The distribution of the observed maximum velocities of the Pa Beta and Br Gamma line wings is displayed in Figure 5.4. The top panel shows vblue (solid line) and vred (dotted line) for Pa Beta, while the lower panel has the same plots for Br Gamma.
Figure 5.4: Histogram of the
maximum velocities seen in the Pa Beta
and Br Gamma
line wings. The Pa Beta
data is displayed in the upper panel and the Br Gamma
data on the
lower. In each panel, the histogram of the blue wing maximum velocity
is represented by a solid line while that of the red wing is represented
by a dotted line.
It is clear from Figure 5.4 that, typically, the blue wing
extends further than the red one for both Pa Beta and Br Gamma, the difference
being of about 100 km/s. Whilst both the mean and the median of the
distribution of the Pa Beta blue wing maximum velocity have values around
-300 km/s (the mean is 
km/s
and the median -300 km/s),
the corresponding values for the red wing are very near +200 km/s
(the mean is 
km/s and the
median +200 km/s). The same is valid for the Br Gamma lines: the blue
wing has maximum velocities with mean
km/s and median -325 km/s
whereas the corresponding
values for the red wing are 
km/s and +170 km/s.
There is a simple explanation for this result if the line wings are symmetric relative to the line peak and extend up to 250 km/s either side of the peak, which itself should be blueshifted by about 50 km/s. As will be seen in the next section this is not actually true though. Extra emission on the blue wing, lack of emission on the red wing or absorption of the emission in the red wing needs therefore to be invoked to explain these observations. This will be further discussed in Section 5.4.