An Observational and Theoretical Investigation of Stellar Flares.
Abstract
Multi-wavelength observations of a giant flare on the star AD Leo were obtained with the 2.1m and 0.9m telescopes at McDonald Observatory and the International Ultraviolet Explorer satellite. The quality, spectral coverage and time resolution of the data represent a major improvement over any published stellar flare data. A self -consistent theoretical model was developed to investigate the effects of chromospheric heating by thermal conduction and soft x-ray irradiation from a flare heated corona. Assuming a one-dimensional coronal loop geometry, atmospheres were produced for overlying coronal temperatures of 8, 10, 15, and 20 million degrees Kelvin. The atmospheres satisfy the equations of hydrostatic equilibrium, steady state energy balance, and statistical equilibrium and radiative transfer in many optically thick transitions of hydrogen, ionized calcium and ionized magnesium. A second theoretical model was then developed to predict the temporal evolution of the coronal temperature under the influence of a time varying flare heating rate. Combining the models, the chromospheric emission model predictions in the hydrogen Balmer lines, Ca II K, Mg II h + k and the optical continuum were compared to the observations, with the result that much of the gradual phase flare emission could be produced by the x-ray and conductive heated atmospheres. However, some additional heating and a more complex flare geometry, including several emitting regions, are probably required to reproduce all the flare emission features in detail. The models also lend insight into the impulsive phase flare emission, but do not reproduce it. Soft x-ray and conductive heating of the chromosphere is a natural consequence of the coronal temperatures that have been observed during the gradual phase of flares on the sun and on M dwarf stars. The improved flare observations and quantitative flare models presented here show that these heating mechanisms can produce atmospheres whose emission matches many of the observed stellar flare features. Future studies must incorporate these effects as well as considering other heating mechanisms and more complex flare geometries.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- 1989
- Bibcode:
- 1989PhDT.........1H
- Keywords:
-
- Physics: Astronomy and Astrophysics;
- A Stars;
- Coronal Loops;
- Flare Stars;
- Giant Stars;
- Hydrostatics;
- Spectral Resolution;
- Stellar Flares;
- Stellar Models;
- X Ray Irradiation;
- Balmer Series;
- Conductive Heat Transfer;
- Energy Budgets;
- Heating;
- Hydrogen;
- Iue;
- Mathematical Models;
- Observatories;
- Radiative Transfer;
- Steady State;
- Telescopes;
- Temporal Resolution;
- Astrophysics