The Cat Eye nebula was the first planetary which was spectroscopically investigated and displayed its typical line spectrum, by the English amatuer astronomer William Huggins in 1864. The following table summerises the emission lines I have detected. The spectrum is fairly typical of a planetary nebula showing strong hydrogen balmer emission lines and OIII emission lines. Due to the extended nature of the object, it is not possible to split the two oxygen lines. Also, the Hydrogen Beta line is merged in with the Oxygen. A rather peculiar feature is the emission line at 10049Å far into the infra red. Normally such regions are absorbed by the Earth's atmosphere. I noted this line whilst imaging, but put it down to an internal reflection. After analysis it appears to be exactly where the one of the infra red hydrogen emission lines should be. Obviously I am a bit skeptical on that one! The atmospheric absorbtion occours most strongly in particular bands. I note from the reference that there ae strong SIII lines at 9068Å and 9531Å. If the H line is there, then so should these, unless they are being absorbed and the H I is not. Another possibility is some kind of non-linearity in that infra red region - maybe we are infact looking at the SIII.
Another suggestion, from Robin: Its the second order spectrum of the bright OIII line... I am inclined to think this is correct, as I can also see the second order Ha on the original image.
There are possibly some other emission lines between Ar III (7135Å) and H I (10049Å) but are too vague to pin down.
|4861Å||H Beta||Certain - well merged|
|4958Å||OIII||Certain - merged|
|5006Å||OIII||Certain - merged|
|7065Å||He I||Maybe - bit merged|
|7135Å||Ar III||Certain - bit merged|
|10049Å||H I||Uncertain. Suprising in IR|
From the same night:
2x Barlow shot
Captured in k3ccdtools. Stacked in Registax. Saved as TIFF. Open in photoshop and rotated and cropped. Saved as Tiff. Open in IRIS and saved as FITS. FITS opened in analysed in VSpec. Dispersion = 21.32 Å/pixel
References: Hyung, S et al
Exposure Details :
StarAnalyser 116x6.2s on 200mm @ F5 with SC3.5
Spectroscopy and vspec tutorial
NGC 7027 - Another spectrum of a planetary nebula
PK 64+ 5.1 Campbell's Hydrogen Star BD+30 3639
Curdridge Observatory, Southampton,UK