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Fig. 3 shows the distribution of neutral hydrogen maxima
(shaded curves) in the spiral arms of our Galaxy.
The position of the Sun is marked by
the symbol and
its circular orbit is plotted as a dashed curve.
The following maximum velocities (relative to the Local
Standard of Rest) of neutral hydrogen gas are observed
by measuring 21-cm emission along certain lines-of-sight:
(i) , ;
(ii) , ;
(iii) , ;
(iv) , ;
(iv) , .
Draw the 21-cm line profiles (i.e. 21-cm intensity as a
function of frequency ) you would expect to observe
in the directions
, , and .
Label the points on these profiles corresponding to
Do not undertake any detailed velocity calculations,
but make sure that the profiles are qualitatively
accurate and display all the necessary features
in correct positions.
Compute and then plot the rotation curve of the Galaxy
interior to the Sun ( ) using these data.
Remember, the rotation curve is a graph of circular speed
as a function of Galactic radius R.
Assuming that the mass distribution is spherically symmetric
for , compute and then plot a graph of the mass M(R)
enclosed within a radius R, as a function of .
Evaluate numerically the total mass interior to the Sun.
Express your answer in solar masses.
Compute and then plot a rough curve of mass density
as a function of .
Tue Oct 19 13:15:33 PDT 1999