Other
Scientific paper
Sep 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997phdt.........5b&link_type=abstract
Thesis (PHD). THE UNIVERSITY OF WISCONSIN - MADISON , Source DAI-B 59/01, p. 257, Jul 1998, 137 pages.
Other
3
Scientific paper
The ROSAT PSPC observations of classical novae have set important grounds for future research and established observational results that proved unprecedented consequences pointing out the importance of studying X-rays for a better understanding of the classical novae phenomenon. The major characteristics of the X-ray emission spectrum of classical novae is differentiated using the ROSAT data as a soft component (photospheric emission from a hot stellar remnant) and a hard component (thermal X-ray emission from hot shocked plasma). The only novae detected to show both components is V1974 Cyg 1992. However, this thesis shows that the other ROSAT detections of classical novae do show strong evidence for two component emission also. The most important development is the observational verification of the standard novae theory in the X-ray wavelengths by the work done as a part of this thesis using hot WD model atmospheres. Furthermore, the most likely reason why there are so few detections of novae in soft X-rays is the transperancy time scale of the nova shell determined by this work as well. Also, clumping of the nova ejecta is expected to reduce the solid angle over which soft X-rays are seen causing partial attenuation. The detection of X-ray knots in the old nova shell of classical nova Persei 1901 also presented in this thesis confirms the origin of the low efficiencies in X-ray emission and short cooling time scales of the hard X-ray component of classical novae. The most likely origin of the hard X-ray component is found to be the interaction of a fast wind with either a prior slower wind from the nova or a pre-existing old nova shell. The comparison of the hard X-ray detections discussed in this thesis have shown evidence for two-component emission; a low temperature (~ 1 keV) high emission measure and a lower emission measure higher temperature (10-5 keV) component. The emission measure is found to decrease in time at constant temperature while the neutral hydrogen absorption also decreases about a factor of 10 as expected from an expanding shell of material.
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