The luminosity function is a good tool to compare the stellar content
of different regions.
It gives a first hint on the ratio between massive (bright) and less
massive (faint) stars.
However, different evolutionary states of the stars smear out some properties.
But in contrast to the mass function no stellar evolutionary
models or other theories are needed for the construction of the
luminosity function.
We assume that the luminosity function is a power law with
where 
is the slope of the luminosity function.
Figure 12: Luminosity function (LF) for LH47/48.
a) The LF for all 3522 main sequence stars.
b) Comparison of the LF of inside the shell N44
(filled circles) and outside (open circles).
The slopes of weighted linear regressions are given (inside:
straight line, outside: dotted line)
The luminosity function has been constructed from main sequence stars.
Only stars with 
mag and stars which do not belong to the
"red clump" have been selected; in total these are 3522 objects.
The star counts have been binned to interval widths of 1 mag.
Figure 12 (click here)a shows the luminosity function found for all those stars.
The error bars represent 
errors.
In the range from 
to +2 mag the assumption of a power law
seems to be correct.
The first bin (
mag) contains too few stars, probably some
stars are already missing due to evolutionary effects.
At 
mag (i.e. 
mag) incompleteness of the data
sets in.
The straight line represents a weighted linear regression for the range
to +2 mag (i.e. V = 13 to 21 mag).
The slope of the line is 
.
Figure 12 (click here)b shows a comparison of the luminosity function
between the interior and the exterior of the superbubble N44.
For the inner part all main sequence stars with a distance of less than
from the centre of the shell have been taken into account
(1204 stars),
for the outer part only stars more distant than 
(1601 stars)
from the centre have been selected.
Error bars have been omitted in Fig. 12 (click here)b for clarity.
There is a clear difference of the luminosity function between the two samples.
In the inner part the luminosity function flattens significantly
towards brighter stars.
An error-weighted linear regression gives 
for
the interior of the shell and 
for the exterior.
The fits have been calculated for the same magnitude range as in
Fig. 12 (click here)a, i.e. from 
to +2 mag.
The solid line represents the fit for the inner region, the dotted line the fit
for the outer region.
The slope of the luminosity function for the entire region (
)
is in good agreement with the value of 
found
for the luminosity function of
NGC1962-65-66-70 (LH58; Will et al. 1995b).
Malumuth & Heap (1994) found 
for the inner region of 30 Dor
and 
for the outer parts
.
For NGC595 in M33 Malumuth et al. (1996) give 
.
For more slopes of luminosity functions in recent papers see
Will et al. (1995b).