Tegmine - Zeta Cancri: Resolved but not Split with a 4 inch

[Mr Spock]

[Stu]

14 minutes ago, Mr Spock said:

I think I’ll forgive him one small mistake out of three, given his wonderful images 👍

[Mircea]

In my understanding, what Rayleigh and Dawes set are criteria not limits.

Those numbers are not like crossing a border or turning a switch. A good telescope will continue to show the Airy discs of binary stars much bellow the values suggested by Dawes or Rayleigh criteria.

As an example, on July 30, 2020, I was lucky enough to see the one third overlapped Airy discs of STF 2215 ( mag. 6 + mag. 6.9, separation 0.44'') with my 200mm F/ 6.16 Dobsonian.

 

The importance of splitting of the components of double stars is much overrated. That is important if one is measuring using a filar micrometer. Because you don't know where to position the threads on an elongated image to be sure you bisect through the center of the Airy discs. The famous black strip of sky seen with split double stars is a guarantee you set the threads of the micrometer to the right place in order to obtain a valid result.

For us, visual observers of double stars it is vain to struggle for splitting. If one obtain an image like that called ''resolved'' in David Knisely's diagram, we are good.

 

On the topic: I first split Tegmine as a triple star with my 125mm Newtonian on April 10, 2013. This should be close enough to a four inch refractor which I don't have.

 

Clear sky, Mircea

[John]

56 minutes ago, Mr Spock said:

I notice even Mr peach can't spell Albireo 

Capital "P" Mr Speck Spock ? 🙂

Edited March 8 by John

[John]

2 hours ago, josefk said:

Off topic but that’s a good representation of Sirius A/B on there (the larger pic without diffraction spikes). I’m encouraged that I was closer than I thought with my little scope the other night. A little semi steady knot of brightness against other scintillating brightness. I still can’t “tick it” but still very encouraging. Thanks. 

Yes, I thought that. Observing the "Pup" star is not really like resolving or splitting other double stars. The scattered light that surrounds Sirius A (diffraction rings, just scatter or a mixture of both) usually extends beyond the 11 arc seconds that separates it from Sirius B so the challenge is to spot that dim speck of light glimmering though that halo. There have been nights of exceptional seeing when the Sirius A halo is tighter but mostly it's a slightly different game from splitting the usual challenging pair.

 

[John]

15 minutes ago, Mircea said:

The importance of splitting of the components of double stars is much overrated......

 

 

Personally I find it satisfying to see that thin dark line between the airy disks. 

I'm not doing "science" though - it's just for fun 😁

[josefk]

26 minutes ago, Mircea said:

The importance of splitting of the components of double stars is much overrated

...you underestimate our collective OCD and the satisfaction of "done" 🤣

[Mircea]

2 hours ago, josefk said:

...you underestimate our collective OCD and the satisfaction of "done" 🤣

OMG, what I have done !?

It is not my fault, it is the fault of Tegmine who is only a miniature of Beta Mon ... 

[lunator]

I've come to this a bit late,  

I tend to try and keep descriptions simple. 

Pairs are Round, elongated, Notched or Split.

The last 3 descriptions are all  resolved as you can see there is more than one star. 

Amongst the pro's such as Paul Couteau and Bob Argyle it is generally accepted you can resolve a pair down to half the Raleigh Criteria. So for a 100mm/4inch scope pairs can be resolved down to 0.7". The disk will be very overlapped to no dark line but certainly you could see more than one star.

As a separate point. Paul Couteau said the resolving magnification started at twice the aperture diameter.

Cheers

Ian

[Mircea]

Ian

Thank you for quoting Couteau and Argyle about resolving down to half the Rayleigh Criterion. I'm convinced they are right.

I searched in my observation log for Tegmine. Up until 2020 I found the observations in the attachment.

On March 13, 2017, I resolved Tegmine with my 90x600mm refractor. AB was not split but the Airy discs of the three stars were clearly seen.

The Dawes Criterion for 90mm aperture is 1.29'', the separation of AB at Tegmine was 1.114'' at the time of the observation but I made a mistake of no material consequences by noting 1.14''.

 

A bit of history.

The larger AB,C pair of STF 1196, now of 6'' separation, was discovered by Christian Mayer before 1779.

Christian Mayer is the founder of double star astronomy not William Herschel. He published the first catalog of double stars in the History of Astronomy in 1779. The main instrument of Mayer was the wall quadrant of Mannheim Observatory ,

made by J. Bird. The optical part of the Bird quadrant is a Dollond refractor of three inch and two line aperture and eight feet focus.

The Mayer Catalog contained 72 stars, the bulk of which were discovered by him. Star Mayer 22 is Zeta Cnc or STF AB,C with a separation of 7.7'' at the time of discovery.

 

I see on StelleDoppie the year of discovery of STF 1196 being 1825. From this and from the STF symbol ( mnemonic: Struve The Father ) , I infer that AB was discovered by Friedrich Georg Wilhelm Struve, also known as Vasily Yakovlevich Struve.

Between 1820 and 1839 he was professor at the University of Tartu. The famous Fraunhofer 9.5'' refractor arrived at Dorpat on November 1824.

So, I guess STF 1196 AB was discovered in 1825 at the Dorpat Observatory, by Struve The Father, with the 9.5'' refractor. But I believe we should also remember Christian Mayer, the discoverer of AB,C pair as part to the story.

Mircea

3 hours ago, lunator said:

 

Amongst the pro's such as Paul Couteau and Bob Argyle it is generally accepted you can resolve a pair down to half the Raleigh Criteria. So for a 100mm/4inch scope pairs can be resolved down to 0.7". The disk will be very overlapped to no dark line but certainly you could see more than one star.

As a separate point. Paul Couteau said the resolving magnification started at twice the aperture diameter.

Cheers

Ian

 

Edited March 8 by Mircea

[lunator]

Mayer and Herchel are slightly over looked with regards to double stars. The Struve catalogue did "hoover up" some of their discoveries.

The way I like to tell people about the potted History of Double star observing is Galileo wa first to see a visual double through a telescope. Mayer created the first  Catalogue. W. Herchel did the first systematic study of them and discovered Newtonian motion outside the solar system ( By accident tho' 😬).

Struve did the first large systematic study, although John Herschel should also be included in this for his work especially for the Southern Hemisphere. 

I generally stop at this point as Aiken et al are less well known. 😀

Cheers

Ian

[F15Rules]

On 07/03/2024 at 07:10, Saganite said:

Ever the pessimist , on Monday evening  with my 152, I saw a thick black line with a disc either side.....

..but what about with Foxy, your ED103Swt, Steve??🤔. 

That extra 3mm could make all the difference!!😁

Dave

[Mircea]

Ian

Very good points made by you, that is a  concentrated history of double star astronomy ! 

 

I agree with all but one: Galileo. Unlike general wisdom, my opinion is that Galileo was a genius scientist ( '' learned'' or similar term in those times ) but not a great observer.

He observed many times in Orion but didn't noticed the Great Nebula M42. It was Claude Fabry de Peiresc the first who took notice of this huge object, visible with naked eyes.

 

Anyway, it was not Benedetto Castellani, one disciple of Galileo, the one who made the first discovery of a double star by observing Mizar ?

I know that Galileo observed himself Theta 1 in Orion as triple star , there is a  sketch in his papers. But he swept the discoveries of double stars under the rug because apparently those were disproving the Heliocentric theory.

Not a very honest attitude from a scientist.

 

Mircea

[jjohnson3803]

I'll have to try it with my 72ED just for grins, although I rather doubt that's going to work.  Then I can try my ST102.

 

[John]

5 hours ago, jjohnson3803 said:

I'll have to try it with my 72ED just for grins, although I rather doubt that's going to work.  Then I can try my ST102.

 

I could see the close pair was a double with my 70mm ED - two closely overlapped airy disks, kind of peanut shaped. No split though.

 

Edited March 27 by John

[F15Rules]

Just spent a very enjoyable hour and a half with Superfox, my lovely new to me Vixen SD115s, observing Tegmine and Theta Aurigae.

I found that the seeing did improve over the 90 minutes, and it was fascinating to try different permutations of eyepieces and barlows. 

My findings were as follows; (all at F7.7, 890mm Focal length).

1. Vixen LVW 5mm at 178x -  Split and Resolved intermittently..this was when the seeing was at its most unsteady earlier on. Contrast was good. Edge sharpness was good across virtually the whole 65 degree field. No false colour noted. I'm so pleased now to own almost the full set of these fine classic eyepieces.

2. Tak Abbe ortho 12.5mm with stacked Baader zoom 2.25x barlow and short WO 1.6x barlow to give c263x.

This was the first and most consistent split. I could see little or no visible image deterioration from the stacked barlows , no false colour and excellent sharpness across the fov (admittedly only a modest 44 degrees, but using an eq mount with RA drive the image hardly moves anyway!).

These Tak Abbes have wonderful contrast and my 12.5mm pair are supremely comfortable for binoviewing.

3. Pentax XL Zoom 8-24mm with Baader 2.25x zoom threaded in to give a high power zoom from 3.55mm (250x in my scope) to 10.66mm (83x).

This eyepiece wouldn't be my first choice for high power on close doubles, but it gave an early session resolved view at 250x on Tegmine..I suspect it would have done even better later in the session but I didnt get time to try it again. 

The Pentax really comes into it's own on short sessions of changeable skies and seeing, where I can simply dial in the best power for the conditions..on such nights, or short sessions, I can often manage with the Baader 2.25  barlow, the Pentax zoom, and my Axiom LX 23mm 84 degree UWA for low power wide field.

For the last part of my session I spent some time on Theta Aurigae, an old favourite of mine..as a lad in the 70s I used to struggle to split this unequal pair..at mags 2.7 and 7.2 and just  a 3" split, my little 60mm refractor rarely, if ever, split them. But in a modern 80-100mm scope the pair is a delightful sight, with the tiny, faint companion twinkling next to its very bright prime star close by.

The Vixen made short work of this pair and I easily split it at 70x. If you haven't looked at this lately do check it out while it is still very well placed high up in our skies..

It was SO good to be out again at last  tonight, and thanks to John for pointing to Tegmine, a real jewel of a double!👍😀.

Dave

 

 

Orion, Sirius and Procyon slowly sinking west over our house twilight turns to night..

Superfox ready for some tight doubles action!

 

Edited March 28 by F15Rules
Photo added

[John]

What a great report 🙂

Raining (again !) here 😒

Gives me time to fettle my new project though 😉 

[Stu]

1 hour ago, John said:

Gives me time to fettle my new project though 😉 

Very mysterious John, when is the grand reveal?

[John]

2 minutes ago, Stu said:

Very mysterious John, when is the grand reveal?

In due course Stu. I'm taking it carefully 🙂

[Whistlin Bob]

I don't have a 4 inch frac, but I was inspired by this thread,and after a dreadful March we finally got a clear night.

I was observing with a 14" dob, and thought I'd see what it could do on Tegmine,which I've not observed before. The third component was a nice easy split, but the 2 close stars were suffering a bit from the 'hairyness' that you often get with dobs. Problem solved with the aperture mask- which gives 160mm of unobstructed F10 aperture. Even with this the split wasn't easy- but with a little patience the little black line gradually emerged into view 😃

[John]

43 minutes ago, Whistlin Bob said:

I don't have a 4 inch frac, but I was inspired by this thread,and after a dreadful March we finally got a clear night.

I was observing with a 14" dob, and thought I'd see what it could do on Tegmine,which I've not observed before. The third component was a nice easy split, but the 2 close stars were suffering a bit from the 'hairyness' that you often get with dobs. Problem solved with the aperture mask- which gives 160mm of unobstructed F10 aperture. Even with this the split wasn't easy- but with a little patience the little black line gradually emerged into view 😃

Occasionally I used an aperture mask with my 12 inch dob which gave a 4.5 inch F/14 unobstructed aperture. The views were very much like a 4.5 inch apochromat refractor. Theoretically the larger scope should split the close pair easily but the less "tidy" star images ("hairyness" is a good description !) makes things challenging.

Glad you got it with the mask 🙂

Edited March 30 by John

[IB20]

Just finding this system without a finder has been a labour of love! If I ever see Al Kirkab again I might scream…

Finally found two yellowish white stars with the 17.5mm Morph in the 125mm. Honing in with the 4mm TOE shows a triple system. With settled seeing the close pair were resolved but flitting from peanut to snowman to definite separation. A great target! Just don’t ask me to find it again 🤣 

[Mr Spock]

I've been on this just now. With the 100mm I can see two clear, but joined discs. I put the 120mm achro on and that splits them at x250 - I can see a fine line of dark between them. That old Helios is quite good on doubles, I don't see much CA at all.

[lunator]

I had a look tonight in the Dob, I hadn't planned to but M44 looked very good so after viewing it I hopped over to have a look. It was clearly resolved but not split at x150 and x100. 

Cheers

Ian

[wookie1965]

Well I resolved Tegmine in the Vixen 102m with a barlowed 6mm, I have split it a few times but that was with my 5" Meade I should never have sold that.