Object of the Week, June 23, 2019 - M57, the Ring Nebula

[Howard B]

Planetary Nebula

Lyra
RA 18 53 35
DEC +33 01 45
Magnitude 8.8 (v)


There’s a lot of information available about M57, the Ring Nebula, and given its iconic status as one of the northern hemisphere’s most interesting and brightest planetary nebulae, there’s not much I’ll add here. However, given that this beautiful nebula was the first deep sky object I ever observed through a telescope in 1968, there are a few things I’m still curious about even though I’ve observed it approximately a million times since then.

3560

Color
I’ve found that M57 is a favorite for kids to look at through my 28-inch scope. After they’ve had a look, I’ve made it point to ask them what colors they saw, and they almost always instantly answer “red, green and blue”. The most I’ve detected is a very slight warm hue along the outside perimeter of the Ring.

Young eyes seemingly have no problems seeing these colors, so I’m curious if any of you have been able to see any definite colors in M57, and if so under what circumstances.

Central stars
The actual white dwarf central star has a well-deserved reputation for being difficult to see, and even though it’s rather easy in scopes 16-inches and larger, the seeing still needs to be rather steady to see it well. Also, a second and only slightly fainter star can be seen “within” the Ring just slightly northwest of the actual central star.

Even so, I’ve seen it definitely only and handful of times with my 28-inch scope and only suspected it once or twice with my old 20-inch. What’s the smallest scope anyone here has used to see this second “central star”?

Also, there’s a third star superimposed on the southwest border of the Ring, and even though it’s considerably brighter than either of the central stars it’s also fighting the much brighter nebulosity of the Ring's annulus. I’ve never seen it in my own scopes but had a remarkable view of it through the 90-inch Bok telescope on Kitt Peak a few years ago.

Uwe started a wonderful thread on these and other M57 stars a few years ago here:

http://www.deepskyforum.com/showthread.php?381-Messier-57-stars-inside

He saw many of the fainter stars in the PanSTARRS image above with Jimi’s 48-inch scope while using a “central star filter” that suppressed the nebula but allows stars to come through nearly undimmed. Has anyone else had a similar experience using a filter like this?

Halo
The outer halo can be seen fairly easily on a great night with a big scope, but those opportunities are few and far between. What’s the smallest size scope someone has used to see it? I’ve seen it with and without a nebula filter at low power and the view seemed much the same either way, but I prefer the view without the filter. Is your observing experience similar? To me the size of outer halo appears about the same as in the PanSTARRS image - how big does it appear to you?

Interior nebulous structure
You can see two parallel, nebulous streamers running through the interior of M57’s round central cavity along the nebulae’s outer major axis in the HST/ESA image below. I saw these streamers quite clearly from my light polluted backyard with my old 12.5-inch f/7.8 scope at 260x with a UHC filter in 1988 – and never since! And not because I haven’t tried. No matter what scope/filter/magnification combination I’ve used, these streamers have never appeared again.

3561

Did I get an observation of a lifetime back then with that 12.5-inch scope or is this a fairly common feature that others see in M57 all the time?

Give them a go and let us know!

[Ivan Maly]

I think I always see it as green (the sort of OIII-green, or turquoise, without the filter) in the main bright ring. At least, that I would remember, with 16 inches under normal remote-site conditions, as well as with 20 under good rural sky.

The very fact that you posed this question, though - about color - took me aback, so I actually had to rummage through my notes to make sure I have recorded the color and it's not false memory! So here you are:

16", 2014, SQM 21.4, F/4.5 with 40 mm Pentax XW (i.e. undermagnified and D.eff more like 11 inches) and 8 mm Ethos: "M57 at the low power is a round, slightly turquoise ring (without a filter). At the high power without a filter, the appearance of a ring with smeared-out W and E edges is observed. The color is not pronounced."

Now about the interior streamers. I saw at least, the long, medial edge of the more central one for the first time with our club's F/5 Obsession under its rural sky with my 13 mm Ethos and no filter, during the same observation in good seeing when I first saw the central star. I need to record them (or it - the edge), but, again, in my mind's eye this is what I have since seen with my transportable 20 from remote sites as well. We did tend to have unusually good seeing when I was out with it last year.

"Central stars": the NW star was clearly seen during the mentioned observation with the F/5 20 and in the position of the SW star was a compact enhancement of the nebulosity (my personal term for it was a "globule") but I could not see it as anything more definitely stellar (~250x, good seeing, rural sky).

Halo: still need to look for it! Or just "at" it, as it may be. Thanks for the reminder.

[Ivan Maly]

Looked at it last night under good conditions except turbulence (SQM 21.8, seeing 5/10, altitude 55 deg) with my 20-inch. No halo, unsurprisingly no central star(s), but the edge crossing the interior diametrically was plain (360x).

[Bruce Sokol]

About 6 or 8 years ago at RTMC I viewed M57 with a 28" f/4.3 under good seeing at I'm guessing about 150x to 200x. It looked green to my 60 + year old eye. It was a quick look, the line for the scope was long.

I has helping a friend set up his Servo Cat on his 20" Obsession one summer night, and we used M57 to test the tracking . WE kept increasing the power up to about 2,000x, the seeing was that good in San Diego that night. We saw the two central stars with no problem.

In 2012 on a night with excellent seeing in the Anza Borrego Desert with my 18" Obsession at 1,000x the central star was just staring at me! Also visible was the dark pillars of nebulosity shown in the Hubble photo above.

[Raul Leon]

Hi,
When I observe M 57 I mostly see a very washed out green, but as I've gotten older I hardly see that anymore. 3562

[Uwe Glahn]

Hi Howard,

some words around M 57.

Color:
For me always difficult to detect colors. Last nights I tried to re-observe the nebula with bigger EP of my 27-inch and can confirm what you said about the nebula. No noticeable color but a thin "warm" or "reddish" tone at the very edge. The nebula itself was somewhat beige to turquoise for me. All in all very difficult.

Central Stars:
In the past I was able to see the second CS with my 16-inch under perfect seeing conditions. Interestingly I documented a third faint condensation within the SW edge of the PN which I recorded as similar difficult as the second CS. Later comparison showed, that this was a third star.
3563
sketch: 16", 720x, NELM 7m0+, Seeing I-II
With an 21-inch I also documented a popping second CS.

Halo:
I was searching after the Halo a long time and finally catches the faintest parts with my former 16-inch. But it was always a fight and the appearance through a large telescope is totally different.
3564
sketch: 16", 180x, UHC, NELM 7m0+, Seeing III
For me the Halo is nearly invisible without a filter. UHC or better [OIII] brings out the outer halo much better. Let us not forget that we saw a different halo through an [OIII] as the most H-alpha photographs. I pictured an [OIII] halo in my project (still in work) at the very beginning. [link to halo project] (http://www.deepsky-visuell.de/Projekte/Halo.htm)
Interestingly the filamentous structures at the end of the bright shell is also very prominent and not more difficult as the halo itself.
Best "halo moment" was the view through Barbarella 2013. OMG, after years of fighting (and mostly losing) against the halo, the outer parts were direct vision, what a view...thanks Jimi, I never forget THIS.

Interior nebulous structure
Difficult structures indeed. I've been always careful because the brain often brings longish lines between the long axle of structures. Yes, I saw them too, but no, I'm not sure if these structures I saw were real. But I stayed tuned in this topic.

[Ivan Maly]

Thanks, Uwe - now with OIII at 150x I was able to see the what you call filamentous structure outside the bright shell (20", SQM 21.5, seeing 5/10). Higher magnification did not improve the view. This is the interior blue structure in the first and the green structure in the second image in Howard's post. I think I had seen it before, but it was well forgotten.

[Howard B]

I was at the Golden State Star Party (GSSP) for five nights, and not only enjoyed five mostly clear nights but also the first light of the new spray silver coating on my 28-inch mirror.

The new coating performed exactly as I expected - wonderfully - and I was able to make some lifetime observations. I finally saw, unequivocally, color in the Ring Nebula. The new coating helped a great deal, but what made the observations so distinct was flashing my observing eye with white light for a couple of seconds before looking in the eyepiece.

I saw the main ring as an unsaturated but distinct green-blue turquoise with a thin orange perimeter. I couldn't tell if the interior of the ring had any color but I could see that along the interior major axis edges that the background was much darker than the rest of the interior. Pretty awesome really. Low power showed all this best.

I tried the same thing on the Dumbbell Nebula with much the same result - the bright parts of the Dumbbell had an unsaturated but distinct green-blue turquoise with a thin orange perimeter at the outer edges of the major axis of the nebula - it was exquisitely beautiful. And finally, the Lagoon Nebula finally had a definite red-ish hue.

Evidently, briefly flashing your observing eye with white light reactivates the color sensing cones in your eye after it's become dark adapted. I discovered that my right eye is slightly more sensitive to color, which is interesting because my left eye is more sensitive for seeing faint objects. Perhaps this helped me I gravitate toward observing the bright planets and the moon with my right eye years ago.