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WRAK
Pooh-Bah


Reged: 02/18/12

Loc: Vienna, Austria, Europe
Star pattern for TML test with light pollution
      #5727549 - 03/12/13 07:08 AM

I have some ideas how light pollution influences the magnitude limit of a scope but not enough real data to put these ideas to test - so I am looking for a star pattern of use for this purpose.
This would ideally be a line (or another geometric pattern like an arc) of stars with confirmed magnitudes starting with a +10mag star (assumed TML for a 50mm scope with NEML of 3.2) going up in reasonable steps of ~0.2mag to about +12.5mag (assumed TML for a 300mm scope with NEML of 3.2) visible from the northern hemisphere.
The field around Alpha UMi has a rather random distribution of stars with magnitudes in this range so this is not so perfect.
Near Pollux (to be more spedific: about 15 arcminutes from HIP 38101) I have found an arc of stars from +10.85mag to +12.1mag covering only a part the the range I am looking for.
Any suggestions?
Wilfried


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Cotts
Just Wondering
*****

Reged: 10/10/05

Loc: Toronto, Ontario
Re: Star pattern for TML test with light pollution new [Re: WRAK]
      #5727599 - 03/12/13 08:08 AM

Wilfried, there are charts in the excellent, and out of print, book 'Visual Astronomy of the Deep Sky" by Roger Clark which are exactly what you are looking for.

There are about a dozen or more open clusters around the sky which are shown with and without magnitudes. I have used them by taking a photocopy of the 'no-magnitude' diagram to the eyepiece and circling every star I could see. It is then a simple matter to compare what you saw with the chart with the magnitudes on it.

I could photograph a couple of pages and post them here but I suspect it would be a violation of the TOS. I will check with my fellow Mods and get back here. Since the book is out of print it shouldn't be a problem....

Dave


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WRAK
Pooh-Bah


Reged: 02/18/12

Loc: Vienna, Austria, Europe
Re: Star pattern for TML test with light pollution new [Re: Cotts]
      #5727970 - 03/12/13 11:50 AM

Dave, thanks for your efforts, sounds good. No need to challenge copyright issues - just give me the NGC numbers for the mentioned open clusters and I will look myself for star maps.
Wilfried


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Cotts
Just Wondering
*****

Reged: 10/10/05

Loc: Toronto, Ontario
Re: Star pattern for TML test with light pollution new [Re: WRAK]
      #5728466 - 03/12/13 04:01 PM

The maps are from a 1961 paper by Hoag et al. But you may find them lurking on the web somewhere...
NGC 225
1647
2129
2422
6494
6823
6910
7031
7235

That's it. Post here if you actually find any of these...

Dave


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Cotts
Just Wondering
*****

Reged: 10/10/05

Loc: Toronto, Ontario
Re: Star pattern for TML test with light pollution new [Re: Cotts]
      #5728471 - 03/12/13 04:05 PM

Here's the book on Amazon. http://www.amazon.com/Roger-N.-Clark/e/B001H9TUB8

Nice price!

Dave


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WRAK
Pooh-Bah


Reged: 02/18/12

Loc: Vienna, Austria, Europe
Re: Star pattern for TML test with light pollution new [Re: Cotts]
      #5728603 - 03/12/13 05:09 PM

Dave - NGC 2129 seems to be of special interest. Easy to locate near M35 and covering the range from some bright stars to very faint ones. Thanks.
Wilfried


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fred1871
scholastic sledgehammer


Reged: 03/22/09

Loc: Australia
Re: Star pattern for TML test with light pollution new [Re: WRAK]
      #5729402 - 03/12/13 11:55 PM

Wilfried, NGC 2129 has had photometry done on it since the paper of Hoag et al in 1961, and the more recent work should be an improvement given advances in instrumentation since then.

You'll find online at a few locations a paper by Carrarro, Chaboyer and Perencevich (2005) that uses CCD photometry for the cluster, and provides a list of stars (with Hoag's numbering) with new photometry. It's in pdf form for ready access.

The Hoag paper is also listed in the bibliography of the Carrarro paper if you need the source.


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WRAK
Pooh-Bah


Reged: 02/18/12

Loc: Vienna, Austria, Europe
Re: Star pattern for TML test with light pollution new [Re: fred1871]
      #5729659 - 03/13/13 03:53 AM

Fred, found the Carraro et al article but so far no image reference for the used star numbers. But I think the DSS image on Sky-Map.org will do it: http://www.sky-map.org/?ra=6.018333333333331&de=23.3166666666667&zoom...
With the cursor over the individual star you get the data for it.
Wilfried


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fred1871
scholastic sledgehammer


Reged: 03/22/09

Loc: Australia
Re: Star pattern for TML test with light pollution new [Re: WRAK]
      #5729764 - 03/13/13 07:00 AM

It will depend on the source of their data.

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fred1871
scholastic sledgehammer


Reged: 03/22/09

Loc: Australia
Re: Star pattern for TML test with light pollution new [Re: WRAK]
      #5729846 - 03/13/13 08:27 AM

Wilfried, I've now located the Hoag et al 1961 paper - available online via the ADS - the paper is VERY long because they did photometry on many clusters, but a photo chart for NGC 2129 is there, with rulers each side, and a list of stars (location by grid, X and Y coordinates) with photometry in a table. This is done for each of the many clusters.

The original source is Publications of the US Naval Observatory, 2d series, volume 17, from page 347 onwards.
The NGC 2129 chart and data is on page 406.


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WRAK
Pooh-Bah


Reged: 02/18/12

Loc: Vienna, Austria, Europe
Re: Star pattern for TML test with light pollution new [Re: fred1871]
      #5731631 - 03/14/13 04:51 AM

Fred, thanks for the hint. Found the article with the NGC 2129 chart - the grid system is a bit inconvenient to use but I will be able to countercheck the magnitude of at least some stars I have so far selected for a magnitude limit check.
Wilfried


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WRAK
Pooh-Bah


Reged: 02/18/12

Loc: Vienna, Austria, Europe
Re: Star pattern for TML test with light pollution new [Re: WRAK]
      #5733639 - 03/15/13 08:44 AM

This seems to get tricky - just checked the magnitudes of some of the stars in NGC 2129 with the current AAVSO data (http://www.aavso.org/download-apass-data - works quite efficient, with a 0.001 radius degree you get usually only the data for the star at the given position) and got for several stars serious differences to the values of the other sources.
But I think the AAVSO values should be the most reliable ones.
Wilfried


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fred1871
scholastic sledgehammer


Reged: 03/22/09

Loc: Australia
Re: Star pattern for TML test with light pollution new [Re: WRAK]
      #5735465 - 03/16/13 02:42 AM

Wilfried, I expect some differences will be due to different filters used for photometry, quite apart from small errors. AAVSO are using a pretty standard set of filters for various wavebands, based on their description - you need to check against filters and methodology used in the science papers referred to - the older Hoag material, and the more recent paper I listed. The latter shows some of the differentials of their magnitudes compared to Hoag's for the cluster they re-studied. Newer material will often be better due to new instrumentation providing smaller errors if used well; but some differences will be due to filter differences (waveband centre and width).

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Ed Wiley
scholastic sledgehammer


Reged: 05/18/05

Loc: Kansas, USA
Re: Star pattern for TML test with light pollution new [Re: WRAK]
      #5736102 - 03/16/13 11:53 AM

M67 is a classic open cluster for photometry calibration and is well placed now.

http://binaries.boulder.swri.edu/binaries/fields/m67.html

http://binaries.boulder.swri.edu/binaries/fields/m67ids.txt

Would V10-13 be a suitable magnitude range?

Ed


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WRAK
Pooh-Bah


Reged: 02/18/12

Loc: Vienna, Austria, Europe
Re: Star pattern for TML test with light pollution new [Re: Ed Wiley]
      #5736337 - 03/16/13 01:45 PM

Ed, V10-13 is perfect. The documentation with numbers for the stars and the list with relating magnitudes is great. Checked a few stars with AAVSO and the data seems of very good quality.
M67 will soon come into my field of view and should then be certainly useful for my purpose. Thanks a lot.
Wilfried


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WRAK
Pooh-Bah


Reged: 02/18/12

Loc: Vienna, Austria, Europe
Good news and bad news new [Re: WRAK]
      #5740870 - 03/18/13 02:53 PM

Good news first: Already the first observations with the topic of NEML influenced TML showed that I have so far overrated the impact of light pollution on TML by for example about 0.3 mag for a 140mm scope (TML 11.76 for NEML 3 instead of 11.46). The interest in this topic led to the inclusion of more doubles with faint secondaries near the TML of my scope into my session plans and I find the challenge to resolve doubles in this range as quite interesting.

The bad news: The TML part of my RoT model does therefore not work properly for NEML less than 3.5 leading under specific conditions to drastic too large required apertures for doubles with secondaries fainter than +11mag. But before I try to change this I will take some more time for sampling TML observations with regard to light pollution.

Any contributions especially for apertures larger than 140mm would be appreciated very much.
Wilfried


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Ed Wiley
scholastic sledgehammer


Reged: 05/18/05

Loc: Kansas, USA
Re: Star pattern for TML test with light pollution new [Re: WRAK]
      #5741703 - 03/18/13 08:45 PM

Glad to help! This is one of the standard star fields for checking photometry and its good to see it put to other good uses. I hope you continue to share your finding with us.

Clear skies, Ed


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WRAK
Pooh-Bah


Reged: 02/18/12

Loc: Vienna, Austria, Europe
Re: Star pattern for TML test with light pollution new [Re: Ed Wiley]
      #5791745 - 04/11/13 03:08 AM

Yesterday finally clear skies again. Transparency was high but seeing rather moderate (Pickering 5). NEML was +2.85mag as I could barely make out Beta CMi. Then I used the Sky Quality Meter and got values between +17.5 and +18mag for my field of view - indicating that NEML +2.85 was may be a bit on the pessimistic side.
Then I located M67 and checked TML for my 140mm refractor and got +11.83 as faintest star I could resolve indicating a loss of 1.6 magnitudes due to LP - not this bad.
Wilfried


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WRAK
Pooh-Bah


Reged: 02/18/12

Loc: Vienna, Austria, Europe
Re: Star pattern for TML test with light pollution new [Re: WRAK]
      #5804078 - 04/17/13 08:10 AM

Had yesterday another opportunity to visit M67 and more time to make use of the iris diaphragm for my 140mm refractor. Quartermoon made the sky rather bright, SQM showed values about +16.5mag for my field of view. Despite this I had the impression that NEML was this time a bit better than +3mag, may be +3.1 or even better (not sure If I really could make out Eta Leo, this would even mean +3.45mag).
I got the following values for the different apertures:
140 - 11.83 again
130 - 11.64
120 - 11.64
110 - 11.4
100 - 11.3
90 - 11.3
80 - 11.3
70 - 11.3
60 - 11
50 - 10.6.

The value for 130mm should most probably be somewhere in the middle between 11.83 and 11.64 but I missed a star zu check this. The run of 11.3 for apertures between 100 and 70mm should be proof that the used reference star with +11.27mag at the position RA 132.860118 Dec 11.730742 is somehow questionable concerning advertised data or that I have simply failed in my observations - will have to check this again.
Wilfried


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fred1871
scholastic sledgehammer


Reged: 03/22/09

Loc: Australia
Re: Star pattern for TML test with light pollution new [Re: WRAK]
      #5805608 - 04/17/13 09:51 PM

A curious set of numbers, Wilfried. Obviously something has gone wrong, when a 100mm aperture goes no fainter than 70mm - despite twice the light gathering. Indeed, if 70mm gives mag 11.3, and 140mm only goes to mag 11.8, that's a mere difference of ~0.5 mag - however the difference in light-gathering area is a factor of 4:1, or about 1.5 magnitudes!

So either the magnitude sequences are faulty for visual magnitudes, or the gremlins are holding back the larger aperture, or the elves are helping the smaller aperture?

Or is there a problem with the iris diaphragm, perhaps placed where the real aperture effect doesn't match the intended effect?

Whatever the reason or reasons, the limiting magnitude sequence has problems.

I'm currently working on setting up my 80mm refractor side by side with the 140mm. That should allow me to make some interesting comparisons for magnitude limits and for resolution.


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