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7 AQR, BU 1034

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#1 John Fitzgerald

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Posted 18 November 2019 - 09:58 AM

Can anyone on here see the faint companion of 7 Aqr?  Mags 5.7,11.4 sep 2.1 seconds.

 

From the original text:

 

1034. 7 Aquarii R.A. 20" 5om 25s Decl. 1888.68 165.0 1897.72 163.7 2.09 2.05 m 25, I 6.0 ...1i. 5« 3« A Discovered with the 36.inch. It is not a diffi cult pair. The measures of 1888 were made with the 12.inch. The principal star has a proper mo tion of of033 in the direction of 257.8 (Auwers). It is very probable that this is a physical system. [P (x.v)... P (2875). 429)...J .P (Pub. L. O. 11). .Aitken (A.J.



#2 fred1871

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Posted 18 November 2019 - 08:20 PM

The "from the original text" appears to have got muddled in translation at the beginning.

 

Via Sky Catalog 2000 v1 I got a position for 7 Aqr; then to Cartes du Ciel where I could obtain the discoverer designation, BU 1034. That explains the "1034" at the start of the quote. Helps to know it's a Burnham discovery. Position (J2000) is 20h 56.9m -09 42.

 

From WDS, first measure listed as 1888, so that makes sense.... most recent, 2002. Pretty much unchanged since discovery, and no PM numbers for the companion. The small PM numbers for the primary suggest a large distance, and GAIA DR2 gives rather different parallaxes for the two stars (suggesting an optical pair), the more distant being the primary at about 200 parsecs.

 

Observation? well, if Burnham saw it with a 12-inch, and we know it hasn't got closer, that's a starting point for what will show it. Any successful observations with less than a 12-inch? I don't have any attempts listed in my observing notes. I do like the "not a difficult pair" - with the 36-inch, no doubt easy. The delta-m at 5.7 mags suggests it won't be easy at 2.1" for scopes under 12 inches.



#3 fred1871

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Posted 20 November 2019 - 12:34 AM

John, in the other thread (not in Double Stars) where you mentioned 7 Aqr there was a suggestion that someone claimed to see it double with a 4-inch 'scope. Any further detail on the claim? Given the much increased difficulty of very large delta-m pairs, and the secondary star in this case being close to the visibility limit for 4" in a lot of circumstances (urban lights, moonlight, etc) even when a star of that magnitude is not very near a much brighter one, it seems unlikely. Perhaps in the case of a lunar occultation, when otherwise un-viewable stars are recorded?



#4 mccarthymark

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Posted 24 November 2019 - 01:12 PM

I saw it last night:

 

"8" off axis mask (effective f/13) 333x: A star is orange and bright, the mask is giving a good clean image at moments, with some disturbance (seeing 6/10).  B star is faint but a nice hard point outside A's first diffraction, ~2", noticed it right away even though it is on the edge of direct vision, but do not need averted to see it.  Dependent on seeing.  Tried at full 20" aperture but A was too messy, and did not clean up well enough with apodizing mask.  Low in the sky and in fact lost it behind a tree a few minutes after making the observation"

 

I'm at a sea-level red zone so I think there was no trouble atop 4000 ft. Mt. Hamilton in the 1880s to get great images for taking measures with the 12" reflector.  I'd wager it would be "getable" in a 6" in a dark sky with excellent seeing at culmination.



#5 John Fitzgerald

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Posted 24 November 2019 - 03:05 PM

I believe the measure at Lick was done with a 12 inch long focus refractor.  Thanks for the observation post.  I dont have enough aperture to do that big a mask.  Will keep trying in the 6 inch apo.


Edited by John Fitzgerald, 24 November 2019 - 03:08 PM.


#6 fred1871

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Posted 07 December 2019 - 09:01 PM

I did a bit more searching for data on 7 Aqr (BU 1034) because I made an attempt on it recently with my newly obtained 140mm ED refractor. The worrying part was that I could see a minute companion in the right PA and I had not expected that with only 140mm. I've not had another good night since then to confirm the observation. What I did notice was that the secondary star did not look as dim as the listed WDS magnitude of 11.4 (primary, 5.7). That gives a delta-m of 5.7.

 

I went to the Gaia DR2 release and found both stars there. The Gmagnitudes are often somewhat different from V magnitudes, usually slightly brighter, but by differing amounts probably with spectral type having an effect. The magnitudes given in Gaia are 4.9110 and 10.0336. That gives a delta-m of ~5.1, quite a lot less. If we assumed that delta-m and kept the brighter star at 5.7, the secondary becomes 10.8. However, if the secondary is not as late spectral type as the primary (that being K4III - WDS has gK5 not much different), then the visual magnitude could be closer to the Gmagnitude level. That would be a fit for what I saw, if we suppose that the secondary has a visual magnitude somewhere around 10.0 to 10.5.

 

My observation was made about 10 nights ago so there was no interference from moonlight. Power used was 305x; seen also at 350x and glimpsed at 270x. The observation that John Fitzgerald referred to (mentioned above by me in #3 here) claimed a detection with 4-inch aperture on a night of bright Moon, and the description suggested a double seen elongated with a form that might fit for say a magnitude or two difference in brightness and closer together - 2.1" is well wider than Rayleigh for a 4-inch (1.36"). That observing claim I find not credible.

 

I will get back to 7 Aquarii if I can before it gets too low in the early evening. Between the clouds, moonlight, and smoke haze from forest fires (severe, and a lot of them, and very smoky) observing lately has been difficult. For those who would like to try this one, J2000 position is 20h 56m 54s and -09 41 51. It's marked on any of the standard atlases with its Flamsteed number (7) in Aquarius.

 

The observation in #4 above by Mark McCarthy is entirely credible given the aperture and lack of moonlight, despite the recorded difficult conditions. His seeing it with 8-inch mask but not 20-inch full aperture fits the comments by Paul Couteau in his classic book regarding less good seeing conditions - that with unequal pairs the smaller (but still adequate) aperture can sometimes show the double where the larger one won't.


Edited by fred1871, 07 December 2019 - 09:37 PM.

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