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Session 32 - Curriculum in Crisis: Reinventing Stellar Astrophysics for Today's Graduate Student.
Oral session, Tuesday, June 11

[32.02] A Distant Photosphere: CBR Spectral Distortions from the Recombination Epoch

G. B. Rybicki (CfA), I. P. Dell'Antonio (Lucent Technologies, Bell Labs)

The spectral distortions introduced during the hydrogen recombination epoch in the early universe are features of the CBR that could, in principle, determine a host of cosmological parameters, such as Ømega, Ømega_B, and H_0. Previous calculations have indicated that such distortions will extremely small due the small ratio of baryons to photons in the universe. However, because of their potential importance, it seems worthwhile to do a more complete calculation of the distortions, taking special care to include any physical effects that might affect their magnitude.

Such a calculation provides an instructive example of how classical techniques of stellar atmosphere theory can be applied to significantly different regimes of physical parameters and boundary conditions. For example, here atomic transition rates are almost completely dominated by thermal radiative processes induced by the CBR itself, and the ``photosphere'' exists more in time than in space.

Several improvements in the calculation will be described. An new formalism is developed for determining the spectral distortions due to the hydrogen lines, which is based on a perturbation expansion of the excited level populations away from their thermodynamic equilibrium values. The temperature difference between the radiation and electrons is taken into account. A new type of visibility function is introduced that describes where photons were originally generated by true absorption processes, rather than where they were last Thomson scattered. Improved values for the relic ionized fraction, matter temperature, and the visibility function are found for a range of cosmological parameters. Despite these improvements, the spectral deviations found were not significantly different from previous estimates, and are still several orders of magnitude below the expected backgrounds, well below detectability for the forseeable future.

Program listing for Tuesday