Finally a Jonckheere double I could split
Posted 09 November 2012 - 02:10 PM
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.
Posted 09 November 2012 - 07:13 PM
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.
Posted 09 November 2012 - 09:42 PM
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.
Posted 10 November 2012 - 07:50 AM
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 ) about the errors in their database to contribute as good as I can as amateur.
Wilfried, is this chasing of faint doubles, when you're in a heavily light polluted location, some form of hair-shirt wearing? ...
Posted 12 November 2012 - 01:18 PM
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.
Posted 18 November 2012 - 01:49 PM
Posted 18 November 2012 - 07:44 PM
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.
Posted 08 March 2013 - 09:33 AM
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.
Posted 13 March 2013 - 10:52 PM
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.