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WRAK
Pooh-Bah


Reged: 02/18/12

Loc: Vienna, Austria, Europe
Re: Ever observed COU1900? new [Re: Bill Boublitz]
      #5939767 - 06/25/13 01:10 PM

I contacted Brian Mason again regarding COU1900 with the impression that the DeRosa confirmation of COU1900 is probably in error. Brian answered with the for me new information that DeRosa only measured delta-m with 3.08 in the infrared range and that the visual delta-m might be significantly higher or lower than. This answer is for me a bit disappointing because what is then the base for the current WDS entry +6/10mag? And I dislike magnitude data in the infrared range anyway because in my opinion magnitudes are a strictly visual concept.
Wilfried


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7331Peg
Sirius Observer
*****

Reged: 09/01/08

Loc: North coast of Oregon
Re: Ever observed COU1900? new [Re: WRAK]
      #5939921 - 06/25/13 02:43 PM

Wilfried,

Any ideas as to what's involved in getting a photometric value of the secondary's magnitude that is equivalent to the visual value? I understand the magnitudes of variable stars are determined that by way by some amateur astronomers, so it doesn't sound like it's a matter of relying on a large professional observatory to get the data. Of course you have to detect the seondary first, which has been the issue from the start.


John


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fred1871
scholastic sledgehammer


Reged: 03/22/09

Loc: Australia
Re: Ever observed COU1900? new [Re: WRAK]
      #5940436 - 06/25/13 08:34 PM

Wilfried, that's exactly what I was (rather laboriously) pointing out (though I see now it was in another thread). IR delta-m numbers don't tell you what visual delta-m numbers will be. And there's no straightforward translation.

Unfortunately, my comments about this matter (IR versus V magnitudes) is in the thread about "Observations/Images..." towards the end; where I spelled out the issues (23 June 2013).

I'll post a summary version of my comments there to this thread, today. Keeps things tidier and easier to find.

Regarding John's (7331Peg) query, it's a matter of doing photometry in V-band rather than an IR region; that should be possible without a giant telescope given the separation of the components, allowing isolation of the secondary for brightness readings.


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fred1871
scholastic sledgehammer


Reged: 03/22/09

Loc: Australia
Re: Ever observed COU1900? new [Re: fred1871]
      #5940476 - 06/25/13 09:02 PM

In another thread, recently ("Observations/Images...") I wrote some notes on the photometry of COU 1900 following some thoughts by John (7331Peg). The CN date for this is 23 June 2013.

Here's a summary, with lengthy quotations, to get these ideas into the right thread.

The de Rosa paper that provides recent photometry for COU 1900 has the problem that the photometry was done in infra-red, not visual wavelengths. This happens when measures of doubles are made in the IR, as they often are these days with large telescopes. It can lead to confusion.

" In the datarequest key notes [from WDS], I see "More recent additions to the delta-m catalog include filter information (typically, central wavelength & FWHM)..."
That suggests the "2200" listed is the wavelength for the 2010 photometric measure in nanometres. The delta-m catalog supports this.

2200nm is K-band, well into the IR, where a lot of the separation/PA measures are made these days. Therefore, the mag 10.0 estimate for the companion could be a corrected magnitude figure based on the companion's supposed spectral type, resulting in an estimated colour-index, in changing from 2200nm to V-band (standard is ~550nm). No spectral type is given for the companion in the data file ... so what basis was used? We're left wondering.

The WDS summary line includes no code, suggesting the magnitude is visual.

Therefore, the assigned magnitude (10.0) needs some kind of explanation as to how it was derived."

John then queried further:
I dug out the 2011 DeRosa paper (here) which only seems to muddy the waters more.

On page three is a table which includes a magnitude estimate of 5.53 for the primary of Cou 1900 -- it's listed there by its HIP number, 51200, and shows a K filter was used, which is referred to later in the paper as K'.

On page seven you'll find a table of data for the secondaries in the survey (Cou 1900 is shown as 51200 B). The separation (2.41") and the position angle (304.1 degrees) are listed in the second and third columns. The next column has the heading "Magnitude Difference" and has a value of 3.08 entered. I wonder if that is supposed to mean 3.08 magnitudes less than the primary? That would result in a magnitude estimate of 8.61 if that's the case. Again, a filter is shown, H2.

Apart from the filters, Fred, I don't see any reference to wavelength bands after skimming through the paper a couple of times.


To which I replied:

"No, it's straightforward in the sense that it doesn't change what I've said. The table on page 3 of that paper indicates the wavelength band for the magnitudes measured - K in this case, as before the IR band centred on ~2200nm.

The delta-m listed (3.08) I'd expect to be in the same band, and therefore indicates a brightness difference in the K band (IR). How that relates to brightness difference in the V-band (visual, ~550nm) is the issue - that's what I commented on in modest detail, suggesting the logic of what we want to know requires some method of determining the colour-index, to determine the (usually quite different) delta-m in V compared to K. As I haven't yet seen a spectral type for the companion, even a guess on likely colour-index correction isn't possible (averaged differences for the class, vs individually measured).

The primary star is main sequence (MK class V) and a 'Sirian' star, spectrum A2. That tells us nothing about the companion.

So - spectrum information for the fainter star would allow an estimate of possible V-magnitude delta-m, but much more useful would be V-band photometry of the fainter star, giving a direct measure."

SUMMARY: the IR data don't give us anything useful for visual observers, as Brian Mason has indirectly said : to quote Wilfried, passing on what Brian said:
Brian answered with the for me new information that DeRosa only measured delta-m with 3.08 in the infrared range and that the visual delta-m might be significantly higher or lower than.


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WRAK
Pooh-Bah


Reged: 02/18/12

Loc: Vienna, Austria, Europe
Estimating visual magnitude new [Re: 7331Peg]
      #5940912 - 06/26/13 05:11 AM Attachment (14 downloads)

Quote:

... Any ideas as to what's involved in getting a photometric value of the secondary's magnitude that is equivalent to the visual value? ...




John, sorry, have to quit here - no idea, but would be highly interested in a for an amateur feasable solution myself.

If the magnitude of a companion is in question I usually have a look at the APASS page of the AAVSO website (http://www.aavso.org/apass) if there are measurements at the given position - here are also visual magnitudes listed.
If this fails I use the following methods for crude estimations:
- For close doubles comparing the brightness of the comapnion with the first diffraction ring and then compare this impression with the data from a table from Chris Lords paper on Resolving unequal binaries giving an indication of delta-m depending on the size of CO
- For wide pairs I use an iris diaphragm to get to the smallest possible aperture resolving the companion. Given TML for given NEML is then a quite good indication for the visual magnitude of the companion
- For pairs in between I use sometimes my pA calculator in reverse mode if I know the limit aperture for this double - I simply change the magnitude value of the secondary in steps to get the equivalent pA. With the known standard deviation I can even calculate kind of range for a 95% probability range. While this "method" may be of some value for smaller apertures things get rather unreliable with greater apertures.

BTW - for COU1900 I would get a delta-m of ~7 if we take Mark's observation with 381mm aperture as limit observation.
Wilfried


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Nucleophile
super member


Reged: 05/24/13

Loc: United States
Re: Estimating visual magnitude new [Re: WRAK]
      #5941037 - 06/26/13 08:34 AM

Quote:

BTW - for COU1900 I would get a delta-m of ~7 if we take Mark's observation with 381mm aperture as limit observation.
Wilfried




It would be instructive if someone with an 11 or 12 inch instrument could take a crack at it and report their results here.

I saw the companion of COU 1900 again last night. But here is the fun part: the roof of my house partially blocked my view of the part of the sky containing the binary causing the light from the primary to dim somewhat--but the reduced glare of the primary aided in the identification of the secondary--I saw it immediately at 398x. Of course it helped that I have seen it once already and I know how to look for companion.


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Nucleophile
super member


Reged: 05/24/13

Loc: United States
Re: Estimating visual magnitude new [Re: Nucleophile]
      #5941100 - 06/26/13 09:22 AM

Quote:

It would be instructive if someone with an 11 or 12 inch instrument could take a crack at it and report their results here.





I estimate the roof blocked about a third of the aperture when I made this observation.

Did I inadvertently "mask" my aperture to an instrument of this size last night?


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7331Peg
Sirius Observer
*****

Reged: 09/01/08

Loc: North coast of Oregon
Re: Estimating visual magnitude new [Re: WRAK]
      #5941606 - 06/26/13 03:15 PM

A Delta-m of 7 seems like it may be a bit high -- I'm still leaning toward a magnitude of 11 for the secondary, mainly because I think I had a glimpse of it in my six inch refractor. I can't imagine that happening if there was seven magnitudes of difference.

But -- as I said -- I think I saw it. I'm still not convinced enough to call it confirmed, and it'll have to wait until later in the year now. So it's only supposition at this point.

It's good to know Mark has seen the secondary twice, since that eliminates any question of whether it's there or not. The observation with the roof blocking part of the aperture is definitely intriguing.

P.S. -- Thanks for that APASS link. I've been looking for something like that.


John


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Nucleophile
super member


Reged: 05/24/13

Loc: United States
Re: Estimating visual magnitude new [Re: 7331Peg]
      #5941650 - 06/26/13 03:50 PM

by my count, I have seen it at least 4 times with the 15 inch;
11ish sounds about right to me for secondary magnitude
I'm eager to take more cracks at it with the 8 inch.

Edited by Nucleophile (06/26/13 03:52 PM)


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WRAK
Pooh-Bah


Reged: 02/18/12

Loc: Vienna, Austria, Europe
Re: Estimating visual magnitude new [Re: Nucleophile]
      #5941849 - 06/26/13 06:04 PM

Quote:

...
I estimate the roof blocked about a third of the aperture when I made this observation.

Did I inadvertently "mask" my aperture to an instrument of this size last night?




Would call this a peripheral obstruction.
Would may be be of interest to make an aperture mask for your 15" Newton with for example 300mm. Even then your CO would still be rather small with ~0.25.
Wilfried


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Nucleophile
super member


Reged: 05/24/13

Loc: United States
Re: Ever observed COU1900? new [Re: WRAK]
      #5947389 - 06/30/13 12:22 AM

Can I see the companion of COU 1900? Yes, in fact I cant help but see it with my 15 inch reflector now.

The real questions for me is can I see it with another instrument. I used an on axis mask to stop down the 15 to an 11 inch instrument and strongly suspected the companion at 345x--but alas, it was not very dark then and there was some partial occlusion of the aperture by my roof--but it was a promising result at any rate.

I'll be point more than a few instrument at this one later in the year/next year once it comes back into favorable view again. So, its "bye for now" COU 1900--please dont change too much!


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WRAK
Pooh-Bah


Reged: 02/18/12

Loc: Vienna, Austria, Europe
Re: Ever observed COU1900? new [Re: Nucleophile]
      #5947491 - 06/30/13 03:17 AM

Mark, please send your observation report to Sissy Haas (has103@comcast.net) as she has still only one report on COU1900 with 550mm.
I too have to quit now on COU1900 as it is already too low in the sky - but it will come into my field of view again in April next year near zenith and I will then try again. By then I should already have the 8" Royce Dall-Kirkham and I have some expectations regarding the performance of this instrument.
Wilfried


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Nucleophile
super member


Reged: 05/24/13

Loc: United States
Re: Ever observed COU1900? new [Re: WRAK]
      #5947641 - 06/30/13 07:56 AM

will do

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Bill Boublitz
super member


Reged: 05/04/13

Re: Ever observed COU1900? new [Re: Nucleophile]
      #5970443 - 07/14/13 02:07 PM

Interesting note: 07-14-13 a resolution of COU 1900 using 152 mm was reported and filed in the Haas database. No idea whom or any further info, but a number of resolutions were filed this week with this aperture.

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Nucleophile
super member


Reged: 05/24/13

Loc: United States
Re: Ever observed COU1900? new [Re: Bill Boublitz]
      #5970548 - 07/14/13 03:06 PM

that is indeed interesting; am glad some others are still adding data.

I may redo the list with my 15" stopped down to an unobstructed 6" just to get more data points in there.


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WRAK
Pooh-Bah


Reged: 02/18/12

Loc: Vienna, Austria, Europe
Resolution of COU 1900 with 152 mm aperture [Re: Bill Boublitz]
      #5971689 - 07/15/13 05:07 AM

In the very beginning of this thread also Roberto reported a "suspected" resolution of COU1900 with an 6" refractor showing a hint of a reddish companion. COU1900 career as curious object with this new report extended.
Wilfried


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WRAK
Pooh-Bah


Reged: 02/18/12

Loc: Vienna, Austria, Europe
Re: Resolution of COU 1900 with 152 mm aperture new [Re: WRAK]
      #5990704 - 07/26/13 03:21 AM

Mark - just curious: Why did you not send your COU1900 observation report to Sissy?
Wilfried


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