lines, which are then compared to the observational data. In all these steps, the two-component structure of stellar photospheres and chromospheres is fully taken into account. We find that due to the presence of magnetic flux tubes, the heating and chromospheric emission is significantly increased in the magnetic component. The heating and chromospheric emission is found to be the strongest in flux tubes with small spreading factors which are expected to be present in fast rotating stars. For stars with very slow rotation we are able to reproduce the basal flux limit of chromospheric emission previously identified as due to pure acoustic heating. Most importantly, however, we find that the relationship between the Ca II H+K emission and the stellar rotation rate deduced from our models is consistent with the empirical relationship given by observations.

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The author(s) of this abstract have provided an email address for comments about the abstract: cuntzm@cspar.uah.edu

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