[Aavso-photometry] [AAVSO-DIS] Software comparison

[Michael Newberry]

I can comment more on the Mira side of this thread later today. But for now,
let me say that an average magnitude *difference* for two data sets results
from two things: 1) how the background is measured and 2) how the partial
pixels are handled. As a first guess at the cause, Tom should be sure he is
using the same background method (mean, median, mode) in the two software
packages he is comparing.

Michael Newberry


----- Original Message ----- 
From: "Bill Dillon" <dillon1 at houston.oilfield.slb.com>
To: "aavso-discussion" <aavso-discussion at mira.aavso.org>
Sent: Wednesday, May 02, 2007 7:54 AM
Subject: Re: [AAVSO-DIS] Software comparison


> Actually, I'm impressed they only differ by ~0.01 mag (my random errors
> are often bigger than that, depending on the target brightness, exposure
> time, etc.).
>
> You could do a test with an artificial star, but the key is how the
> software handles noise: background stars, merged stars, hot pixels,
> partial pixels in circular apertures, etc.  Perhaps better would be to
> take a field with good comps and, one by one, pretend the comps are a
> variable -- see how close your estimates are to the given value, using
> the same image and different software packages.
>
> If you want algorithm transparency, then maybe IRAF is a way to go.
>
> --Bill
>
>
> Peter Nelson wrote:
>> I seem to recall a post somewhere about some software that could produce 
>> an
>> artificial field with known magnitudes.  If this existed, could we then 
>> test
>> reduction software against this?
>>
>> Regards
>> Peter
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