Summary: ASTR 3730: Astrophysics 1 Problem Set #2
Due in class Friday 26th
1) An optically thick source of blackbody radiation at temperature Tsource is
surrounded by an optically thin cloud of gas at temperature Tcloud:
If an atomic transition in the optically thin gas corresponds to a frequency n0,
sketch the spectrum you would expect to see in the vicinity of this spectral line
along the two lines of sight A and B:
(a) In the case when Tcloud < Tsource
(b) In the case when Tcloud > Tsource
Explain briefly the rationale for your answers.
2) A cyclotron line is observed in the X-ray spectrum of the neutron star Hercules
X1 at an energy of 55 keV.
(a) Deduce the magnetic field strength B at the surface of the neutron star.
(b) If protons are also orbiting in the same magnetic field, calculate the frequency
of the corresponding cyclotron line they would produce. What wavelength does
this correspond to?
(c) What is the relative amount of power radiated by the protons as compared to