Lecture 4 - More Radiative Processes

Question 1

Rayleigh-Jeans regime (when Rayleigh-Jeans approximation holds)

Answer 1

h*nu &laquo_space;kT

Question 2

When is the Antenna Temperature used?

Answer 2

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

Question 3

Is the Brightness Temperature a linear measure of intensity?

Answer 3

No, but the Antenna Temperature is (in the Rayleigh-Jeans regime).

Question 4

Is the Antenna Temperature a linear measure of intensity?

Answer 4

Yes in the Rayleigh-Jeans regime

Question 5

Brightness Temperature is the temperature of a…

Answer 5

Blackbody

Question 6

Is self-absorption important for 21-cm line emission?

Answer 6

Yes, it can be

Question 7

How to measure the emission and absorption from a cloud producing 21-cm line emission?

Answer 7

Measure blank sky and radio source on a off cloud

Question 8

When is the optical depth difficult to measure?

Answer 8

When it’s large (proportional to one over length) because then the measured flux is small. Also when the line are very narrow.

Question 9

Why is equivalent width introduced?

Answer 9

Because it needn’t resolve the spectral feature but only the “missing energy”

Question 10

Abbreviation for intergalactic medium

Answer 10

IGM

Question 11

Partition function

Answer 11

sum over all states s e^(-E(s)/kT)

Question 12

The partition function can be written as the product of two parts, what parts?

Answer 12

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)

Question 13

The Law of Mass Action is a relation between the number density of the reaction particles and

Answer 13

their partition function per unit volume

Question 14

Is the Saha equation applicable to blackbodies?

Answer 14

Yes. The solar interarior is a good example.

Question 15

The departure coefficient is the actual level population divided by …

Answer 15

the level population that would apply if the levels were in LTE.

Question 16

What is the charge of the oxygen ion denoted by OVI?

Answer 16

+5

Question 17

The orbital angular momentum is denoted by a

Answer 17

l (small L)

Question 18

What is m_z?

Answer 18

The projection of l onto the z-axis.

Question 19

For a given n and l how many values can m_z accept?

Answer 19

2l+1

Question 20

What is the maximum number of electrons in a subshell?

Answer 20

2(2l+1). First 2 is from degeneracy

Question 21

How many electrons can be in orbital angular momentum state s?

Answer 21

2 in s (this is l=0)

Question 22

Under what approximation are terms used?

Answer 22

(L, S) terms are used under L-S coupling approximation (angular momentum coupling/spin-orbit coupling)

Question 23

Energy difference for different terms

Answer 23

up to a few eV

Question 24

Energy difference for different fine structure levels

Answer 24

~10^-2 eV (1/137 fine structure constant)

Question 25

Fine structure splitting is caused by…

Answer 25

spin-orbit coupling

Question 26

Energy difference in hyperfine splitting

Answer 26

10^-6 eV

Question 27

How is the Zeeman effect observable in the 21-cm line?

Answer 27

As the difference of the two circular polarsation signals (two modes)

Question 28

The Balmer series are denoted by letter H and concern electronic transitions to level…

Answer 28

2

Question 29

The interaction between magnetic moment of electron and magnetic moment of proton result in a splitting known as….

Answer 29

Hyperfine splitting

Question 30

What values for the optical depth lie in the linear regime of the curve of growth?

Answer 30

Those smaller than one, approximately