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Zeta Sagittarii

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#1 Frisky

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Posted 23 August 2019 - 02:28 AM

I went to the bottom star in the Teapot's handle and tried to split Zeta Sagittarii. The two main components are very bright, below the trees, and the sky conditions were only fair. They wanted to split, but I couldn't do it. It looked like a bright blue star (bluest I've seen) mixed with a red star! It was neat watching that blue and red go across the field of view! Now, the problem with Gamma Cas is you have a big and bright main star with a small, dim companion near to it. With Zeta Sagittarii, you have two bright stars hugging each other! Some of the color I saw might have been due to atmospheric dispersion. Anyone split this double?

 

Joe


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#2 Asbytec

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Posted 23 August 2019 - 02:36 AM

No, but it sounds beautiful. It's a tight pair (triple) at less than 0.5" arc (P.A. 239.1 SEP 0.48 MAG 3.27,3.48). I will give it a look next time I am out. You bet! smile.gif


Edited by Asbytec, 23 August 2019 - 02:36 AM.

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#3 Astrojensen

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Posted 24 August 2019 - 05:24 AM

Wow! Didn't know about that one! Sadly, it's very low in my sky and even an elongation would be a major feat from here.

 

 

Clear skies!
Thomas, Denmark


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#4 fred1871

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Posted 24 August 2019 - 08:13 AM

Zeta Sagitarii is a short period binary, orbit taking 21 years. There's also a wide optical companion of mag 10.6. The binary is resolvable with middling apertures when widest, nearly equal stars at 0.6". They were near that separation a few years ago, but the system is now closing. The ephemeris gives 0.42" (interpolated) at the present date. So a C11 might give a Dawes split in good seeing. An 8-inch at high power in good seeing should give a rod effect; Dawes for an 8-inch is 0.57". Elongation can be detected down to 0.5-Rayleigh, sometimes closer; 0.5-R is 0.34" for an 8-inch.

 

My first observation of Zeta Sgr was decades ago with a 6-inch Newtonian, at a time when the separation was 0.6", around the maximum. At 400x it was an elongated notched pair.  A revolution and a bit later with a 7-inch apo it was seen as a figure-8 pairing at 330x.

 

It will be a number of years before we see it get back to 0.5" or 0.6" and therefore reasonably accessible to medium apertures. Mid last year it was at 0.50". It won't get back to that separation until 2034. It will be in the 0.5" to 0.6" separation range from then until 2039.

 

The discovery designation is HDO 150, and the discovery was made in 1867 by Joseph Winlock with the Harvard 15-inch refractor.

 

Incidentally the stars are Sirian type (A), so both are white, but may look pale yellow to older eyes or through dust or haze.


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#5 Frisky

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Posted 24 August 2019 - 05:08 PM

I think the bright blue and reds I saw were due to the atmosphere. Kind of like the times when Saturn was low and leaving us for the year, and I saw it as red, white and blue, lol!

 

Joe




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