Planetary nebulae, EEVA-style

[Martin Meredith]

I'm starting this thread to encourage posting of short-exposure images of planetary nebulae.

Apart from the obvious suspects, M27, M57 etc, I generally haven't had a lot of success (and have therefore avoided) these objects. They have either been relatively large and faint (many of the Abell planetarles), or small and far too bright for my sensitive, large-pixel sensor, and end up lacking all detail. Recently I've started to pay more attention to the surface brightness and size characteristics, and it seems there is a sweet spot where it is possible to obtain some detail of the structure of these fascinating objects in short observation durations (say 4-10 mins, although I would definitely spend longer than this on the more interesting objects).

I suppose it is logical that most of the planetaries reside in regions where there are lots of other so-far-unexploded stars, so they can be really difficult to find. My own charts are frankly totally useless for finding most planetaries as they don't show sufficient stars (the file size of the charts would be just too big if I included stars down to the magnitude in the image). The planetarium programs I have access to also don't seem to plot enough field stars to help either. Combine this with a very small sensor and it is a bit hit or miss as to whether they appear on the frame at all. On the other hand, it is great fun trying to track them down during (or more likely) after the session!

One thing that definitely helps a lot is colour, not just to appreciate the beauty and variety of these objects, but also to find them in the first place. 

Take this image of the mag 13.0 planetary IC 4673 in Sagittarius (surface brightness 20.3). This is actually 1 minute each of L R G and B, but displayed as mono. Its a typically dense star field on the edge of what I think is Lynds dark nebula LDN 119 to the upper right. Spot the PN? It has an apparent diameter of 0.25' in case that helps (the wider dimension of the image is around 40') ....Actually, it isn't too hard in this case (for bonus points mag 16.something PN M 2-26 is also in the image but it took me an hour to track down).

 

Here's the same thing in colour and the PN can 'immediately' (?) be seen standing out as a grey-blue tear-shaped object.

Closer in, the shape looks more like a curved piece of chorizo

 

Star colours may well look odd as I tend to turn the saturation up more than usual.... Turning the saturation up even more in a longer exposure (about 8 mins) suggests a greenish tinge to the upper half with maybe a hint of pink towards the top. However, there is a lot of interpolation going on here so these could well be artefacts.

So far I've been unable to find out much specific information about this nebula except that the central star has magnitude 17.6 (and isn't visible here).

I observed this one a couple of nights ago on an evening of exceptional seeing. I'll post a few more from that session later.

Thanks for looking

Martin

 

 

 

[Martin Meredith]

From the same session, this is NGC 6445, a mag 13.2 PN, also in Sagittarius, this time with a surface brightness of 22.0.

This 'wide' field shot shows the object, just over half an arc-minute in diameter, sitting in a somewhat less crowded star field. (This is one minute in RGB (4 x 15s subs) plus a few minutes of 5s luminosity subs.)

 

It is described in one abstract as "a non-symmetric type I bipolar nebula with a very bright central ring, opened lobes, and remarkable features." 

Some of the structure can be seen in a single 5s sub

but the addition of colour shows further features. The right hand edge seems more diffuse/wispy than the left. I'm seeing this as a tilted hourglass, presumably the pair of lobes spreading out from a pinched central region. The central star has magnitude 19.0. 

 

Consulting the figures in this paper I see that in fact all I have caught is the 'very bright central ring'. The lobes are barely visible in broadband imaging.  The lobes in the images from the article are visible to differing extents in H-alpha, O-III and S-II. This is definitely one to return to with narrowband to try to catch some of the butterfly-like wing structures (seen in H-alpha) that would be visible to the upper left and lower right. These extend more than 1 arc-minute to each side.

The left panel is my shot inverted and heavily stretched, compared to the H-alpha panel from the above paper.

 

Cheers

Martin 

 

 

Edited August 27, 2020 by Martin Meredith

[Mike JW]

Hi Martin,

I too have tended to avoid PNs for the same reason as yourself. I end up being sure I have got it in the fov but then cannot locate it. I remain undecided as to whether it is better to go for short subs (5sec) or longer subs (10-15 secs). Owen has sent me various challenges which as a rule I cannot seem to get a shot. I have tried different stretches and still failed. Certainly colour would seem to be a helpful approach.

Enjoyed the post with its info.

Mike

[Marvin Jenkins]

I don’t know if this is what you are after but only a month or so after putting my DSLR on my 150 I took a single frame of The Blue Snowball, not even really knowing if it was in the frame.

I would have to look up exposure time and date details, but I was first amazed it was there and secondly even though the focus is poor you can see some colour structure.

Apologies if you were asking for EEVA images only.

[Martin Meredith]

All images are welcome, especially single frames like this. Thanks for posting! It must have been a great to see the planetary appear in the frame. What is the NGC designation of the Blue Snowball? Apparently, the second one I posted is known as the Little Gem.... but to me, that is a name I can only associate with those tiny biscuits with a colourful dollop of icing sugar I used to eat as a kid!

Martin

[Martin Meredith]

16 minutes ago, Mike JW said:

Hi Martin,

I too have tended to avoid PNs for the same reason as yourself. I end up being sure I have got it in the fov but then cannot locate it. I remain undecided as to whether it is better to go for short subs (5sec) or longer subs (10-15 secs). Owen has sent me various challenges which as a rule I cannot seem to get a shot. I have tried different stretches and still failed. Certainly colour would seem to be a helpful approach.

Enjoyed the post with its info.

Mike

Another reason colour helps is because the transmissivity is so much lower.

With some PNs I've had more success with linear 'stretch' ie no stretch. I've a feeling we need an anti-stretch. 

Once I've observed a reasonable number I'm going to see if I can see a pattern to success/failure. 

[Macavity]

When I did my quick Messier & Caldwell (Watec style) "Marathons", I used Four Minute (mile? lol)
exposures. But I do remember one PN cropping up accidentally in M46 -- NGC2438 apparently! 🥳



The above (via 8" F4 Newt) is far to CLOSE UP for these large OC's! 😛

Although "small", I suspected PNs would indeed make good targets for EEVA - Rather than (say)
O'Meara objects (I did the "Hidden Treasures" but NOT the "Secret Deep") or the Herschell 400! 🙀
I did find quite a nice list / PDF plots of PNs from the "Astro (Astronomical?) League" awards?!?

!Planetary.pdf

Edited August 27, 2020 by Macavity

[Marvin Jenkins]

2 hours ago, Martin Meredith said:

All images are welcome, especially single frames like this. Thanks for posting! It must have been a great to see the planetary appear in the frame. What is the NGC designation of the Blue Snowball? Apparently, the second one I posted is known as the Little Gem.... but to me, that is a name I can only associate with those tiny biscuits with a colourful dollop of icing sugar I used to eat as a kid!

Martin

Hi Martin, I looked it up. NGC7662. PK 106-17.1 Mag 8.6 in Andromeda , size listed as 17”.
when I first saw the picture I just laughed, thinking ‘is that it’. It is only when you look at the size and details that I realised it was quite a capture. Sorry to say I do not have a distance for it right now.

I always associate Little Gem with lettuce 🥬 for some reason. 

Marv

[Marvin Jenkins]

Next clear night I am going to have a go at getting a few more single sub pn’s , could become addictive. If successful I will add to the posts.

Marv

[Bill S]

I do like planetary nebulae. A bit of colour certainly helps. I've got a few monochrome snaps that I'm sure the PN is in there but did not spot it. OIII filters are often suggested for visual use with PNs including trying them in  and out of the light path to make them show up. I wonder if this is something to try with EEVA.

Some clear skies would help too... Grumble, grumble...

Best regards

[Macavity]

Found LINK for (visual) Planetary Nebula Marathon - If you need inspiration! 🙃
https://www.jimscosmos.com/planetarynebulae

[Martin Meredith]

Thanks Chris for that link. 

Here's most of the rest that I observed over 2 nights this week. They consist of 8 of the 11 NGC PNs in Aquila (turns out I didn't manage to get 2 of them in the frame) plus Abell 65 which lived up to its billing as faint... These are mainly 4 or 5m total exposures with around a minute of each of RGB.

They are all at the same scale. The ones that are not obvious are Abell 65 (a blue-grey oval smudge a little larger than NGC 6781 below it), NGC 6741 (the pink coloured object) and NGC 6803 (the green-blue oval just above centre). This latter was near the edge of the frame and although it is supposedly elliptical it isn't quite as elliptical as that...

Data laid out as in image

                    mag    SB   cstar diam                              mag   SB  cstar  diam                                        mag   SB    cstar. diam
6778 AQL   12.1  20.0  16.9  0.26'         6804 AQL   12.2   22.5   14.4  0.58'            Abell 65 SGR   13.8   22.7  15.9   1.7'
6751 AQL.  11.5  19.4  15.4  0.34'         6852 AQL.  12.9   21.4   17.9  0.47'            6781      AQL   11.8   23.2  16.8    1.8'
6741 AQL   11.4  17.1  20.3  0.13'         6807 AQL   12.2   14.9   16.3  0.03'            6803      AQL   11.3   16.2  15.2    0.09'
 

The central stars are visible in some of these. NGC 6804 is stubbornly grey no matter how much I push up the saturation. The surface brightness doesn't correspond too well to my impressions here, esp. for NGC 6781.

Some are crazily small and bright. I'd like to revisit these in narrowband at some point.

 

 

To see how small these are, here is the full frame version of NGC 6781 on the tiny Lodestar sensor.

 

cheers

Martin

 

[Mike JW]

Hi Martin, Enjoyed seeing what can be achieved and making me think about camera/filter at some point in the future.

Mike

[Bill S]

This web page has some information about planetary nebulae that may be of interest.

https://www.webbdeepsky.com/publications/free/

The Brightest Pla

The Brightest Planetary Nebulae Observing Atlas - 2nd Edition

Massimo Zecchin

 

Clear Skies Observing Guides (CSOG)

Courtesy of Victor van Wulfen.

Also, the BAA had a recent talk by Owen Brazell about PNs. It may be of interest

 

Best regards

 

netary Nebulae Observing Atlas - 2nd Edition

Massimo Zec

[Mike JW]

Here is my only reasonably successful attempt at a PN (other than M57). Used the 15" Dob and the ultrastar camera, back in May 2020.

Abell 75, also known as NGC 7076, found in Cepheus. I could not find out much info on this emission PN. I came across two magnitude values: mag 13.4 and 14.5, two distance values: 6000 lyrs and 8000 lyrs away, two size values: 1.7 and 1.8 lyrs across. I thought I had picked up the CS (mag 17.4) but high resolution images show two and maybe three stars in the centre. Thus at best my unresolved fuzzy white dot is two stars.

The PN is elongated- no idea why!! Must do some finding out. Quality images show the PN is slightly bi-polar - not picked up at all in my shot. Visually this PN would respond well to an O111 filter.

I wonder if a smaller pixel camera would pick up more detail in this PN?

Mike

 

Edited August 31, 2020 by Mike JW

[Martin Meredith]

Thanks for the contribution Mike. The Abell planetaries certainly are challenging and for EEA observing timescales probably have to be treated like faint/dwarf galaxies, with deep exposures in monochrome as you've done here. Smaller pixels won't help (and will make things harder in my opinion) for these fainter objects as there will be fewer photons per pixel in any given time, so you'd end up binning anyway. For brighter PNs the reverse will be the case and a smaller pixel sensor (everything else being equal) ought to help a lot, assuming the seeing is up to it. Narrowband is worth a try always, assuming it is easy to slot the filter into the light path in a 'what if' kind of way. This is something I hope to do more of. I haven't done a lot of narrowband recently but I remember having a great time a few years back using StarlightLive to combine luminosity and H-alpha for some of the brighter galaxies.

Martin

[Bill S]

It was clear last night so a bit of rambling around Perseus and Auriga. Looked at some Abell planetary nebulae (4 and 5 in Per, 8 and 9 in Aur) as well as flat galaxies in Aur. The most photogenic of the planetaries was Abell 4. I noticed there were some other faint fuzzies and wondered what was what. The plate solved and annotated image is also shown. (Courtesy of Astrometry.net and ASTAP.) A few to work through. I shouldn't have asked. (Only joking. Always nice to find a few more objects.)

Cheers

Bill

 

 

 

[Mike JW]

Much going on in your shot. Must visit this area sometime. No clear spells recently or predicted. Mike

[Gmx76]

Finally a clear night so after some planetary visual I had another go at ring nebula tonight, this is on my Starquest 130P newt with RA tracking and GPCam2 290C, captured in AltairCapture with LiveStacking of 5s frames.   

 

Edited September 6, 2020 by Gmx76
png

[Mike JW]

Making progress. Looks like you have got lots of double stars - tracking issue I assume, but you picked up the central star with a small scope - impressive. Visually i have struggled in a 20" scope. Mike

[Gmx76]

Thanks Mike.  Good point on the double stars, the RA motor seems to slip sometimes, this is the second one and still does it a bit, could be that? - Greg

Edited September 6, 2020 by Gmx76
name

[Martin Meredith]

Thanks Greg -- there's quite a bit of structure in the ring itself I can see in your shot. I wonder if the double stars are the result of the aligner rather than tracking (or perhaps a consequence of the aligner not doing the right thing with a mistracked sub)? Alignment generally needs to correct for rotation and translation differences between subs but not for scale differences, and this case looks to me like it is trying to account for the latter too. Does AltairCapture allow you to specify what kind of alignment constraints to apply? 

Do you typically keep your individual fits files? It would be interesting to have a go at aligning these subs.

cheers

Martin

[Gmx76]

Hi Martin, this is what AltairCapture supports, unfortunately no FITS files saved this time, will need to see if I can do next time.

[callump]

From Wednesday night this is NGC 7094 in Pegasus - a nice planetary not far from M15.

Internet colour images show this as a blueish ring. Below are a luminance image and my first attempt at an RGB.

Taken with C11 on G11, 0.63 FR, ASI174MM mini camera. All layers 6x20s exposures.

 

 

Quite a faint object though the central star is a bright 13th mag. Some hints of the structure you see in deeper images.

Callum

[Martin Meredith]

Great result Callum. I observed this one too a few nights back in LRGB. This is a 7m15 stack. The central star appears really blue -- I guess this is the result of absorption by the nebula.

I tried to orient mine to match yours but I think yours is flipped relative to mine. There's a bonus mag 16.3 galaxy in the shot at my 11 o'clock, your 4 o'clock.

Did you combine L with RGB or is it pure RGB?

Martin