Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997nasa.reptv....h&link_type=abstract
Technical Report, NASA/CR-97-206374; NAS 1.26:206374 Dept. of Physics and Astronomy
Astronomy and Astrophysics
Astronomy
Atmospheric Models, Ultraviolet Spectra, Line Spectra, Local Thermodynamic Equilibrium, Iue, Luminosity, Solar Radiation, Abundance, Metallicity, Luminescence, Iteration, Bolometers, Continuums
Scientific paper
We have analyzed the early optically thick ultraviolet spectra of Nova OS And 1986 using a grid of spherically symmetric, non-LTE, line-blanketed, expanding model atmospheres and synthetic spectra with the following set of parameters: 5,000 less than or equal to Tmodel less than or equal to 60,000K, solar abundances, (rho)(alpha) r-3, vmax = 2000 km/s, L = 6 x 104 solar luminosity, and a statistical or microturbulent velocity of 50 km/s. We used the synthetic spectra to estimate the model parameters corresponding to the observed IUE spectra. The fits to the observations were then iteratively improved by changing the parameters of the model atmospheres, in particular Tmodel and the abundances, to arrive at the best fits to the optically thick pseudo-continuum and the features found in the IUE spectra. The IUE spectra show two different optically thick subphases. The earliest spectra, taken a few days after maximum optical light, show a pseudo-continuum created by overlapping absorption lines. The later observations, taken approximately 3 weeks after maximum light, show the simultaneous presence of allowed, semi-forbidden, and forbidden lines in the observed spectra. Analysis of these phases indicate that OS And 86 had solar metallicities except for Mg which showed evidence of being underabundant by as much as a factor of 10. We determine a distance of 5.1 kpc to OS And 86 and derive a peak bolometric luminosity of approximately 5 x 104 solar luminosity. The computed nova parameters provide insights into the physics of the early outburst and explain the spectra seen by IUE. Lastly, we find evidence in the later observations for large non-LTE effects of Fe II which, when included, lead to much better agreement with the observations.
Hauschildt Peter. H.
Starrfield Summer
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