Astronomy and Astrophysics – Astrophysics
Scientific paper
Feb 1979
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1979apj...228....8l&link_type=abstract
Astrophysical Journal, Part 1, vol. 228, Feb. 15, 1979, p. 8-12.
Astronomy and Astrophysics
Astrophysics
22
Absorption Spectra, Astronomical Models, Cosmic Dust, H Beta Line, Lyman Alpha Radiation, Quasars, Astronomical Spectroscopy, Granular Materials, Optical Resonance, Optical Thickness
Scientific paper
The various mechanisms proposed for suppressing the L-alpha/H-beta ratio in QSOs are considered quantitatively and comparatively. These mechanisms include absorption by dust, continuous absorption of resonantly trapped L-alpha photons, and suppression of L-alpha and enhancement of H-beta by collisional transitions in broad-line emission regions with large electron density and L-alpha optical depth. Analytical formulas describing the transfer of resonantly scattered L-alpha photons are presented, along with the conditions required for the various mechanisms to be effective. Comparison of the mechanisms within the efficiency limits imposed by observational and physical constraints indicates that absorption by dust grains appears to be the most promising mechanism but that models based on this process encounter serious difficulty due to the requirement that the grains not become so hot that they evaporate.
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