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M57 central star?

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#1 2orthern2ights

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Posted 13 October 2013 - 01:21 PM

:question: Does anyone have a picture that points out the central star in the ring. I've read alot about people seeing it on the web but no where can I find directions on how to locate it. The general concensus on the star that is brighter in the center of the ring is that; that is not the star, but a star closer to us in a chance alignment to appear as if it was the central star. Where could the real central star be?

I have read all the pages about amature observations and seeing requirements, etc, etc,. But, at the moment, I can't find it because I have no idea where it is... Quite honestly I'm not gonna hold my breath. It is soo close to the limiting magnitude of my 14" that I doubt I would notice it. Never mind that it is set against a glowing nebula. But a photo should show it. Is it not in this photo?

http://imgsrc.hubble...-13-a-print.jpg

Im assuming that the central star, for the majority of people that peer through a telescope eyepiece, is the bright star in the center of the ring. This summer an amature astronomer, at my 14" telescope, said he witnessed the central star. To his defence, it appears dead center of the ring, it's pretty dim, nowhere can you find somthing to say otherwise... I guess I have seen it too. *reaches for belt notching tool* :grin:

#2 SUN RA KAT

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Posted 13 October 2013 - 02:34 PM

20 second exposure a few nights ago with my C14 with a Lumicon Giant EZ Guider with reducer lens and Nikon D800 @ ISO 1600. System should be around F7. Unguided.

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#3 brentwood

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Posted 13 October 2013 - 03:04 PM

If it makes you feel better, I have looked at the Ring with a 72" (yes really) for 10-15 secs, and could NOT see the central star!

#4 northernontario

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Posted 13 October 2013 - 03:07 PM

I too, with my 16 inch from a reasonably dark yard, have never seen it either.

But

The rest of sure does look nice.

Were you able to see any color with the 72 inch Brentwood?

jake

#5 brianb11213

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Posted 13 October 2013 - 04:00 PM

If it makes you feel better, I have looked at the Ring with a 72" (yes really) for 10-15 secs, and could NOT see the central star!

To see really faint objects requires (a) a MINIMUM of AT LEAST ONE HOUR's dark adaptation in a completely dark environment, (b) experience of how to use averted vision effectively, © object near the zenith in a dark, transparent sky, (d) a magnification of about 20x per inch of aperture to dilute the sky background and (e) seeing sufficiently steady to support that magnification.

Given most of that I've been able to see stars down to mag. 16.2 with my 11" SCT - but if I looked for 10 sec only I don't think I'd get within a magnitude of that. It takes ~10 minutes observing to get sufficient intermittent glimpses with averted vision to spot an object at the limit of vision.

So the central star of M57 catalogued at mag. 14.7 should be an easy object for me, right? No, it isn't. The "bright" background of the nebula makes it very difficult indeed ... perhaps more magnification might help ... I find the mag. 13 star just outside the ring to be really easy with 11" and can see it fairly easily with 4.3". My suspicion is that the magnitude of the central star is catalogued incorrectly.

#6 azure1961p

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Posted 13 October 2013 - 05:53 PM

I agree with Brian though a lot of folks who've found success tend to seem to go around 40x per inch. I'm not in that camp Ive still not seen it. I will say too, 10-15 seconds isn't nearly long enough for a threshold magnitude. On the faintest things Ive blown a whole half hour to confirm a sighting. If I had the ten second rule - I'd probably lose a full magnitude off my best effort.

By the way the central star - is - well - in the center. Really.
Pete

#7 pstarr

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Posted 13 October 2013 - 05:58 PM

Here is a magnitude chart of surrounding stars. If you can't see some of these, you won't see the center star.

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#8 brentwood

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Posted 13 October 2013 - 06:32 PM

When I looked through the 72" (DAO, Victoria BC) I was dark adapted as much as I would have been at home. I am also familiar with using averted vision. I think it as others have said, 10-15 seconds is simply not enough time. When you are in a long line of people, most of whom look for 2-3 seconds, and say, "That's nice", that was about as long as I dared!
BTW, as I would never ask "What magnification is this", the Ring itself was about as big as an oval made with your fingers in front of your face!

#9 jgraham

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Posted 13 October 2013 - 06:38 PM

There was a long discussion of this in the deep sky observing forum. My take-away was that this is not easy. I have tried many times to glimpse the central star with my 16" and 16.5" scopes and at best I can say possibly maybe, but not for sure. Interestingly, my impression is that it is the nebula obscuring the star that makes it tough. If nothing else, it is a fun challenge.

#10 azure1961p

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Posted 13 October 2013 - 06:52 PM

Folks who've seen it weigh big on the need to have great seeing - no doubt the reason the 72" didn't budge. Had the diffraction pattern been defined itd been easy as pie. But such is the smearing effect .

Pete

#11 kfiscus

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Posted 13 October 2013 - 07:46 PM

My observing buddy and I have seen it several times with our Z12s. The seeing has to be very good and you have to use very high magnifications. We never try unless Lyra is near the meridian. This is made much easier with an EQ platform.

#12 Feidb

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Posted 13 October 2013 - 09:02 PM

The central star is an extreme challenge for most nights and apertures. The problem is not only the very dim magnitude (15.7), but the lack of contrast against the brightness of the nebula.

I've seen it twice, once with my home-built 16-inch f/6.4 in the mid-90's and once with my 16-inch f/4.5 commercial scope a few years ago. The conditions were pristine and I caught it just right. It took 300+ magnification both tries. The transparency and seeing were superb.

The thing is that there are some people with super eyes and perfect conditions (both optical and weather) that have caught it in as small as 8-inch scopes, or so I've heard. Yet as one of you pointed out, it can be invisible in a 72-inch.

Dimness and contrast against the nebula. Tough to almost holy grail. The visual mag. of 15.7 which is theoretically beyond the reach of an 8-inch scope? I can't say. I've heard of someone with a 12-inch that sees it quite often.

#13 2orthern2ights

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Posted 14 October 2013 - 12:17 AM

ok... thanks a lot to everyone for weighing in on this one. We still got a problem. No map to the whereabouts of this terrestrial sized 15th magnitude white dwarf that shines in uv and blue. Tomorrow when I get back home I'll look into this. If you got time to look into this that'd be awsome. There are still mysteries in one of the most popular objects on anyones list! Amazing!

#14 Illinois

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Posted 14 October 2013 - 07:35 AM

I looked at M57 many times on my 16 inch dobsonian and I never see a central star. Maybe very crystal clear and very dark sky at high power!

#15 Achernar

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Posted 14 October 2013 - 01:00 PM

I have never seen it, even through my 15-inch because the seeing in general is just not good enough for that. A faint star embedded in nebulosity is a tough nut to crack, I have noted how poor seeing hides the central stars of the planetary nebulae NGC-7662, NGC-6543 and NGC-7009 whereas during good seeing I can see them without too much trouble with my 10-inch. I have tried magnifications as high as 572X on the Ring Nebula without success looking for its central star.

Taras

#16 payner

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Posted 14 October 2013 - 01:48 PM

I have seen the central star through my C-14 (has since gone to a new home :(). Seeing was excellent on those times of viewing it, near a 5/5. Unforgettable once you see it.
Best,
Randy

#17 hbanich

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Posted 14 October 2013 - 02:58 PM

ok... thanks a lot to everyone for weighing in on this one. We still got a problem. No map to the whereabouts of this terrestrial sized 15th magnitude white dwarf that shines in uv and blue. Tomorrow when I get back home I'll look into this. If you got time to look into this that'd be awsome. There are still mysteries in one of the most popular objects on anyones list! Amazing!


The central star really is the one in the middle -

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#18 dpwoos

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Posted 14 October 2013 - 08:46 PM

I am skeptical of most claims. The only reported observation that I 100% accept is by my older son, who observed it in a 60" scope on Mt. Lemmon. He says that it was not super easy to see. Of course, my skepticism doesn't make other claimed sightings false, and everybody decides for themselves who and what to accept, and with what degree of certainty. I do know that it is very easy to see what you want to see, especially if you know the exact location of the target.

#19 kfiscus

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Posted 14 October 2013 - 09:47 PM

To twist your words (but hopefully not your tail) I wanted to see it and it wasn't easy. It took the convergence of very good seeing, a collimated and cooled 12", smooth tracking, and high magnification. The star would show itself for 1/2 a second or so. The central star was easier while out at the Nebraska Star Party and its DARK skies.

#20 David Knisely

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Posted 15 October 2013 - 01:23 AM

brianb11213 wrote:

So the central star of M57 catalogued at mag. 14.7 should be an easy object for me, right? No, it isn't. The "bright" background of the nebula makes it very difficult indeed ... perhaps more magnification might help ... I find the mag. 13 star just outside the ring to be really easy with 11" and can see it fairly easily with 4.3". My suspicion is that the magnitude of the central star is catalogued incorrectly.


According to Brian Skiff of Lowell Observatory, with professional photometry of the central star, all published photometric measurements report the central star's visual magnitude at about 15.0 or perhaps one to three tenths fainter, and with no demonstrated evidence of variability. The smallest telescope I have managed to see the central star in is a 9.25 inch SCT (480x), which was also just barely showing stars down to 15.3 in the area around M57. This would tend to support the figure of magnitude 15 for the central star. Clear skies to you.

#21 David Knisely

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Posted 15 October 2013 - 02:00 AM

I am skeptical of most claims. The only reported observation that I 100% accept is by my older son, who observed it in a 60" scope on Mt. Lemmon. He says that it was not super easy to see. Of course, my skepticism doesn't make other claimed sightings false, and everybody decides for themselves who and what to accept, and with what degree of certainty. I do know that it is very easy to see what you want to see, especially if you know the exact location of the target.


I can understand your skepticism, but I no longer have nearly as much with reports of this elusive object. There is indeed something of an "illusion" caused by the glowing interior of M57 that, at lower powers, can make one seem to see a faint star-like point in the middle of the ring that may not really be there. I recall my first view of M57 in Behlen Observatory's 30 inch Classical Cassegrain (Univ. of Nebraska, Lincoln) at a public night around 1975, and the central star was nowhere to be seen. I asked my professor Dr. Don Taylor about it at the time. He said that he had never seen the star even in Steward Observatory's 90 inch at Kitt Peak, so I flatly passed it off as impossible in amateur telescope. Indeed, at our local star parties, it became something of a joke among us when sighting claims for the star popped-up.

However, a number of years later, I learned just how wrong I was. We were at one of our club's regular star parties south of Lincoln under dark skies when one of our members called out to me to have a look at M57's central star in his 20 inch Obsession. I said to myself, "Yea, right", but then went over to the 20 inch scope and took a look in. At something over 400x, right dead-center in the middle of the ring, THERE WAS THE CENTRAL STAR!! It was OBVIOUS and visible with DIRECT vision. Then, something incredible happened: IT ABRUPTLY VANISHED! It almost seemed to have turned-off as quickly as if someone had turned it off with a light switch. Then, as quickly as it had vanished, it abruptly reappeared right where it had been before. As I watched, it gradually faded, quickly brightened, and then quickly faded out completely, and by that time, I knew exactly what was happening. The seeing was blurring the star's tiny diffraction disk, causing it to enlarge and eventually completely blend-in to the glowing nebular background in the interior of the ring. At times, it would almost blink on and off, while at other times, it wasn't visible at all no matter how hard I tried.

To see the central star, one has to watch the nebula at rather high magnification (well over 300x) to reduce the apparent surface brightness of the interior of the ring, while at the same time, watching for an extended period of time to catch moments of really good stable seeing. Once I understood this, I went back to my 10 inch Newtonian, cranked up the power to around 440x and waited. Sure enough, every once in a while, the faint central star would "pop" on and off as if some giant alien was playing with its power switch. It was quite faint (around 15.0) but it was there. Some nights, the seeing never gets good enough to see the central star at all no matter how big the telescope is, so it is no wonder that some with very large scopes often never see it. While a larger aperture helps, I have seen the central star (barely) in a 9.25 inch aperture SCT (from my magnitude 5.6 driveway no less), so it *is* at least possible in moderate amateur telescopes. A couple of weeks ago, I had it in my 14 inch and it was only visible for a few seconds at a time before it vanished once again, often for a number of minutes.

Again, the keys to viewing M57's central star are:

1. modestly dark skies (and good dark adaptation).
2. apertures larger than eight inches.
3. very high power (well over 300x).
4. very stable seeing.
5. watch for an extended period of time.


It is OK to be somewhat skeptical sometimes, but in this case, the truth of the matter is, the central star of M57 can indeed be seen in amateur telescopes. Clear skies to you.

#22 David Knisely

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Posted 15 October 2013 - 02:05 AM

Here is a magnitude chart of surrounding stars. If you can't see some of these, you won't see the center star.


Uh, that's MY chart BTW.... (prepared from a DSS image I processed with photometry provided by Brian Skiff of Lowell plus other sources).

#23 brianb11213

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Posted 15 October 2013 - 03:10 AM

Excellent post, David!

Again, the keys to viewing M57's central star are:

1. modestly dark skies (and good dark adaptation).
2. apertures larger than eight inches.
3. very high power (well over 300x).
4. very stable seeing.
5. watch for an extended period of time.


Points 1, 2 & 4: no dispute.
Point 3: I'm skeptical of the need for more than 20x per inch of aperture. It's at about this point that the diffraction disc of a point object (star) starts to become extended and there is no further gain in contrast between star & background by going higher. Smearing out the star tends to reduce its visibility in the same way that poor seeing does.

5. I'm glad you mentioned this. I've long since learned that it takes 10 - 15 minutes concentrated effort to be sure of the visibility or otherwise of objects very close to the limit. When seen, they're always seen as glimpses only, even with skilled use of averted vision. (This is also the case when the seeing is "perfectly steady" as is sometimes the case when observing with small scopes.) I think it is because it takes several photons arriving at the same site within a short period of time (~0.1 sec) to generate a signal which the brain can interpret as a glimpsed star. As the star brightness decreases, the average arrival time between the photons increases to the point where the star is not seen steadily ... but the photon arrival is a Poisson process, so that there are occasions when enough photons arrive in a burst to allow an instantaneous glimpse.

At this level a single glimpse isn't enough, you have to look carefully to allow several glimpses all from the same point to be registered before you can be "sure" that the object is seen.

At the limit (i.e. for me to see a mag. 16.2 star at the zenith in good sky conditions with my 11" SCT) this process takes 10-15 minutes.

It is OK to be somewhat skeptical sometimes, but in this case, the truth of the matter is, the central star of M57 can indeed be seen in amateur telescopes.

Indeed. I have seen it with my 11" SCT. But it's an extremely difficult object, in the way that a "normal" mag. 15 star shouldn't be.

#24 Achernar

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Posted 15 October 2013 - 08:14 AM

Interesting how it popped into and out of view, I will try watching M-57 for an extended period to see if it becomes visible that way.

Taras

#25 JimMo

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Posted 15 October 2013 - 11:47 AM

I will try watching M-57 for an extended period to see if it becomes visible that way.

Taras


I've done this many times when it is tracking near the zenith and I've only seen it once in my 14.5" dob under high mag and great seeing from a green zone. It did pop into and out of view and patience was needed because it was mostly out.






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