Astronomy and Astrophysics – Astronomy
Scientific paper
May 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993pasp..105..559d&link_type=abstract
Publications of the Astronomical Society of the Pacific, v.105, p.559
Astronomy and Astrophysics
Astronomy
Scientific paper
The most widely accepted scenario for Type Ia supernovae is the thermonuclear explosion of a C+O white dwarf which, by accretion from a companion, approaches the Chandrasekhar mass. Whilst this scenario can account for most of the observed properties of SNe Ia, the exact nature of the explosion mechanism remains uncertain. This thesis presents the results obtained from hydrodynamical model calculations of post-explosion envelope expansion. The hydrodynamics are followed in spherical symmetry using a Lagrangean code, the energy equation being solved in the diffusion approximation. The conversion of decay gamma-rays into thermal energy is treated as an absorption process, while the time-dependent opacity is calculated as a function of composition, density, temperature and velocity gradient. The results of these models--light-curve shape, maximum luminosities, and expansion velocity profiles---are compared with the bolometric observational data (SN1981B, SN1972E and the composite light curve obtained by Leibundgut for 9 SNe Ia in Virgo) and current theoretical models of the explosion mechanism. Delayed detonation and deflagration models (Bravo 1990), adopting different C ignition densities, have been investigated. In all cases, the resulting light curve is in satisfactory agreement with observations. As the ignition density varies, the maximum of light remains nearly constant and the dispersion in the rates of decline of the light curve is compatible with observations. Moreover, variation in the ignition density readily accounts for the dispersion of 1000 km s^-1 in the observed expansion velocities. Delayed detonation models yield high kinetic energies, that result in (especially for the highest ignition densities) high expansion velocities, steep post-peak declines of the light curves and velocity distribution of intermediate-mass elements that are higher than that inferred from observations. Conversely, deflagration models provide less energetic explosions. However, in this case, the amount of intermediate mass elements and the isotopic abundance of iron peak elements produced, give a worse fit to the observational data than delayed detonation models. The use of SNe Ia as distance indicators has also been examined. The "best" model calculations lend support to low values of the Hubble Constant (54< H_o <64 km s^-1, Mpc^-1). (SECTION: Dissertation Abstracts)
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