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Analysis and Interpretation of Astronomical Spectra 80
17.3 Broadening of the Emission Lines
P Cygni profiles are not only characteristic for stars with strong expansion movements, but
also for Novae and Supernovae. Anyway such extreme events show more often just a
strong broadening of the emission lines. This applies also to Wolf Rayet stars, even though
with significantly lower FWHM values (see [33]). According to [160] the expansion velocity
can be estimated, by putting in to the
conventional Doppler formula, instead of :
The scheme [160] shows for the Nova V475 Scuti
(2003) four developmental phases within 38 days. Here,
nearly the tenfold expansion velocity of the P Cygni oc-
curred, already an order of magnitude at which the rela-
tivistic Doppler formula should be applied {20}.
17.4 Splitting of the Emission Lines
In sect. 16.7 the determination of the rotation velocity by evaluating the double peak pro-
files in Be stars, was already presented. Split emission lines can also be observed in spectra
of relatively old, strongly expanded and thus optically transparent stellar envelops. Text-
book example is here SNR M1.
The chart at right explains the split up of the O III
emission lines due to the Doppler Effect.
The parts of the shell which move towards Direction
earth cause a blueshift of the lines and the earth
retreating ones are red-shifted. Thereby,
they are deformed to a so-called velocity el-
lipse. This effect is seen here at the noisy
[O III] lines of the M1 spectrum [33].
The chart at right shows the splitting of the Hα line in the central Hα SNR
area of the Crab Nebula M1 ([33] Table 85). Due to the transpar-
ency of the SNR, with the total expansion velocity is calculated, Δλ ≈ 31Å N
related to the diameter of the SNR, (here about 1800 km/s). The
Bradial velocity is finally obtained by halving this value. It yields
therefore just below 1000km/s 1
Olll 5006.84 An
Olll 4958.91
Hβ 4861.33
He II 4685
