Delta Cygni (again !)

[John]

I'm getting rather fond of this rather tight unequal brightness double in Cygnus

After observing it last night with my 6" F/8 refractor and splitting it fairly easily, I thought I stretch my 4" F/6.5 ED refactor a bit and give it a go with the smaller aperture.

The brighter componant (mag 2.8) is bright enough to produce a single diffraction ring around it's airey disk. The fainter componant (mag 6.33) sits right on the diffraction ring with the 4" aperture which makes the view rather lovely IMHO - rather like a pale silver ring with a diamond embedded in it, encircling the bighter star

I believe the separation of this pair is around 2.5 seconds of arc which, if the componants were of equal brightness, would be a relatively easy split witht he 4" but the inequality of magnitude between the stars is what puts the challenge into this object.

Cygnus is such a rich constellation - full of "treasures"

[Dave Smith]

Thanks, I must give this a go with my 4".

Dave

[Mark at Beaufort]

John I have undertaken a number of double star observing nights recently and Delta Cygni is on the must do list. I will see how my 4" gets on.

Mark

[lunator]

John

It is a lovely sight

Cheers

Ian

[Dave Smith]

Wonderful, thank you John. I managed to split it with my FL102S with 5mm eyepiece. I initially tried with binoviewers and 8-24mm zoom set on 8mm and was beginning to wonder whether I was on the correct star, but with my single 5mm Nagler it popped into view. To me the main star was bright white but the secondary had, I thought, an apple green hue. It was tangled up with the diffraction rings and was, as has been said, a wonderful sight. I am really getting hooked on these double stars and have just bought the Cambridge Double Star Atlas that will keep me happy for a long time:)

Dave

[John]

Nice one Dave

I tried it again myself tonight but this time with my 6" F/8 - much easier to split of course but the view was not quite as "tidy" as the ED102 produces.

..... I am really getting hooked on these double stars and have just bought the Cambridge Double Star Atlas that will keep me happy for a long time:)

Dave

As I'm getting hooked as well I'll have to put that one on my "wanted" list

Lovely scopes the FL102's - one has just come up on Astro Buy & Sell but I'm having to be strict with myself ..... I really can't justify two Vixen 102mm's

[Dave Smith]

Lovely scopes the FL102's - one has just come up on Astro Buy & Sell but I'm having to be strict with myself ..... I really can't justify two Vixen 102mm's

I wonder if that is the one that was on sale at Kelling in April. As far as I know it didn't sell. It is a wonderful scope.

Dave

[John]

I wonder if that is the one that was on sale at Kelling in April. As far as I know it didn't sell. It is a wonderful scope.

Dave

It has a couple of rather deep, though small, dents in the tube but the seller has reflected this in the price - £550 delivered I think

[mdstuart]

Just had a go and delta cygnus is a tough one. Izar is a clean "3mm" split in my 4mm Ortho so x300..Both stars are sharp points. Move to Delta Cygnus and whoa where is that double..Its so..much fainter than the primary..But at x300 it is pretty obvious 1mm to the left (techinical term) of the primary about "0.5mm away". AS you say the primary shows some airy disks but mainly to the left of the star?

Anyway pleased to see it..

Aslo checked out U cygnus nearby. That one is very red and pretty bright in its cycle to my eyes.

Mark

[John]

Just had a go and delta cygnus is a tough one. Izar is a clean "3mm" split in my 4mm Ortho so x300..Both stars are sharp points. Move to Delta Cygnus and whoa where is that double..Its so..much fainter than the primary..But at x300 it is pretty obvious 1mm to the left (techinical term) of the primary about "0.5mm away". AS you say the primary shows some airy disks but mainly to the left of the star?

Anyway pleased to see it..

Aslo checked out U cygnus nearby. That one is very red and pretty bright in its cycle to my eyes.

Mark

It's quite a tough one Mark - but gives a sense of achievement when you manage it

Izar is another of my favourites as well

Binary stars are suprisingly addictive - especially as it does not really get dark enough at the moment for much DSO work. The close ones are a good test of the scope, the seeing and the observers eyes !.

[mdstuart]

Now I need a slightly harder one!

[John]

Now I need a slightly harder one!

Try Zeta Herculis - it's the toughest double that I've tried so far - I think I've just managed to split it with my 6" F/8 refractor but it's very, very tight - possibly not much over 1 arc second separation.

I'd be interested to hear what you make of it

[mdstuart]

I decided to do a tour of the doubles in Hercules. I enjoyed Alpha,Rho,95,100 and Struve 2319.... all fine doubles and all relatively easy even in the 9mm lens..

Rechecked Delta cygni. Still fine, lovely faint star right next to the Primary.

Zeta Hercules no chance. Even after cooling the scope at x 300 it is a ball of wobbly light.So I need better seeing or adaptive optics to pick this double out...

If you can split it then it proves a 6 inch refractor outperforms a 10 inch F5 dob for this type of double star.

Mark

[John]

Zeta Hercules no chance. Even after cooling the scope at x 300 it is a ball of wobbly light.So I need better seeing or adaptive optics to pick this double out...

If you can split it then it proves a 6 inch refractor outperforms a 10 inch F5 dob for this type of double star.

Mark

Hi Mark,

As I said my report on Zeta Herc, it's really, really tight with my 6" refractor - I get a similar result to you with my 10" F/4.8 Orion Optics newtonian.

My refractor has a Chromacor corrector fitted which moves it's optical performance close to an ED scope of that aperture by correcting the majority of chromatic abberation and the under-correction that my scope (like many Chinese achromats) has. So the airey disks of stars are pretty tight which helps split those tight doubles.

I'm still trying to find an up to date figure for the separation and position angle for this one - it's period is only 34.5 years so the PA changes relatively quickly.

[mdstuart]

http://www.dibonsmith.com/her_zeta.gif

Gives you what you want I think..

Mark

[Moonshane]

does that mean that the secondary is at the minute almost behind the primary? or are we looking at the stars from above like the drawing?

I had a go at these two last night with the dob. Delta Cygni was readily split even in quite poor seeing conditions. The colour of the secondary looked a little orange but maybe that's my eyes! A ND filter helped a little.

I then tried Zeta Hercules but no chance at all with that one. I'll try both with my refractor next time out.

[John]

does that mean that the secondary is at the minute almost behind the primary? or are we looking at the stars from above like the drawing?

...

I think the diagram gives the position as we see it - it looks as if Zeta Herc is approaching it's max separation but even then it's really going to be tight given the inequality in brightness of the componants.

I'm beginning to doubt whether I really split it now TBH

I'll give it another try when I get a chance.

[John]

http://www.dibonsmith.com/her_zeta.gif

Gives you what you want I think..

Mark

Thanks Mark - I'm having a mental block here (must be the sun !) - is North at the bottom on that diagram ?.

[Moonshane]

I'm beginning to doubt whether I really split it now TBH

cheers John, just checking.

oh no, it looks like you'll have to spend more time at the scope - how awful

[mdstuart]

Right lets see how close we can go with relatively close mag double stars high up at the moment..

Delta Cyg is 2.5 but with wide mag variation...

2.0" The close ones in Alkalurops (BOO) I know these are relatively easy..

1.9" STT296 (BOO)

1.8" STF 1884 (BOO)

1.7" STF 2218 (DRA)

1.6" SFT1932 (CRB)

1.5" Lambda (OPH)

1.4" STF2107 (HER)

1.3" STF 2114 (OPH)

1.2" STF 2289 (HER)

And then Zeta 1.1"

Mark

[John]

Great list Mark - I'm going to be away for a while so I'll give them a go when I get back.

I managed Pi Aquillae last night which is a more or less equal brightness 1.4" pair.

[mdstuart]

Well I managed pretty much all of the list.

The verdict..2" is relatively easy with two relatively equal mag 6 stars. At 300x using the 4mm Ortho two little full stops about 1mm apart.

At you go closer it gets progressively harder. At 1.2" then two dots are almost touching and the view goes from one wobbly object to two little dots as the pair go accross the FOV. Working out the PA seems to be quite tough at times with my estimates often at odds with the literature but hey they may have moved..

It is certainly harder to split the pairs that were lower in the sky. So looking through more atmoshpere makes it tougher.

I have been told to make a mask to cover most of the Scope opening but leaving the outside ring to make Zeta Hercules less bright. Apparantly I might then split it.

To be honest I need more than x 300 as even if the stars were solid dots they would be too close physically to see as two objects!

I have ordered a 6mm Burgess TMB eyepiece and I may get a barlow to try things at 3mm or x400..

I would be interested in your view on these close pairs..

I will try Pi aquila.

Mark

[Mark at Beaufort]

The sky was clear, transparent and steady last night so decided to view this close double with my 4" frac - 5mm Nagler and 2x APO barlow giving 284x magnification.

The companion was faint against the primary but was clearly visible in the frac which is at the limit of the scope but pleasing to see it.

Feeling confident went over to Zeta Hercules but I could only detect a 'blob'.

I would recommend the Cambridge Double Star atlas which provides good star maps as well as a host of info on great doubles to view.

Mark

[Mr Spock]

Out of all my scopes my OMC-140 splits doubles the best. Yes, even better than the 250mm...

It's all down to the clean airy disk with little in the way of diffraction rings.