The Double Double

[Rockrae78]

Just had another thought... maybe its my eyes! 

[Moonshane]

look out for my big dob in Saturn 30 if it's clear my eye will be glued to the scope though so an 'ahem' might be necessary.

[Moonshane]

Just had another thought... maybe its my eyes! 

nah, it's an easy split once you know what to look for.

[Moonshane]

I see it like this at about 200x

[Rockrae78]

Would the use of a focal reducer (with the CPC 800) be limiting my efforts when trying to resolve them?

[Moonshane]

only if it's of poor quality. if you are getting 150x or more then you should be able to split it. not long until Friday

[Marki]

Lots of fascinating info in this thread. Thanks for the assorted links to Smyth and others - I love this forum :-). I've generally only seen the components as white, with a hint that the primaries are a slightly bluer cleaner white (well, thats how it seems to me).

Took me a fair while to split it, but once I'd got it once I found it much easier and could do it with much lower magnifications, although I find they look nicer at higher mags. I find seeing conditions make more difference than a dark or Light polluted site (or even what aperture scope I'm using). On a really good night I can get a split at approx. x75-80; the next night I'll barely see it at x200!

[Merlin66]

With practise and good seeing conditions, it's possible to split the double double with less than x50 magnification.....

[Pig]

White to me also at both high an low mag

Would the use of a focal reducer (with the CPC 800) be limiting my efforts when trying to resolve them?

It shouldn't do. However, any extra glass in the set up will have an effect I find the 14mm best for splitting them.v

[acey]

I see it like this at about 200x

Very nice sketch. It shows (among others) the two intermediate stars F and G which Webb apparently considered a good test for a 4-inch scope. Interesting to compare it with the pic I posted earlier in this thread.

[Moonshane]

I should stress this is not my sketch just an example I pulled off the interweb to illustrate what I see.

[chiltonstar]

Interesting that the sketches are not drawn to scale - the distance between the two pairs (210") is far greater than shown in the sketches wrt the sep of each pair....

Chris

[Rockrae78]

Epsilon Lyrae

Epsilon Lyrae.png

This is the view I see... Except that I can't resolve them.  I've only had the CPC 800 since May, so only been trying with that scope since then, and with a focal reducer.  Was wondering if this would affect it, because it does give a more 'zoomed out' sort of view. 

[AlexB67]

Double stars thus far have not made it on my radar much, must make more effort on that, this looks like an interesting pair ... pair Skies clearing, I may just have to pull out the heritage on this one for a quick peek ... if skies hold up.

[bingevader]

I'd definitely let doubles make their way onto your radar. Some of them are quite beautiful.

The Double Double stars have always been white to me though.

I'm sorry Rae, I don't know what the problem is, because they should be a relatively easy split in your CPC800. I don't have a problem in my 8" or etx90. I don't know about this 50x magnification malarkey mind you. It takes the 14mm at 86x before they resolve into 2 monkey nuts with a definite narrowing in the middle. At 200x they're clearly split though.

When you say they don't resolve, are the conditions good enough or are you suggesting there's a problem with the 'scopes collimation or something.

Either way, Moonshane will sort it if you're able to meet at PSP!

Cheers

[Stu]

This is the view I see... Except that I can't resolve them. I've only had the CPC 800 since May, so only been trying with that scope since then, and with a focal reducer. Was wondering if this would affect it, because it does give a more 'zoomed out' sort of view.

I would think that any eyepiece with a focal length of 20mm ie x101 mag would at least show them as 'peanuts', and if the seeing is good, scope cooled etc then you should be able to split them. Definitely with a 10mm at x200 ish you should split them.

Stu

[Astro Imp]

I would think that any eyepiece with a focal length of 20mm ie x101 mag would at least show them as 'peanuts', and if the seeing is good, scope cooled etc then you should be able to split them. Definitely with a 10mm at x200 ish you should split them.

Stu

I manage to split them (just) with a 7mm EP in my 150P which gives 107x.

[Rockrae78]

I'm sorry Rae, I don't know what the problem is, because they should be a relatively easy split in your CPC800. I don't have a problem in my 8" or etx90. I don't know about this 50x magnification malarkey mind you. It takes the 14mm at 86x before they resolve into 2 monkey nuts with a definite narrowing in the middle. At 200x they're clearly split though.

When you say they don't resolve, are the conditions good enough or are you suggesting there's a problem with the 'scopes collimation or something.

I don't think its got anything to do with collimation. Both scopes are fine.  Not tried recently with the SLT 130 - last time I tried was very early in the year, when it is fairly low down (for me), and given that there is more atmospheric disturbance lower down, then that could have been a factor. 

First tried with the CPC 800 over summer.  I put it down to the fact that it just wasn't dark enough (it was at zenith - or near enough - at that point so should have been better seeing conditions), but since trying at the Brecon Beacons at the beginning of Sep, I thought I would have got it easily, but I didn't.  Admittedly, the lowest power EP I had with me was the 8mm (and no Barlow) but I think that the 6mm PLOSSL is way over the top for that scope anyway.

I used the scope all weekend, and lots of others looked through it too... I was mightily impressed with the views it gives (it was the first time at a dark sky site with this scope) and was chuffed to knock a few other things off my list, but just frustrated that I couldn't get this. 

Think my next step would be to try again without the focal reducer (just in case) and hope that Shane can give me some help at PSP2013...

[acey]

Splitting the double-double is not hard: each pair has a separation of roughly two and a half arcseconds, which can be resolved by an aperture of 2 inches. It just needs enough magnification to turn two and a half arcseconds into a distance that the eye can resolve: for some people that's as little as x25; with a 2-inch lens it should be possible to go up to about x100. If the double-double can't be split then it's because the seeing is very poor, or the optics (scope/eye) are poor (or the observer is looking in the wrong place).

As I said in my earlier post, the double-double wasn't considered a serious test object by 19th-century observers - the test was the intervening "debilissima" pair, which was considered a test for a 4-inch, and generated a lot of comment. This 1880 article ("Double Stars For August") is interesting:

http://adsabs.harvard.edu/full/1880Obs.....3..508G