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Unformatted text preview: Astro 405/505, fall semester 2007 Homework, 11th set, return before Friday, November 30, 4pm. Dont forget to give your name. Problem 21: Optically thick free-free emission Suppose you observed two clouds of ionized hydrogen gas with thickness R . One cloud has the temperature T and the hydrogen density n i, . The second is located right in front of the first cloud and has a temperature T = 4 T and hydrogen density n i = n i, / 4 . Assume LTE and determine the intensity spectrum of bremsstrahlung as a function of the optical depth through the first cloud. Sketch the spectral energy distribution assuming the clouds are optically thin at h kT . Note which could dominates in the different parts of the spectrum. You may set the Coulomb logarithm constant and use j = C 1 n 2 i T- 1 / 2 = C 2 n 2 i T- 3 / 2 - 2 C i = const . It is useful to use a Taylor expansion of the exponential function for small arguments....
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