ASTRONOMY 402T – Spring 2018
Problems for Tutorial Week #2
For all tutorial assignments you should come to your tutorial session prepared to work quantitative problems on the board. Bring your calculator so we can review and correct any errors. Remember to leave adequate room on your submitted work for your in-class additions, and for me to write comments and corrections. Thanks!
PART A
1. Calculate the temperature of an asteroid of radius r at a distance of 4 AU from the Sun. Assume that the asteroid is spherical and radiates (isotropically) as a perfect blackbody.
2. At what wavelength (in μm) does the spectrum peak?
3. If a “Deep Impact” mission were successful in blasting the asteroid into fragments of ~0.1 μm (!), what effect would this have on equilibrium temperature of each particle? What effect would it have on the extinction properties of the asteroid?
4. A blackbody’s absorptivity and emissivity are both equal to one everywhere. If the asteroid’s emissivity were to drop to one third of its absorptivity, how would that affect the equilibrium temperature in general? Calculate the new equilibrium temperature for question 1.
PART B
The left figure is the spectral energy distribution (SED) of M82; the right figure is the SED for the bulge in M31. The mid-to-far IR regions of the SEDs are governed largely by thermal emission from dust.
- Assuming that the dust behaves like a blackbody, calculate the dust temperature in each galaxy.
- Given the differences between these two galaxies, what do you conclude is the reason for the different dust temperatures you derive?
PART C
Do this Extinction exercise from the Gallery of Planetary Nebula Spectra.