In this diagram, which uses 3.6 Å resolution spectra, we compare the
spectrum of an O7 dwarf (O7 V) star with an O7 supergiant (O7 If). A number
of features are seen to be luminosity sensitive. First, the hydrogen
lines (only
H
is shown here)
are slightly weaker in the supergiant, whereas the He I lines
are quite insensitive to luminosity differences. However, note that in the
supergiant star, the N III 4634-42 feature actually goes into emission and the
neighboring He II 4686 line decreases in strength (in O6 stars, it
actually goes
into emission in the supergiant). Note that the nearby He II 4542 line actually
increases slightly in strength as we move toward higher luminosities.
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