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Re: (IAAC) Markarian 205 - 8inch F/10

>>What I didn't think about with my last contribution to this discussion was
>>the use of a prism. Prisms are readily and cheaply available and if you
>>don't have one lying around you can get them cheaply from places selling
>>government surplus equipment. They don't need to be spectroscope 60 degree
>>prisms, though these are nice. 45 degree prisms used in the correct
>>orientation give quite adequate dispersion to give some idea of the spectrum
>>of a planetary, especially if you use a low telescopic magnification.
>>The only awkward bit is finding the correct viewing angle but this is just a
>>matter of wiggling your head and prism around until you see something.
>>Those gifted with a manual dexterity greater than mine could contrive an
>>ingenious arrangement to support the prism between the eye and the scope.
>>This will give a good idea of the distribution of emmission features around
>>the nebula at different wavelengths and also a good idea of why a nebula
>>does or does not respond to a particular filter.
>>Nick

>yes this idea was posted by Ed Barker in the WSDSOH Vol 2 some 20 years
>ago. It is not easy but can be done. The other method is to get a
>transmission grating and use that. Bausch and Lomb many years ago made an
>SDE eyepiece which was preceisly that

I recently purchased the Rainbow Optics Star Spectroscope just to do that
kind of things and tried some weeks ago on bright planetary nebulae (N6210,
6572 & 7027) with a 13" telescope. I have been pleased with the results,
although I will look forward to enlarge the spectrum widening on future
sessions. I saw elongated OIII emission lines, with Hß (quite faint on
7027) very near and a curious "ghost" image near the end of the blue
spectrum (I guess it is OIII at 4363A melted with Hgamma at 4340A). As it
is the first observations I have made with the spectroscope, I think this
tool will bring new enjoyment in my planetaries' observations...

A thing that was not noted before (I believe, tell me if I am wrong):
central stars embedded in too bright nebula are easily seen because the
emission images (slitless viewing spectrograph) are crossed by the thin
continuous spectrum of the central stars (as was the case with 6572 and
6210, a continous spectrum showed in 7027 but had to belong to the nebula).

clear skies, Yann.


Yann Pothier	tel: 01 43 41 43 29
11 impasse Canart, 75012 PARIS, FRANCE
Email: ypothier@abi.snv.jussieu.fr
Site : http://pegase.unice.fr/~skylink/publi/cielextreme
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