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#1 Asbytec


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Posted 21 January 2013 - 08:55 AM

STT 517AB is an extremely tight pair in Orion. It is distinctly elongated at 263x. At 384x, the pair resolves into two touching, yet distinct orbs. The preceding companion (listed at PA 241 and 0.67" arc Sep) is noticeably dimmer listed at mag 6.99. The primary is listed at magnitude 6.79. At 512x, there is no improvement in the view.

Most of the time STT 517AB appeared to be an elongated yellow pair. I observed them for about 30 minutes, watching them dance, jitter, blur, and sharpen during that time. I could hold their discs steady most of the time and at times catch a faint arc of a diffraction ring near the primary.

During some fleeting moments, I could make out some contrast differential between them. More often, I viewed the slightly dimmer companion as a less bright disc touching a slightly brighter primary disc. Rarely, however, a faint and fleeting line would form between the discs. Generally, the pair appeared pinched.

I really would like to revisit this pair in better seeing. I really felt like there is some visible contrast distinction between the components. I am just not sure if better seeing will simply show a dimmer disc or a weak contrast drop off between them. I am very sure this is not a classic Dawes split, it's a bit too dim and tight. Nor is it completely a Sparrow "split," either. Very close, though. (72 Pegasi was simply elongated with a fainter companion and no split at 0.57" arc.)

In any case, it was a nice challenging pair.

Seeing was 6/10 to 7/10, mostly, and NELM mag 4 with a half moon nearby.

263x (OU 12mm HD Ortho 2x Celestron Shorty working at 1.6x.)
384x (8mm TMB II 2x Celestron Shorty working at 1.6x.)
512x (6mm TMB II 2x Celestron Shorty working at 1.6x.)

#2 PJ Anway

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Posted 21 January 2013 - 02:53 PM


Thanks for the observations. Nice to know someone is getting some photons. Been cloudy and snowy here on the "North Coast".

I checked my "Norton's Star Atlas" cir.1937 (6th edition) and it shows up on Map 5 about a degree south of Rho Orionis, labeled OƩ 517. My 18th edition (as in so many cases) does not label it. I just love the older edition, it has so much more to offer for double star enthusiasts.

#3 Asbytec


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Posted 21 January 2013 - 10:13 PM

Thank you, PJ, had two nights of "photons" since Christmas. I need a good atlas, too.

#4 fred1871


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Posted 23 January 2013 - 02:41 AM

The Tri-Atlas,free online, does provide a lot of double star labels, and goes faint (C series especially). For the brighter pairs the maps in the Cambridge Double Star Atlas are very useful. :)

#5 Asbytec


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Posted 23 January 2013 - 04:50 AM

Thanks, Fred, I use the mag 8.5 atlas and sometimes the tri atlas for fainter stars. Maybe I'll pick up the Cambridge atlas when I get the the US (on vacation.) There are some online resources, too, that seem pretty helpful. But, I star hop all the time, no computers or goto...nor even any motor drives. (lol) Getting back to basics is part of the enjoyment.

Just downloaded the WDS catalog, it has a RoT attached to the end of it. :confused:

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