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Journal of Physical Studies 24(1), Article 1903 [11 pages] (2020)
DOI: https://doi.org/10.30970/jps.24.1903 PHYSICAL AND EVOLUTIONARY CHARACTERISTICS OF THE ENVELOPES OF SYMBIOTIC NOVAE V1016 Cyg AND HM Sge
V. V. Holovatyi,
B. Ya. Melekh1
1Department of Astrophysics, Ivan Franko National University of Lviv,
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The study has established the electron density and temperature, ionic and elemental abundances, optical thickness at the ionization potentials of H$^0$ , He$^0$ and He$^+$ in nebular envelopes of the symbiotic novae V1016 Cyg and НМ Sge. Also, the temperature of the central stars and their radii as well as other characteristics of these objects were obtained. The photoionization and optimal photoionization models of the envelopes of V1016 Cyg and НМ Sge were calculated using required input data (gas density distribution, spectrum of the ionizing source as well as chemical abundances) obtained previously by diagnostic methods. In particular, the optimal photoionization models were found using a three-stage approach developed by us previously to model the planetary nebulae envelopes. As a result, the chemical abundances and physical parameters of these objects were determined in a more correct way than before. A similarity between radial density distributions and ionization potentials of ions was detected. Such similarity, if it is detected also in other compact nebular environments, can open a new approach to the determination of the gas density distribution along the sight line. Also, it was shown that the character of the radial density distribution within these objects is similar to that seen in some planetary nebulae. It was demonstrated that the electron temperature radial distribution in such kind of nebular objects is sensitive to the boundary between He$^{++}$ and He$^+$ ionization zones. The compactness of such nebular objects in most cases allows using only spectroscopical methods to determine their internal structure. Therefore, to calculate more detailed models of V1016 Cyg and HM Sge, with deviation from spherical symmetry, it is necessary to obtain the spectroscopic observational data of these objects with a high signal-to-noise ratio over a wide wavelength range (e.\,g., $\lambda$3500\,\AA-$\lambda$7500\,\AA).
