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General Astronomy >> General Observing and Astronomy

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David Knisely
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Reged: 04/19/04

Loc: southeastern Nebraska
Re: M57 central star? new [Re: dpwoos]
      #6138285 - 10/15/13 03:00 AM

Quote:

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.


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David Knisely
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Reged: 04/19/04

Loc: southeastern Nebraska
Re: M57 central star? new [Re: pstarr]
      #6138290 - 10/15/13 03:05 AM

Quote:

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).


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brianb11213
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Reged: 02/25/09

Loc: 55.215N 6.554W
Re: M57 central star? new [Re: David Knisely]
      #6138328 - 10/15/13 04:10 AM

Excellent post, David!

Quote:

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.

Quote:

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.


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Achernar
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Reged: 02/25/06

Loc: Mobile, Alabama, USA
Re: M57 central star? new [Re: David Knisely]
      #6138601 - 10/15/13 09:14 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


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JimMo
I'd Rather Do It Myself


Reged: 01/08/07

Loc: Under the SE Michigan lightdom...
Re: M57 central star? new [Re: Achernar]
      #6138984 - 10/15/13 12:47 PM

Quote:

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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Dwight J
scholastic sledgehammer
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Reged: 05/14/09

Loc: Lethbridge, Alberta, Canada
Re: M57 central star? new [Re: David Knisely]
      #6139048 - 10/15/13 01:18 PM

Having the central star vanish is exactly what has happened the 3 X I have seen it (2X in a 13.1" & 1X in a 16"). About 20 seconds after seeing it the star winked out of our vision. Waiting 30 seconds to a minute and looking again had it reappear. Since it is a very tiny spark perhaps while concentrating on it I did not breath or did so in a shallow manner and the O2 level in my blood dropped. Stepping away recharged my oxygen level and I was able to see it again. My observing buddy had the same experience. I know that I did spot it as when I saw it I stepped away from the scope so my buddy could have a look and he exclaimed "I see the central star!" This happened on two of the three occasions. Seeing may br a function of the atmospheric seeing as it is very very small. It was also directly overhead and we were at dark sky sites ranging from 3000 - 4400 ft elevation. Seeing the central star is certainly a rare event as I must have looked at M57 over a thousand times. Some say the star is variable in brightness and this may play a role in it's visibility.

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Bill Weir
Carpal Tunnel
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Reged: 06/01/04

Loc: Metchosin (Victoria), Canada
Re: M57 central star? new [Re: brentwood]
      #6139135 - 10/15/13 01:58 PM

Quote:

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!




So how long ago was that? There hasn't been an eyepiece on the Plaskett in decades.

I'm not surprised you didn't see the CS because almost more than anything seeing the CS of M57 depends on seeing. Despite the often good seeing experienced on Observatory Hill if you were looking though that scope on a Saturday evening public night with many people in the dome there was probably an amazing heat plume rising through the slit. The pinpoint of the white dwarf can't be spead out due to poor seeing or it becomes diffused into the background brightness. This is why patience and tracking help so much in catching these fleeting glimpses. I also wonder as to the quality of the figure and roughness of surface to that almost 100 yr old mirror. I've imaged with it and seen the images done by others. The stars alway have a fair deal of bloat to them.

Actually fairly regularly I will see the CS in M57 with my 20" if I take the time to observe it and then it will flicker in and out. Even with my 12.5" I've seen it on more than a few occasions with the often good seeing experience here at the southern tip of the island and from the top of Mt Kobau. I consider looking for the CS in M57 similar to planetary observing. You are waiting for those moments within the regular seeing where the pockets of good seeing pass by and the detail shows through.

Bill


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David Knisely
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Reged: 04/19/04

Loc: southeastern Nebraska
Re: M57 central star? new [Re: Dwight J]
      #6139190 - 10/15/13 02:27 PM

DwightJ wrote:

Quote:

Some say the star is variable in brightness and this may play a role in it's visibility.




According to Brian Skiff of Lowell Observatory, professional photometry of the central star has given it a magnitude of about 15.0 with no evidence of any variability. Viewing the central star in M57 depends largely on the stability of the atmosphere, so if seeing isn't rock-solid, you won't see it no matter how big the telescope is. Clear skies to you.


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David Knisely
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Reged: 04/19/04

Loc: southeastern Nebraska
Re: M57 central star? new [Re: brianb11213]
      #6139212 - 10/15/13 02:40 PM

brian11213 wrote:

Quote:

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.




I performed experiments during good seeing, and the results were that unless the power is fairly high, the star remains invisible. In my 10 inch f/5.6 Newtonian, I was unable to see it if the power was less than 300x (I was at 288x when doing the experiment), and it was decidedly easier to pick up at powers above 350x. In fact, most of the time when trying for the star, I use from 384x to 471x even in my 14 inch. It just takes a bit more power to dim down the interior glow of the nebula and let the star stand out a bit more, especially considering the low resolution of the dark adapted human eye using averted vision. The consensus among most experienced deep-sky observers is that to see the central star, something over 300x is often necessary. Indeed, Brian Skiff has recommended something closer to 500x:

Photometry of M57 Field Stars

Clear skies to you.


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Dwight J
scholastic sledgehammer
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Reged: 05/14/09

Loc: Lethbridge, Alberta, Canada
Re: M57 central star? new [Re: David Knisely]
      #6139222 - 10/15/13 02:45 PM

Thanks David for clearing up that variability issue for me. That just leaves steady air as the requirement (as well as a scope large enough to see 15th mag stars) to see the CS of M57. That certainly explains why seeing it is rare for me as my area of the world is plagued by poor seeing.

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brentwood
Carpal Tunnel
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Reged: 11/04/05

Loc: BC Canada
Re: M57 central star? new [Re: Dwight J]
      #6139313 - 10/15/13 03:31 PM

"So how long ago was that? There hasn't been an eyepiece on the Plaskett in decades."
I think that it may have been before we moved to Victoria, so sometime before 1984. I am sure that was the time when the attending astronomer asked the audience if anyone in the audience knew where the various objects in the sky actually were so he could manually position the slit correctly!
For years, I simply wrote off my lack of a CS sighting to an idea that the scope was only transmitting a tiny portion of the aperture to the eyepiece for guiding purposes. It wasn't until we moved here and I had some of the astronomers as customers that I found out that this was not the case.
The next time we went, they had a camera in the eyepiece position and we viewed the image on a monitor. I remember that we were looking at M13 and I found that I was just tall enough to look through one of the old 5"? guidescope/finder that amazingly was not capped. To me this had a much better view! Soon we had a line up there!
Best viewing I ever had up on the hill was 10-12 years ago at a close Mars opposition, with the 48" through I think a coude focus. That was a real WOW! very steady seeing, and the disk was THIS big!


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payner
scholastic sledgehammer
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Reged: 03/22/07

Loc: Bluegrass Region, Kentucky
Re: M57 central star? new [Re: David Knisely]
      #6139504 - 10/15/13 05:38 PM

Quote:


I performed experiments during good seeing, and the results were that unless the power is fairly high, the star remains invisible. In my 10 inch f/5.6 Newtonian, I was unable to see it if the power was less than 300x (I was at 288x when doing the experiment), and it was decidedly easier to pick up at powers above 350x. In fact, most of the time when trying for the star, I use from 384x to 471x even in my 14 inch. It just takes a bit more power to dim down the interior glow of the nebula and let the star stand out a bit more, especially considering the low resolution of the dark adapted human eye using averted vision. The consensus among most experienced deep-sky observers is that to see the central star, something over 300x is often necessary. Indeed, Brian Skiff has recommended something closer to 500x:

Photometry of M57 Field Stars

Clear skies to you.




That's been my experience, high magnification with excellent seeing ... steady skies with no twinkling of the stars. The point made about it coming into and out of view has been my experience too. Having the planetary near the zenith and the necessary seeing conditions are uncommon for most of us and makes it an event that one doesn't forget.

Best,
Randy


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blb
Post Laureate


Reged: 11/25/05

Loc: Piedmont NC
Re: M57 central star? new [Re: David Knisely]
      #6139529 - 10/15/13 05:58 PM

Quote:

Quote:

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).



David, I found that photo to be such a help that I saved it for future use. Sorry I did not give you the credit. You certainly deserve a lot of credit for all the help you provide. To be honest, I had forgot whose photo it was after having it for a couple of years. Sorry but thanks.


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bremms
Carpal Tunnel
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Reged: 08/31/12

Loc: SC
Re: M57 central star? new [Re: blb]
      #6139559 - 10/15/13 06:16 PM

The central star is quite blue.. Integrated magnitude may be 14.6- 15.0. Visual it is 15.8-16.0 or even fainter. A good bit of the energy is in the far blue end of the spectrum as the surface temperature is about 100,000K. If you are a little older it might be more difficult. The spectral distribution makes it difficult. That being said, I saw it one time from a green Zone 30 years ago in a 16" F5 Cave. Seeing and transparency were very good that evening.
We used a 5mm Clave' and a Barlowed 10.5mm RGO (mine) about 400x. It was not visible under about 300x.

Edited by bremms (10/15/13 06:28 PM)


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Dave Mitsky
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Reged: 04/08/02

Loc: PA, USA, Planet Earth
Re: M57 central star? new [Re: bremms]
      #6139578 - 10/15/13 06:28 PM

I was able to hold M57's central star fairly steadily at high power through John Vogt's homemade 32" Dob on one occasion.

Dave Mitsky


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Dave Mitsky
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Reged: 04/08/02

Loc: PA, USA, Planet Earth
Re: M57 central star? new [Re: Dave Mitsky]
      #6139580 - 10/15/13 06:30 PM

Please keep in mind the TOS regarding photographs.

Please do not copy e-mails, articles, pictures or posts from publications or from other online sites unless you are the owner of the material or have received explicit permission from the owner to do so. This permission must be included in your post. Using another person's work without permission is, at the very least, poor netiquette, and is not permitted on this forum. A summary or short quote is allowed without permission, but you must include the identity of the original source. The best way to direct fellow CN members to material you have found is to simply include a link, when possible, in your post.

http://www.cloudynights.com/ubbthreads/showflat.php/Number/233117

Dave Mitsky


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jhayes_tucson
professor emeritus
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Reged: 08/26/12

Loc: Bend, OR
Re: M57 central star? new [Re: Dave Mitsky]
      #6139596 - 10/15/13 06:44 PM Attachment (4 downloads)

I was able to view it last Friday with C14, a Canon 7D, and 30 seconds of unguided exposure at ISO 6400. Total beginner's luck. (I couldn't see it visually, but then again, I didn't spend much time trying.)
John


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David Knisely
Postmaster
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Reged: 04/19/04

Loc: southeastern Nebraska
Re: M57 central star? new [Re: bremms]
      #6139682 - 10/15/13 07:33 PM

Quote:

The central star is quite blue.. Integrated magnitude may be 14.6- 15.0. Visual it is 15.8-16.0 or even fainter. A good bit of the energy is in the far blue end of the spectrum as the surface temperature is about 100,000K. If you are a little older it might be more difficult. The spectral distribution makes it difficult. That being said, I saw it one time from a green Zone 30 years ago in a 16" F5 Cave. Seeing and transparency were very good that evening.
We used a 5mm Clave' and a Barlowed 10.5mm RGO (mine) about 400x. It was not visible under about 300x.




Ah, no not quite. The professional V-band photometry indicates a visual magnitude of the central star of about 15.0 with a few measurements 0.1 to 0.3 magnitudes fainter than this. The star has been seen in apertures of nine inches and larger, so that would suggest the 15th magnitude visual measurement to be fairly accurate. Clear skies to you.


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2orthern2ights
journeyman


Reged: 10/13/13

Re: M57 central star? new [Re: David Knisely]
      #6140052 - 10/15/13 11:33 PM

Thanks for the replies everyone. I'm off to bortle 1ish in a week. For certain, I'll be looking for that central star when I get there.

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blb
Post Laureate


Reged: 11/25/05

Loc: Piedmont NC
Re: M57 central star? new [Re: 2orthern2ights]
      #6142934 - 10/17/13 01:13 PM

David wrote;
Quote:

...Viewing the central star in M57 depends largely on the stability of the atmosphere, so if seeing isn't rock-solid, you won't see it no matter how big the telescope is. Clear skies to you.



Does that mean that seeing any stars of 15th mag. and fainter is totaly seeing dependent even with larger telescopes. I mean, most people who have 18-inch to 24-inch telescopes have trouble seeing the central star. True?


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