Hydrogen line spectrum in quasars. I - Approximation procedures for line transfer versus an exact treatment

Details Hydrogen line spectrum in quasars. I - Approximation procedures for line transfer versus an exact treatment Hydrogen line spectrum in quasars. I - Approximation procedures for line transfer versus an exact treatment

Dec 1981

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1981a%26a...104..264c&link_type=abstract

Astronomy and Astrophysics, vol. 104, no. 2, Dec. 1981, p. 264-275.

Mathematics

Probability

26

H Lines, Quasars, Radiative Transfer, Approximation, Astronomical Models, Emission Spectra, Photons, Probability Theory

Scientific paper

Approximation procedures frequently used in handling self-absorption effects in the hydrogen emission lines of quasars are discussed and compared with an exact numerical treatment of line transfer. The model here is a finite slab with prescribed density and temperature. It is noted that if a medium has finite thickness and is such that subordinate lines are not thermalized, then a semi-infinite 'local escape probability,' which implicitly assumes that photons emerge from only one surface of the slab, will overestimate the line fluxes. In this way, the intensity ratio H-alpha/H-beta can be greatly underestimated. A modified form of the 'local escape probability' is proposed which allows for the possibility of photons escaping from both sides of the medium. With this probability, it becomes possible to obtain much more accurate line ratios and fluxes. It is also found that natural broadening effects (representable by a Voigt profile) may be important in subordinate lines.

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