Astro 405/505, fall semester 2005
Additional problems
Problem 1: plasma
You intend to study a gas cloud that collapses to form a star. Suppose the cloud has a radius
R
= 10
15
cm, a temperature
T
= 1000
K, a density of neutral atoms
n
n
= 10
12
cm

3
, and a
density of ionized atoms (and electrons)
n
e
= 10
8
cm

3
.
Explain with what technique you would describe the collapse.
Problem 2: emission spectra
Suppose an emission region is homogeneous and the radiation coeFcients have the following
form:
j
ν
=
A ν

1
α
ν
=
B ν

3
σ
= 0
A, B
= const
.
Calculate the angular distribution of the intensity,
I
ν
, that would be seen by an observer at a
±xed position at a distance
D
from the emission region, and the total ²ux.
a) Assume the emission region has the form of a cube with sidelength
R
, that is observed
exactly along the normal of one of the sides.
b) Assume the emission region has the form of a sphere with radius
R
.
Problem 3: stellar emission
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 Fall '08
 RABE
 Physics, emission region

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