h8 - T = 12 Gyr in the Galactic plane in the solar...

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Homework # 8, due 26 Apr 1. Show that a simple closed-box model with instantaneous recycling results in the gas-phase metallicity increasing linearly with time. If this is true, what cosmic time does [Fe/H]=-3 correspond to? Also show in this model that the distribution of stars in metal- licity dN/d ln Z has a maximum where Z = p , the eﬀective yield of heavy elements deﬁned in the lecture notes. 2. Explore the evolution of the solar neighborhood with a galac- tic chemical evolution model with instaneous recycling and infall which obeys f ( t ) = A ( 1 - t/τ f ) . Assume an infall timescale of τ f = 24 Gyr. Determine the value of A from the observed surface density Σ T ( T ) = 50 M ± pc - 2 of stars and gas at the present time
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Unformatted text preview: T = 12 Gyr in the Galactic plane in the solar neighborhood. Assuming the Schmidt SFR = g , determine the value of that will give the present gas fraction g ( T ) / T ( T ) = 0 . 24 at the present time. Hint: Note that df dt + f = e-t d dt fe t if is a constant. 3. Explain why the value of [O/Fe] observed in stars is both greater than 0 and does not vary with [Fe/H] for metal-decient stars for [Fe/H] &lt;-1 . 5, but decreases with increasing metallicity for more metal-rich stars. When [Fe/H]=0, what value should [O/Fe] have? 4. Do problem 4.13 in the text....
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This note was uploaded on 01/25/2012 for the course AST 346 taught by Professor Lattimer during the Spring '11 term at SUNY Stony Brook.

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