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Cosmic Challenge: Ring Nebula Central Star and Galaxy IC 1296
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Cosmic Challenge: Ring Nebula Central Star and Galaxy IC 1296
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Target |
Type |
RA |
DEC |
Const |
Mag |
Size |
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IC 1296 |
Galaxy |
18h |
+33° |
Lyra |
14.3 |
0.9'x0.5' |
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M57 central star |
Central
star in |
18h |
+33° |
Lyra |
15.2 |
n/a |
As we say
goodbye to summer and get ready to welcome in autumn, I thought I would offer
not one, but two challenges this month to bridge the seasonal change. Both
appear right next to each other in our sky but are millions of light years
apart. And both require all the aperture you can throw at them to be seen.
One of the classic challenges facing deep-sky observers at this time of year is
spotting the Ring Nebula’s central star, the progenitor sun
that started it all some 6,000 to 8,000 years ago. Seeing the Ring's central
star is one of those tests that every visual amateur needs to take at one point
or another.
Looking through observing handbooks, reading on-line deep-sky logs, speaking
with friends and colleagues who I consider to be seasoned veterans, and my own
personal experience all seem to show that spotting the central star takes
nothing short of "the perfect storm." Unless everything comes
together just right, the star will remain hidden from view.
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Above: Summer star map showing the location of this month's Cosmic Challenge.
Credit: Map adapted from Star Watch by Phil Harrington
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Above: Finder chart for this month's Cosmic Challenge.
Credit: Chart adapted from Cosmic Challenge by Phil Harrington
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You might
be wondering what all the fuss is about. After all, the star is listed as 15th
magnitude, which is dim, but within the grasp of 15-inch (38cm) telescopes,
perhaps even less under dark, transparent skies. So then, why is the central
star so difficult through even the largest backyard scopes?
Here’s an interesting observation that I
have noticed time and again when trying to see the central star. Seeing the
star requires transparent skies, but not necessarily dark skies. Many amateurs
equate one with the other, that dark skies are transparent skies, and vice
versa. Not so.
From a stargazer's perspective, sky conditions can be divided into three
categories: transparency, seeing, and sky darkness. "Transparency"
refers to how clear the sky is, while "seeing" refers to the
steadiness of the air mass overhead. Clouds, haze, humidity, and artificial and
natural air pollutants all adversely affect both in different ways. Finally,
"sky darkness" speaks to the ambient level of background light. Light
pollution raises this level. People often confuse the terms transparency and
sky darkness. It is certainly possible to have a city sky that is more
transparent than a rural sky, but because of the lower level of sky darkness
(due to urban light pollution), fainter stars will still be visible from the
country site, even with its poorer transparency.
But to the topic here, I have seen the central star on several occasions
through my 18-inch (46cm) reflector from my naked-eye limiting magnitude 5
suburban backyard, but have missed it entirely on many other occasions using
the same equipment from markedly darker sites. Why? Those other sites were
darker (i.e., less light pollution), but the sky was not as transparent. That
increased level of haze lowered the contrast between the star and the
surrounding nebulosity just enough to mask the star.
That brings us to the second ingredient to seeing the star: seeing. Without
steady seeing conditions, atmospheric turbulence will blur the star just enough
to blend its already low-contrast glow into the Ring's donut hole. Without both
conditions -- exceptional seeing and transparency -- the central star will
evade even the most careful search. But it still takes more than these. Your
telescope's optics must be clean, as well. Any contamination, notably skin oils
on the eyepiece's eye lens, will be enough to lose the star.
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Above: M57's central star and galaxy IC 1296 as sketched through the author's 18-inch (46cm) reflector. South is up in this portrayal.
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Take a look at this amazing image of M57 and IC 1296 posted by CN member tolgagumus in the CCD/CMOS Astro Camera Imaging & Processing forum back in September 2018. It's the culmination of almost 30 hours of data collection taken with a Planewave 14-inch (36cm) CDK modified Dall-Kircham scope and a Finger Lakes Instrumentation MLx694 CCD imager at DSW Remote Observatories in Rowe, New Mexico. You can read more details about the image by following the link back to the forum.
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Above: M57 and IC 1296. Credit: CN member tolgagumus, http://tolgaastro.com/
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A faint, far-off barred spiral galaxy floats in the same field as you try to eye the Ring's central star. Can you also spot IC 1296? It is a tougher task than its 14th-magnitude rating would imply. That's because, as we have seen so often before, the galaxy's surface brightness skews the integrated magnitude. In 15-inch-plus (38cm+) telescopes, 14th-magnitude galaxies are fairly routine. That's assuming their light is concentrated evenly across their disk. In the case of IC 1296, the central hub of the galaxy is nearly stellar in appearance, while its broad spiral arms are unusually faint.
Back in
August 2013, a Type-II supernova, SN2013ev, appeared in IC 1296. Even though it
barely cracked 16th magnitude, it was actually easier to spot than its home
galaxy because its feeble light was concentrated into a point source.
IC 1296 is just 4' northwest of M57, near a diamond of four 11th- to
14th-magnitude stars, as shown in the accompanying sketch and image. More
specifically, it is positioned 20" southeast of the star at the diamond's
northern facet. Proper magnification, in addition to dark skies and properly
collimated optics, are key to spotting its dim glow.
I can probably count on one hand the number of times in the past half-dozen
years when I have seen both of these challenges through my 18-inch (46cm) scope
from my suburban backyard observatory. Summer haze, air turbulence, and light
pollution quickly extinguish both. But on those rare evenings when the humidity
is low, the seeing is calm, and the Ring is high in the sky, the elusive
central star and its tiny galactic companion shine through. Indeed, under
superior skies, telescopes as small as 10 inches (25cm) have shown both, so be
sure to give it a go.
Have a favorite challenge object of your own? I'd love to hear about it, as
well as how you did with this month's test. Contact me through my web site or post to this
month's discussion forum.
Until next month, remember that half of the fun is the thrill of the chase.
Game on!
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About
the Author: |
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Phil Harrington's Cosmic Challenge is copyright 2020 by Philip S. Harrington. All rights reserved. No reproduction, in whole or in part, beyond single copies for use by an individual, is permitted without written permission of the copyright holder. |
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15 Comments
I once viewed the Ring, on a moonless night, through the Great Lick Refractor, a 36" doublet. Even with the huge aperture and knowing what I was trying to see the central star eluded me and the two fellow astronomers I was with at the time.
IMO, with most amateur kits, visually see seeing the central star is not going to happen.
I viewed this little gem from a dark sky site (B3) in June with my C9.25. My notes from that nights session:
"Rapidly becoming one of my favorites. In the 40mm it's just a little ring, but is clearly a star that has blown off it's hydrogen layer. Nice view in the 25mm, but degrades with the 13.8. Neither eyepiece would reveal the central star."
And believe me, I looked for it!
I guess this item has popped up yet again when talking about the potentially "difficult". The Central Star of M57 is visible in instruments *smaller* than 15 to 18 inches, but it requires certain conditions be met (and not necessarily the darkest skies are needed). The star itself is around magnitude 15.2, which, under outstanding conditions might be reachable in an eight inch scope (although with many things astronomical, the larger the aperture, the better). The smallest aperture I have seen the central star in was my 9.25 inch SCT, although it was pretty marginal in that instrument. I recall my first serious attempt to see the central star in a truly large scope when I was an undergraduate at the University of Nebraska using their 30 inch Classical Cassegrain at Behlen Observatory near Mead, Nebraska. I had previously failed to see it in 10 and 12.5 inch scopes during some of our club star parties over the years, so I thought that the 30 inch should do the trick, if seeing the darn thing was possible at all. When I got my turn at the big scope, I didn't see the star, and mentioned it aloud in the dome to Dr. Don Taylor, who was running the scope at the time. Taylor stated bluntly that he hadn't even seen it in the 90 inch at Steward Observatory on Kitt Peak! From that point on, I considered the star a virtual impossibility in any amateur instrument. Claims made by smaller apertures I also considered "illusions" caused by the glowing interior of the Ring, which at low power can induce a sort of "false" central star effect (one reason I discount observations of the star at powers much under 300x).
However, years later, I was proven quite wrong one evening at our club observing site (Zenith Limiting Magnitude 6.6 or so). One of our new members had moved up from Texas, and had a new 20 inch f/5 Obsession. He mentioned about having the central star in his scope, so like a skeptic, I went up the ladder to take a look in and disprove what he was claiming. He was running some ridiculous power well over 400x, but what I saw just stunned me and also quickly solved the mystery. The central star was quite prominently visible with direct vision for a number of seconds, but suddenly, it winked out, as if someone had just shut the darn thing off with a switch! Then, a few moments later, it reappeared at its full brightness just as suddenly as it had vanished. It kept up this perplexing "flashing" behavior for a while until I noticed that the diffraction disk of the 13th magnitude star east of the Ring got bigger and more diffuse when the star was not visible, but shrunk down to its tiny disk when the star popped out. I also saw it in a nearby Sky Designs 17.5 inch, and the central star behaved in exactly the same way. It was not visible at powers much under 300x, but once the power got high enough, it was not all that difficult. The higher magnification may serve to help reduce the effects of the glowing center, but if the seeing is less than perfect, the star's diffraction disk will blur to a point where it completely blends into the glowing background nebulosity. If seeing is not first rate or the power isn't high enough, you will *never* see the central star in ANY aperture. You also have to often watch for quite a while and wait for those brief moments when the seeing settles down enough to make the star visible. Once I understood that, after a number of tries, I succeeded in sighting the star in my 10 inch f/5.6 Newtonian, although again, often it appears faintly only for a few brief moment before vanishing. One night, I had been working double stars from my mildly light polluted (ZLM 5.4) driveway in my town of 12,800, and was using my 9.25 inch SCT at some pretty high powers (my 5-8mm Speers Waler at the 5mm setting, or about 470x) I had forgotten to replace that eyepiece with a lower power one and just commanded the NexStar 9.25 to go to M57 just for a final look at the end of the observing session. Once the slew was completed, I took a look in and was astounded. There, right in the middle of the ring was the faint glimmer of the central star, just shining there steadily with averted vision. After a couple of seconds, the "star" must have sensed I was looking at it and it must have said to itself, "I have been SEEN!", whereupon, it promptly vanished :-). I watched for quite a while after that, and once or twice, I saw it come on and then almost instantly go out, but it was never visible for much more than half a second or so. Again, observing at high power (more than 300x) and observing the nebula for and extended period of time to catch those moments when the seeing becomes really stable are the keys to success in viewing M57's central star.
As for IC 1296, the first time I saw it was at the Nebraska Star Party in Dave Hamilton's 12 inch Portaball, but all I can get of it in my 10 inch Newtonian is just a hint of a fuzzy patch. In a 24 inch Obsession however, it was full of faint but easily visible spiral structure at high power. Clear skies to you.
Phil,
Great challenge for folks to try.
I can confirm what David said above. I looked for the central star with my C14 at 261x under good seeing conditions and transparency and with M57 almost at the zenith and could not detect the central star. The Ring Nebula looked like this:
https://www.cloudyni...0-m57-20100831/
Three nights later, with the same scope and conditions but using 391x, this time I detected the central star:
https://www.cloudyni...1-m57-20100902/
I didn't know to look for IC 1296 but I will next time! Thanks, Phil.
I have seen it pretty definitively with my C9.25.
Conditions were excellent transparency (No Saharan Dust). While my location is bortle 6, to my west is very dark skies.
It was during rainy season so the seeing was particularly excellent. The central star was very apparent. I had to use averted vision at times. No luck with the galaxy on visual.
I have seen the central star a couple of times with my 15-inch Dob, and even a 10-inch Dob once under skies that were hardly ideal thanks to light pollution and the haze that hangs over the Gulf Coast. However, the seeing became very steady, and when it's gets very steady, the star became remarkably easy to see when the magnification's high enough. When it declined, the star vanished as though it never was there. I have looked for IC-1296, and only suspected that I spotted it once.
Taras
I confess to never having seen it in any of my scopes, which top out at 12.5", but I've not tried with really high magnification under good seeing. Where I live, in Northwestern Pennsylvania, we're so often under the jet stream. I've always been intrigued that Walter Scott Houston wrote that the 12" Porter Turret telescope at Stellafane often showed it when larger scopes failed.
I'm heading up to Cherry Springs State Park in Pennsylvania on 9/11 and staying until 9/20. Maybe one of those nights will cooperate.
I've seen the central star many times in my 18" Obsession at 350x or more, and believe good seeing is more important than transparency or a dark sky. It goes without saying that observing it when its near the meridian will help.
When you can see the 16th magnitude star just west of the ring nebula at 300x or more you have a chance to see the central star. Most of the time you'll get few pops for a split second, its like its winking at you.
On the nights when the seeing gets really good I've used 1,000x, and the central star becomes visible with direct vision for several seconds.
Once when helping my friend set up his servo-cat drive on his 20" Obsession in his back yard in the city, (Bortle 7 zone) we wanted to test his drive with high power.
M57 was high overhead, the transparency was average, but the seeing that night was extraordinary. I used my TV 3-6mm zoom and at 3mm, (846x) the central star was visible. My friend wanted to test the drive at extreme power, so I used my TV Big Barlow and an extension tube between the barlow and the 3-6 zoom for a power of around 2,100x.
I almost fell off the ladder, there were two stars visible, the central star and a slightly fainter star nearby. Both stars were visible 100% of the time with direct vision, it was an amazing site I'll never forget.
IC 1296 is a good visual challenge being easy to locate but hard to detect. I've gotten it with an 8" reflector under Bortle Class 4 skies that was flocked to maximize contrast. Everything had to come together--clean mirror, clean eyepieces, good transparency, dark sky and I used an observing hood.
Best reserved for larger apertures, yes, but it was one of those "not that I SHOULD, but wondering if I COULD" kind of deals on the nights I went for it.
Clear Skies,
Phil
Phil,
Just thinking about your points on transparency and sky brightness.
Some years ago I did some reading and research on "Concurrent Photon Amplification" in silver halide photography. See: https://apps.dtic.mi...s/ADA151831.pdf . I am wondering if the eye works similarly (though non-integrating!), Do all the photons need to come from the star? Can some from background sky brightness boost the total sufficiently to allow the star to be seen?
You succeeded where I failed with a telescope with almost twice the aperture, and thus seeing IC-1296 with an 8-inch is a real accomplishment.
Taras
https://www.astrobin...f22blj/?nc=user
Hi, Phil! I especially appreciate your insight regrading transparency and seeing. I would detect the star with my superb Cave Astrola 12.5" rarely, 17.5" Coulter occasionally, 29" Coulter frequently, and 36" New Moon/Fullum regularly. With the giant apertures, it's ~the other star~ that is possible but terribly difficult. I made a sketch of that when I first noticed the 2nd one at the 29". I did the observation "in the blind" to see if my clocking of that relative to the central one and field stars was in the right place... which it is! One of the very 1st things I did with the 36" first light was the central star. Conditions were ok and I could see it ok. Transparency is the key... very good!
I guess there would then be six factors?
>transparency (sky and scope coatings and cleanliness)
>seeing (sky and scope thermals and wavefront)
>darkness (sky and scope baffling/blackening)
>aperture
>experience
>health (eyes, etc. etc.) Tom
I've seen M57's central star on a few occasions through large apertures working at high magnifications. I can't remember what the smallest aperture has been.
Great article, Phil!
Though I have no hope of eye-balling The Ring's central star here on the ever-turbulent Texas Gulf Coast, I do agree that 'seeing' is really the determining factor in what sort of object detail can be viewed. I've owned several scopes ranging from 2.5" to 10" in aperture, and though I've tried on many occasions, I never could really see the GRS on Jupiter. Recently, however, a day or two after our first cool-front, I finally spotted the GRS using a 5.5mm eyepiece on my 80mm APO refractor. The combination gave me an 87x view. Not only could I see the GRS for the first time, I could see additional banding as well. Revealed to me was the fact that even with good seeing, high magnification is not 'key' to revealing object detail. In fact, for every increase in magnification, detail seemed to decrease accordingly.