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# hw_2 - C/P 740 Dr Herbst Winter Quarter 2008 HOMEWORK...

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C/P 740 Winter Quarter 2008 Dr. Herbst HOMEWORK ASSIGNMENT # 2 Due: Tuesday, 22 January 1. Estimate the concentration ratio of dust particles to H atoms assuming the standard size for the particles. Then, assuming dust particles to have a density of 2.5 gm cm -3 , estimate the mass ratio of dust to gas. Assuming the dust particles to be composed of carbon, is the cosmic abundance of this element (C/H = 2 x 10 -4 ) sufficient to account for the dust-to-gas mass ratio? 2. Estimate how many atoms there are in a dust particle of standard size, and how many of these are on the surface of the particle. Use chemical ideas of bond length and remember that crude approximations are common in astronomy. 3. If the optical depth for visible wavelengths in the red is 10, what would you expect the optical depth to be for radiation of 30 microns wavelength? What percentage of the radiation at this wavelength would get through the cloud? 4. Determine the frequencies of the lowest three rotational transitions of the common
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