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Asbytec
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Reged: 08/08/07

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Re: Putting the "Rule of Thumb" to test new [Re: WRAK]
      #5641916 - 01/25/13 03:54 AM

Wilfried, will observe those and some Fred mentioned in my other thread. Will report back when I get a chance to observe them. Weather looks to hold tonight, fortunately. Wish I had some spare good weather to share with you, but it's been in short supply here, too.

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fred1871
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Reged: 03/22/09

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Re: Putting the "Rule of Thumb" to test new [Re: WRAK]
      #5642126 - 01/25/13 08:51 AM

Wilfried, some thoughts.

First, regarding some of the suggested pairs - A 320, A 2804 - I'm inclined to think they're becoming as much a test of the observer's eyesight as of what the telescope can do, if we're talking about 150mm telescopes. These pairs seem to be a test of Lewis's "faint pairs" visibility. I observed some pairs like this in the 1990s with a 7-inch (18cm) refractor, and thought such doubles were as much a test of sky brightness and observer vision, along with air steadiness, as a test of what the telescope could do.

They're of interest of course, but I suspect results will prove even more varied than with less faint pairs, making an RoT for such pairs uncertain, and if factored in perhaps reducing the accuracy of an RoT for less faint pairs as seen with modest telescopes. I'm thinking aloud here, not attempting anything definitive.

BU 1190 is a different category - obviously difficult, but depending more on nearly 3 mags delta-m at quite close separation (1.6") - because the secondary star is mag 9.8 this is less of a test of eyesight.

I'd be surprised if A 320 is a "bogus double" - as 7 measures are listed in the WDS. Of course, if the detailed list tells us that most of these were attempts without success it could be "bogus", but that seems an unlikely scenario. More likely is that it's a neglected double because it had not changed very much between 1902 and 1963.


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Asbytec
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Re: Putting the "Rule of Thumb" to test new [Re: WRAK]
      #5642220 - 01/25/13 09:48 AM

Wilfried, I have A320, A2804, BU1190, and A2634 on my short list. Weather was clear tonight with a nearly full moon. A quick observation of Psi 2 Ori, a nice, clean split, however showed seeing was going to be a problem.

So, working up the list in order of Ra, I struggled with A2705, an equal magnitude, close pair. It should have been pretty easy, but truth is I could only get a hint of it's companion. And it was not easy, not at all. So, I tried STF 849 again with the same result. I just could not get a good split in those conditions.

Seeing is weird here, I could hold the Airy discs pretty steady for periods of time, but the star images were jumping around quite a lot. I suspect some larger scale seeing issues. And, the moon was not far removed from last night, yet there was no improvement in NELM (still about 3.5.) The sky was still fairly well lit, about the same or worse. Visually, I just could not make out stars near 11th magnitude.

I am sure I can get a better split on A2705, but it will have to wait for steadier seeing. I did not pursue any others, observing Jupiter and the moon just showed me how futile it would be to attempt some difficult observations.


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WRAK
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Reged: 02/18/12

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Re: Putting the "Rule of Thumb" to test new [Re: Asbytec]
      #5642987 - 01/25/13 05:06 PM

Norme, sorry to hear that conditions were not good enough to give this a serious try.
Fred, concerning A320 and A2804 you are probyably right - this is why I have a +9mag switch in my model for the influence of the magnitude of the secondary for the required aperture. Even the statistical analysis tends in the same direction as as the least square method for the parameter pr2 in pr1*(m2-pr2) results in a value near 9.
Now I am considering a further component for the influence of m2 fainter +11mag as there seems to begin another level of difficulty here.
Wilfried


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Asbytec
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Re: Putting the "Rule of Thumb" to test new [Re: WRAK]
      #5645673 - 01/27/13 09:31 AM

Wilfried,

I was able to observe A2705 and confirmed a clean split at 263x and 320x: a tiny disc and a faint speck of a companion at PA ~250. I could hold the faint companion steady for brief periods. In fact, it looks pretty close to any limit with NELM 3.5 to 4 in good seeing on this night. Since I had trouble with STF 489 on the previous night in rough seeing, I reconfirmed the split made a few nights earlier. STF 489 was indeed split.

I attempted A2804, but failed to split it. The primary was bright enough, barely, but I did not see the companion. On this pair, I found myself using more averted vision. I had some difficulty finding it, it did not show in my finder, but nearby HIP 25066 was, so I hopped over HIP 24997 to get on A 2804. I am sure I was on the right star. Want to try again later this week when the moon moves away.

I could not find BU1190 at the stated coordinates. It is near 59 Ori. I got clouded out and was unable to try A320.

Anyway, seeing was pretty good at 8 or 9/10 and 3.5 < NELM < 4.0. The moon is one day past full, I believe.

Edited by Asbytec (01/28/13 11:34 PM)


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WRAK
Pooh-Bah


Reged: 02/18/12

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Re: Putting the "Rule of Thumb" to test new [Re: Asbytec]
      #5646448 - 01/27/13 05:00 PM

Norme, thanks - I have added ADS2705/AG72 to my data set, will have to think about this because the current RoT model shows a req. ap below 100mm but this seems a bit low.
Wilfried
PS: BU1190 is HIP 28187 and should be therefore not so difficult to locate


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fred1871
scholastic sledgehammer


Reged: 03/22/09

Loc: Australia
Re: Putting the "Rule of Thumb" to test new [Re: WRAK]
      #5646920 - 01/27/13 08:52 PM

A comment on fainter pairs. I've found that below mag 9.0 the difficulty of seeing pairs increases significantly. So Norme's current failure with A 2804 is not a surprise, especially with so much moonlight added. This is a pair of mags 9.8 and 10.5 (rounded), at 1.1". We're hitting the 10th mag wall here as well as the stars being a challenge to the eye, which has less resolution as things get dimmer. Averted vision will show fainter, but is less good for detail. A 2804 is listed for 161mm. Much the same I'd expect to apply to A 320 (listed 160mm)- same separation (1.1"), slightly dimmer primary (10.0).

My past experience with a 7-inch refractor would suggest these pairs, faint and very close, would be a good challenge for that - a bit larger than Norme's 15cm, and with no CO and higher transmission otherwise, a further small bonus in light grasp. And for dim pairs, avoiding averted vision with its reduced resolution matters for close pairs; wider ones allow a.v. to give benefits.

More thoughts - historical examples - in the next note.

Edited by fred1871 (01/28/13 06:36 AM)


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Asbytec
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Re: Putting the "Rule of Thumb" to test new [Re: fred1871]
      #5647086 - 01/27/13 10:29 PM

Fred, thank you. Double stars can be challenging, and a successful split is rewarding. I want to split them all.

Wilfried, since BU1190 is HIP 28187, maybe I can find it. Thanks.

I agree, something weird seems to be happening around mag 10, companions are getting fainter and we tend to use more averted vision with less resolution, maybe.


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fred1871
scholastic sledgehammer


Reged: 03/22/09

Loc: Australia
Re: Putting the "Rule of Thumb" to test new [Re: WRAK]
      #5647109 - 01/27/13 10:41 PM

The large number of rather faint pairs in Wilfried's list for Orion got me wondering what had been possible for some of the 19th century observers, using moderate sizes of telescope similar to many of us currently. So I went back to Lewis's lists from his 1914 paper and, ignoring the overall averages which I think are generally unhelpful, looked instead at averages for individual observers with specific telescopes.

One who struck me as of particular interest was Ercole Dembowski (1812-1881), where Lewis gives averages for Dembowski's use of his 7.4-inch (~19 cm) Merz refractor. Dembowski had a particular interest in a revision of Struve's Dorpat Catalogue, and was regarded in his time as an exceptional observer for accuracy. After his death his observations, from various sources, were collected and published, the editing being done by Otto Struve and GV Schiaparelli.

To the point - the average for nearly equal faint pairs of Dembowski, 7.4-inch scope, was mags 9.3 and 9.5 at 0.7". Remarkable with a Dawes' Limit of 0.62". This is a stand-out result when compared to the other observers Lewis lists with telescopes under 25cm. SW Burnham with his 6-inch has 0.9" for mag averages of 8.6 and 9.8 (though somewhat less equal pairs, increasing the difficulty). Burnham with 9.4-inches (~24cm) has 0.6" at mags 8.3 and 8.8 averages. W Struve and Secchi, similar apertures (9.6-inch), manage 0.5" with stars 8.4 and 8.7 (Struve) and 8.4 and 8.9 (Secchi).

For 9th magnitude pairs (average 9.6 and 10.0) at 0.9" we have to go to Hough with the Chicago 18.5-inch (47cm) Clark refractor. Yes, it might be under-achievement with that size of telescope - because Schiaparelli with 19.2-inches (48.8cm) manages 0.4" at mags 9.2 and 9.5. The Dawes Limit for 19.2-inches is 0.23".

For now, not much point looking at what various observers did with 28-inch and 36-inch telescopes. Scary close with faint stuff.

One could of course scale these results for different apertures to get a rough idea of what might be possible - or follow Treanor's example, graph the results - but this time for faint pairs, instead of unequal pairs. Both approaches could be informative.

Potential problems? most likely the photometry of the pairs. To eliminate that would require re-doing Lewis - find the original publications, identify the closest faint pairs, then get modern photometry (Tycho, etc) for these. In the case of doubles that appear not to have changed much, or binaries with high-graded orbits, identification would provide a check on separation measures as well.

The above is a "thinking aloud" exercise. I feel the old observations (yes, all done with refractors) might throw some more light on the faint pairs issue after further analysis. So the above notes are offered for others to also consider in relation to the (multiple) vexed issues of the limits of resolving doubles of various types.


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WRAK
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Reged: 02/18/12

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Re: Putting the "Rule of Thumb" to test new [Re: fred1871]
      #5647372 - 01/28/13 03:00 AM

Quote:

Norme, very well done in splitting ADS 2705 - at only 1.0" and listed magnitudes 9.24 and 9.95 this is a tribute to your eyesight and observing skills...



Ups - what are we talking about? May be we should indicate the WDS# for clarification: For ADS 2705 I found WDS03428+3016 AG72,ADS2705 6.4" +10.52/10.78mag.
Obviously you and Norme mean A2705 with WDS05307+1154 and for this one I get with CO 0,28 a req. ap of 153mm.
Fred thanks for the necessary hints to make this evident.
Wilfried


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fred1871
scholastic sledgehammer


Reged: 03/22/09

Loc: Australia
Re: Putting the "Rule of Thumb" to test new [Re: WRAK]
      #5647444 - 01/28/13 06:06 AM

Yes, an easy mistake (and careless on my part too) - confusing A (Aitken's own discoveries) with ADS (his obsolete general catalog of doubles, with discoveries by all and sundry). Different numbering. The 'A' doubles are still listed in WDS. ADS numbers need a translation. It's almost like John Herschel's GC of deep sky objects (nearly all discovered by John and William Herschel) being confused with Dreyer's NGC. The earlier numbering is no longer used, that avoids confusion.

So I'd agree, we should do best to use WDS designations - my long-time preference anyway - that gives us the RA and Dec and the Discoverer designation - the standard way of referring to doubles. And it should avoid confusions.

I'll now look at the lists again and see if I need to revise any comments. I've been trying to stay with "A" not "ADS" designations.

Added comment - I've now revised my previous post to delete discussion of a pair I mis-identified.

Suggestions I made there, regarding scaling of telescopes relative to each other with different sizes, I'll repeat at another time when I've worked through some new examples.

Edited by fred1871 (01/28/13 06:40 AM)


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Asbytec
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Re: Putting the "Rule of Thumb" to test new [Re: fred1871]
      #5647503 - 01/28/13 07:27 AM

My apologies, yes, A2705. Careless on my part and corrected, as well.

Fred, I am curious why I was able to get down to a 9.9 mag companion (a distinct tiny speck fluctuating in and out, but not difficult) where some of the great observers topped out at lesser magnitudes at similar separations. I did have exceptional seeing and some moon light.


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WRAK
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Reged: 02/18/12

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Re: Putting the "Rule of Thumb" to test new [Re: Asbytec]
      #5647579 - 01/28/13 08:31 AM

Quote:

... curious why I was able to get down to a 9.9 mag companion ...




Norme - this does not seem so difficult. My own so far best result in this area was J781 in Cyg. Jonckheere advertised this double with 3" +9.4/9.4mag but the latest WDS entry is 3" +11.4/11.5mag. While I do not fully buy the WDS data (nearby +10.81mag TYC2669-00673-1 seemed a bit brighter than J781) this was a positive resolution with a 140mm refractor even if already with averted vision.
Wilfried


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fred1871
scholastic sledgehammer


Reged: 03/22/09

Loc: Australia
Re: Putting the "Rule of Thumb" to test new [Re: Asbytec]
      #5649004 - 01/28/13 07:14 PM

Quote: some of the great observers topped out at lesser magnitudes at similar separations

I think the data used by Lewis , which gives averages for the individual observers, is biased by selection. First, it deals with pre-1914 work. So later observers, like Jonckheere, who increasingly worked on finding faint doubles, as the brighter ones were largely discovered already (so they thought), are not included.

In the earlier era there was far more interest in the bright to middling pairs. These appeared to provide plenty of examples, were more accessible to moderate telescopes, and easier to measure than faint pairs. Also, if you assumed that on average faint means further away, then fainter pairs (on average) were less likely to show orbital motion. So were less interesting.

Some early observers did list a lot of dimmer fairly wide pairs, John Herschel in particular. But the Struves, Burnham etc were plenty busy enough without checking through 10th magnitude and fainter stars for new pairs. Aitken did add a lot of fainter pairs, especially when he took to using Lick Observatory's 36-inch refractor, rather than the 12-inch he'd used for some surveys.

The Southern Hemisphere observers added a lot of fainter pairs after the large refractors (26-28-inch) became available in South Africa. But that was in the later 1920s, continuing into the 1950s. Earlier work in the south had been mostly with more modest equipment - Russell's Sydney Observatory group (11.4 and 7.25-inch refractors) 1870s-90s, Innes (mostly a 9-inch refractor) early 20th century. There was a brief period when TJJ See took the Lowell 24-inch refractor to Mexico, which resulted in some more southern discoveries, but See didn't spend long enough in Mexico to add huge numbers of new pairs. Many of his southern doubles are faint companions to fairly bright stars (from Lewis - m8.0 and 11.5 at 0.9"; mag 7.4 and 12.6 at 1.4", as averages).

The emphasis on (dim) red dwarf binaries is post-Lewis, likewise most of the work of Jonckheere, plus the Nice (France) surveys by Couteau et al which found bright new pairs as well as a lot of faint ones, especially with the 30-inch refractor.

But if you look at Lewis's averages for observers with the Lick 36-inch you'll find dim stars; and that's true to some extent with the 18-inch and larger scopes as well. One example - Hough with the Chicago 18.5-inch is listed for uneven pairs (averages), mags 7.1 and 11.5 at 1.1", and for the very unequal, 6.6 and 12.2 at 1.9".

Typically, even with the biggest telescopes, there was simply less interest in finding faint companions to faint primaries. Lewis (28-inch), Burnham and Aitken (36-inch), do have dim very close pairs to their credit. These are around mag 9.0 to 9.5, at 0.2"-0.25". Hough with the 18.5-inch did average mags 9.6 and 10.0 at 0.9", but that's still within the magnitude 10 limit and it's about as faint as anyone went in that period with less aperture than Lewis on the Greenwich 28-inch. "Close" rather than "how faint" was the watchword for the bigger scopes; with allowance for dim companions to brighter stars - Aitken is listed, for very uneven pairs, 36-inch again, as mags 7.5 and 13.7 (!!) at 2.5"; Burnham, same scope, 5.7 and 12.3 at 0.9" (!!!). Don't try this at home.

Edited by fred1871 (01/29/13 04:35 AM)


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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: fred1871]
      #5649687 - 01/29/13 04:12 AM

Fred, you impress me with your insightful in-depth knowledge of double stars and their history.

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fred1871
scholastic sledgehammer


Reged: 03/22/09

Loc: Australia
Re: Putting the "Rule of Thumb" to test new [Re: Asbytec]
      #5649786 - 01/29/13 07:20 AM

Thanks, Norme. Twenty years ago I started taking a more serious interest in doubles, so I've had a good amount of time to learn what I can from the experts, and to do a lot of practical observing. Because I have some background in history studies that was a natural extension.

It's good that we have forums like this to discuss astro matters. It allows a range of people with different areas of knowledge to contribute. Each of us can bring something useful to the group discussions, and we all benefit. I offer what I can.

Having said that, I'll say I'm finding the RoT issue more complex than I'd previously thought, and I didn't expect it to be simple.

I'll now have to get my SCT sorted out so I can do some experimenting with CO effects again. And, unlike much of my past SCT observing, push the limits. Except for faint pairs the C9.25 (235mm) didn't really do better than the 140mm refractor. Wilfried has likewise commented he prefers, for doubles, his 140mm refractor to his C9.25. So the next step is trying tougher doubles to see what the particular limits are for the SCT.


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WRAK
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Reged: 02/18/12

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Re: Putting the "Rule of Thumb" to test new [Re: fred1871]
      #5649811 - 01/29/13 07:54 AM Attachment (36 downloads)

Going forward step by step I have some days ago included the effect of CO in my current RoT model using the observations published in the mentioned paper of Lord with 6" and 10" reflector. While I think the CO implementation is quite OK (modifying Dawes criterion as base and including CO in the delta-m component) there are other issues open, especially influence of light pollution (NEML component works linear over all aperture sizes and this is certainly wrong) and influence of secondary magnitude fainter +11 is not very well handled. And I am also not sure how to handle the not this good quality of the advertised data of the included observations mentioned above. I will adapt the magnitudes to the current WDS data and let the separations as they are but would be happy to have better data available. Some observations have to be excluded as they are appearently wrong in all aspects. And I am not sure how to handle the heavily overperforming observations. The model states the modified Dawes criterion as lower limit as I do not see any sense in a RoT requiring less aperture than Dawes - should be enough for a 50% chance. But if I include observations with effective aperture below Dawes then I get a bias in the results of the statistical analysis or at least a significant higher average error.
Since it will take some time to get a handle on all these questions I upload the current state of the ROT model (filled with Orion doubles as a starter for CO 0.28 and NEML of 4.5) to give the opportunity to check the CO-implementation against own observations.
Wilfried


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Asbytec
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Re: Putting the "Rule of Thumb" to test new [Re: WRAK]
      #5649833 - 01/29/13 08:18 AM

Yea, when you start getting down to a modified Dawes, you really need a "perfect" aperture. Those do not exist. I think a reasonably good Strehl can get close, though, when induced aberrations are controlled.

For example, modified Dawes in my scope is right at 0.71" arc. Best I have done so far is 0.74" arc (as reported), right in the middle of theoretical and modified Dawes. STT 517 was too tight at 0.67" arc (but I will look again tonight.)

But, for an inherently aberrant aperture (Strehl of 0.94) to match or even exceed calculated Dawes means it's important. Most scopes (including SCTs, and especially refractors) seem to be optically this good or better these days. Well, IMO...

As for overachieving, I hate to fail. I will observe something until I am reasonably sure I saw it, even if that takes a hour. But, I've toned it back for the sake of getting a confirmed and readily visible disc. For example, even though I know where 42 Ori companion is, it was not easy nor clean. Success, maybe, but probably not good useful data. And, yes, you simply must screen the outlying observations, the most errant data points. That's smart data collection.

Edited by Asbytec (01/29/13 08:30 AM)


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Asbytec
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Reged: 08/08/07

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Re: Putting the "Rule of Thumb" to test new [Re: Asbytec]
      #5650027 - 01/29/13 10:47 AM Attachment (36 downloads)

It cleared late tonight, so I revisited BU1190. I gotta say this was not a clean and distinct split allowing the companion to be readily seen. So, no, it was a fail. However, on a personal note, I did manage the companion enough times to pick it out at PA 330. But, that took a long hard observation. So, while it was an enjoyable challenge, it was not one that shows a clear disc often enough to call it a good split.

I also revisited STT 517 AB in what I hoped was good seeing. It was not, about 6/10. So nothing new to report there: elongation with a pinch. But, I do have to ask a question. Even though this one is very tight, why is it I very occasionally get a hint of dark space? I would not call it a split based on the elongated and pinched appearance predominating, however there are those curious times when it does look separated. Can moderate seeing cause this effect?

I did try BU1048, but failed to split it even in over performing mode. BU1048 is one of those doubles seemingly easy enough with 2" sec sep, but I could not split it. The rolling first ring gave tantalizing hints that attracted my attention, but no faint speck ever materialized.

I did not attempt many of the much fainter doubles on the Orion list. With the weather, seeing, and a few other reasons, I went with some of the brighter 8th and 9th mag pairs. The ones I thought might have the best chance of success.

Seeing was 6/10 as Orion hoovered over a nearby apartment complex. 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.

Wilfried, I have one more night before I put my scope in storage for my vacation to the US. If you have a couple of doubles near the zenith, maybe in Gemini, you'd like some reports on, please post them. I will try to get them for you.

Attached is my Orion list. Green highlight means a distinct companion was readily seen or a dark space separated the pair. Red means I failed to achieve a clean, distinct split. The blue ones were on my "to do" list.

At a glance, what I thought was interesting was I managed a couple tight ones above the 150 Ra limit, but failed a couple of wider pairs at or just below that limit. It's a small sample, for sure, but interesting none the less.


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WRAK
Pooh-Bah


Reged: 02/18/12

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Re: Putting the "Rule of Thumb" to test new [Re: Asbytec]
      #5650641 - 01/29/13 04:02 PM Attachment (41 downloads)

Norme, thanks for your support. I am grateful for your additions to my data set of limit observations.
I have uploaded a list of doubles in Gemini of interest for any double star observer with a small telescope based on an intermediate state of my current RoT model for CO = 0.28 and NEML = 4.5 sorted by required aperture for a 50% split probability. I have marked the for you probably most interesting range from 140-160mm required aperture in yellow. Any observation report out of these range would be of interest to me.
Wilfried


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