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Asbytec
Guy in a furry hat
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Reged: 08/08/07

Loc: La Union, PI
Re: Putting the "Rule of Thumb" to test new [Re: WRAK]
      #5651351 - 01/29/13 11:12 PM

I will try some of them tonight and report back, Wilfried. I am happy to have gotten involved with your fascinating project. Thank you for both the personal learning experience and the opportunity to participate. If I had the time, I would spend the rest of our observing season working on it.

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azure1961p
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Reged: 01/17/09

Loc: USA
Re: Putting the "Rule of Thumb" to test new [Re: WRAK]
      #5651684 - 01/30/13 06:59 AM

6/10 seeing Norme? Why you just had good seeing for Connectivut in winter!

Pete


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Asbytec
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Reged: 08/08/07

Loc: La Union, PI
Re: Putting the "Rule of Thumb" to test new [Re: azure1961p]
      #5651690 - 01/30/13 07:02 AM

Yea, Pete, it's not been stellar like the past tropical dry seasons and earlier this season. Something screwy with the weather, well last month or so since Christmas.

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WRAK
scholastic sledgehammer


Reged: 02/18/12

Re: Putting the "Rule of Thumb" to test new [Re: Asbytec]
      #5651696 - 01/30/13 07:10 AM

Quote:

... BU 1190 was higher in the sky and seeing was a little better at around 7/10 with a brief period of very calm skies after a patch of cloudiness passed. NELM was right at 4, maybe slightly better...




Norme, I think we may consider BU1190 and STT517 as positive limit observations. Congratulation on STT517 - even the modified Dawes limit for your scope would require 159mm aperture.
Wilfried


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Asbytec
Guy in a furry hat
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Reged: 08/08/07

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Re: Putting the "Rule of Thumb" to test new [Re: WRAK]
      #5652007 - 01/30/13 10:40 AM

Wilfried, sure, that sounds correct. One observation I mentioned above really seemed like a limit. STT 517 was very, very tight. Touching, elongated, and slightly notched and certainly not enough dark space to call it comfortably split.

Okay, got a few tonight in Gemini. I began sampling ADS2525 and HEI 121. Both are dim stars in a sparse star field, star hopping took a lot of time. My neighbor's security lighting was reaping havoc with my view through the finder and my dark adaption (worse than the moon earlier this week...LOL.) I spent a good amount of time trying to find them, but was just not able.

BU 100: Try as I might, I failed to split this double. I even cheated and looked up the Rho and Theta for the companion and still failed. I could, however, see a dim star about 6" arc south of BU 100. I have not looked up that star's magnitude just yet, but I am curious about it. I did spend a lot of time with this first double of the evening, because at mag 11 I really needed to be fully dark adapted to have a chance. Still, no success. At 3.2" sep, it sits very near my 4th diffraction ring (~3.6" arc.)

STT 145: Split. Companion easily seen near PA 340 just outside the first ring at 263x (UO 12mm HD Ortho, 1.6x Barlow.)

A2450: Split. Faint companion easily seen at ~3" arc sep near PA 120 to 130 (south east, anyway.) However, it's PA is listed at 053. I suspect this is incorrect, but I just don't know. If it's correct, then I failed to split it and simply observed another star near PA 130. But, my gut tells me the listing is incorrect. That pair just looked and felt like a double. Stellarium, ironically, shows the companion more south of PA 90, too.

STT 171. Split - maybe. Okay, now we're getting into easier splits with Ra near 140, right? Wrong. This was a very difficult split. In fact, I had to cheat - look up the PA to find it. Afterward, however, I was able to observe the companion. But, it was not easy, not obvious, nor clearly a double star, it was truly difficult just to see the faint companion even fleetingly. So, I guess, NOT SPLIT. (LOL) Wow...very difficult.

Tonight, seeing varied from 6 to 7/10 with NELM of 4.4.

Wilfried, I wish I had gotten more. I just spent too much time early in the evening trying to find the dimmer stars and ran out of time later in the night.

I hope to keep tabs on your progress while I am traveling and wish you the best of luck.

EDIT: Wilfried, just ran across this. Sounds interesting.

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

Edited by Asbytec (01/30/13 10:46 AM)


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WRAK
scholastic sledgehammer


Reged: 02/18/12

Re: Putting the "Rule of Thumb" to test new [Re: Asbytec]
      #5652879 - 01/30/13 05:57 PM

Norme, thanks for your reports, quite interesting. Thanks also for the link - thats a very interesting website for double star aficionados I knew already. It gave me a lot of ideas for the RoT quest. The tables are a bit hard to read, but the formulas and algorithms are excellent.
Wilfried
PS: Have a nice trip


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WRAK
scholastic sledgehammer


Reged: 02/18/12

State of the affairs new [Re: WRAK]
      #5655543 - 02/01/13 03:40 AM Attachment (27 downloads)

Heading for a short vacation (out from the winter into the spring) it is may be a good time to try an evaluation of the current quality of the RoT model even if certain weaknesses are already known and the existing data set of about 100 observations is far too small (I think I need at least more than 300 observations). I decided to compare it with the best of the other RoT models I know so far - and I think this is Lord's approach. Due to my respect for Lord's work I gave his algorithm the benefit of minimizing errors by choosing the best possible value of the parameter n with value 4-12 depending on aperture class, obstruction size and seeing quality regardless of the actual data. As you can see in the chart Lord's algorithm works extremely well with a broad range of observations but freaks out rather extreme with others - especially with close but faint doubles.
My current RoT model gives slightly larger errors in a broad range but does not freak out - certainly because it works with it's own data set and this is kind of compensation. The weakness of the RoT model is certainly the range with very faint secondaries. There is also some bias to recognise concerning the used data of the Lewis collection - Lord's alorithm does rather well with these observations and my RoT model rather not this good although I have adjusted the advertised magnitudes to the current state of knowledge.

Statistical evaluation: Standard deviation for Lord's algorithm is 25.4mm (error in relation to the used aperture) and correlation between actual aperture and predicted aperture is 0.947. Standard deviation for the current RoT model is 14.7mm and correlation is 0.963 - means in total slightly better values for the current RoT model.
After a creative break I will continue and attack the faint secondaries.
Wilfried


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fred1871
professor emeritus


Reged: 03/22/09

Loc: Australia
Re: State of the affairs new [Re: WRAK]
      #5657536 - 02/02/13 02:59 AM

Wilfried - what software are you using to generate the observing lists by constellation?

The various software packages I have do not always include standard (WDS) identifiers for doubles, even when they claim to, but give me single identifiers for SAO, or WDS, or HD, or just about anything. I don't want to waste time going through multiple identifying catalogs to get to the WDS standard designations (which means accepted discoverer, as well as position). I want a program that can give me the standard designation for each double, even if like your lists I get multiple extra identifiers as well - that's not a problem, and might at times help.



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WRAK
scholastic sledgehammer


Reged: 02/18/12

Re: State of the affairs new [Re: fred1871]
      #5657567 - 02/02/13 03:55 AM

Fred, I use AstroPlanner. It allows you to directly select doubles with selected properties from the WDS catalogue or else if you have any identifier for a double you can lookup synonyms and select the appropriate WDS designation for it.
Wilfried


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WRAK
scholastic sledgehammer


Reged: 02/18/12

Re: State of the affairs new [Re: WRAK]
      #5657595 - 02/02/13 05:29 AM

Second thoughts regarding the error chart shown above: The RoT model shows a tendency to request slightly smaller apertures than used for the observations - as most of the observations are done with fixed apertures it seems reasonable that the same observations could have been done also with a slightly smaller aperture. So these "errors" do not seem this bad.
Concerning the cases with required apertures greater than used for the actual observation - these are quite often observations with apertures quite below the Dawes criterion and I do not allow the model to go below the (for reflectors modified) Dawes criterion. So this is a must have deviation and is not to be sonsidered as "error".
Wilfried


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fred1871
professor emeritus


Reged: 03/22/09

Loc: Australia
Re: State of the affairs new [Re: WRAK]
      #5659166 - 02/03/13 12:04 AM

Wilfried, thanks for the information about AstroPlanner. The trial version is so limited, now I've looked at it, that I didn't get a sense of how much it could do.

Some observations. You mentioned STF 450 in Taurus being more difficult than you'd expected. I had a look at it a couple of nights ago and found it very easy. Despite modest altitude(~26 degrees) and seeing not great in that direction, I could see the companion at 80x, and it was obvious at 114x (140mm refractor).

I've been working through more Orion doubles and some of these won't be "at the limit" examples. But two I've looked at in recent nights don't appear to be on your Orion list - or I've overlooked them there.

One is BU 15 (0547.8, -0218), mags 7.4 and 11.6 at 2.0". The separation appears to be the same in 1987 (last measure) as it was when Burnham discovered it in 1872 with 6-inch refractor. This one took a bit of magnifying to see the companion, but 285x showed the lesser star as a tiny speck separated but close to the primary. Seeing was very good at that time.

The other one I didn't find on your list was STT 119 in Orion. Again, it's a pair which seems to be at the same separation recently (2009) as it was when discovered (1843). Magnitudes in WDS are 8.08 and 8.93 - separation only 0.6"! 140mm refractor again, this one took a lot of magnifying, being "not single" at 285x, and at 400x a definite pair, a bit uneven, notched but not resolved into separate points. Seeing very good - I looked at this one straight after BU 15. Very pleasing result given the stars' modest magnitudes; and NELM was at least 5.5.

I'll add some more observations as I work through the details of them and cross-match my observing list with your Orion list. My main problem at the moment is late sunsets plus daylight saving (Summer), so it doesn't get properly dark until 9:30pm, and I sometimes get clouds rolling in well before midnight. The weather pattern this Summer has been very unusual and not great for astronomy.


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WRAK
scholastic sledgehammer


Reged: 02/18/12

Re: State of the affairs new [Re: fred1871]
      #5659293 - 02/03/13 02:12 AM

Fred, yes - STF450 should be easy in a 140mm refractor. But I had somehow the impression that the companion is fainter than advertised compared with +10mag stars in the same field of view.
Congratulation to BU15 and STT119 - both doubles seem to be very limit observations with a 140mm refractor. Both are not on my list for reasons I don't know - maybe the selection feature of AstroPlanner is not this perfect.
No experience with the trial version - you need access to the full database of catalogues including WDS, so the trial version does not show full performance concerning double stars.
Wilfried


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fred1871
professor emeritus


Reged: 03/22/09

Loc: Australia
Re: State of the affairs new [Re: WRAK]
      #5661202 - 02/04/13 06:57 AM

A couple more observations. Norme managed a "sort of" split with BU 1190 in Orion (0557.4, +0002)- I've now had a look at it in fairly good conditions, and the close companion was visible at 285x and 333x (7mm and 6mm orthoscopics with 2.5x Powermate). Like Norme, I found it not a clean easy split, but it was a definite one with my 140mm refractor. [mags 6.95, 9.8 at 1.4"]. With averted vision I caught glimpses of the mag 12.1 companion at 6.7" (same magnifications). No moon at the time. A tough combination for 140-150mm.

BU 13 (0534.5, -0429) I also caught up with - mags 7.2 and 9.2 at 1.0", so I thought it'd be not too tough - it was harder than I expected, and took 400x (140mm refractor) to give a clear separation in the steadiest moments. That appeared to be a seeing effect, and my impression was that less power would show it in steadier conditions.

The continuing issue with this project of observing marginal pairs for the telescopes used, is getting "good enough" atmospheric conditions to make it possible. As so often remarked, a pair that's invisible as such one night is clear and obvious on another - SW Burnham went further, and remarked on the difference occuring even with nights that appeared to be equally good. Hence, I suppose, Wilfried, your "50% probability" model.


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WRAK
scholastic sledgehammer


Reged: 02/18/12

Re: State of the affairs new [Re: fred1871]
      #5661868 - 02/04/13 02:09 PM

Fred, it seems that you have excellent conditions now.
With the STT119 observation you have reached a sensational 0.73 Dawes ratio if the advertised data is correct. Regrettable STT119 is a bit too faint to try to measure the separation with a self made interferometer consisting of several simple aperture masks with two 10mm holes in different distances (minimum contrast of the interference lines at 95mm distance would mean 0.60" separation and a minimum at 85mm distance between the holes would give 0.67" separation with an average error of only 0.05" - but due to the small holes it works only with equal doubles brighter +6mag). I have to admit that I never tried such measures myself but it sounds this interesting that I will do this cerainly on occasion.
Wilfried


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fred1871
professor emeritus


Reged: 03/22/09

Loc: Australia
Re: State of the affairs [Re: WRAK]
      #5662819 - 02/05/13 01:28 AM

Wilfried, some nights I have (nearly) excellent conditions for part of the night and in some parts of the sky. STT 119 is not unique among close pairs I've seen as double, whether split (separated) or elongated. A few brighter ones have been even closer - in the 0.5"-0.55" range - only elongated of course.

At 0.5", I'd be getting near-enough to 0.5 of the Rayleigh Criterion. And that would fit with what Couteau gives as the limit for detecting elongation with the Nice 20-inch (50cm) refractor. As 14cm will be less atmosphere-limited than 50cm, I think that's a reasonable target to aim for, under the best conditions.

Taylor (in the Argyle book) detects elongation down to around 0.5 of Dawes, 0.4 of Rayleigh. That's remarkable, but a few other observers are on record for similar feats - the oft-mentioned SW Burnham for one. I think I'm doing quite well as an observer but I've definitely not reached those remarkable levels of discerning close pairs.

One example among the closer pairs I've seen - Zeta Bootis, a binary at present getting closer year by year. I observed it in May 2009 and May 2010 with the 140mm refractor - both times with 400x. In 2009 it was elongated with a hint of notching. In 2010 it was a "rod" without a hint of a notch. I plan to get back to it this year to see if I can get any suggestion of elongation. Separations, based on the grade 2 orbit (~124 years) are just under 0.6" in 2009, 0.55" in 2010, and will be 0.47" by May this year. So, this year if I detect anything "out of round" I'll set a new personal record. Delta-m for Zeta Boo is only 0.1 magnitude.

The interferometer idea sounds interesting, but as you say the stars need to be pretty similar in brightness, and with only 140mm I'd think STT 119 a bit faint, well below mag 6. For measuring, especially for close pairs, I'd think the CCD technique described by Rainer Anton in the 2nd edition of the Argyle book might be more useful.

Edited by fred1871 (02/07/13 05:28 PM)


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WRAK
scholastic sledgehammer


Reged: 02/18/12

Re: State of the affairs new [Re: fred1871]
      #5667148 - 02/07/13 01:59 PM

I think I found a solution for my dilemma regarding Dawes criterion and overperforming observations - currently I do not allow the RoT model to result in values below Dawes because I think this is hard enough for a 50% split chance. On the other hand I need at least some overperforming observations as counterbalance to the certainly existing underperforming observations in my data set - but this results in some bias as the statistical analysis has to struggle to minimize errors it cannot avoid.
So I think I will allow the RoT model to result in values below Dawes but in an additional cut off step I will set all sub Dawes values to Dawes criterion (modified for CO if necessary). This will may be result in a greater standard deviation but the quality of the model should be improved this way.
And I will apply a similar approach to the other end of the observations with very faint magnitudes of the secondary - here I will first made a more or less "educated" guess for an additional component of the model but also make a cut off for all results above the required aperture according to the TML (corrected by NEML) required by the magnitude of the secondary.
Wilfried
PS: The CCD would make it necessary to split the double I think. Curiously this is not necessary for the interferometer at all


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fred1871
professor emeritus


Reged: 03/22/09

Loc: Australia
Re: State of the affairs new [Re: WRAK]
      #5667599 - 02/07/13 06:14 PM

Wilfried, I think allowing for "overperforming" (detecting doubles closer than Dawes) is necessary to allow for - these are mostly fairly bright pairs where a split is not possible, but a notched or elongated - rod or olive - image is visible.

That's different from what is seen with significantly uneven pairs. Pairs with moderate delta-m can show, be detected, as elongated in some cases. But those with a larger delta-m are more difficult to see in this form; usually the primary so overwhelms the dim companion that it's not detectable, unless separated, rather than overlapping or an extension of the primary.

That's part of what makes an RoT hard to establish. There's a gradual change in what can be seen. If delta-m is large, we depend on the fainter star being in a diffraction gap; if it sits on a diffraction ring it immediately becomes much more difficult, how much more depends on the ring brightness and the star brightness.

And it gets messy. A CO changes the relative brightness of rings according to the CO size (% of diameter of main optics). Looking at some of Suiter's illustrations, I notice on p.165 (2nd edition of Star Testing) a set of pictures showing "in-focus diffraction patterns resulting from central obstruction".

Unobstructed, first ring moderately bright, 2nd ring less, 3rd ring less than second.
25% CO - first ring bright, 2nd ring very faint, 3rd ring middling bright.
50% CO - first ring very bright, 2nd ring bright, 3rd ring faded to near invisible, 4th ring increased though very faint.

A very interesting pattern of change, according to CO obstruction ratio!

Low-order spherical aberration is often treated as having much the same effect as CO. However the pictures on p.191, showing the effect on the diffraction pattern of various levels of SA, with obstructed and unobstructed apertures, is different from the pure CO effect.

With an unobstructed aperture, increasing SA firstly reinforces the brightness of the first ring, then the second as well. With an obstructed aperture (33%), the first ring gets brighter, but already with no SA there is some reinforcement of the 3rd ring, visible at 1/8 wave SA as well. By 1/4-wave SA the 2nd ring is broader and somewhat brighter than the third (itself reinforced), and with even more SA the pattern of brightness, 1st brightest, 2nd is 2nd brightest, 3rd is 3rd brightest shows.

What I find interesting here - first, with no CO the diffraction ring brightness pattern of increasing SA is different from adding CO without SA.

Second, 33% CO, as with 25% CO, reinforces the third ring brightness rather than the second, with little or no SA; but with increased SA, the pattern is similar to, though worse than, the unobstructed pattern for increasing SA.

A lot of SCT and Mak-Cass scopes have CO in the 25-35% range. Those that have very little low-order SA may show this effect of faded second diffraction ring and reinforced third diffraction ring. Of course, atmosphere makes such a difference that in the real world this effect is likely lost as a visible effect, merely becoming one of multiple factors mixed together to determine what one sees.

My conclusion is the obvious one - the less SA the better, and smaller CO ratios are better than large ones. Nothing new there.

How much effect there is on uneven doubles observed in Mak-Casses, where low-order and high-order SA need to be balanced, but some aberration remains, I don't know.

Very faint pairs? - I'm increasingly feeling these are an eyesight test to a much greater degree than uneven pairs of middling brightness. I've got my C9.25 going again and the extra light (a whole magnitude!) over the 14cm refractor is very nice, despite less perfect optics and more sensitivity to atmospheric wobbles. Perhaps I'll try some of your faint Gemini pairs with that. They're certainly beyond my eyes with 140mm - super-vision people like SJ O'Meara might manage them.

Regarding CCD imaging - yes, some kind of split is necessary for measuring. Agreed, an interferometer works differently. You've reminded me to look up information on Finsen's eyepiece interferometer, which allowed him to measure pairs too close for normal micrometers, down to around 0.1" or better with the Innes 26.5-inch (67cm) refractor in South Africa (1940s-1950s). I'll find the reference and give it in this thread - I'm fairly sure it's in one of the journals online through ADSABS.


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fred1871
professor emeritus


Reged: 03/22/09

Loc: Australia
Re: State of the affairs new [Re: fred1871]
      #5668175 - 02/08/13 12:20 AM

I've now found the reference for WS Finsen's own article about his eyepiece interferometer.
Monthly Notices of the Royal Astronomical Society, 1951, v 111, p 387 ff.

Bob Argyle, in the 2nd edition of his Double Star book for the Webb Society (1986), remarks :
"with this instrument more than 13,000 examinations of 8,117 stars ...were made. As a result 73 new pairs were found, 11 of which have periods ranging from 21 years down to 2.65 years. In addition, 6,000 measures of pairs too close for the [filar] micrometer were made".
These results appeared in various papers over time.

The interesting thing is the micrometer itself. Whether something similar could be made for amateur use on mid-size scopes? I'll leave that for the instrument designers and engineers to work out.


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WRAK
scholastic sledgehammer


Reged: 02/18/12

Re: State of the affairs new [Re: fred1871]
      #5668910 - 02/08/13 12:28 PM

Quote:

...The interesting thing is the micrometer itself. Whether something similar could be made for amateur use on mid-size scopes? I'll leave that for the instrument designers and engineers to work out.



Look at this: http://www.observatory.org/bfm.htm - may be a bit expensive but seems of high quality.
Concerning eyepiece interferometer: Do you know any commercial products?
Wilfried


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fred1871
professor emeritus


Reged: 03/22/09

Loc: Australia
Re: State of the affairs new [Re: WRAK]
      #5669681 - 02/08/13 07:57 PM

Interesting filar micrometer, sounds good, price is up where I'd expect as a minimum if it's well made. Should be suitable for long focal length instruments. A 25mm eyepiece suggests very long focal length systems to get decent magnification; I'd hope the thing would still work with shorter eyepieces, or only wide pairs would be measurable (at 4m fl the magnification is only 160x). Personally, I'm more tempted by CCD imaging, maybe with a video style camera for "lucky imaging" in the same way the planetary imagers do it.

Finsen's eyepiece interferometer? - there are photos of the device with the article. Likely made as a 'one-off' by the instrument shop at the observatory. I've never seen an advertisement for this kind of micrometer. Several other types, yes, in the past, but not this type.

An alternative for very close pairs, not too uneven, is speckle interferometry - and the article in Argyle's current book suggests ways for the amateur observer to do it. The potential accuracy is very good. However people like myself, who like simpler techniques, will probably follow Rainer Anton et al into "lucky imaging". That could be next year's project - this year I'm staying visual.


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