[Aavso-photometry] Determination and use of BVRI transformationcoefficients with Maxim DL

[Steven Orlando]

----- Original Message ----- 
From: "Steven Orlando" <sorlando at sorlando.com>
To: "Lionel Catalan" <lcatalan at lakeheadu.ca>
Sent: Saturday, January 12, 2008 3:08 PM
Subject: Re: [Aavso-photometry] Determination and use of BVRI 
transformationcoefficients with Maxim DL


> Lionel,
>
> Canopus/Photored can do transforms, extinction coefficients, and the 
> newest version can even generate an AAVSO report for you via ensemble 
> photometry.
>
> http://www.minorplanetobserver.com/MPOSoftware/MPOCanopus.htm
>
> Price is reasonalbe as well.
>
> IMHO the best photometry data reduction software I've encountered.
>
> Steve
>
> ----- Original Message ----- 
> From: "Lionel Catalan" <lcatalan at lakeheadu.ca>
> To: <aavso-photometry at mira.aavso.org>
> Sent: Saturday, January 12, 2008 1:10 PM
> Subject: Re: [Aavso-photometry] Determination and use of BVRI 
> transformationcoefficients with Maxim DL
>
>
>> Arne,
>>
>> I have ordered your book at my university library, and it will be
>> coming through interlibary loan hopefully soon...
>>
>> I am using Excel to do the transformations. I don't think that Maxim
>> can do these transformations. In fact, I don't know any software that
>> can apply colour transformation coefficients. Do they exist for
>> Windows?
>>
>> I understand that the zero point is the same for the reference and
>> target star when doing differential photometry in Maxim. My question
>> is related to the use of transformation equations such as:
>>
>> B-V = Qbv + Tbv (b-v)
>> V = v + Qv + T(B-V)
>>
>> where v and b are "instrumental" magnitudes of a target star
>> determined by Maxim (after choosing a reference star). It seems to me
>> that the Qv to be used in the second equation will depend on the
>> particular reference star that I chose and may be different from the
>> Qv that I determined on the M67 field. Am I wrong about this?
>>
>> Lionel
>>
>>
>>
>> On Jan 12, 2008 10:46 AM, Lionel Catalan <lcatalan at lakeheadu.ca> wrote:
>>> Following the procedures outlined in the AAVSO CCD variable star
>>> manual, I determined the colour transformation coefficients (Tbv, Tvr,
>>> etc) and the terms Qbv, Qvr, etc for my system by taking sequential
>>> exposures of M67 with B, V, R and I filters. Since all the stars were
>>> in the same frame and the elevation was high, I did not include first
>>> order or second order extinction coefficients in my analysis. Maxim DL
>>> requires that I select a reference star and set its magnitude to
>>> calculate the magnitude of all the other stars in a given frame.
>>> Therefore, the determined numerical values of the terms Qbv, Qvr, Qri
>>> and Qvi are dependent on the particular reference star that I
>>> selected. If I now want to use my colour transformation coefficients
>>> for another star field, I assume that my values of Tbv, Tvr, etc would
>>> still be valid, but I wouldn't be able to use the same reference star,
>>> and therefore I would have to recalculate values of Qbv, Qvr, etc
>>> based on some standard star in the new field. Does this make Maxim DL
>>> innapropriate or at least inconvenient for using transformation
>>> coefficients?
>>>
>> It is clumsy, but ok.  You just select one of the sequence stars for
>> that new field as your "reference star", and use your Tbv etc.
>> with respect to the magnitudes that are returned by MaxIm.
>> In general, you can do the color-correction transformation on any
>> field, whether conditions are photometric or not.
>> When doing this kind of differential photometry, where you are
>> actually calculating something like
>>
>> Vstar = (vins_star - vins_comp) + Vcomp
>>
>> what happens is that the zeropoint is constant for both stars, and the
>> subtraction will remove it from the solution.  You can see the full
>> derivation in my old book, Astronomical Photometry.
>>
>> Does MaxIm actually apply the coefficients, or are you using ancillary
>> software (like an Excel spreadsheet) to do the transformation?
>> Arne
>> _______________________________________________
>>
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>