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Spectroscopic Atlas for Amateur Astronomers 153

spectrum to the right). This reflects the high effort, required for these large appearing PN
(in this case 86"x72"). Typical for this high excitation class are the old age of about 20,000
years, and the large extent of the nebula of about 1.4 ly.

Table 84A M57, Intensity profile along the longitudinal axis of the Ring Nebula

T84A shows for the strongest emission lines [O III] and [N II], the intensity profile along the
entire 50μm slit, positioned on the longitudinal axis of the Ring Nebula. This profile has
been generated with Vspec and a 1D-spectral stripe, rotated by 90° with the IRIS software.

Table 85 Red Rectangle Object type: Post AGB Star/ Excitation class: very low,
Nebula HD44179 Protoplanetary Nebula can't be determined quan-
titatively with sect. 28

This highly interesting object, discovered not until 1974, is a
protoplanetary nebula which is located at a distance of about
2'300ly in the constellation Monoceros. With an apparent mag-
nitude of Vvar= ~+9.02m the so called Post-AGB-Star has just left
the last carbon-star-stage on the AGB and begins now to repel
its envelope as a planetary nebula. In amateur telescopes the ob-
ject is visible just as a star. Only large professional telescopes
show the small bi-cone-shaped nebula. Image HD44179: by
HST. The object is a spectroscopic binary. By repelling its envelope, the ex-carbon star has
changed its spectrum radically and presents itself now as spectral type, depending on the
source, in the range of a B8 to A0 giant. This would correspond to an effective temperature
of about 10'000K. However, for the Post AGB component just 7500 – 8000K are assumed
[eg 208]. The corresponding ionisation energy is still by far too low for an ionisation of the
nebula, so here just the hydrogen Hα-and the sodium D1/D2 lines appear in emission.
Highly-resolved spectra show here the Na I emissions with double peaks, what is inter-
preted as a combination of perspective- and Doppler effects, caused by the bipolarly occur-
ring mass loss [208]. In such spectra C2 Swan emissions testify from the former stage as a
carbon star [209]. The slim hydrogen absorptions indicate a photosphere or rather a
pseudo-photosphere of low density.

Table 86 M1, NGC 1952 Object type: SNR Excitation class: E >5

T86 shows the emission spectrum of the Supernova Remnant (SNR) M1 (approx. 6300 ly).
The 50μm slit runs in ~N–S direction through the central part of this young SNR. The causal
SN type II was observed and documented in 1054 by the Chinese. Today, the diameter of
the expanding nebula reaches approximately 11 ly.

Vesto Slipher in 1913 recorded the first spectrum of M1. At that time he already noticed a
massive split up of the most intense emission lines. Unaware of the nebula expansion, he
interpreted this spectral symptom incorrectly as the newly discovered Stark effect caused
by the interaction with electric fields. 1919 exposed R.F. Sanford, the M1 spectrum with
the 2.5m Hooker Telescope, and at that time the "fastest" film emulsions, while no fewer
than 48 hours! The result he describes sobering as "disappointingly weak", a well clear in-
dication that even today this can’t be really a beginner object. The expansion of the nebula
was found not until 1921 by C.O. Lampland, by comparing different photographic plates!

With the C8, a 200L grating and an Atik 314L+ camera, cooled to –20°C with 2x2 binning
mode, after all still 2x30 minutes were needed to record a spectrum of passably acceptable
quality. As an annoying side effect of the long exposure time, light pollution and airglow
(Table 96) was recorded in a comparable intensity to the signal of M1, despite a quite