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fred1871
scholastic sledgehammer


Reged: 03/22/09

Loc: Australia
Re: State of the affairs new [Re: WRAK]
      #5669916 - 02/08/13 10:42 PM

Wilfried, I'm still wondering about some doubles that you didn't get on your list with AstroPlanner when you used it to filter the WDS for a list. Have you been able to find why those pairs (I think around 2-3 February the comments on these) did not show on your list?

My reason for asking is that I'm looking for software that can produce lists, by constellation, with data from the WDS - and all the software packages I've tried so far have either edited out too many doubles - perhaps they use default criteria that are wrong - or want to give me lists with unhelpful names for stars (HD, SAO, HIP, etc) instead of staying with the WDS names, which refer to discoverers.

AstroPlanner looked likely to be what I was seeking, until I found it had left out doubles that should have been on your list. So I'm now wondering if there are limitations to it that mean it won't give me what I want - the ability to filter by magnitude, NOT separation, and use the WDS, and have selection by constellation.

Your lists show it can do what I'm looking for EXCEPT that some doubles were somehow missed, when they should have been listed.


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WRAK
Pooh-Bah


Reged: 02/18/12

Loc: Vienna, Austria, Europe
Re: State of the affairs new [Re: fred1871]
      #5670127 - 02/09/13 04:13 AM

Fred, I found these "missing" doubles via AstroPlanner without problems with a new search with the accordingly parameters. I do not remember how I exactly did this search for the Orion list so may be it was my combination of parameters leading to this result but I have no real explanation - but I think AstroPlanner is an excellent tool for double star session planning.
Wilfried


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fred1871
scholastic sledgehammer


Reged: 03/22/09

Loc: Australia
Re: State of the affairs new [Re: WRAK]
      #5671205 - 02/09/13 06:51 PM

Thanks, Wilfried - sounds as if AstroPlanner will match up with what I'm looking for. There's a lot of useful software around, but the problem is finding the examples that do what the individual observer wants.

I'll have some more observing data soon. I'm analysing some recent, and some not so recent, observations, including some with the 9.25" SCT - a good'un for testing CO effects (~36% by diameter!) and for fainter but not very uneven pairs - it makes the faint ones much easier to see merely through extra light, before any other factors are considered.


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

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Re: State of the affairs new [Re: fred1871]
      #5671253 - 02/09/13 07:20 PM

Hello guys, interesting conversation. I especially appreciate Fred's input on SA and CO. The complexity of which speaks to the difficulty and seems to be a necessary aspect of such a project.

I was really enjoying observing stars associated with this project while testing both my own limits and those of my scope.


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WRAK
Pooh-Bah


Reged: 02/18/12

Loc: Vienna, Austria, Europe
Re: State of the affairs new [Re: Asbytec]
      #5672635 - 02/10/13 04:21 PM

The effects of spherical aberration for double star resolution seems to me to be a complex topic - anyway as most observers will not know any specific SA value for their scope it cannot be used in a RoT model with benefit, so I tend to see SA as random factor in this regard.
Other factors with some relevance could be the existence of spiders producing spikes at least for brighter primaries and therefore changing the diffraction pattern and also the focal ratio especially of Newtons as "fast" reflectors seem to be of no good use for double star resolution due to coma. But for now I tend to shelve such considerations for possible future extension as I am struggling to come to a decent enough RoT model with the factors in evaluation so far.

Fred - looking forward to your C925 observation reports with great interest.
Wilfried


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

Loc: La Union, PI
Re: State of the affairs new [Re: WRAK]
      #5672935 - 02/10/13 07:40 PM

Wilfried, yes, using SA explicitly would seem too complex and unhelpful. I found assuming Strehl to be interesting for calculations involving MTF. With Strehl, peak intensity is either explicit for unobstructed apertures or implicit for obstructed samples. Strehl and obstruction both determine light distribution, of course. Light distribution seems to be part of the problem. So, while specific measures of SA are both difficult to know and use, assuming a Strehl might offer some utility.

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WRAK
Pooh-Bah


Reged: 02/18/12

Loc: Vienna, Austria, Europe
Re: State of the affairs new [Re: Asbytec]
      #5674305 - 02/11/13 03:59 PM

Norme, I fear Strehl is in the same leage with SA - an amateur observer knows rarely the Stehl value of his scope I think and it is usually certainly not part of an observation report at least as far as I know. My data set of limit observations would shrink to zero if I would require Strehl as known factor including most of my own observations - I know the Strehl value of two of my scopes but not of my preferred 140mm refractor used with the iris diaphragm.
Wilfried


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fred1871
scholastic sledgehammer


Reged: 03/22/09

Loc: Australia
Re: State of the affairs new [Re: WRAK]
      #5675159 - 02/12/13 01:49 AM

Wilfried, I can only agree that the short Newtonian is generally found to be problematic for doubles - there is the occasional one of exemplary optical quality and with a Paracorr and thermally stable and with a (relatively) small CO, plus very accurate collimation, that might well be good for double stars. But I suspect that it's a minority of short Newtonians that fit the whole description. Pete's experience in going from a 10-inch f/5 to an 8-inch f/9, and the big improvement for doubles, is a useful cautionary tale.

Spherical aberration is a common issue with all kinds of telescopes. In small amounts it need not be a big problem. Indeed, WR Dawes in 1867, in the introduction to his doubles catalog where he also announced what is now known as the Dawes Limit, remarked on SA in some detail: in particular, that a larger refractor with obvious SA outperformed a smaller one without noticeable SA - but the effect of SA was to produce a large amount of "false and scattered light" around brighter stars. Nevertheless, this affected "how a telescope shows a difficult object, than whether it can show it at all" [obviously for double stars, not detail on Jupiter]. His conclusion, that test objects are of "comparatively small importance in the trial of a telescope" because "so much must depend on the eye and habit of the observer, and the circumstances under which the scrutiny is performed", sounds curiously modern.
But it does suggest that for high contrast objects (doubles) SA is less of a problem than for low contrast objects. Dawes is more optimistic than I am about scattered light and its effect on faint companions.

More thoughts on SA, including its interaction with CO etc shortly. Meanwhile, thanks Wilfried for the AstroPlanner recommendation. I find it does quite well what I'm looking for, and without needing to do acrobatics to get standard double star designations, such as chasing through multiple tables of equivalence, or manually re-labeling most things, or trying to re-program a program when it doesn't do what it says it does. Some software writers don't appear to know enough about astronomy. And their "preferences" (if one can call it that) then get used by lots of other folk, leading to further confusions and extra work and identification muddles. The Haas project struck this, with a need to translate the original lists into equivalences for some observers for non-standard (in doubles terms) designations such as SAO, a catalog that's effectively obsolete, needed due to the software packages they had and the limitations of those. Yes, some software makes me grumpy.

Strehl? - MTF? - EER?. Comments to come on all that.

Edited by fred1871 (02/12/13 01:51 AM)


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WRAK
Pooh-Bah


Reged: 02/18/12

Loc: Vienna, Austria, Europe
Re: State of the affairs new [Re: WRAK]
      #5677221 - 02/13/13 08:47 AM

Quote:

...
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 was not such a good idea - the statistical analysis resulted in a parameter value of very near 1 and did not bring any reasonable advantage in terms of standard deviation and correlation.
I think I will simply dump the obvious over- and underperforming observations to get clear of the huge errors they produce.
Wilfried


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

Loc: La Union, PI
Re: State of the affairs new [Re: WRAK]
      #5677818 - 02/13/13 02:53 PM

If your using actual observations with real world Strehl and SA, then tweaking the model to those observations would seem to account for them on average and implicitly.

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WRAK
Pooh-Bah


Reged: 02/18/12

Loc: Vienna, Austria, Europe
Re: State of the affairs new [Re: Asbytec]
      #5679164 - 02/14/13 10:55 AM

Norme, you may probably be right about Strehl and SA, but I don't have any observations reports including these values - but what I will do is at least eliminating the obvious underperforming observations resulting from using fixed apertures and lack of better competing observations, because these are certainly "wrong". This will give then more room for real limit observations including the overperforming ones.
Wilfried


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WRAK
Pooh-Bah


Reged: 02/18/12

Loc: Vienna, Austria, Europe
Re: Putting the "Rule of Thumb" to test new [Re: fred1871]
      #5681071 - 02/15/13 10:19 AM Attachment (21 downloads)

Quote:

The large number of rather faint pairs in Wilfried's list for Orion got me wondering ...



... me too with the rather moderate proposed apertures for splitting these - as already mentioned there exists certainly a weakness in the current model regarding secondaries fainter than +11mag. As we come here close to the telescope magnitude limit at least for smaller scopes in combination with light pollution we need here an additional component working with the difference between the magnitude of the secondary M2 and the with NEML adapted TML similar to Peterson's approach.
A possible procedure could be to run the current model and then calculate the NEML adapted TML for the proposed aperture and compare this value with M2. If the TML is clearly above M2 then no further action is needed but if it is rather equal or even below then the proposed aperture is to be increased accordingly - what this means exactly is meanwhile not very clear, I will have to work this out.
First step is certainly to have a clear model how NEML works on TML. My first idea was that for a scope it certainly does not mean a full magnitude loss according to NEML, rather may be half of it. But this did not correspond very well to the existing observation data set suggesting a dependance on aperture in terms of less aperture means less magnitude loss.
On next possibility I will make a set of observations for the influence of NEML on TML with different apertures for a better data base for this purpose. Meanwhile I will work with a first approach for delta_TML = LN((6.5/NEML)^2.512)*(TML/13.43)^2.512 with TML = 2.7+5*LOG10(D_mm) and 13.43 as the assumed turning point from which the magnitude loss increases above the assumed half magnitude loss indicated by NEML. The image shows the effects of this algorithm for a NEML of 3.5.
Wilfried


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WRAK
Pooh-Bah


Reged: 02/18/12

Loc: Vienna, Austria, Europe
Final steps new [Re: WRAK]
      #5684994 - 02/17/13 11:21 AM

I hoped to be able to derive from the formula above the for the compensation of NEML required TML value but failed miserably - may be due to my cold induced loss of clear thinking. Peterson's approach works surprisingly good with M2 fainter +11mag - but not this good for brighter companions and did not provide any help for considering light pollution besides a seeing factor, but this is another topic. But numerical approximation proved again to be a good substitute so I got this fixed. Applied on the mentioned Orion list this added step to the RoT model did not change anything down to a moderate NEML of 4.5 but with lower values of NEML the effects get at least for wide doubles with faint companions quite drastic. With a for suburbs unfortunately usual NEML of 3.5 this gives (with zero obstruction):
SLE832 11.1" +10/11.8mag 150mm instead of 99mm
BAL2147 7.6" +8.7/11.8mag 150mm instead of 113mm
HJ700 11.5" +9.9/11.7mag 140mm instead of 96mm
But there is no change for doubles rather close like for example:
TDS3160 1.5" +9.5/11.7mag 174mm remain.
I will now produce a new spreadsheet for an at the moment final beta version of my RoT model and post it here soon including a list of doubles from the upper part of Eridanus.
Wilfried


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WRAK
Pooh-Bah


Reged: 02/18/12

Loc: Vienna, Austria, Europe
Re: Final steps new [Re: WRAK]
      #5690200 - 02/20/13 05:17 AM Attachment (48 downloads)

I have now uploaded the 3rd version of my RoT model and time will show if this is any good. The answer to the question which aperture is required for resolving unequal doubles with faint companions showed to be quite complex. While the single components of the model are based on more or less educated guesses the parameters are calculated with statistical analysis of limit observations (nonlinear regression). Some guesses were evidently not this good because they did not deliver on the numbers and had to be replaced by better ones - I am sure this process could be repeated several times to get even better results but this may be a task for the future. On the other side it was difficult to get enough solid observations to be able to do solid calculations - my data set is still far too small.
The process of developping the model was quite interesting as I gained a lot of for me new insights:
- Light pollution is for doubles with secondaries brighter than +10mag of no real concern
- For doubles with companions fainter than +11mag the by light pollution reduced telescope magnitude limit plays a significant role at least for wider separations
- The effect of central obstruction on the diffraction pattern seems on first look not this significant - but when calculating for required aperture small differences suddenly become a significant advantage for close doubles of similar brightness. With increasing magnitude difference this advantage gets smaller and results finally in an disadvantage for scopes with CO.
The uploaded spreadsheet is filled with doubles from the upper part of Eridanus. Any response with observations would be apprediated.
Wilfried


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fred1871
scholastic sledgehammer


Reged: 03/22/09

Loc: Australia
Re: Final steps new [Re: WRAK]
      #5690268 - 02/20/13 07:10 AM

Wilfried, I will provide some more data points soon - I've had too many other things needing doing to be able to go through observations from recent weeks, some of them likely to be limit or near-limit observations.

I can only agree about light pollution being a limiting factor, especially for small and moderate telescopes, in seeing faint companions. Larger telescopes are less affected for 11th magnitude stars UNLESS very close to much brighter primary stars.

Regarding CO - my current impression is that medium CO (25-35%) is not very helpful for seeing close even pairs, compared to unobstructed apertures. The reduction in disc size is very little. Other factors, such as less good optics, collimation being even slightly off, thermal issues, seem to cause more loss than any gains from reduced disc size. And air turbulence unhelpfully interacts with CO as Danjon and Couder noted long ago.

I've worked out some further questions regarding CO and its interaction with optical quality as well. More on that also after tomorrow, because I'm preparing other material for a presentation that will keep me busy tomorrow.

Thanks for the Eridanus list. I'll look through it as well, and see what I can usefully observe, to add to pairs in Orion and Gemini I've already looked at. Gradually the data points will build up to good numbers.


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fred1871
scholastic sledgehammer


Reged: 03/22/09

Loc: Australia
Re: Putting the "Rule of Thumb" to test new [Re: Asbytec]
      #5696159 - 02/23/13 08:23 AM

Quote:


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. ...






Wilfried and others, the above is quoted from Norme's observations reported 30 January 2013. As I've now caught up with a few of these I thought I'd provide my observing notes, done without benefit of checking what Norme wrote.

The folowing are with my 140mm refractor, seeing started at fairly good, becoming good-plus (7/10) for the more difficult ones. Unfortunately I didn't get to STT 171. These are in Gemini. Night of a 6 day moon recently. Nelm in the observed area was perhaps 4.5, despite moonlight.

For purposes of comparison, I started with STT 140, listed for a mere 117mm aperture - the mag 10.1 companion was seen at 160x, not very difficult; delta-m here is 3.2 mags. I compared it with A2450, same separation, delta-m 3.0, but fainter - mags 8.05 and 11.06. A2450 also showed as a double at 160x - however on the Gemini list it's got 140mm aperture indicated. It was nearly as easy as STT 140 - only the fainter magnitude of the companion made it less obvious.

BU 100 - mags 7.3 and 11.1 at 3.2" (listed for 144mm) was easier - the companion star showed at 100x. It was noticeably easier than A2450, and at 160x the companion was obvious.

STT 145 - mags 7.3 and 9.9 at 1.5" - listed for 147mm aperture. More difficult, but the companion was a just visible speck close to the primary at 160x, and more clear at 230x.

My feeling is that the model used for the Gemini doubles (since revised) was not entirely consistent in predictive capacity; and that exceeding it was not of high difficulty for at least some doubles.

I still have some other pairs, already observed, to provide notes for. And if the weather here ever stops being cloudy I can move on to Eridanus.


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WRAK
Pooh-Bah


Reged: 02/18/12

Loc: Vienna, Austria, Europe
Re: Putting the "Rule of Thumb" to test new [Re: fred1871]
      #5698452 - 02/24/13 03:24 PM

Quote:

... My feeling is that the model used for the Gemini doubles (since revised) was not entirely consistent in predictive capacity; and that exceeding it was not of high difficulty for at least some doubles...



Fred, you are probably right - it seems that at this stage I had too many underperforming observations in my data set (mostly from Lord's paper) resulting from the use of fixed apertures but meanwhile I have eliminated most of these. The Eridanus list should already do better.
Wilfried


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WRAK
Pooh-Bah


Reged: 02/18/12

Loc: Vienna, Austria, Europe
Re: Putting the "Rule of Thumb" to test new [Re: WRAK]
      #5749123 - 03/22/13 07:13 AM

As I already posted in the thread "Star pattern for TML test with light pollution" I found a glitch in the last module of the RoT model checking the result against the for resolving of faint companions required telesocpe magnitude limit including the influences of light pollution for NEML below 3.5 as it seems that I have overestimated the influence of light pollution on TML.
I will certainly try to correct this but I have to sample more TML-observations depending on NEML.
As I have only a NEML range 2.5-3.5 available I would appreciate reports from other observers very much. As the advertised magnitudes for faint stars are often not very reliable I recommend the check with http://www.aavso.org/download-apass-data - when restricting the parameter "Radius" to 0.01 you will get most probably only one result and this should be the observed star.
Wilfried


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WRAK
Pooh-Bah


Reged: 02/18/12

Loc: Vienna, Austria, Europe
Putting the "Rule of Thumb" to test - next step new [Re: WRAK]
      #5781195 - 04/06/13 06:50 AM

Foul weather for weeks made not only obervations impossible but stalled also other planned outdoor activities - so I had some time at hand to "play" with numbers.
Target was to gain some impressions how Lord's RoT works compared with the current version of my RoT model. As data set for this investigation I used the set of pairs of the Sissy Haas project and as additional tool I used the AstroPlanner implementation of Lord's algorithm giving not a number but a verbal rating from "UN" for unresolvable to "E" for easy for a given combination of avertised date for the double, telescope aperture, central obstruction size and seeing.

Assuming perfect seeing and zero central obstruction when using the algorithm of Lord's RoT results in a required separation for a split and when you use this result in AstroPlanner you always get a "D" for difficult - I interpret this as comparable with my model approach of a 50% probability for a split meaning a fair chance.
Applied to the Sissy Haas set of doubles and "translated" from separation into aperture you get a set of apertures required for a 50% split probability.

Comparing these results with the results when applying my current RoT model to the same set of doubles gives some interesting insights:
- Lord's RoT is rather conservative when the separation is small - with only few exceptions my RoT requires far smaller apertures with the exception of fainter doubles as the aspect of faintness is not part of Lord's model (a +4/6mag pair gets the rame rating as a +8/10mag one - this I consider a main weakness of Lord's RoT)
- For separations somewhat larger beginning with 3" Lord's RoT is consistenly below the values delivered by my RoT model: The main reason for this is probably the fact that as far as I know Lord had no observation reports available for scopes with apertures smaller than 75mm so his results for larger separations are projections from the other observations with larger apertures and such an approach is prone for desaster. As I have meanwhile with the help of an iris diaphragm a lot of limit observations below 75mm aperture I am quite confident in the numbers of my model
- The combination of somewhat larger separations with not this large difference in brightness of the double star components poses also a problem for the Sissy Haas project because nobody uses scopes with apertures smaller than 50mm so observation reports in this range without the use of aperture masks or iris diaphragm are of no value for the project
- Using the results of my RoT model for the aperture in the AstroPlanner implementation of Lord's RoT gives for separations below 3" separation most of the time "VD" for very difficult oder "ED" for extremely difficult - this may be the other side of the coin regarding available observations: Lord had a lot of observations with apertures above 140mm in his data set while I have only a very limited data set in this range available and especially no own observations. But here I have some plans (see below)
- Things get again very interesting when using the AstroPlanner implementation of Lord's RoT to determine the aperture required for an "XD" (exceedingly difficult) rating - Lord's RoT delivers here extremely optimistic values with in average about 42% smaller apertures as required for a "D" rating. This indicates an extreme wide variation is his data set of observations most probably due to the use of fixed apertures with only a few observations really at the limit and most above. This would also explain the rather pessimistic results for the average "D" rating of Lord's RoT
- In average Lord's "XD" rating corresponds very well with the double standard deviation of 14% for my RoT model meaning reducing the for a 50% chance split required aperture by 28% resulting in a probability of about 3% for a split means once in a while under the very best conditions.

Today I have received the delivery of an iris diaphragm with an inner diameter of 225mm for use with my C925 SCT which means I can then cover the range of 170-225mm (and 235mm without iris) with own limit observations. Below 170mm will not be very useful as then the CO would exceed 50%. But the small gap between 140 to 170mm should pose no serious problem for the validity of the statistical analysis. I can only hope for a good performance of the C925 I did not use so far for double star observing as I do not like the handling, feeling and image quality in terms of crisp spurious disks of this scope this much.
Hope for more clear skies for the rest of the year then.
Wilfried


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WRAK
Pooh-Bah


Reged: 02/18/12

Loc: Vienna, Austria, Europe
Re: Putting the "Rule of Thumb" to test - next step new [Re: WRAK]
      #5815849 - 04/22/13 05:47 PM

The hope for good performance of the C925 did so far not realize - the secondary mirror has somehow gained some freedom for rotation and shifting and therefore collimation is non existent and the star test showed severe distortions of the diffraction pattern. Has to be corrected.
Second mishap was a not this perfect iris diaphragm - changing the aperture required too much force to be useful on a telescope so I had to return it for exchange.
As I do not like the problems with dew on the schmidt plate of the C925 I ordered a Mewlon 210 to have another option - will arrive in a few weeks.
Wilfried


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