Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994apj...437..794p&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 437, no. 2, p. 794-801
Astronomy and Astrophysics
Astrophysics
2
Cataclysmic Variables, Galactic Nuclei, Nuclear Fusion, Stellar Mass Ejection, Stellar Temperature, Thermonuclear Reactions, White Dwarf Stars, Abundance, Accretion Disks, Atmospheric Models, Computerized Simulation, Energy Distribution, Hydrodynamic Equations, Rosat Mission, Stellar Coronas, X Ray Spectra
Scientific paper
Recent nucleosynthesis and hydrodynamic calculations of the consequences of accretion onto massive ONeMg white dwarf stars show that under certain circumstances significant amounts of the beta-unstable nuclei can be produced and ejected by the resulting explosion. We use these calculations as a guide in order to obtain the conditions under which the heating of the ejected material by the nonthermal electrons and positrons produced by the decays of the beta-unstable nuclei is sufficient to overcome the cooling from adiabatic expansion and lead to the production of X-ray-emitting coronal gas. These conditions are as follows: (1) a mass fraction for Na-22 of the order of 10-3 or greater, (2) an expansion velocity in the range approximately 102 - 103 km/s, (3) a photospheric radius of approximately 1014 cm, (4) if the density distribution in the atmosphere satisfies a power law, then the exponent must be less than 3 for heating to overcome adiabatic cooling. Both the simulations of the outburst and the model atmosphere fits to the observed energy distributions, however, imply that the exponent is greater than or = 3 during the early phases of the outburst. Nevertheless, for a value of the exponent of 2, we predict the time when hot coronal gas can form during the expansion phases of the envelope.
Pistinner Shlomi
Shaviv Giora
Starrfield Sumner
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