Astronomy and Astrophysics – Astronomy
Scientific paper
Jun 1988
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1988taui.reptq....a&link_type=abstract
M.S. Thesis Tel-Aviv Univ. (Israel). School of Physics and Astronomy.
Astronomy and Astrophysics
Astronomy
Astronomical Models, Atomic Energy Levels, Emission Spectra, Helium, Helium Ions, Ionic Collisions, Brightness, Collision Rates, Gas Density, Ion Recombination, Optical Thickness, Temperature Effects
Scientific paper
The comparison of HeI line intensities obtained from observations and model calculations makes possible the determination of the physical properties of the regions emitting these lines. In order to obtain as much information as possible from a theoretical model it should correspond to different physical properties (temperature, density, optical depth, ionization degree, etc.). The line intensities do not fully explain the observed spectra of the various objects but with their help it is possible to obtain better understanding of the physical processes occurring in the region. The purpose was to improve some older calculations of the HeI spectra and to calculate, for additional physical conditions such as high density, the optical depth of lines and various ionization degrees. In order to make these calculations a model of 136 atomic levels was used. One to 132 are real levels and 133 to 136 are fictitious levels that represent a weighted collection of real levels. Spectra were obtained for a wide range of densities, 100 to 10(exp 14) per cc, two temperatures (10,000 and 20,000 K) and different degrees of ionization. For each of these models, the spectra were calculated for an optical depth in the range tau(3889) between 0 and 100. Collision processes were found to be important for all densities larger than 10,000 per cc, therefore the spectra obtained are not pure recombination spectra. As a result of collision processes there is an enhancement of certain lines and an attenuation of others. For densities of N(sub e) greater than 10(exp 9) per cc, collisional ionization and three body recombination become important, so that to obtain good results for high densities, these processes have to be taken into account. Different optical depths influence the line intensity also, in a density-dependent way.
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