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  #1  
Old 28-08-2018, 09:00 PM
Wavytone (Nick)
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Anyone for Doubles ?

As many might be aware many of the basic lists of double stars have a rather northern-hemisphere bias. So... for those keen to push the limits of their scope, here are two lists of bright doubles for the southern hemisphere selected to challenge scopes in the range 4" to 12" aperture.

The first list is pretty easy. It includes a couple of really easy ones like Acrux, but then a couple of wide pairs with huge magnitude differences that will test the contrast of your scope - Sirius and Antares. Then it drops down to a more serious challenge - pairs with separations under 5 arcseconds.

The second list is extracted from the WDS and is a much harder challenge for scopes in the range 100mm to 400mm aperture:

- separation between 0.3 to 2 arc seconds;
- stars south of +15 degrees declination;
- both components brighter than magnitude 7.5.

For these you're really going to need excellent seeing and crank up the magnification to the max - when you're seeing donuts you're getting warm.

I've sorted it by separation, if you want it in other sort orders please ask.

If you have a go please advise what you can/cannot resolve and the make/model and aperture of your scope.
Attached Files
File Type: pdf Easy List Bright Double Stars.pdf (81.3 KB, 56 views)
File Type: pdf Harder List Bright close southern doubles .pdf (64.4 KB, 48 views)

Last edited by Wavytone; 28-08-2018 at 09:17 PM.
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  #2  
Old 29-08-2018, 12:03 PM
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mental4astro (Alexander)
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Thanks for the lists, Wavy.

Going to come in very handy for my start testing

Alex.
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  #3  
Old 29-08-2018, 12:25 PM
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Atmos (Colin)
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When I eventually get myself an AZ-EQ6 I should try these with a 4” doublet first before trying again with the Mewlon 250. Can also get mono and bino viewing for both.
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  #4  
Old 31-08-2018, 08:02 AM
morls (Stephen)
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Great lists Nick, thanks. Should be fun once the skies clear.
Stephen
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  #5  
Old 31-08-2018, 09:35 AM
Wavytone (Nick)
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Hi Stephen good luck !

The second list is much harder than it looks.

A couple of nights ago I had a go at Rho Cap when it was near the zenith. The scope must be collimated perfectly, the seeing very good and enough magnification to cleanly show the airy disk and a couple of rings around a star like Acrux, for example.

Despite separation of 1.8 arcsec I had to push the magnification up past 300X - even had it at an insane 500X for a while - to be sure I could see it split cleanly, given the difference in magnitudes.

So these really are a supreme test of scope and eyeball.

I’ll add that some of these doubles have noticeable colour differences.
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  #6  
Old 21-09-2018, 02:51 PM
Kerber1955 (Ross)
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Rho Cap - interesting binary that's been getting wider in recent years. I looked through my observing notes and found I'd not looked at it since 1997 (!!) despite having it on a list of changing pairs to follow up. This year it will happen.



Back in '97 I found it a tight pair, 1.3" apart at the time, instead of 1.8" now; and the 2 magnitude or so brightness difference makes it tougher. Anyway, in '97 it was a neat split at 330x with a 7-inch refractor on a night of good seeing. The secondary star was visible at 180x, but not as clean or clear.



I'd tried it the previous night without success, but the seeing on the previous night was not at all good; on the successful night, I rated the seeing as very good.



Seeing conditions make a very big difference with these tougher doubles, especially the unequally bright as well as close examples.
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  #7  
Old 21-09-2018, 09:36 PM
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netwolf
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Thx for the list Nick, been looking for a SH list to try on my etx125 and skywatcher mac. I almost got Sirius once but not 100 percent sure, it was a long night and best night I had with the skywatcher mak did many doubles.
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  #8  
Old 21-09-2018, 11:01 PM
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AstroJunk (Jonathan)
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Great lists.

Every visual observer needs to hone their skills on close doubles - Apart from many being very lovely in them selves, it's a real test of visual acuity and the ability of an observer to make the best of their equipment and circumstances!

My tip with Sirius B is to make a careful note of where you think it may have been in the eyepiece before looking to see where it actually should be. If they coincide the all is good. This technique works best with alt-az mounts of course because that PA isn't changing in a hurry . Seeing is everything for that pair!!!
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  #9  
Old 30-09-2018, 08:21 AM
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darrellx (Darrell)
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Hi All

I am interested if and how anyone is measuring doubles. I have been keenly and regularly observing doubles for a long time and have started to become more interested in measurements in the last 4 or 5 years.

Visually, I have tried my illuminated reticle eyepiece with crosshairs. For software I have tried Reduc (Florent Losse) and XParallax (Valencia University). I have decided to go down the AstroArt path for image processing, and part of my reasoning was that it includes some Photometry and Astrometry tools. I will see how they go. Also, I now have AstroArt7. So far, I have had limited success regarding accuracy.

If anyone is using something like a filar micrometer, I would be interested to know where you got it.

I don't want to hi-jack the thread, but this seemed to be a good place for the question.

Thanks
darrell
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  #10  
Old 02-10-2018, 07:45 AM
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mental4astro (Alexander)
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Darrell,

I can't help you with your question, but you are not hijacking this thread at all! This thread is EXACTLY the right place for your question! I hope someone will soon be able to help you out.

Alex.
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  #11  
Old 02-10-2018, 11:06 AM
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big-blue
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I keep an eye on a number of close doubles as a guide to seeing quality. One of my regulars is Beta Muscae, which I looked up in the list provided by Nick. I noticed that separation is given as a very tight 0.8" which surprised me as I have split it cleanly with an ETX-125 on a good night, and I do not think the ETX is that good !

Looking up other references via Google, there is a range of separations all the way from 0.8" up to 1.6" and the upper end reflects my experience.

How can there be such a range of reported separations, given that its period is quite long and the separation has not changed much in the last 50 years (even tho PA might have changed) ?

See attached diagram picked off the web (And the web is never wrong is it !?)
Or are modern authors still quoting the 1880 separation ;-)

I do not mean to criticise the provided list, as I have already printed it out as an observing reference. ( & thankyou Nick for providing it)

Just wondering how precision measurements can be reported so differently.

Thoughts ?
cheers

Last edited by big-blue; 02-10-2018 at 11:18 AM. Reason: image attached
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  #12  
Old 02-10-2018, 11:15 AM
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big-blue
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cannot see my attachment in my post above.... see this link
http://www.southastrodel.com/PageDS012.htm
& scroll down about 2/3 to diagram of Beta Muscae.
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  #13  
Old 02-10-2018, 03:20 PM
Wavytone (Nick)
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Sorry my error - I think - there are two entries for Beta Muscae, one at separation 0.8" and the other about 1.4" - depending on epoch - which is most likely tallies with what you saw in the ETX, Andrew James was using a C8. I doubt you split 0.8" with an ETX.

The entry at 0.8" is from the WDS. I'll check that one in my beast as there's clearly an error in one of the catalogues.

Just goes to show how few reliable measures there are on some bright doubles. There was one in my WDS list selection that had just ONE accepted measure. Double star measures are not hard to do from a light-polluted backyard if you have a high-magnification scope and a micrometer.

Last edited by Wavytone; 02-10-2018 at 08:57 PM.
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  #14  
Old 03-10-2018, 06:00 PM
Graeme Bluestar (Graeme)
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Darrell,
I have been carrying out double star measurement for the last ten years using various cameras/scopes for imaging, and Reduc for the measurements. Over that time a number of my results papers have been published in both the Journal of Double Star Observations(USA), and the Webb Society Double Star Section Circular (UK). I have also been involved in the discovery of three new pairs.
If you are interested in taking the next step on from enjoying their visual beauty I would be happy to help you where necessary.
After spending some years simply admiring the views with my 6" refractor the bug really bit me and I took the next step of recording and publishing my results.
Filar micrometers are not that common and I found modestly priced cameras etc. were quite suitable. A relatively small $$ outlay can get you on the way to carrying out scientifically valid research.
regards,
Graeme
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  #15  
Old 09-10-2018, 07:41 AM
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darrellx (Darrell)
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Graeme

Thanks for the response and kind offer. You have some impressive achievements listed there.

I have been observing Doubles for a long time and have been using my cmos cameras to take some images and try to make accurate measurements. I try to calibrate my images on known separations, then manually measure whatever my targets happen to be.

The problem I am having at the moment is Reduc. Some years ago, I had it working, but since upgrading to Win10 I just cannot get a stable install running. As soon as I start to do something, it hangs and shuts down. Once I get it working, I will send you a screen shot with a question or two.

Thanks
Darrell
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  #16  
Old 15-10-2018, 11:55 PM
Kerber1955 (Ross)
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With regard to the separation of Beta Muscae being a puzzle, I have the WDS data file for this pair, which I obtained some time ago.

Early measures were erratic, to put it politely; including repeats by some of the same people. Back around 1900, the separation was most likely around 1.2" to 1.3" and changing pretty slowly. It became wider, and by the late 1940s was about 1.40" (Simonow at Stromlo; van den Bos in Johannesburg).

It didn't widen much more after that, and by 1991 Hipparcos got 1.206" with the same year a speckle measure by Hartkopf (4-m scope) giving 1.201". No doubt the third decimal is cancy with these.

By 2015 Tokovinin with 4.1m and speckle got 1.0218"; Rainer Anton using "lucky imaging" (0.5m scope) had measures of 1.010" and 1.002" in 2016: say 1.005"

So, the mentioned 0.8" is not something that's happened in the last 100+ years. 1.4" fits for mid-20th century; and for more recent dates you have the numbers above.

Beta Mus had an orbit calculation done in 1964, and it was a pretty bad effort. The Orbit Catalogue gave it a Grade 5 rating, which means it's not regarded as being much more than a first attempt.

More recently (2012) there's a new orbit, the period now is given as 194 years, near enough half the period of the older orbit, which had a 383 year orbit. The new calculation, although looking more plausible (helped by another 50 years of measures) is also Grade 5. It will help when Beta Mus has travelled more of its orbit.
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  #17  
Old 16-10-2018, 03:05 PM
Tropo-Bob (Bob)
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Quote:
Originally Posted by Kerber1955 View Post
With regard to the separation of Beta Muscae being a puzzle, I have the WDS data file for this pair, which I obtained some time ago.

Early measures were erratic, to put it politely; including repeats by some of the same people. Back around 1900, the separation was most likely around 1.2" to 1.3" and changing pretty slowly. It became wider, and by the late 1940s was about 1.40" (Simonow at Stromlo; van den Bos in Johannesburg).

It didn't widen much more after that, and by 1991 Hipparcos got 1.206" with the same year a speckle measure by Hartkopf (4-m scope) giving 1.201". No doubt the third decimal is cancy with these.

By 2015 Tokovinin with 4.1m and speckle got 1.0218"; Rainer Anton using "lucky imaging" (0.5m scope) had measures of 1.010" and 1.002" in 2016: say 1.005"

So, the mentioned 0.8" is not something that's happened in the last 100+ years. 1.4" fits for mid-20th century; and for more recent dates you have the numbers above.

Beta Mus had an orbit calculation done in 1964, and it was a pretty bad effort. The Orbit Catalogue gave it a Grade 5 rating, which means it's not regarded as being much more than a first attempt.

More recently (2012) there's a new orbit, the period now is given as 194 years, near enough half the period of the older orbit, which had a 383 year orbit. The new calculation, although looking more plausible (helped by another 50 years of measures) is also Grade 5. It will help when Beta Mus has travelled more of its orbit.
Thanks Ross,

I have occasionally tried and have always failed to split this one. Seeing is not the best here and it a little low from my tropical location.

I will try again, next year.
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  #18  
Old 16-10-2018, 03:22 PM
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Regulus (Trevor)
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I'll add my thanks to the list too Nick. This will be very useful.

Trev
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