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Two Splits in Ori

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#1 Asbytec

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Posted 24 January 2013 - 10:11 AM

I was able to split both BU13 and STF849. They are what I would consider easy splits with both primary and companion resolved into distinct discs. BU 13's tiny speck of a companion appeared to rest just inside the first ring at PA 140, mag 7.5 and 9.2, respectively. STF849 appeared more like other very tight, nearly equal magnitude doubles at PA 240. I could tell STF849 companion, preceding the primary, was a tad dimmer (mag 9.2 and 9.5, respectively.)

Now, the exciting thing is, this is with a gibbous moon about 4 degrees away. In fact, the FOV was so bright I could see floaters. (LOL) Star hopping to STF849 was pretty difficult, it took several tries to nail it's tiny speck and position from 69 Ori (using HIP 28978 and 29001 as pointer stars.) It was just faintly visible only during moments in the finder. But, I managed to find it with perseverance.

A survey of the moon in 7/10 seeing, and a quick check of Jupiter rounded out the evening.

#2 fred1871

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Posted 25 January 2013 - 01:40 AM

This is relevant to the RoT thread as well, but I thought I'd post here.

Norme, I notice that in Wilfried's list BU 13 and HEI 670 (described earlier) are both listed for 147mm aperture as tests. I'd expect BU 13 to be slightly easier for 150mm on the numbers - almost the same separation, and smaller delta-m (1.6 vs 2.4), despite BU 13 being less bright (9.2 mag vs 8.4 for the secondary). And a bit easier appears to be your experience...

STF 849 looks on the numbers to be a harder version of HO 22 - STF 849 is a tiny bit closer (0.9" vs 1.0") and dimmer by ~0.8 mags. Seeing it with a gibbous moon nearby is a real achievement. I would've waited for the moon to move well away, as being able to make out close DIM pairs is a test of eyesight, not just telescope. Very well done!

There are plenty more pairs in Orion we can use for tests. Once I get sky again I'll be back to it. Meanwhile, here's another data point for Wilfried's collection - Psi-2 Ori (KNT 3) of mags 4.6 and 8.6 at 2.9". This one I picked up with the 8d moon earlier this week, the 140mm refractor, and good seeing on the night as previously mentioned. It needed 400x to see the companion with certainty, and it was definitely separated from the primary. 285x suggested it was there. I don't think this one is on Wilfried's Orion list. It's not the toughest pair I've split, but on the night it was pretty much the limit - better air steadiness (excellent, rather than good-plus at the time), would I expect make it plain rather than suspected at 285x with 140mm.

Seeing can vary during the night, so sometimes equally difficult pairs will fall on different sides of the line - one splits, the other doesn't. And where I am can have differences in air steadiness in different directions, so the Orion area might be in good+ seeing at one time of the night, and only fair at another, due to air currents from nearby buildings, roads, etc.

Currently I'm waiting for the weather to clear - cloud has moved in from a tropical cyclone heading south, so parts of Eastern Australia will be cloudy/wet for a few days.

#3 Asbytec

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Posted 25 January 2013 - 02:26 AM

Thank you, Fred, maybe you could tell I was pleased with actually finding STF 849, much less splitting it. I would have waited, too, but time is getting short and the weather has been mostly bad, lately.

It was my first experience with close, dim pairs. I was expecting something more difficult approaching mag 10. There seems to be some hint those types of pairs are difficult. That seems balanced somewhat by resolution where a CO tends to improve the observation. So, I wasn't sure what to expect.

I'd like to try some more of Wilfried's list in the coming week, but Psi-2 Ori sounds like one to try. HO 22, too. It's curious that such high magnifications are required for such a well separated pair. But, understanding why is the fascinating journey of discovery.

I am hoping the weather will hold for the week I have left. I hope to keep tabs on the progress while traveling through May.

#4 WRAK

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Posted 25 January 2013 - 03:12 AM

Fred, KNT3 is not on my list because the current RoT model delivered a req. aperture of 99mm and I started the list with 100mm. I am somewhat puzzled that KNT3 should be this hard. For example STT111 with 2.8" +5,65/9,68mag should certainly be a tad harder and was for me some time ago a not so difficult split with 120mm. My be Norme could try both.
Norme - for other suggestions for observations in Ori see the RoT thread.
Wilfried






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