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Research project - Limit for uneven Double Stars

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#1 FrenchStar

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Posted 28 July 2012 - 02:43 PM

I invite you all to read the September 2012 issue of Sky and Telescope(It's at page 68).

Sissy Haas is asking our help to complete a very interesting project. I invite you all to participate!

#2 Astrojensen

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Posted 28 July 2012 - 03:17 PM

Nice, but I don't subscribe to S&T.


Clear skies!
Thomas, Denmark

#3 FrenchStar

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Posted 28 July 2012 - 03:20 PM

Me neither! When I heard about this project, I bought it at the store... :grin:

#4 fred1871

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Posted 28 July 2012 - 08:34 PM

Thanks for the notice - despite being an S&T subscriber I hadn't yet seen the September issue. I've now accessed it online.

It's good to see Sissy Haas back, as she's been absent pretty much since the publication of her double star book.
The project is a neat idea, though I suspect it won't lead to anything as definitive as the Dawes Limit, simply because there are too many factors involved.

Even Dawes limited his description to stars of a cetain brightness level, and with telescopes of moderate size. Once you get into pairs where delta-m can be anything at all, and separation ditto, with the two interacting - not to mention telescopes of different sizes (probably by a large amount), a big range of observer experience and visual acuity, magnification used, etc etc - well, we can hope the project can come up with some useful and interesting results but I suspect they'll be more approximate than the Dawes Limit.

Regardless of the above musings, I'll be joining in and recommend others to be part of it as well. We'll see where it goes once there are lots of observers involved.

Haas refers to Chris Lord's work, which is the best attempt I've seen thus far on this vexed question. And she's well aware of various complicating factors involved. So I wish her project well and look forward to seeing the results of it - obviously, given the RA spread of test stars, it'll take at least a year to get them observed and the results collated and analysed.

It occurs to me that a useful approach is to use aperture stops or a diaphragm on a telescope - so a pair might be easy at full aperture, difficult at 3/4 aperture, not seen at 1/2 aperture. That way the same observer can give results for multiple apertures.

Now if only the clouds will move away!!

#5 fred1871

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Posted 28 July 2012 - 08:54 PM

A further thought - we might end up with different results according to the size of the central obstruction in telescopes - from zero to around 40%. It's a big factor as pairs become more uneven in magnitude.

Hmmm... an term in an equation, or separate equations based on CO? :question:

#6 JimP

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Posted 29 July 2012 - 08:03 AM

I too am very happy to see Sissy return. I will join up and do my best to help out. It will be a fun project and nice to be working on a double star project. I will, of course, be very interested in the results. The more contributors to the project the better! I hope everyone with an interest in double stars will participate.

best,

JimP

#7 JimP

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Posted 29 July 2012 - 08:07 AM

For those who are interested, but do not have access to S&T, Sissy's e-mail address is <has103@comcast.net>

best,

JimP

#8 FrenchStar

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Posted 29 July 2012 - 09:05 AM

And she's well aware of various complicating factors involved. So I wish her project well and look forward to seeing the results of it - obviously, given the RA spread of test stars, it'll take at least a year to get them observed and the results collated and analysed.

It occurs to me that a useful approach is to use aperture stops or a diaphragm on a telescope - so a pair might be easy at full aperture, difficult at 3/4 aperture, not seen at 1/2 aperture. That way the same observer can give results for multiple apertures.


My observing group did contact Sissy Haas and we asked her about the time frame of this Project. It is at least a year of collecting data, if not two.

#9 fred1871

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Posted 29 July 2012 - 07:42 PM

Did the listed email address for Haas work?
I've had my emails bounce back, undelivered, from the listed email address and from a second attempt at "haas103" instead of "has103".

#10 FrenchStar

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Posted 29 July 2012 - 08:57 PM

Did the listed email address for Haas work?
I've had my emails bounce back, undelivered, from the listed email address and from a second attempt at "haas103" instead of "has103".


Hello,

Here is the email I used: has103@comcast.net No error message, yet.

Frenchstar

#11 azure1961p

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Posted 29 July 2012 - 11:05 PM

It occurs to me that a useful approach is to use aperture stops or a diaphragm on a telescope - so a pair might be easy at full aperture, difficult at 3/4 aperture, not seen at 1/2 aperture. That way the same observer can give results for multiple apertures.

Now if only the clouds will move away!!


Excellent advice Fred. Id say thats more meaningful than selecting endless doublestar combinations [in varying seeing conditions] and such. The stars can be chosen easier and more effectively and the results attained far quicker.

Fact is though, a telescope isnt needed at all if some way of creating artifical stars in a darkened room can be a constructed with the brightness calibrated to match the stellar magnitude scale. In that case it could be done with excedingly accurate and excellent results.

I will say if this is leading up to some contrived "Sissy Limit" or some such Ill stay with Lords and be done with it.

Im still gagging on the Caldwell gaff.

Pete

#12 fred1871

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Posted 30 July 2012 - 08:43 AM

Pete, I don't think the artificial stars viewed naked-eye is a solution - it won't give the same result as real stars viewed through telescopes. Telescope vision differs in a number of ways from naked eye, one being improved visibility of faint stars with magnification, contrast effects, only part of the pupil being used at higher powers thereby reducing astigmatism in the eye as well as reducing other eye aberrations... Others will no doubt think of further differences. :grin:

Besides, anything derived by such an experiment would immediately get lots of complaints just because it's an artificial arrangement.

#13 Simoes Pedro

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Posted 30 July 2012 - 01:45 PM

What's the project?

#14 blb

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Posted 30 July 2012 - 02:12 PM

Here is the email I used: has103@comcast.net No error message, yet.

Frenchstar


That is the email address that is given in the article.

What's the project?


It is in an article by Sissy Haas in the Sept. issue of S&T, Page 68-71, titled Finding the Limit for Uneven Double Stars. Anyone interested in double stars should participate in helping determine this. This information will be used to refine or make a new chart like this one found on page 5 of her book Double Stars for small telescopes

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#15 Astrojensen

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Posted 30 July 2012 - 02:34 PM

Haven't read the article, but I have one immediate question: Does the unequal doubles need to be truly split (difficult to judge) or merely detected as doubles? (IE one component is technically behind the other a little, but it betrays itself by putting up a slight bulge in the first diffraction ring of the main star).


Clear skies!
Thomas, Denmark

#16 FrenchStar

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Posted 30 July 2012 - 03:23 PM

Haven't read the article, but I have one immediate question: Does the unequal doubles need to be truly split (difficult to judge) or merely detected as doubles? (IE one component is technically behind the other a little, but it betrays itself by putting up a slight bulge in the first diffraction ring of the main star).



Hello!

Here is what Sissy Haas has to say about it (from an email exchange with her) :

"It needn't be split by any space, or even a one hundred percent ball. But so long as you've UNQUESTIONABLY seen a second body next to the main star, then I think we can call it resolved. The thing that's most important is that the observation be honest.

Don't claim to have seen the companion if you suspect but don't feel certain. And as you don't need me to tell you, a companion you ALMOST think you saw might show up on a better night."

#17 blb

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Posted 30 July 2012 - 05:06 PM

I really wish that this project went beyond a magnitude difference of 4.0 to at least 5.0 or 6.0. There are many challenge objects that we look at that have a greater difference in magnitude. For example I looked at Sirius, the Dog Star and the Pup last winter with my 4" TV102 refractor. Those stars have a magnitude difference of 10.0 and I could see the companion (Pup). Limiting this to a magnitude difference of only 4.0 is to limit the chart to only the brighter pairs. I personaly would like to have information on seeing those pairs with a greater difference magnitude.

#18 Fuzzyguy

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Posted 30 July 2012 - 08:51 PM

It occurs to me that a useful approach is to use aperture stops or a diaphragm on a telescope - so a pair might be easy at full aperture, difficult at 3/4 aperture, not seen at 1/2 aperture. That way the same observer can give results for multiple apertures.


I'm not a scientist, optical engineer or astro physicist nor do I play any of these on TV, but if you put field stops on reflectors wouldn't that increase the percentage of CO? And wouldn't this affect results and skew the data? Or does CO only affect lunar, planetary and DSO viewing? I'm kinda new to this, so just thought I'd ask. :question:

#19 drollere

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Posted 30 July 2012 - 08:55 PM

i'm not much interested in the "rules" that float around among astronomers about seeing, magnification, resolution, and so on. and i agree with some of the previous posts that this particular objective -- resolution as a function of aperture and magnitude difference -- is likely to yield disappointing results.

the analogous problem is magnitude limit by aperture. bradley schaefer took a thwack at it with a dataset of observer reports; then nils carlin and chris lord tried to improve on it with more complicated formulations. in schaefer's case, his predictions are inaccurate by about one to one half magnitude, equivalent to the difference between a 6" and 8" telescope.

the problem is that these are all attempts at what is called predictive psychophysics. and those have always come to grief. the simple problem of color matching (color discrimination), which has had several large industrial and academic research projects thrown at it, discovered in the end that human visual response is not at all easy to predict with any accuracy. there is simply too much variation across individuals. and with a target task like double star observing that depends quite a lot on experience and skill and instrument, and the terrifically weak criterion in play (what does "resolve" or "recognize" or "separate" mean, exactly?), well ...

i recently completed a campaign of observing every double star listed in Haas and the Cambridge Double Star Atlas visible from my latitude, over 2100 in all, and there are several dozen pairs i couldn't resolve.

i plan to report those in a separate topic. meantime, i found on reexamination that many pairs i couldn't resolve a year ago i can resolve now, in some cases easily. certainly that's in part due to a year's worth of observing experience, but perhaps also to variations in seeing, atmospheric dispersion, eyepieces, etc. across observing nights.

if your own observing can't predict your own observing, what point is there in the prediction?

#20 fred1871

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Posted 31 July 2012 - 12:00 AM

Yes, you're quite correct about changes in central obstruction ratio.
My suggestion about stopping down telescopes would require those using reflectors to indicate the relative size of the secondary obstruction - with an SCT, a central obstruction that starts off large (35%) will be a monster by the time of half-apertture (70%) - very unsuitable for uneven doubles.

Bigger SCTs can use off-axis masks - perhaps a 12cm mask for a C14 or similar.

Netwonians can do better but the relative size of the CO still needs to be noted - so a scope with a 20% obstruction at full aperture will still be manageable, though less effective for its aperture, at 75% aperture where the CO becomes about 27%.

Refractors do best on this - no CO, so you're simply extending the f-ratio. Of course, that will lead to speculation about longer f-ratios being more effective than short (haven't we heard some comments about that before? :grin:).

The project itself is a can'o'worms, as Bruce has now remarked, though he used other words. Even so, I think something interesting might come of it, even if only to suggest that Chris Lord's multi-factored approach represents a fair approximation to what we can predict - and that in terms of a "best-case".

I think we're all familiar with the experience of seeing/not seeing particular pairs at different times.

#21 theskyhound

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Posted 12 August 2012 - 12:55 PM

I see this issue all the time, because I use these models in my software. I model everything; the faintest star you can see, how difficult it is to detect a faint fuzzy, how difficult it is to split a pair, and I predict SNR for images.

The pedants always say the same thing: there is no way you can do that accurately, particularly for things near the limits. And they are right! But here's the thing: just being in the ballpark is enormously useful in real world applications.

As a start, these algorithms allow you to clearly state those things that are simple to predict. How do most people pick easy pairs? By using pre-compiled lists of stars that others have observed. But this is usually just the tip of the iceberg of objects available. So everyone ends up observing the same subset of the available pairs again and again. Now imagine a program that looks at every pair of stars that has been cataloged, looking for pairs that are easy to split in a 4-inch telescope. Making that particular prediction is not all that difficult and the results will be fairly accurate. If you toss in a filter to select objects that are well placed on a given evening, then you have something quite useful. I can't stress this enough: the emphasis is always put on the most difficult circumstances to predict, but in fact most of the utility comes from being able to predict things that are more easily predicted.

For those things that are difficult to predict, where the prediction is questionable, a predictive algorithm is still quite useful. The algorithms tend to break down at the edges of perception; in other words they break down for the pairs that are difficult to split. This is a happy coincidence. After all, if we could accurately predict whether or not a challenging pair can be split under every conceivable circumstance, then there would be little point in going out to the telescope to try. For the challenging pairs the very point of observing them is to try to push your limits, not knowing if you are going to be successful. If our predictive algorithm says a pair is going to be very difficult to split, sure, it may not be perfectly accurate. In truth the pair may be easier than predicted, or it may not be splittable at all. But if used correctly, the algorithm can still predict which pairs are challenging, regardless of whether or not the detailed prediction is accurate.

So I very much support the efforts of people like Haas! In my world these models aren't just an academic exercise, or something futile. If you start with these algorithms, and toss in some cleverness and ingenuity, they can in fact be extremely useful in real world applications. In particular, they can be an invaluable tool for selecting objects to observe that are appropriate for a given telescope and conditions.

Clear skies,
Greg

#22 azure1961p

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Posted 12 August 2012 - 02:02 PM

Hi Greg,

I agree no formula here is perfect and there will be a lot of perception issues between observers but it does, or potentially does, leave a fair *jumping off point* from which to at least have some sort of handle on the challenges. Ill find it in bad taste if after a group compilation the *limit* is merely a banner for one persons name. Havent know this to be Haas at all but mentioning it regardless.

Pete

#23 WRAK

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Posted 14 August 2012 - 04:00 AM

Any realistic "formula" can only give a probability for splitting as even an easy double can be tricky under specific circumstances not covered by the formula. So with a reasonable big number of observers for a specific double you get a percentage of splits that can be used as probability - means that even your own yes or no can be the other way around next time.
But certainly aperture, separation, magnitude delta and seeing are not enough relevant criteras - magnitude loss due to light pollution, altitude depending on location and time of observation and yes focal length will play a role here. And seeing should best be split in stability and transparancy. So this gives in total about 10 parameters and I am quite sure probabilities calculated on such a frame would be of high reliability.
Wilfried

#24 Ed Whitney

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Posted 19 August 2012 - 09:36 PM

This has been very interesting reading. However, even thou there will be many reports and observations for Ms Haas to evaluate and then come to some sort of final conclusion, do feel that this is a worthwhile project.

It might just turn out to be that the journey was more important than the result. And then, there could even be a totally unexpected "bonus" or revelation that was never dreamed of at the start.

In any case, I'm on board to try to help Ms Haas. :)

#25 KirtErie

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Posted 26 September 2012 - 08:34 AM

I get my copy each month from the local library. If your library does not have it on the shelf, ask if the interlibrary loan system can get one delivered.






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