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M. Sako (Caltech)
I will discuss how radiative transfer effects can alter the emergent line spectrum from an optically thick, highly ionized medium. One example of resonance line overlap, in which the \ion{O}{8} Ly\alpha (n = 2 arrow 1) line scatters with the \ion{N}{7} Ly\zeta (n = 7 arrow 1) line, is investigated in detail. It is found that, depending on the temperature and optical depth, a large fraction of the \ion{O}{8} line can scatter into \ion{N}{7}, which can subsequently increase the intensities of the \ion{N}{7} lines by suppressing the \ion{O}{8} line intensity. I solve the radiative transfer equation to calculate the destruction/escape probabilities for each of these lines as a function of optical depth as well as destruction probabilities due to underlying photoelectric opacity. Other important overlapping lines and continua in the X-ray band are also identified. These calculations demonstrate that global spectral modeling that do not account for these effects yields unreliable line intensities, and, consequently, abundance estimates, especially when the optical depth through the medium is large.
This work was supported by NASA through Chandra Postdoctoral Fellowship Award Number PF1-20016 issued by the Chandra X-ray Observatory Center, which is operated by the Smithsonian Astrophysical Observatory for and behalf of NASA under contract NAS8-39073.
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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.