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Unformatted text preview: Exam # 2, 10 May Lots of partial credit given, so give at least a qualitative answer to each item. Some useful constants are given at the end of the exam. 1. In this problem, you will explore a closed box model for galactic chemical evolution in the disk. In this model, assume there is no inflow or outflow, and also that there is instantaneous recycling. Make the usual assumptions that lead to the definitions of p , the amount of metals made in a stellar generation, and R , the return fraction. For the Salpeter mass function, R . 3, so assume this value. Assume a Schmidt Law for the dependence of the star formation rate on the surface mass density of gas in the disk, g : ( t ) = 2 g ( t ) . Note the exponent of 2 instead of 1 that we used in the lectures. Determine the dependence of metallicity and the gas fraction f g = g / ( g + ) on time in this model and adjust the remaining parameters of the model, p and , to fit the observations that the metallicity when the Sun formed was...
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 Spring '11
 Lattimer
 Galaxies

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