Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1987
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1987phdt........12s&link_type=abstract
Ph.D. Thesis Ohio State Univ., Columbus.
Astronomy and Astrophysics
Astronomy
Astronomical Models, Main Sequence Stars, Radiation Pressure, Stellar Atmospheres, Algorithms, Computer Programs, Line Spectra, Photoionization, Temperature Effects
Scientific paper
Model atmospheres for main sequence stars illuminated by incident power law flux characteristic of the broad line regions of active galaxies are computed using the ATLAS 6 computer code. Modifications of the temperature correction algorithm are given to allow improved convergence of atmospheres subjected to these extreme conditions. It is found that while the calculated Lyman alpha/H beta ratio matches the observed values fairly well, H alpha/H beta is predicted to be approximately 0.5 which is low compared to observed values of 3 to 4. While this problem might be rectified by assuming a system of broad line emitters that is composed of both a stellar and more standard photoionized cloud component, the number of stars required to reproduce the observed flux in H beta is much too high to be realistic for these regions. This large space density might be reduced by lowering the stellar surface gravity of the models, thus increasing the stellar radius. The stellar radii are found to be unaffected by the heating due to incident radiation, since in these plane parallel atmospheres the effective gravity is correspondingly increased by the incident radiation pressure. In a more realistic spherical calculation, where the atmosphere is finite in extent, angular force gradients set up by the incident radiation pressure may promote atmospheric expansion perpendicular to the direction of the incoming beam, or perhaps mass loss through ablation.
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