Other
Scientific paper
Jan 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992phdt........18s&link_type=abstract
Ph.D. Thesis Ohio State Univ., Columbus.
Other
Abundance, Chemical Composition, Dwarf Novae, Ejecta, Emission Spectra, Galactic Structure, Stellar Spectrophotometry, Continuous Spectra, Ionizing Radiation, Photoionization, Satellite Observation
Scientific paper
Ground-based optical and satellite ultraviolet spectrophotometric observations are combined in order to study the shells of Classical Novae PW Vulpeculae 1984 and QU Vulpeculae 1984. First, the chemical composition of each shell is derived from emission line ratios carefully selected to minimize the effects of variations in the physical conditions within the shell, such as density in homogeneities. The results indicate that PW Vul has a nearly solar composition, with the exception of nitrogen, which is enhanced. QU Vul shows a strong enhancement of helium and several intermediate weight elements. These results are in qualitative agreement with current theories of nova outbursts, suggesting that PW and QU Vul's outbursts occurred in a carbon-oxygen and an oxygen-neon-magnesium white dwarf, respectively. Next, the source of ionizing radiation is investigated from the observed continuous spectrum, and from radiative-equilibrium photoionization modeling. A flat, featureless continuum indicates that the expanding shell is hotter than the temperature derived from emission-line diagnostics. Thus, a model is proposed in which the 'cold phase' has a temperature of 104, and the 'hot phase' is in the range of 105 to 106 K. Methods are presented to constraint the temperature and density of the hot phase, and other properties of the shell, such as the mass, the energetics, and the geometry. The results suggest that the tenuous hot phase dominates the mass of the outburst, while the cold phase is denser, strongly inhomogeneous, and responsible for most of the emission line spectrum. These results bring new light and challenges to the fields of nova outbursts and galactic structure. The large ejected masses in combination with the enhanced abundances suggest that novae may be significant contributors to the chemical enrichment of the Galaxy. In particular, the observed mass of aluminum in the Galaxy can be explained as the result of nova outbursts similar to the QU Vul system, provided that these systems represent only 1-2 percent of the total nova rate. However, theoretical challenges now exist to explain the mechanisms that allow such large ejecta in oxygen-neon-magnesium novae.
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