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Delta Cygni

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#1 Kon Dealer

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Posted 08 July 2013 - 11:08 AM

Last night had the best viewing conditions (for me) in months.
Using my 102mm refractor, Izar was an easy split at x77, the Double Double cleanly split at x68 and fairly convincingly at x51.
I then turned my scope to new challenges. Marfik at 1.4 arcsecs was easy at x180.
Best of the night was Delta Cygni, or Rukh (SAO 48796).
The large magnitude difference (2.9 and 6.3)with a listed 2.9 arcsecs separation made this quite a challenge.
At x180 a the small, slightly grey secondary could just be seen, positioned at 9 o'clock, relative to the large white primary, just outside the first (and only) diffraction ring.
:cool: :cool:

#2 ggalilei

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Posted 08 July 2013 - 11:29 AM

My eye does not have such good resolution as yours. I can get an easy split of Izar at 160x but I doubt I can do much better. I tested my limit on the double double and I got down to 68x (I realize that others can split it around 50x).
Delta Cygni and Izar are beauties, aren't they? I always go back to them no matter what else I'm observing.

#3 azure1961p

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Posted 08 July 2013 - 07:56 PM

Anton,

Its not a fair test of your scope which has super resolving power. The fact is those same doubles at those magnifications are overwhelming saturated in glare and irradiation. Those tests where across a field of scopes everyone try's to get the lowest power split or duplicity is really only fair when the apertures are alike. A far more revealing test is going by the power per inch rule.

Kon it sounds like you had a phenomenal night with some real showpieces. Delta Cygni is one of my big favs. I love the grey powder blue of the companion.


Pete

#4 Svezda

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Posted 08 July 2013 - 08:42 PM

It's interesting that you experienced your best seeing conditions for splitting doubles in months...I had the same impression, and so I checked your location in case it was not far from me...but I saw that you are in England and I am in...Texas! The first sign it was going to be a great night: Saturn at about 20-30deg elevation by the time it gets around my trees is usually a boiling mess. Last night it was as sharp as a Voyager image. I was stunned! So, on to some challenging doubles. I tried Zeta Herculis since so far, even with my 14.5 inch/37cm Newtonian I hadn't really cleanly split it but last night I saw a fine but tiny black space between the stars (I think it is now about 0".9arcsec sep.). There is a pretty tough mag delta, too, so I was really pleased. Other doubles in the ~1 arcsec sep. category were very cleanly split with no 'wavering' between fuzzy and sharp as I usually experience. I wished sooo much that Jupiter had been visible during such a night - it would have been unforgettable.

#5 fred1871

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Posted 08 July 2013 - 10:32 PM

As mentioned in another thread, Zeta Herculis is now at 1.3" separation - it's a short-period, fast-moving binary.
A week ago I observed it with a 140mm refractor, the companion visible at 160x, with neat clean separation at 230x. And, yes, the seeing was good at the time. :grin:

#6 Kon Dealer

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Posted 09 July 2013 - 10:45 AM

As mentioned in another thread, Zeta Herculis is now at 1.3" separation - it's a short-period, fast-moving binary.
A week ago I observed it with a 140mm refractor, the companion visible at 160x, with neat clean separation at 230x. And, yes, the seeing was good at the time. :grin:

Will have to try Zeta Herculis (subject to "seeing").
At 1.3" it should just be within reach of my 102mm. :D
Failing that I'll try my 6 and 8SE to separate.
That said I prefer the colour and less prominent diffraction patterns I get with my refractor.

#7 ggalilei

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Posted 12 July 2013 - 03:31 AM

I tried again Izar tonight at lower power, 85x on the Traveler. Indeed I could clearly see the pair ..... but not as pretty as at 160x!

#8 Jon Isaacs

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Posted 12 July 2013 - 05:52 AM

As mentioned in another thread, Zeta Herculis is now at 1.3" separation - it's a short-period, fast-moving binary.



Where is this information coming from? SkyTools 3 is telling me it's currently at 1.17 arc-seconds.

Just wondering.

Izar is a favorite, Delta Cygni was a nice split the other night in my 80mm FD. In my experience, low power splits depend on the seeing and as Pete mentioned, the exit pupil. Some night Delta Cygni is clean at 100x, some night it takes considerably more.

Jon

#9 azure1961p

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Posted 12 July 2013 - 11:42 AM

Safari gives it at 1.2" for Zeta H - they probably rounded it off.

Pete

#10 7331Peg

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Posted 12 July 2013 - 02:04 PM

You can find the current PA and separation of Zeta Herculis HERE (use the data to the left of the diagram under Orbital Elements), which comes from the WDS Ephemerides table, which can be found HERE. In the first column on the left, scroll down to the WDS coordinates 16413+3136, which are arranged in numerical order.


John :refractor:

#11 astro4565

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Posted 12 July 2013 - 04:28 PM

I split Delta Cygni last fall with a Williams Optics 120mm f/7.5 refractor. I don't know if I will be able to split Zeta Herculis with the 120. Has anybody split it lately with less than a 5" scope? I will try it first with the 15" Obsession cause I may need the resolving power of the 15" and some good seeing to split Zeta Herculis.

#12 Astrojensen

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Posted 12 July 2013 - 05:17 PM

I split it last year with a 63mm Zeiss Telemator. Can't remember the magnification used, but two years ago, I split it with 100x on the binoviewer on the Telemator.

Edit: I read your question as if you were asking about Delta Cygni, but then realized, that you were asking about Zeta Herculis. Sorry.


Clear skies!
Thomas, Denmark

#13 Jon Isaacs

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Posted 12 July 2013 - 07:02 PM

You can find the current PA and separation of Zeta Herculis HERE (use the data to the left of the diagram under Orbital Elements), which comes from the WDS Ephemerides table, which can be found HERE. In the first column on the left, scroll down to the WDS coordinates 16413+3136, which are arranged in numerical order.


John :refractor:


Those numbers are very much in agreement with SkyTools 3 which also uses the WDS orbital elements to calculate the current separation.

Skytools 3 provides 1.17 arc-seconds for 2013.5 where as the Sixth Orbit catalog provides 1.163 arc-seconds for 2013 and 1.186 arc-seconds for 2014. That's close enough for me..

What I was wondering where the 1.3 arc-seconds came from, maybe from the Stelledoppe which lists sep last as 1.3 with no units.

Jon

#14 fred1871

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Posted 12 July 2013 - 08:27 PM

Not sure if I misread the 6th orbit catalog or mis-remembered or had a typo (it was a few days ago) - but, yes, 1.2" should be the right number, not 1.3".

Regarding Sky Tools, I have it but no longer use it for double star listings and similar. For current data and ephemeris information I go directly to the WDS and the 6th Orbit Catalog. For making lists of doubles to observe, I now use AstroPLanner in preference.

My change of what to use started when I found that in SkyTools, asking for a listing by WDS designation - in other words, by discoverer designation, the standard long-time way of listing doubles - gave me lists using a mix of various designations only a few of which were discoverers. Lots of SAO, HD, etc. Not helpful, not useful, and leads to the common "which star is that" conundrum. Why SkyTools does it that way I have no idea. That it won't give what's asked for goes beyond "glitch".

The Stelle Doppie data is interesting - we have the problem of "Sep Now" given as 0.87 (not correct); while "Sep last" is 1.3". That number correctly reflects the last measure in the WDS, which was 1.3" in 2011.

Returning to Zeta Her - at 1.2", and delta-m of 2.4 mags, it won't be a walk in the park for a 102mm telescope (suggested above, for trying). As always, brightness difference at this level makes pairs tougher. Zeta Her is an interesting object partly because of the short period, with changing separation and angle - an orbit period of just over 34 years gives noticeable change without waiting centuries. The 2004 measure, listed in the Haas book, was 0.9" at PA 229 - 9 years later, PA is around 150 and separation noticeably wider at 1.2".

#15 7331Peg

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Posted 13 July 2013 - 02:28 PM

The Stelladoppie site is a great resource, but there are errors you have to watch for that apparently come from the way the information is pulled in from the WDS. For a quick look at a double star's data, it's much quicker than scrolling through the WDS. But for essential data I follow the same route Fred does.


John :refractor:

#16 Nucleophile

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Posted 13 July 2013 - 03:05 PM

The Stelladoppie site is a great resource, but there are errors you have to watch for that apparently come from the way the information is pulled in from the WDS. For a quick look at a double star's data, it's much quicker than scrolling through the WDS. But for essential data I follow the same route Fred does.


John :refractor:


Agreed.

I use Stelle Doppie a lot for compiling/evaluating lists--but if the binary has a "Y" under the "ORB" column, I know to look at the orbit catalog for the correct estimated separation. If the "Y" is not checked, I have not found any issues yet with the Stelle Doppie data----it appears faithfully pulled from the WDS in these instances. Just something to be aware of.

#17 Bonco

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Posted 13 July 2013 - 03:26 PM

I find it interesting that several decades ago many writers wrote Delta was a good test for a 6 inch scope. Well maybe, but my 60mm f/15 has no trouble with it, however it does require very good observing conditions. Relatively easy in my 75mm f16.
Bill

#18 saemark30

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Posted 24 July 2013 - 12:10 PM

I used a 80mm ED scope at 200x to see this double.
With a diagonal it appears to be at NW corner 345 deg.
It this correct?
Does someone have a drawing?

#19 lionel

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Posted 28 July 2013 - 12:35 AM

Zeta Her was a moderately difficult split in my 5" refractor last night with the seeing at P5-P6. The secondary was visible in steady moments about 50% of the time at 257x, just touching the primary. I guesstimated the PA at 150 deg (2013 PA = 153 deg - 6th OC.)

Lionel






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