Midterm 2011 Solutions

# To first order you can assume nearly all h atoms are

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Unformatted text preview: Dense Gas? Hot or Cool Gas? Continuum Hα line Li I line TiO molecular bands Page 7 of 19 Physics 160 Fall 2011 Midterm Exam (b) Based on the presence of TiO molecular bands, what spectral class do you think this star is? (c) The photospheric temperature of this star is 3000 K. What fraction of all neutral Hydrogen atoms in the photosphere are in the n=3 state, and thus capable of producing an Hα emission line? To first order, you can assume nearly all H atoms are in ground state. Hint: this is going to be a very small number. Page 8 of 19 Physics 160 Fall 2011 Midterm Exam (d) The photospheric pressure of this star is about 106 N/m2. Assuming a pure, neutral hydrogen ideal gas, what is the number density of H atoms at the photosphere? (e) What is the number density of H atoms in the n=3 state in this photosphere? (f) Based on your answers above, is it reasonable to believe that the emission from Hα comes from the photosphere? Use Kirchhoff’s laws to explain where this emission is probably coming from. Page 9 of 19 Physics 160 Fall 2011 Midterm Exam (4) Assume a star of mass M and radius R has a constant density. (a) Write down an expression for the density ρ0 of the star. (b) Using the equation of mass conservation, write down an expression for M(r), the mass of the star interior to radius r. Assume that M(0) = 0. Page 10 of 19 Physics 160 Fall 2011 Midterm Exam (c) Using the equation of hydrostatic equilibrium, write down an expression for P(r), the interior pressure of the star as a function of radius. Assume that P(R) = 0. (d) Write down an expression for P(0), the core pressure of the star. (e) Using the Sun’s mass and radius, evaluate P(0) and compare it to the known ce...
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## This document was uploaded on 02/26/2014 for the course PHYS 160 at UCSD.

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