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Finally a Jonckheere double I could split

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#1 WRAK

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Posted 09 November 2012 - 02:10 PM

Jonckheere doubles are at least in the +10mag range very often advertised with wrong magnitudes and therefore hard to find not to speak to split with a small telescope.
In the observations lists from Lewis I found 3" J781 +9.4/9.4mag observed with a 3" refractor - this aroused my curiosity and so I checked myself.
J781 is to find about 5° north of Albireo close to STT390 as a rather faint double of about +10.8mag - at least nearby +10.81mag TYC2669-00673-1 seems a bit brighter. And I could split it with my 140mm refractor with x140 but only with averted vision. My naked eye magnitude limit today was about +3.2mag but still it seems quite a feat to split this double with 75mm even with black skies and perfect seeing although I am no longer surprised by reports of incredible splits with very small scopes.
In the same session I could split 2.5" AG380 +9.4/10.5mag with an aperture of 90mm - in terms of separation and delta-m certainly more difficult than J781 so I don't think I am wrong if I estimate J781 fainter than advertised.
Would appreciate counterchecks of my +10.8mag impression.
Wilfried

#2 fred1871

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Posted 09 November 2012 - 07:13 PM

Wilfried, is this chasing of faint doubles, when you're in a heavily light polluted location, some form of hair-shirt wearing? :grin: Some of the doubles you're pursuing aren't even on my fairly comprehensive observing lists because they're falling into the realm where the primary is 10th magnitude, and doubles that dim multiply hugely in numbers. My "doubles to observe" list for Cygnus runs to more than 350 systems but I didn't have J781 on it - though it's now added in. I had thought 350+ was plenty to look at in one constellation, so around 9.0 to 9.5 as a primary was the cutoff. So if I add in all the doubles that almost made the cut... ummm.... the list expands to what, 500 or so? It begins to feel like chasing down 15th magnitude galaxies visually with a 30cm telescope - an achievement just to find them. And there are so, so many...

I'll see if I can pick this one up before it hits my evening twilight zone. The few J doubles I've observed do show you're right about magnitudes often being dimmer than listed. J 2267 in Aquila, which I observed in September this year, looked to me closer to magnitude 11 for each star, rather than the 9.5 listed. That was with the 235mm SCT. A few other J pairs I've looked at were never brighter than the listed magnitude, some were definitely fainter.

#3 fred1871

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Posted 09 November 2012 - 09:42 PM

Now I've checked via planetarium software I can see that Cyhnus is gone from my latitude in hours of darkness. Next year ...

But, there are J doubles in Pegasus - I'll see if I can check some of those for magnitude differences from what the listings say.

Incidentally, J 1694 in Aquila, which I observed the ssame night as J 2267, mentioned before, I saw readily enough with the C9.25 - the old magnitudes listed for it were 8.6 and 11.5, but these have been revised to 9.12 and 12.0. Not a huge difference this time, but would be enough to make it rather more difficult for a 140mm telescope with light pollution.

#4 WRAK

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Posted 10 November 2012 - 07:50 AM

Wilfried, is this chasing of faint doubles, when you're in a heavily light polluted location, some form of hair-shirt wearing? :grin: ...

Quite the contrary - I have no problems with splitting doubles in the +9.5/10.5mag primary/secondary range or even a bit above. And J-doubles in this range are most satisfying because the advertised parameters are usually wrong and so I can inform the WDS-guards (does not seem such an easy job :tonofbricks:) about the errors in their database to contribute as good as I can as amateur.
Wilfried

#5 drollere

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Posted 12 November 2012 - 01:18 PM

fred, it's a challenge to look for J doubles in the cygnus galaxy band ... good luck. there are *lots* of faint doubles in there, not to mention distracting field stars. sweeping the domain, i once found a single 15' field that contained over a dozen faint visual binaries.

it's fun just to roam around: at medium power and good aperture, some of the fields are esthetically breathtaking. one of my favorite areas of the northern sky.

#6 WRAK

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Posted 18 November 2012 - 01:49 PM

I used the WDS 2012.05 data advertising +9.4/9.4mag for J781. Meanwhile I checked the current WDS data and found +11.5/11.4mag for J781AB - Brian Mason seems to have in between corrected some of the wrong Jonckheere magnitudes. But +11.4mag for B could be a bit on the faint side because J781BC is advertised with +10.98/14.3mag.
Wilfried

#7 fred1871

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Posted 18 November 2012 - 07:44 PM

I think Brian Mason et al at the USNO do revise the magnitudes of doubles as new data becomes available.

Last night - first observing night for a while, I've been out of town for a week - I had a look at J231 in Aries. My observing list for "pairs to observe" in Aries hasn't been revised since I put it together from the 1996 WDS. Magnitudes for this one were listed as 9.0 and 10.8 in the 1996 WDS - separation of 5.0".

Just before I looked at J231 I observed STF 214 - for which the older data gave mags 8.7 and 11.0 at 5" as well. The numbers suggested similar objects, but they were very different, using my 140mm refractor.

The magnitude revision on STF 214 now gives 8.7 and 10.2 (at 5.2") - it was not difficult at 114x, and the secondary star was just seen at 80x.

J231 was very obviously much fainter at first glance. It was "not single" but not resolved at 114x, and I could just make it out as a dim quite unequal pair at 160x. I estimated the magnitudes as no brighter than 10 and 12.

Having now checked the current WDS, the listed magnitudes are 10.61 and 12.4 - the same delta-m as before, so I suspect the accurate photometry of the primary star has simply resulted in shifting both magnitudes by 1.6 fainter. But it looks a good fit for what I saw. Separation is now given as 5.4". For 140mm in suburban skies it's not easy due to the dim magnitudes.

So we have another example of J magnitudes being too bright originally. No doubt a consequence, as remarked elsewhere, of Jonckheere moving from telescope to telescope, plus the scopes mostly being large in amateur terms (generally 14-32-inch - ~35-80cm - aperture). At least this time the WDS has been revised already. :)

#8 WRAK

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Posted 08 March 2013 - 09:33 AM

The number of Jonckheere doubles I could split is on the rise:
Last evening an unexpected clear sky so I did a session with my 140mm refractor on Alt/Az-mount in Orion with Alpha Ori as starting point at about 45° altitude with NEML about 3 and fair seeing (Pickering 6-7) combined with good transparency. The route included J407 1.8" +8.7/10.4mag: with magnification of x140 resolved at 6 o'clock (limit aperture 116mm). Further J310 2.4" +9.8/10mag:with magnification of x70 resolved at 10:30 (limit aperture 80mm).
I don't know if the current WDS values are ident with the original Jonckheere numbers but the advertised parameters for these two J-numbers seem to be correct.
Wilfried

#9 fred1871

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Posted 13 March 2013 - 10:52 PM

I've been looking at some of the doubles in Canis Minor, and came across J281 the other night. Old magnitudes were listed at 9.0 and 9.5. The 140mm refractor showed it, but at mags I estimated at 11-12. It's an uneven pair, and I've now checked the WDS which has new photometry - mags 11.08 and 11.86. That's a good fit for what I saw. Separation is 5.0" (2000), and it took 160x for an easy view (relatively speaking). With somewhat less power, it was double but not as clear.

So, once again, an example of magnitudes originally much too bright - by about 2 magnitudes. Yet it's not a consistent pattern; some pairs as we've both found are about where the early magnitudes suggest. To discover if it relates to which telescope Jonckheere was using we'd need to go back to his original publications.

Still, it was nice to split a dim pair, and one that's not wide; no moon, fairly dark suburban sky, NEML 5.0 or perhaps a little better.






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