Planetary Nebula in Cygnus and Binoviewing O-III

[josefk]

The postman brought an Astronomik O-III Nebular filter yesterday so this was a "getting to know you" session deliberately looking for small and possibly marginal Planetary Nebula to see what it added. I thought PN with a filter would be a not too bad way of using an evening where the moon was up and very bright being nearly full. The location was Fineshade woods Northamptonshire. Notionally Bortle 4 not that that meant anything last night. I thought seeing was "ok" - when i had a quick look at Mars and Jupiter to end the session there was glare in the damp air and some light boiling. The scope used was my 7.3" Cassegrain.

First up - not PN. I had a few "September" Herschel objects to catch up; four in fact. I managed three; H VII-51, H VI-32, and H VI-40. All three are Open Clusters in Cygnus and pretty faint against this moonlit night. Only H VI-32 (NGC 7086) really appeared as a cluster (Mag 8/12') - my notes "a light dusting of castor sugar with a few grains of granular sugar". The other two are Mag 8 or 9 and 4' or 5'. I couldn't see nearby NGC 7044 so that remains to be found another night. This was all at 80x/1 degree/2.4 exit pupil.

My kit was cooled now so on to the Planetary's. The grand plan with the new O-III was to use it on one side of a binoviewer and "wink" rather than "blink" the unfiltered side in and out to try and identify/isolate any small PN in it's respective star field. mmmmh. The jury is still out after one moonlit night but i think the jury will return a split decision.

I hadn't really found any success stories/positive experiences of using a filter like this - only plans and proposals to try it. i think now i know why. I found the ergonomics a bit tricky - maybe its just me - but when closing one eye at the Binoviewer i was finding the open eye left with the O-III under it was seeing either nothing or EP reflections (a hood helped). A very slight move of my head or eye then "re-found" the now dimmed star field but only a second or two later. For a "big" PN like NGC 7027 (0.3' x 0.2') the slight delay didn't matter - the big PN was clear and definite in the O-III side and therefore obvious one or both eyes open. The snag is that NGC 7027 doesn't need to be blinked to find it - it's big. :-).

For a small PN like NGC 6884 or NGC 6881 (each 0.1') the technique (at these exit pupils) didn't work - the ergonomics got in the way but much more significantly at Mag 11 and Mag 13.6 respectively for these small PN using the BV was just giving away too much light (in the one eyed view) and i didn't faff about trying to get a bigger exit pupil than through the BV than the 1.2mm i was set up for - i just switched to mono. 

Using 2x TV Panoptic 24mm eye pieces, one fitted with with an O-III filter and one not and using them alternately in a regular cyclops diagonal at nearer 2mm exit pupil was much more successful and will be very useful in this kind of session for me with one massive caveat. Being still pretty inexperienced i expected the O-III to work like welding goggles - blocking everything except O-III. It doesn't; bright stars get through and quite strongly. They also glow a little bit - just like a small PN!!!. Basically it means for me with the very small PN identifying their position visible or not from the field stars in the FOV is critical - only then does the O-III help in confirming the observation. it would be very easy  for me to make an ID mistake on a bright star beating the O-III.

So with the process tuned last night i observed these Planetary Nebula in Cygnus:

1. NGC 7027 (Mag 8.5/0.3' x 0.2') Easy with O-III but also didn't need it. Nice at an unfiltered 200x with a hint of blue showing at this magnification.
2. NGC 6833 (Mag 12.1/0.0') Identified by location. O-III helped confirmation but could be seen without.
3. NGC 6884 (Mag 11/0.1') Identified by location. O-III helped confirmation but more magnification (unfiltered 200x) equally helpful to "fatten the PN up" and increase contrast.
4. NGC 6881 (Mag 13.6/0.1') Identified only by precise location. Not visible without O-III. Even with O-III needed averted vision but when it appeared it could be held and position was precise every time. This was a needle fine micro dot - possibly the most marginal observation this year so perversely very satisfying.
5. NGC 7026 (Mag 10.89/0.5' x 0.2'). Could be seen with averted vision without O-III by looking at nearby f2 Cygni. Once it popped in it could be held for a short while. With O-III it could be seen easily with direct vision and looked like a fat double with the star BUP 9010 just a few arc-seconds away.
6. IC 5117 / Aro 112 (Mag 11.5 / 0.0'). Very tricky. Confirmed with O-III but again only when already sure of location. 

...and that was that. Lessons learned. Food for thought. etc. A very satisfying session overall and a good start to the weekend.

Mars still horrible to finish with big diffraction beams - my DIY off aperture mask wasn't successful :-(. Jupiter with maybe 5 or 6 bands but a bit soft and it's moons a bit soft too.

Have good weekends all. 

Joe

 

 

Edited October 8, 2022 by josefk

[josefk]

Interesting (for me) addendum following some reading yesterday - NGC 7026 and BUP 9010 was mistakenly catalogued as a 4 element multiple star system by SW Burnham (not Robert Jr) in 1879 so my observation at the eyepiece wasn't complete nonsense. The PN NGC 7026 is listed as the primary. There are two other components to go back for! 🙂