Question for the double splitters

[Bigzmey]

I have my own opinion on this but like to pass it by other folks.

One very enthusiastic fellow claims that he had successfully split Almach B and C which are currently at 0.16" separation using 10" DOB at 800x power. He detected it as a slight elongation of the airy disk and confident enough to call it real. B is mag 5.3 and C is mag 6.5. 10" scope Rayleigh limit is ~0.5".

What do you say, Aye or Nay?

[Don Quixote]

Not in my sky.

[sdbodin]

Well, this is one tough split now. I searched my record and found that I notched it in 1981 when the two were at maximum, about 0.6", with my 6 inch folded Newtonian. My WDS calculator has the current separation at 0.21", maybe a really good 10 with a really good night of seeing could see a slight elongation. I would be better convinced if the observation had a position angle estimate, should be about 120 deg.

In any case, Almach AB is a beautiful gold and blue double.
Steve

[Bigzmey]

I can believe 0.6" with 6". This is about 80% of Rayleigh limit of 6" scope. It is easier to push slightly below Rayleigh with smaller scopes.

To pull 0.21" you need to start with out of this world seeing and even with large scope it would be difficult. For 10" that would be ~40% of Rayleigh limit.

I say scope slightly out of collimation, slight mirror flow, or averted imagination.

[Shabadoo]

No.

[bladekeeper]

Yeesh. I'm voting averted imagination.

[j.gardavsky]

Hello Andrey,

this is a good estimate.

In addition to it, the close doubles require as well an excelent seeing better than 1 arc second.
Regarding the telescope optics quality, the Airy disc with the first ring should be looking like in a textbook.
The diffraction limit can be improved by taking a narrow passband blue filter.

All together, plus quite a bit of luck, the Airy disc on a 0.2 arc seconds double may look during the seldom and short periods of best views, like an egg, revealing the PA for a check.
Another check would be the crossings or touchings of the diffraction rings, as both the primary and secondary have their own diffraction rings, slightly shifted to each other.

Best,
JG