Glad I remembered Tegmine (Zeta Cancri) !!!

[John]

What a wonderful triple star !

I have not observed Tegmine for a long while but after observing the open clusters M44 and M67 in Cancer I suddenly remembered Zeta Cancri and panned my ED120 refractor over to it. The 2mm-4mm Nagler zoom eyepiece provided me with the fire power to get a split of the close pair (I think its a touch over an arc second now ?) and with the 3rd star just over 5 arc seconds away these 3 form a wonderful tight group.

I'll try this one again with my Tak 100 on another night and see if I can get the close pair split with that.

I've really enjoyed "discovering" Tegmine again tonight with the ED120 though

I'll re-vist again often while Cancer is well placed.

[Paul73]

That is a new one on me. I’ll have to give it a go next time out. I’ve just been playing in the same area but headed North from M44 to Iota Cancri; a really nice wide blue/yellow double. 

Paul

[cotterless45]

Tegmine is a favourite , nice to compare it with the brasher beta Monocerotis and the gentle sigma Orionis. Tegmine is a great tester for seeing and Optics.

 

Stu sent me this , interesting to see how binaries open and close . Porimma is super wide and almost glowing , I remember it being very tight. 

[wookie1965]

I have tried several times to get the third component here but fail miserably, I got the 5" Meade just so I could split these tighter doubles but not managed it.

[Geoff Barnes]

I've been having a bit of "double trouble" with Tegmine lately.

Having recently had a couple of good sessions spying doubles I found the very tight split of Porrima quite easy at 175x helped no doubt by its high altitude here (about 65 degrees).

So I've been turning my attention to Tegmine to see if I can split the very tight 3rd star which I've not seen before.

Tegmine is sinking rapidly down to my norrhwest horizon between two trees just after sunset so time is running out.

Thursday evening  I had the scope set up in what I thought was a good position but frustratingly the tree on the right obscured my view to the,extent that I could make out the A and B stars very fuzzily, no hope of C at all.

Undaunted I set up slightly further left on Friday after sunset confident of seeing them. Dammit! This time the stars had just disappeared behind the tree on the left!

The weather is turning offensive again now for a few days, but I am determined to try again next week before it becomes impossible for this year.

At least if I fail I will have the Double Double in Lyra to try for soon, a real tough one here as they are very low on my north horizon and rather shimmery at best. 

[Voyager 3]

On 27/03/2020 at 02:45, John said:

What a wonderful triple star !

I have not observed Tegmine for a long while but after observing the open clusters M44 and M67 in Cancer I suddenly remembered Zeta Cancri and panned my ED120 refractor over to it. The 2mm-4mm Nagler zoom eyepiece provided me with the fire power to get a split of the close pair (I think its a touch over an arc second now ?) and with the 3rd star just over 5 arc seconds away these 3 form a wonderful tight group.

I'll try this one again with my Tak 100 on another night and see if I can get the close pair split with that.

I've really enjoyed "discovering" Tegmine again tonight with the ED120 though

I'll re-vist again often while Cancer is well placed.

Did you try with your tak John ?

[John]

5 hours ago, Voyager 3 said:

Did you try with your tak John ?

Hello,

I'm not sure that I have actually tried with the Tak 100 since I posted that report. Cancer will be getting more favourably placed for me over the next month so I will remember to give it a try next time that I have that scope out

It should make a fine challenge if the seeing is good.

 

[John]

18 hours ago, Voyager 3 said:

Did you try with your tak John ?

I'm observing Tegmine with my Tak FC100-DL tonight.

I can't quite split the close pair (Zeta2, 1.11 arc seconds I think) consistently and convincingly but I am getting a heavily "notched" pair as per the illustration below. Maybe a split during moments of best seeing ?. The split between Zeta1 and Zeta2 is no problem at all. I was using magnifications from 225x to 360x. 300x was probably the optimum.

 

Edited January 21, 2021 by John

[JeremyS]

Thanks for posting the graphic to demonstrate double star resolution again, John. It’s very helpful 

And good to hear the Tak 100 is pulling this star apart...almost.

[Saganite]

I am finding the same John with my Vixen ED103  and Nagler 3-6 zoom, 264x and seeing the notched resolution at best.

[John]

14 minutes ago, Saganite said:

I am finding the same John with my Vixen ED103  and Nagler 3-6 zoom, 264x and seeing the notched resolution at best.

I guess we can't complain - the theoretical resolution limit (Dawes) for a 4 inch scope is 1.14 arc seconds. The Zeta2 pair are 1.11 arc seconds I think so our scopes are doing pretty well in the probably-not-too-perfect UK January seeing 

 

Edited January 22, 2021 by John

[John]

Observed this one tonight with the ED120. That 20mm additional aperture makes a difference - got a clear split at 257x and 300x

 

[Captain Scarlet]

I remember I found this and split its components shortly after you started this thread. Now it's come back around the block and you've reminded me of it, it was on tonight's list. But clouds rolled in around 6pm. I'll have another chance within the next few nights though I think.

M

[JeremyS]

Those extra 20mm make all the difference! Great result, John 👍

[Marki]

Well done, John. Couldn't quite crack it with my SW150ED tonight at x240 - heavily "notched" for sure but I couldn't swear to a clean separation. Had a go later when it was a bit higher with my TAL125R at x224 and got pretty much the same result.  Seems I need to push the mag a bit higher then.

 

 

[Pixies]

This thread inspired me to have a shot at this target last night. The great seeing was very promising, too!

At first I thought it was easy! I landed right on it but then realised I had the zoom out and what I was seeing were the 'easy'  pairing  and another star! So I upped the magnification and realised how tricky this is!

At highest power on the zoom (x150) no luck at all. With the barlow and x330 there was something but hard to make out as I was stretching the limits of the zoom/barlow optics. So I went simple and got out the very rarely used 4mm Cirtle-T ortho. Normally I only use this for star tests! Well, it worked. Was it a perfect split, I don't know. The seeing was amazing and the steadiest diffraction rings I'd ever seen, but I guess the limited contrast of a Newtonian makes it harder than what I understand is the refractor's great advantage. But I'm happy. 

I stuck a sketch in the sketching forum. I'll put up a copy here and ask for comments on whether you think this is a split and am I getting a good result out of an 8" bob at x300 (as I have no comparison to make). Thanks.

Edited January 24, 2021 by Pixies

[Nik271]

Nice! This is definitely a 'resolved' star. A 'split' means you also get to see a black line separating the Airy discs. I think this is a very good result for your scope - the separation according to stelle doppie is 1.11''

The big advantage of refractors is that the diffraction rings are less bright and this helps with splitting close doubles. This helps refractors up to a point.  In principle a well collimated 8nch Newtonian even with 30% central obstruction has the resolving power to beat most refractors up to 120mm.

[John]

Great sketch !.

If not a 100% split, it is very close indeed.

I think the challenge is that our eye and brain tend to "join things up" if we sense they might be there from the other evidence, ie: the heavy notch between what are virtually touching airy disks. IMHO the "cleaner" star images presented by a refractor make it a bit easier to determine whether that black gap is really present in full or not although the larger aperture presents a smaller airy disk so the split will be there if a little masked by diffraction effects.

It's a strangely compelling business, isn't it ? 

 

 

[Marki]

Much better conditions tonight for me. Cold, clear and steady seeing and significantly better tranparency than yesterday (well, taking the moon into consideration). I'm using my 5" achro (TAL125r) tonight. Decided to have another crack at Tegmine, after getting my eye in on Beta Mon and a few other targets. I was able to push the magnification more this evening than yesterday, This target began to resolve very nicely at x253, but not quite split. Popped in an 8mm baader ortho and the baader x2.25 barlow for x316 and was rewarded with a sliver of clear sky between the A/B pair. Really happy!

Right, now I've warmed up a bit off out again!

Edited January 24, 2021 by Marki
Typos

[Captain Scarlet]

I split it with my 12" last night. It was a little breezy and moving around from time to time. It was definitely there at 304x but to be absolutely sure I ramped up to 522x.

Cheers, Magnus

[Pixies]

I actually managed it at  x203 (1218mm focal length Bresser 8" with 6mm Ortho) back on Feb 16th - but that was a night of exceptionally good seeing, here. I managed a few other firsts that night, too.  It was nearly there with the 7mm Ortho, but not quite.