Classical novae have fundamental importance in astronomy as they are relevant to both an understanding of individual stellar evolution and to taking proper distance measurements on galactic and cosmological scales. Also, novae are significant sources of interstellar material, especially carbon, nitrogen, oxygen and aluminum. These standard candles are only behind supernovae and gamma-ray bursts as the third brightest objects in the sky, and the most probable progenitors of the brightest, type Ia supernovae. Just after a nova outburst the system enters into the constant bolometric luminosity phase and the nova maintains a stable hydrogen burning in the surface layers of the white dwarf. As the expanding shell around the nova attenuates, progressively deeper and hotter layers become visible. At the end of the constant bolometric luminosity phase, the hottest layers are exposed and novae radiate X-rays. This work uses the static, plane-parallel model atmosphere code TLUSTY to calculate atmospheric structure, and SYNSPEC to calculate synthetic X-ray spectra of novae. It was necessary to incorporate atomic data for the highest ionization stages for elements ranging from hydrogen to iron for both programs Atomic data on energy levels, bound-free, bound-bound transitions and natural broadening were taken from NIST and TOPbase. Extensive tests revealed the importance of line opacities on atmospheric parameters and on the final spectra. A correlation can be defined between effective temperature and surface gravity. The spectral appearance is not very sensitive to the joint changes of both. Due to this effect both parameters might be over-estimated with static models. These tests also showed that N VI and N VII lines are good indicators of effective temperature. Model fitting of V4743 Sgr and V2491 Cyg confirmed the anticipated impact of modeling geometry and stellar wind. Both novae are close to or over the Eddington limit. Ionization balance and line profiles also indicate this. These results are consitent with previous studies; further and unambiguous details require a comprehensive update of TLUSTY, what is under way.
- Pub Date:
- June 2010
- Physics, Astrophysics;
- Astrophysics - Solar and Stellar Astrophysics
- Ph.D. dissertation, Florida Institute of Technology - 2010. 188 pages, 69 figures. Defense version. The official dissertation has been published by ProQuest/UMI. (Publication No. AAT 3407244, 2010