Lecture 4 - More Radiative Processes Flashcards
Rayleigh-Jeans regime (when Rayleigh-Jeans approximation holds)
h*nu «_space;kT
When is the Antenna Temperature used?
In the Rayleigh-Jeans regime since that is the criterion for the Antenna Temperature to correspond to a physical temperature. It is therefore only used in Radio Astronomy.
T_A=lambda I_nu / 2k
Is the Brightness Temperature a linear measure of intensity?
No, but the Antenna Temperature is (in the Rayleigh-Jeans regime).
Is the Antenna Temperature a linear measure of intensity?
Yes in the Rayleigh-Jeans regime
Brightness Temperature is the temperature of a…
Blackbody
Is self-absorption important for 21-cm line emission?
Yes, it can be
How to measure the emission and absorption from a cloud producing 21-cm line emission?
Measure blank sky and radio source on a off cloud
When is the optical depth difficult to measure?
When it’s large (proportional to one over length) because then the measured flux is small. Also when the line are very narrow.
Why is equivalent width introduced?
Because it needn’t resolve the spectral feature but only the “missing energy”
Abbreviation for intergalactic medium
IGM
Partition function
sum over all states s e^(-E(s)/kT)
The partition function can be written as the product of two parts, what parts?
The translational (integration over 6D phase space divided by h^3 (cell size)) and the inertial (same as partition function but some over particle instead of state, with degeneracy for each particle)
The Law of Mass Action is a relation between the number density of the reaction particles and
their partition function per unit volume
Is the Saha equation applicable to blackbodies?
Yes. The solar interarior is a good example.
The departure coefficient is the actual level population divided by …
the level population that would apply if the levels were in LTE.
What is the charge of the oxygen ion denoted by OVI?
+5
The orbital angular momentum is denoted by a
l (small L)
What is m_z?
The projection of l onto the z-axis.
For a given n and l how many values can m_z accept?
2l+1
What is the maximum number of electrons in a subshell?
2(2l+1). First 2 is from degeneracy
How many electrons can be in orbital angular momentum state s?
2 in s (this is l=0)
Under what approximation are terms used?
(L, S) terms are used under L-S coupling approximation (angular momentum coupling/spin-orbit coupling)
Energy difference for different terms
up to a few eV
Energy difference for different fine structure levels
~10^-2 eV (1/137 fine structure constant)
Fine structure splitting is caused by…
spin-orbit coupling
Energy difference in hyperfine splitting
10^-6 eV
How is the Zeeman effect observable in the 21-cm line?
As the difference of the two circular polarsation signals (two modes)
The Balmer series are denoted by letter H and concern electronic transitions to level…
2
The interaction between magnetic moment of electron and magnetic moment of proton result in a splitting known as….
Hyperfine splitting
What values for the optical depth lie in the linear regime of the curve of growth?
Those smaller than one, approximately
