(IAAC) Cats's eye nebula
Further observations on the Cat's Eye nebula
23 and 23 September 1997
At last some darker skies again although 23 Sept was a bit hazy which made
the sky somewhat brighter than optimum.
I tried observing the Cat's Eye nebula using both the UHC and my newly
aquired OIII filter as well as unfiltered. Very rough ASCII diagram.
**####** * "wings"
***####** # "body"
Both the UHC and OIII show the roughly rectangular body of the nebula with
high contrast but compared with the unfiltered views the "wings", which give
it the eye shape, are less conspicuous. This must reflect some differences
in the spectral emmision of the different parts. Interestingly the "body"
corresponds to the red part on the Hubble image and the "wings" to the green
false colour(?) areas. My observations on both nights confirmed the apparent
red edge visible most clearly in the "wings". I observed it through a
vertexface of a 45 degree prism to get some spectral dispersion. The blue
green body was unchanged but a red component was visible as an arc following
about 2/3 of the edge of the unfiltered image appearing to correspond the
red edge visible in the lower magnification images. The sky was brighter
than on the 22 on 23
Sept 26 1997
Observed Cats Eye under very clear skies. The red was most promininent in
the wings and did resemble the location of red areas a Kitt peak colour
photo in Sky And Telescope (April 1995. pp 96-98; Dennis di Cicco Planetary
Nebulae from the City).
Using the 45 degree prism again the red spectral band image could be quite
elusive but when best seen showed as a red ring in contrast to the much
solider looking image in the blue green OIII line. With the higher
dispersion of a direct vision prism, the red image could not be seen but the
OIII image was still clear and a second fainter image to the blue side of
the OIII image was also clearly visible.
From these observations the light contributing to the visual image seems to
come from a several spectral lines rather than the OIII line visually
dominant for many other planetaries. Red as well as blue-green colour is
visible with a 20" in this nebula.
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