PHYS3116 - Assignment 2 (Worth 10%)
Submit in pdf format by email to s.brough@unsw.edu.au by
5pm Friday 12th November.
1. Running the stellar model program:

a. [10 marks] With input parameters corresponding to a sun-like star (M = Msol, X = 0.74, Y = 0.24; with starting values of Log(Radius) = 8.9, Log(Luminosity) = 26.6, Log(Core Pressure) = 16.5, and Log(Core Temperature) = 7.2). Present the output values for radius, luminosity, core pressure, and core temperature. How many iterations does the code require?

b. [5 marks] Comment on the results of the model in (a). How do the radius, core temperature, luminosity and core pressure compare with your expectations for a sun-like star? Give reference to the output values, as well as the shapes of the graphs.
c. [5 marks] Choose two stars of different mass and radius from the list of possible options below (the R, L, P and T values are not the actual values for the star but a set of initial guesses that can be used to run the code). Model these and comment on how the luminosity, core temperature, and core pressure vary with changing mass and radius but not composition? M X Y Log(R) Log(L) Log(P) Log(T) 1.3*Msol 0.65 0.25 9.8 26.0 16.7 7.4 1.5*Msol 0.65 0.25 9.3 26.0 16.7 7.4 1.7*Msol 0.65 0.25 9.02 26.0 16.7 7.4 1.9*Msol 0.65 0.25 8.956 26.023 16.715 7.423 2. Using Kepler’s third law, estimate the total mass (in units of solar mass) of the Milky Way enclosed within the Sun’s orbit. Assume the Sun is 8.5 kpc from the centre of the Milky Way and has an orbital speed of 220 km/s [5 marks]. 3. Thinking about the properties of galaxies and how astronomers use them: a. [1 mark] Choose one of the galaxies listed below from the Hubble Space Telescope image archive: https://www.spacetelescope.org/images/archive/category/galaxies Sombrero NGC 1300 NGC 4621
b. [5 marks] For your chosen galaxy, use the NASA/IPAC Extragalactic Database (NED): https://ned.ipac.caltech.edu/forms/byname.html to find its Morphology, Distance Modulus and Apparent Magnitudes (in the B and K bands). You will need to follow the links to the photometric data points from the original galaxy page to find the apparent magnitudes. c. [4 marks] Calculate the Absolute magnitudes (in the B and K bands) and the B-K colour for your chosen galaxy. d. [2 marks] Write a short paragraph on what the morphology and colour of the galaxy imply for your chosen galaxy’s star formation history. 4. [15 marks] Plot surface brightness vs radius for different Sersic profiles (n=1-10) for a galaxy with effective surface brightness μ= 25 mag arcsec-2 and effective radius, re= 10 arcsec. You do not need to use a specific program or language to do this, only a labelled plot is required. Jupyter notebooks will not be accepted. 5. Consider a stellar-mass black hole (10 solar masses), an intermediate-mass black hole (104 solar masses) and a supermassive black hole (109 solar masses): a. [4 marks] Calculate the Schwarzschild radius for each mass of black hole. b. [4 marks] Calculate the average density for each black hole.