Propeller in M13

[davo]

I was told about this but have found nothing about where exactly to look. Do the stars make the propeller or do the gaps inbetween the stars make it? Either way can someone enlighten me on how to see it or paste a link. Thinking about it can it be seen visually through a scope without imaging? Where do i look?

Thanks

Dave

[Psychobilly]

Have a look at the image in this thread - There's a darker "3 bladed" propellor shape visible..thats waht your looking for....

Peter....

[davo]

I'm so stupid. I still really cann't see it.

[barkis]

Look about two thirds down the main Glob and slightly to the left. There is one blade pointing to 4 Oclock, one to eight Oclock, and the other to 12 Oclock. It is faint, but it is visible.

Ron.

[Andrew*]

That's funny, becuase for some odd reason I always thought of the propeller as being a 4-pronged chromosome shape of brighter stars right at the core... It all makes sense now...

Andrew

[davo]

Wayhey! I see it. I cann't miss it now!

[davo]

I guess this can only be imaged and not seen visually? If so sorry to post under "Visual Observing" but now i know what i'm looking at i don't know how i missed it.

:-)

[John]

That's funny, becuase for some odd reason I always thought of the propeller as being a 4-pronged chromosome shape of brighter stars right at the core... It all makes sense now...

Andrew

Me too Andrew - you live and learn eh !

John

[acey]

There's a photo and diagram in this thread that seems show it in a different place:

Society for Popular Astronomy :: View topic - M13 - Cliff Meredith

I'm confused!

[Kai]

At SGL4 i had my 12 inch Flextube pointing at M13 and im sure i could see the Propeller , but then again it might of been my averted imagination.

[Doc]

It's easier to pick up visually, photo's go to deep and ruin the affect. I've seen it with my 8mm Hyperion. I could just make out the shape. It's really hard but if you stare it does seem to pop out. As for the position it's pretty near the top.

[Psychobilly]

Could be seen through Robs 14" SCT at SGL4...

Mine looks a bit like this one....

http://www.jburnell.com/M13.html

and this one...

http://apod.nasa.gov/apod/ap071115.html

Peter...

[acey]

I decided to consult some sources - and at last I know where the propeller is really meant to be!

The feature was first seen by Lord Rosse's observing team in the 19th century, as a very large Y shape centred near the core of the cluster, the arms extending to the edge, dividing the whole of it into unequal thirds. Other observers however could not see it.

You can see Rosse's sketch here:

1886AJ......7..156H Page 156

as well as a drawing by the authors of the 1886 paper who looked hard with 6- and 12-inch scopes and eventually persuaded themselves they could see the Y-shape, but in a slightly different position, from which they concluded that it had moved!

Reading their paper makes me wonder if the propeller is a bit like the canals of Mars... a random/psychological pattern that you'll see if you look hard enough for it.

Steven Coe offers a visual description (made with a 13-inch and mag 6 sky) in "Deep Sky Observing" p287:

"The dark 'Propeller' feature is seen on the south side as small, thin dark lines. These three dark lanes divide the globular into unequal thirds, and there is a faint double star in the westernmost dark lane".

Stephen O'Meara says in "The Messier Objects" p70 (viewing with 4-inch and mag 8 sky):

"Only once did I recognize Rosse's classic dark Y shape, just southeast of the core, and, surprisingly, that was on a foggy night!... Interestingly, I discovered my own Y in the northwest halo, just inside the northern wing...[which] shows nicely on a photographic plate made with the Lowell Observatory's 13-inch telescope."

This remark is significant - it shows that the propeller disappears if the stars are too bright (as happens on CCD images) and also that you can find other propellers if you look for them.

For example, this page

(IAAC) OBJECT: M13 Hercules Cluster (Globular) INST: 18" F/4.2 Newt.

has the following description of a CCD image (with a shifted propeller and a new one made of stars):

"Within the core is a noticeable sideways "Y" dark lane on that NE side. Being that each leg of the Y is about the same length, it is nick-named the "propeller". Also easily discernible is the "little propeller", or a small group of stars just below the core (assuming NE is "up") The bright group of stars near the center of the cluster is clearly shaped as a small "X". The bottom right hand part of the X is dimmest."

I've never seen the propeller myself - but I've never looked for it, not knowing where to look. Now I do!

Andrew

[Psychobilly]

The orientation of the image will depend on the scope and optical setup used and whether the image has been rotated and flipped to align it to a naked eye sky view... I know I never bother to correctly orient my images...as its for "art" rather than science that I take them...

Peter...

[SteveL]

The first time I could really see the propellor in an image was in one of Pete Lawrences images a while back.

[MikeD]

Just to confuse things, in my image I got two propeller's mirrored, and at a push it continues to make a pentagon.

Mike.

[acey]

The orientation of the image will depend on the scope and optical setup used and whether the image has been rotated and flipped to align it to a naked eye sky view...

True - but it doesn't change N,S,E and W.

Rosse's sketch, and the 1886 sketch by Harrington, both show a Y centred just south of the cluster centre (towards the prominent star chain dubbed "the hook"), with one arm pointing almost exactly due north.

The Pete Lawrence image is aligned with North approximately towards the left (the galaxy visible in lower left, NGC6207, is almost exactly due north of the bright yellow star to its right). There is indeed a propeller arm pointing in approximately this direction, with the propeller centred south of the core, towards the curved "hook" of red stars. So it matches Rosse's propeller.

Still two mysteries, though. Why did Harrington see it in a different position? And does any image show what he and Rosse both saw: a propeller whose blades extend all the way to the cluster's edge?

Andrew

[Psychobilly]

Apologies to the "observors" for introducing all these images into a thread in this section....

Peter.....

[Talitha]

No apologies needed as far as I'm concerned, Peter. The images aren't being posted to gather praise, they're illustrating and explaining what's being discussed.

Interesting thread, btw. I'd heard of the propeller but had always assumed it was the outward spiraling chains of stars and nebulosity seen visually. I love being an Amateur.. so much to learn every day!

[Psychobilly]

Cheers Carol... It was a case of "a picture is worth a thousand words"....

It has been intersetting following the links and reading the info about the various interpretations of the "propellor" or should taht be "propellors"....

Peter....

[Talitha]

Actually, what interests me the most is Professor Harrington's comment (in Andrew's ADS link) that they've been seen while using 6" and 12" scopes... the trick seems to be kicking the magnification up to about 500x to 600x. Maybe I can squeeze them out of the 8"SCT this summer.

Thanks for starting the discussion, Dave!

[acey]

It shows up nicely in this newly posted image

http://stargazerslounge.com/imaging-deep-sky/79843-m13-first-image-while.html

The view is north-up so the propeller is slightly to the lower-left of centre, above the hook.

The image also shows a clear difference in brightness between the inner core region and the outer stars. I think Rosse was referring only to the inner core, in which case the propeller really does appear to cut it into three pieces.

For visual observation, it does sound like very high power is needed - so it'll be a challenge for my dob. But as soon as the Moon gets out of the way I'll have a go.

Andrew

[jcm]

I looked back at some of my images. The wider field ones did seem to show the propeller slightly more clearly. In the image below its a bit left and down ( south east) of the centre.

John

PS a bit difficult to see due to the reduced resolution.

[acey]

Have a look at the image in this thread -

Peter, looking at your pic again I realise that what I originally saw in it was the wrong propeller. As well as the "real" propeller (which I can see clearly now after looking at so many images!) there's another smaller one on the right (western) edge of the cluster, adjoining a circular region void of stars, and with one arm pointing to the right. In your image it actually looks darker than Rosse's propeller.

Andrew

[Talitha]

"Wrong propeller"????

"Real propeller"???

Andrew, I'm wondering if image processing has anything to do with photographic detection of the propeller... think it might?

TBH, I've been unable to see it in some images, but in others it sticks out like a 'sore thumb' as we say in the US.. maybe visual atmospheric conditions and/or photographic processing determine the visibility of this feature?

In any case, it's on my "challenge list".. again, thanks again to Dave for opening this discussion.