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Spectroscopic Atlas for Amateur Astronomers 190

32.2 Spectra of Gas Flames

Table 110: Swan Bands in comparison to the following spectra:
butane gas torch, comet Hyakutake and carbon star WZ Cassiopeiae

The Swan Bands, already described in sect. 23, are of great importance for astrophysics.
They are generated e.g. in the cool atmospheres of carbon stars as absorption bands and in
the comets of the solar system as emission bands. Molecular band spectra are generated
by complex rotational and vibrational processes of heated molecules [3]. The required exci-
tation energy to generate Swan Bands is relatively low. Therefore this spectral detail can be
easily simulated by the intense combustion of hydrocarbons with do it yourself equipments
from the hardware store!

Table 110 shows the Swan Bands, generated with a butane torch. The wavelengths of the
most intensive band heads are λλ 6191, 5636, 5165, 4737 and 4383. Further a number of
fainter C2 absorptions are still recognisable, with wavelengths according to [110]. Some of
these lines are also visible in the profiles of the carbon stars in Table 64.

In this table, spectra of the butane gas flame (C4H10), comet Hyakutake and the carbon star
WZ Cassiopeiae (excerpt from Table 64) are superposed. The shape of the Hyakutake pro-
file (March 28, 1998) was transferred to and accordingly scaled up in the drawing from an
ESO/Caos project http://www.eso.org/projects/caos/.

Striking are the amazingly similar emission spectra of the comet Hyakutake and the butane
gas flame within the domain of the C2 Swan bands! That’s why for both cases the same
physical process is taking effect. WZ Cassiopeiae shows the Swan Bands in absorption in-
stead of emission. Therefore the shape of this profile runs inversely to the others.

The line identification is based amongst others on [110], [210].

Tests with acetylene flames (C2H2), carried out in the workshop of Urs Flükiger, yielded
similar results (Photo below).