Self-similar magnetohydrodynamics. II - The expansion of a stellar envelope into a surrounding vacuum
Abstract
The axisymmetric self-similar expansion of a stellar envelope into a surrounding vacuum is treated. Two exact solutions are presented to describe the time-dependent magnetohydrodynamics of the envelope, assuming a polytrope with adiabatic index gamma equals 4/3. The boundary conditions at the interface with vacuum are treated explicitly, and a matching solution of Maxwell's equations is obtained to describe the electromagnetic waves propagating into the vacuum, ahead of the expanding envelope. As the envelope disperses to infinity, out of the gravitational bound of the stellar core, the magnetic field is stretched to a radial configuration. The energy properties are discussed, showing, in particular, why the gamma equals 4/3 polytrope exhibits self-similar expansion and how the total magnetic energy in the envelope may be either decreasing or increasing with time during the expansion, depending on the distribution of the plasma.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- October 1982
- DOI:
- 10.1086/160346
- Bibcode:
- 1982ApJ...261..351L
- Keywords:
-
- Similarity Theorem;
- Stellar Coronas;
- Stellar Envelopes;
- Stellar Mass Ejection;
- Vacuum;
- Adiabatic Conditions;
- Boundary Conditions;
- Boundary Value Problems;
- Electromagnetic Wave Transmission;
- Magnetohydrodynamics;
- Maxwell Equation;
- Novae;
- Polytropic Processes;
- Stellar Magnetic Fields;
- Supernovae;
- Time Dependence;
- Astrophysics