d = 1/p
L = 4 pi sigma R^2 T^4
Stefan-Boltzman Law: F = sigma T^4
Wien's Law: Lambda = 0.0029/T
Brightness: b = L/(4 pi d^2)
1. a) The star Drex has a parallax of 0.05 arcsec. How far away is it in parsec?
b) How far away is Drex in light years? (1 pc = 3.26 ly)
c) The star Xerd is at a distance of 10 ly. What parallax will it have?
(4 marks)
2. A star has T=12000K and a luminosity of 256Lsun. How much bigger is its radius than the radius of the sun (use T=6000K, L=Lsun)? Use proportionality for full credit (3 marks)
3. Sketch the Hertzsprung-Russell diagram. Mark on the position of the main sequence, the sun, white dwarfs, red giants and red super giants. Clearly mark on your diagram which direction L and T increase in. (4 marks)
4. a) Define the terms Luminosity class, Temperature class, Photometry and Spectroscopy. (1 mark each)
b) Describe the way distances to stars without measured parallax's can be obtained using the spectroscopic parallax method (2 marks)
5. The spectrum of the star A is found to have its peak emission at a wavelength of 300 nm, and the star B has its peak at 900 nm. Both stars have measured parallax's, A with a parallax of 0.1 arcseconds and B with a parallax of 0.2 arcseconds. The ratio of brightnesses of A and B is measured at the Earth to be b_A/b_B=1/4
a) What are the distances in parsecs to A and B? (2 marks)
b) What is the relative temperature, T_A/T_B of the two stars? (2 marks)
c) What are the relative luminosities of A and B, given as the ratio L_A/L_B? (2 marks)