On the Evolution of Stars that Form Electron-degenerate Cores Processed by Carbon Burning. V. Shell Convection Sustained by Helium Burning, Transient Neon Burning, Dredge-out, URCA Cooling, and Other Properties of an 11 M_solar Population I Model Star

Details On the Evolution of Stars that Form Electron-degenerate Cores Processed by Carbon Burning. V. Shell Convection Sustained by Helium Burning, Transient Neon Burning, Dredge-out, URCA Cooling, and Other Properties of an 11 M_solar Population I Model Star On the Evolution of Stars that Form Electron-degenerate Cores Processed by Carbon Burning. V. Shell Convection Sustained by Helium Burning, Transient Neon Burning, Dredge-out, URCA Cooling, and Other Properties of an 11 M_solar Population I Model Star

Apr 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999apj...515..381r&link_type=abstract

The Astrophysical Journal, Volume 515, Issue 1, pp. 381-397.

Astronomy and Astrophysics

Astronomy

75

Nuclear Reactions, Nucleosynthesis, Abundances, Stars: Abundances, Stars: Evolution, Stars: Interiors, Stars: Supergiants, Stars: Supernovae: General

Scientific paper

A stellar model of mass 11 M_solar and Population I composition is evolved from the hydrogen-burning main sequence through the core carbon-burning phase. In contrast with 9, 10, and 10.5 M_solar models studied in earlier papers of this series, carbon burning is ignited at the center of the 11 M_solar model. Like the 10.5 M_solar model, the 11 M_solar model experiences a dredge-out episode at the end of the carbon-burning phase. At the beginning of this episode, a semiconvective zone forms at the base of the hydrogen-rich envelope and carries hydrogen inward in mass toward the outer edge of a fully convective zone that is sustained by helium burning at its base. Hydrogen diffuses into the helium-rich convective zone untila hydrogen shell flash occurs. Helium burning dies out and the outer edge of the convective layer,sustained by fluxes due to hydrogen burning, extends outward in mass through hydrogen-rich material, mixing freshly synthesized nuclei outward. Then, hydrogen burning dies out and the outer edge of the convective shell, now sustained primarily by fluxes due to the release of gravothermal energy, moves outward until it reaches the inner edge of the convective envelope. Freshly synthesized material is then convected to the surface. Mixing during the final phase of homogenization in the convective envelope is maintained by fluxes due to the release of gravothermal energy. At the end of the dredge-out phase, the surface nitrogen abundance has decreased and the C/N ratio has changed from less than unity to larger than unity, showing that mixing has extended into regions where helium burning has manufactured substantial quantities of ^12C and destroyed ^14N. Prior to the dredge-out phase, neon burning is narrowly averted, and, after the dredge-out phase, neutrino losses due to electron capture and decay reactions between A=25 and A=23 isotopes in and above convective Urca shells cool the inner portions of the electron-degenerate oxygen-neon (ONe) core. Ultimately, the model becomes a thermally pulsing super-asymptotic giant branch (TPSAGB) star with an ONe core of mass ~1.368 M_solar. Hydrogen and helium burning over a period of ~1.4x10^4 yr of TPSAGB evolution add a carbon-oxygen layer of mass ~0.014 M_solar to the electron-degenerate core. Then, electron captures on products of carbon burning lead to the collapse of the core into a neutron star and expulsion of the envelope in a weak Type II supernova explosion. The ratio of helium to hydrogen in the ejecta is approximately twice solar.

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On the Evolution of Stars that Form Electron-degenerate Cores Processed by Carbon Burning. V. Shell Convection Sustained by Helium Burning, Transient Neon Burning, Dredge-out, URCA Cooling, and Other Properties of an 11 M_solar Population I Model Star does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

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