Mathematics
Scientific paper
Jan 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996nasa.reptt....m&link_type=abstract
Technical Report, NASA/CR-97-205855; NAS 1.26:205855
Mathematics
Atmospheric Heating, Chromosphere, Magnetic Fields, Acoustic Propagation, Acoustic Properties, Signatures, Coronas, Mathematical Models, Hydrodynamic Equations, Cool Stars, Dwarf Stars, Hertzsprung-Russell Diagram, Emission Spectra, Energy Budgets
Scientific paper
In a qualitative sense, the heating of chromospheres and coronae has long been ascribed to either acoustic or magnetic heating. However, quantitative discussions of the energy balance with detailed comparison to the fluxes of chromospheric emission lines have begun to appear only recently. The aim of this work is to obtain more quantitative information on the acoustic/magnetic mechanisms by comparing data with models of acoustically heated atmospheres. Mechanical energy in acoustic form is inevitably present in all stars with convective envelopes. Once the acoustic waves are generated, their propagation and dissipation in the chromosphere and corona can be computed by ab initio models, again using the well defined equations of compressible hydrodynamics (e.g. Mullan and Cheng: Papers I-III). In contrast to the ubiquitous acoustic modes, magnetic modes need not be present. And even in stars where magnetic heating is at work, the atmospheric heating always includes an acoustic component as well. In order to evaluate the magnetic contribution in such stars, we need to separate out the acoustic contribution. To address the "acoustic-magnetic" mixture, and separate the components, our strategy in this work has been to select stars in those parts of the HR diagram where the magnetic contribution is "turning on". By studying such stars, we hope to quantify the acoustic component which pervades the atmospheres of all cool stars, and characterize how the magnetic components alter the emission measure distribution in the atmosphere. Two groups of stars are suitable for our purposes: they are the groups which have recently been the subject of detailed quantitative modelling as regards acoustic propagation, i.e. the coolest dwarfs and the warm stars.
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