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STF 2681 in Cygnus...a faint double double

double star
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#1 John Fitzgerald

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Posted 09 September 2020 - 10:13 PM

STF 2681 AB m 8.0,10.6, Sep 6.8" at PA 39 degrees.

  

STF 2681 CD m 8.9,11.8, Sep 23.3" at PA 101.

 

The CD pair lies about 40" to the south of AB.

 

The observation was made on the evening of 7 September 2020.  Transparency wasn't the best.  The B companion required averted vision to hold steadily in my 6" f/8 apo at 243x using a 5mm Pentax XW ocular.  It seems fainter than listed, maybe it's a bit variable?   

 

Smoke and humidity combined make for poor transparency.


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#2 VanJan

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Posted 10 September 2020 - 01:34 PM

With 90mm refractor at 230X on 10 July 2014: White, no color, white, no color. B star only glimpsed. 11thmv companion p. Wide 9th and 10thmv pairs s and sp.

 

I suspect that it is the proximity of the B star to the primary that lessens its visual "oomph" in the eyepiece, though more like a teasing tap in my telescope. slap.gif

 

Nice effort under less than optimal conditions! waytogo.gif


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#3 fred1871

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Posted 10 September 2020 - 09:17 PM

I had the same thought as VanJan - proximity of the B star to the primary is a common cause of close companions looking less bright than they are. The magnitude for B is double decimal, which means a modern photoelectric magnitude, perhaps Tycho, not an older eye estimate.

 

I looked through my observing records from the Northern hemisphere, since the Declination of this double double is barely above my Northern horizon from SE Australia. I have notes of STF 2681 from a night of better conditions than your recent night, John. My notes say  "no cloud or haze, crescent Moon, seeing fair+.

 

With a C8 at 80x all four stars were seen, B looking quite near star A. Going to 135x improved the visibility of B and the D wide companion to C, but they didn't require averted vision at 80x. So the observing conditions were reasonable, despite a suburban location. The naked eye limit there was typically around mag 5 with crescent Moon, similar to where I live now. It's a neat little group but less striking than some others, such as Epsilon Lyrae and Nu Scorpii.


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#4 John Fitzgerald

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Posted 10 September 2020 - 10:15 PM

I am going to revisit STF 2681 on a night of good transparency.  The naked eye limit the night of the observation was around 3.5 to 4, due to the smoke/haze.


Edited by John Fitzgerald, 10 September 2020 - 10:17 PM.


#5 ssmith

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Posted 13 September 2020 - 10:45 PM

A good recommendation John - not often that you find two actual physical systems so close together in the sky - even though they are not physically close to one another.  Here is a photo:

 

STF2681 Cyg C9 9-12-20 3fr PCC NonLinear edit2.jpg


Edited by ssmith, 13 September 2020 - 11:20 PM.

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#6 John Fitzgerald

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Posted 25 September 2020 - 09:29 AM

Thank you VERY MUCH for the photo.  I still think the visual magnitude of B might be a little less than stated.  I revisited it with my 6 inch f/8 apo the last two nights (23rd and 24th), and the B component could only be held steady with averted vision.  The best magnification for detection was 152x with my 8mm TV Radian.  Of course, the moon was nearby, which probably detracted from the detection limit.  The D component was obvious.


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#7 John Fitzgerald

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Posted 14 October 2020 - 03:43 PM

I tried again with much better transparency from home on 12 Oct. with my 6" apo.  The companion could be held steadily, without averted vision, at 173x.

 

I then revisited this double last evening (13th) from my dark site, using my 12" Dob.  The B component was readily visible, but still appeared like a tiny pinpoint at 152 and 190x.  The 12" of course made everything brighter.  It wasn't very much easier than with the 6" apo.  I still think the given magnitude might be somewhat too bright, or maybe it's tilted toward the IR band.


Edited by John Fitzgerald, 14 October 2020 - 04:46 PM.

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