科研之友
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摘要
We investigate the escape of Ly beta from emission nebulae with a significant population of excited hydrogen atoms in the level n = 2, rendering them optically thick in H alpha. The transfer of Ly beta line photons in these optically thick regions is complicated by the presence of another scattering channel leading to re-emission of H alpha, alternating their identities between Ly beta and H alpha. In this work, we develop a Monte Carlo code to simulate the transfer of Ly beta line photons incorporating the scattering channel into H alpha. Both H alpha and Ly beta lines are formed through diffusion in frequency space, where a line photon enters the wing regime after a fairly large number of resonance scatterings with hydrogen atoms. Various line profiles of H alpha and Ly beta emergent from our model nebulae are presented. It is argued that the electron temperature is a critical parameter which controls the flux ratio of emergent Ly beta and H alpha. Specifically for T = 3 x 10(4) K and H alpha line center optical depth tau(alpha) = 10, the number flux ratio of emergent Ly beta and H alpha is similar to 49 percent, which is quite significant. We propose that the leaking Ly beta can be an interesting source for the formation of H alpha wings observed in many symbiotic stars and active galactic nuclei. Similar broad H alpha wings are also expected in Ly ff emitting halos found in the early universe, which can be potentially probed by the James Webb Telescope in the future.
- 出版日期2018-2
