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

[John]

Tegmine close pair: ~4 inch to get resolution, ~5 inch to split 🙂

 

[lunator]

I've had a look through my imaged and had dug out 2 pics, one from 2007 and one from 2022. It amazing to see the orbital motion over 15 years. The image scale is very different but hopefully it is clear.

Cheers

Ian

[Stu]

8 hours ago, lunator said:

I've had a look through my imaged and had dug out 2 pics, one from 2007 and one from 2022. It amazing to see the orbital motion over 15 years. The image scale is very different but hopefully it is clear.

Cheers

Ian

Amazing! Just shows the benefit of keeping long term records.

[josefk]

Resolved but not split in a 130mm refractor last night - terrible fuzzy/bouncy seeing really at magnifications above x125 and i shouldn't have spent as long trying as i did. Never mind. 

Using the newly learnt nomenclature i found AB to be unresolved at x125 while i had I had two resolved but bouncy balls drifting repeatedly across the FOV at x200, x250, and a waste of time x303. At these higher magnifications AB was very clearly resolved and at times as resolved as i imagine it could be without actually splitting (a real figure of eight impression). Tantalising but ultimately futile versus the seeing. 

 

[John]

10 hours ago, lunator said:

I've had a look through my imaged and had dug out 2 pics, one from 2007 and one from 2022. It amazing to see the orbital motion over 15 years. The image scale is very different but hopefully it is clear.

Cheers

Ian

Very interesting images Ian 🙂

I must dig out the sketches I made of Zeta Herculis when I first split it and more recently. I recall that those showed a noticeable change in position angle over a period of a few years as well. Unless it was just my lousy sketching 🤔

The Universe in motion - great stuff 🙂

Edited April 2 by John

[Mr Spock]

Thought I'd add my drawing from a few nights ago.

[SuburbanMak]

On 01/04/2024 at 11:39, John said:

Tegmine close pair: ~4 inch to get resolution, ~5 inch to split 🙂

 

This tallies absolutely with my recent side by side observation using a 5" SW Mak and my 4" Tak FC100 DC. 

The Mak (which actually operates around 120mm,  so slightly less than 5") showed a clean black line between the two elements, the 4" Tak showed a "snowman" - overlapping discs, so resolved but not split.   

[John]

1 hour ago, SuburbanMak said:

This tallies absolutely with my recent side by side observation using a 5" SW Mak and my 4" Tak FC100 DC. 

The Mak (which actually operates around 120mm,  so slightly less than 5") showed a clean black line between the two elements, the 4" Tak showed a "snowman" - overlapping discs, so resolved but not split.   

I'll be interested to see if there are conditions under which a good 4 inch can get a definitive split of the close pair of Tegmine. As someone else said in this thread, seeing any stars at all has been a challenge over the past months, let alone actually splitting these close ones 🙄

[Mr Spock]

2 minutes ago, John said:

I'll be interested to see if there are conditions under which a good 4 inch can get a definitive split of the close pair of Tegmine.

Should be impossible. At 1.1" the larger airy disks of a 4" will always overlap. You need the smaller airy discs of a 5" and above to separate them.

[Mr Spock]

The Dawes limit for 100mm is 1.16", and the Rayleigh limit 1.38". I have definitely split 1.2" with the 100mm. At the very best a 1.1" pair looks like an 8.

[Zermelo]

1 hour ago, SuburbanMak said:

This tallies absolutely with my recent side by side observation using a 5" SW Mak and my 4" Tak FC100 DC. 

The Mak (which actually operates around 120mm,  so slightly less than 5") showed a clean black line between the two elements, the 4" Tak showed a "snowman" - overlapping discs, so resolved but not split.   

I've split it several times in my SW127 Mak. I'm still not sure if the "effective" aperture of 119/120mm affects the resolution as well as the image brightness. In any case, I've split doubles in the Mak below the theoretical Rayleigh limit.

[Nik271]

Obstructed optics can split slightly closer pairs of double stars, in the special case when the unobstructed optic presents touching central discs, like this:

(Excuse my terrible drawings,  it's for illustration puspose only)

Unobstructed aperture: 

 

With 30% obstruction the central disc is a but smaller at the expense of the larger first ring, which becomes fatter and brighter, like this:

 

This is very useful for pairs of equal stars at the Raleigh limit. Of course obstructed aperture is more often a liability e.g. for  unequal stars where the dim companion is exactly on the first diffraction ring.  Observers of double stars in the 18 and 19 century were aware of this and I have seen entry in Herschel's catalogue where he recommends adding an obstructon to the refractor for some close pairs.

  

Edited April 4 by Nik271
corrected typos

[F15Rules]

4 hours ago, Mr Spock said:

Thought I'd add my drawing from a few nights ago.

A sketch like that, showing an image from a 4.75" cheap achromat worth perhaps £150 versus a Japanese hi end 4" apochromat costing c £2k does beg the question..why pay out the £2k??🤔🤦‍♂️🤷‍♂️

Dave

[Mr Spock]

20 minutes ago, F15Rules said:

A sketch like that, showing an image from a 4.75" cheap achromat worth perhaps £150 versus a Japanese hi end 4" apochromat costing c £2k does beg the question..why pay out the £2k??

Try the same on the moon or Jupiter 

[Stu]

43 minutes ago, F15Rules said:

A sketch like that, showing an image from a 4.75" cheap achromat worth perhaps £150 versus a Japanese hi end 4" apochromat costing c £2k does beg the question..why pay out the £2k??🤔🤦‍♂️🤷‍♂️

Dave

Indeed! I recall getting better resolution on Zeta Herculis with a Heritage 130p than my rather lovely and expensive Vixen FL102S. It just shows that aperture does count for that and the the optics on the Heritage scopes are actually very good.

Do I prefer the aesthetics of the views in the Vixen to a 130p? Yes I do, but in that instance (and likely some others) the resolution benefits of the additional aperture do show through.

[F15Rules]

Of course, I was being tongue in cheek (being myself the owner of an Apo wich costs almost £3k new), but it does beg the question..

...and it does also remind us that even the most humble, cheap scope available today is far superior to the tools that early astro explorers such as Galileo could dream of..we are very fortunate!

If only we had their levels of dark skies!😊

[Zermelo]

31 minutes ago, F15Rules said:

we are very fortunate!

We are indeed.

[Zermelo]

1 hour ago, Nik271 said:

Obstructed optics can split slightly closer pairs of double stars, in the special case when the unobstructed optic presents touching central discs, like this:

(Excuse my terrible drawings,  it's for illustration puspose only)

Unobstructed aperture: 

 

With 30% obstruction the central disc is a but smaller at the expense of the larger first ring, which becomes fatter and brighter, like this:

 

This is very useful for pairs of equal stars at the Raleigh limit. Of course obstructed aperture is more often a liability e.g. for  unequal stars where the dim companion is exactly on the first diffraction ring.  Observers of double stars in the 18 and 19 century were aware of this and I have seen entry in Herschel's catalogue where he recommends adding an obstructon to the refractor for some close pairs.

  

Excellent, that makes sense.

Now that I have a dual saddle mount, I can pair the Mak with my 4" acro, and switch between them depending on the magnitude difference!

[John]

According to the Stella Doppie database, there is nearly 1 magnitude difference between the stars of the close pair of Tegmine. 

I wonder, at what point is a brightness difference going to start adding to the challenge of splitting these stars ?

Does anyone know of a more equal pair of around the same separation ? - it would be interesting to compare those with Tegmine.

 

[Mr Spock]

21 minutes ago, John said:

Does anyone know of a more equal pair of around the same separation ? - it would be interesting to compare those with Tegmine.

From Stelle Doppie

name       cst      SAO         coord                        wds_name       last       obs    pa    sep    m1    m2      d_mag

Grafias    Sco    159665    16 04 22  -11 22 23    STF 1998 AB    2019    626    12    1.1    4.84    4.86    0.02
 

[John]

5 minutes ago, Mr Spock said:

From Stelle Doppie

name       cst      SAO         coord                        wds_name       last       obs    pa    sep    m1    m2      d_mag

Grafias    Sco    159665    16 04 22  -11 22 23    STF 1998 AB    2019    626    12    1.1    4.84    4.86    0.02
 

Thanks - a 1.1 arc sec separation in Scorpio - that should be fun 🙂

[Mr Spock]

3 minutes ago, John said:

in Scorpio - that should be fun

3° lower than Rigel, 5° higher than Sirius. Shouldn't be too difficult 

[Zermelo]

1 hour ago, John said:

I wonder, at what point is a brightness difference going to start adding to the challenge of splitting these stars ?

This is quite interesting

http://fisherka.csolutionshosting.net/astronote/astromath/ueb/Unequalbinaries.html

[IB20]

Took a low res shaky phone video on Friday, you can make out the companion, just. 

[lunator]

I've has a crack at cleaning up the 2007 image. I have scaled the 2022 image to match the 2007 one. I have put together a gif.

I might try and improve the 2007 image more if I can.

Cheers

Ian