Lecture 3 - Radiative Processes Flashcards
What four parameters do the specific intensity depend on?
Frequency, direction, position and time
Energy density is 1/c times the integral of…
the specific intensity over the solid angle
What is the Photon Occupation Number (in thermal equilibrium)?
The Bose-Einstein distribution function. In general it is the average over both spin states (while the specific intensity is the sum over both spin states)
How many spin states do a photon have?
Two
What is the unit of optical depth?
one over length
Effective absorption coefficients are denoted by the letter…
k (or kappa)
Source function in terms of (spontaneous) emission and absorption coefficient
j/k
How does the the equation of radiative transfer transform If the emitting and absorbing material are in thermal equilibrium and the region of total optical depth is isothermal?§
The integral (second term) transforms to B_nu(T)(1-e^-tau_nu)
What does the Lorentz line profile describe?
The cross section for an atom in level i absorbing a photon by going to level j
Minimum velocity for Doppler Broadening to dominate Natural Linewidth
10 m/s
