Four experiments on thermal instabilities in stellar envelopes

Details Four experiments on thermal instabilities in stellar envelopes Four experiments on thermal instabilities in stellar envelopes

Sep 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994apj...433..293r&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 433, no. 1, p. 293-302

Astronomy and Astrophysics

Astrophysics

7

Dwarf Stars, Giant Stars, Stellar Envelopes, Stellar Evolution, Stellar Interiors, Stellar Models, Stellar Temperature, Thermal Stability, Mathematical Models, Radiative Transfer, Stellar Structure, Thermodynamic Equilibrium

Scientific paper

Four easily reproducible numerical experiments are presented demonstrating the role of radiative opacity in giving rise to the thermal instability of stellar envelopes which is responsible for the runaway expansion of stars to red giant size. The experiments also demostrate that the cause of the runaway expansion is the increasing absorption of radiative energy in the envelope, while the rapid penetration of convection through the envelope is responsible for the quenching of the instability and the restoration of thermal equilibrium. We argue that evolutionary changes of stellar structures (i.e., expansions or contractions) are always driven by local departures from thermal equilibrium. When such departures are and remain small, the stellar structure is thermally stable and evolves on a nuclear timescale. When they grow larger and larger, a thermal instability can develop, such as for example when the envelope expansion results in a decreasing ability of this envelope to transfer outward the energy being generated in the core. It is concluded that the dwarf to giant transitions of stars can be understood in simple physical terms.

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