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Observing >> Double Star Observing

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astro4565
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Reged: 11/27/10

Loc: UT
Omicron Persei new
      #6172277 - 11/02/13 04:58 PM

Anybody split this double star with a 120mm refractor? My NGC-Max guide says this star is 1.0" arc-seconds. I guess seeing would have to be excellent to split this double. Any reports on Omicron Persei would be appreciated. May have to try this one on a clear cold night.

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azure1961p
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Reged: 01/17/09

Loc: USA
Re: Omicron Persei new [Re: astro4565]
      #6172384 - 11/02/13 06:26 PM

I'd personally not even mother. That great s difference in magnitude at that distance is too staggering for me to consider with my 8". Maybe a bigger scope can pull it off but it'd not be easy,

Pete


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fred1871
professor emeritus


Reged: 03/22/09

Loc: Australia
Re: Omicron Persei new [Re: azure1961p]
      #6172583 - 11/02/13 08:45 PM

Omicron Persei will be a tough one - 2.8 mags brightness difference (current WDS numbers, probably from Tycho) and only 1.0" separation. If the stars were equal, 120mm could show a Dawes Limit touching discs view; but with the big brightness difference, it becomes very much harder, and is likely to be marginal with 140-150mm scopes, though the secondary will sit in the first dark interspace of the diffraction image at that aperture.

It could be possible with a good 8-inch (200mm) - the secondary star on the outside edge of the first diffraction ring. For a 7-inch the secondary will sit on the diffraction ring, making it hard to see. Hmmm. Think I'll try it with my C9.25 when it gets into my midnight sky, a month from now. With that aperture the secondary should be nicely outside the first diffraction ring, with Rayleigh being ~0.6" for that aperture.

Doubles like this one need both sufficient aperture, and preferably an aperture that avoids putting the secondary star on the first diffraction ring.

An historical note - SW Burnham discovered Omicron Per (BU 535) as a double in 1878 with the 18.5-inch refractor in Chicago (though it had been measured by another observer the previous year). The separation has been pretty constant since then, but the angle has gradually changed.


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azure1961p
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Reged: 01/17/09

Loc: USA
Re: Omicron Persei new [Re: fred1871]
      #6172600 - 11/02/13 08:57 PM

I need to cross reference SS more. They have an almost 5 Delta-M!!!!!!
Well your finds top the scale the other way then.

Pete


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Asbytec
Guy in a furry hat
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Reged: 08/08/07

Loc: La Union, PI
Re: Omicron Persei new [Re: azure1961p]
      #6172695 - 11/02/13 10:08 PM

I could not do it at 150mm aperture obstructed, "I also did not resolve Atik (P.A. 23 SEP 1 MAG 3.91-6.7) but it does seem doable."

I agree with Fred, and Pete, at ~ 3 mag difference inside the first ring things get interesting. It might be doable, though difficult.

Edited by Asbytec (11/02/13 10:11 PM)


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astro4565
member


Reged: 11/27/10

Loc: UT
Re: Omicron Persei [Re: Asbytec]
      #6173504 - 11/03/13 11:03 AM

I guess Omicron Persei is in the same catagory as Zeta Herculis. You need at least an 8 inch scope with superb seeing. I may have better luck with Eta Geminorum.

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