[Aavso-photometry] What are transformation coefficients??

Wed Mar 12 13:52:52 EDT 2008

Hi all,
  After all the discussion that is going on this group lately this may seem a very naive question, but what do transformation coeffs signify??. I read something about it in aavso's astronomical photometry manual but didn't really get it.
  Is it that: According to size of telescope and type of detector  the number of photons collected from a particular star will differ. So for large telescope we will get larger counts and less for smaller telescope. But since people with different instruments,  observing the same star should get same results , we transform this absolute count to some standard count. But in differential photometry since we take differece between the count of two stars, why do we need transformation coefficients here?? shouldn't we get same results irrespective of the instrument used (atleast under ideal conditions).

  Trupti

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Today's Topics:

1. Re: Transformation Coefficients (Michael Crook)
2. Re: Transformation Coefficients (Steven Orlando)

----------------------------------------------------------------------

Message: 1
Date: Tue, 11 Mar 2008 20:01:29 +0000 (GMT)
From: Michael Crook 
Subject: Re: [Aavso-photometry] Transformation Coefficients
To: Tim Crawford , aavso photometry

Message-ID: <496215.87404.qm at web86211.mail.ird.yahoo.com>
Content-Type: text/plain; charset=iso-8859-1

Tim,

I will be observing LPVs and I understand it is
important to transform in these cases due to the
colour differences between the red variables and the
comparisons. 

Is there an 'idiots guide' available to transformed
differential photometry? (I mean a REALLY basic
guide?)

Cheers,

Mick 

--- Tim Crawford wrote:

> While we still have somewhat of a related thread
> going
> RE this specific topic (Michael Koppelman's last
> post
> on the topic: Differential vs. absolute magnitudes)
> I
> thought I would post some recent values showing the
> difference between not transformed differential
> photometry and transformed differential photometry
> for
> the benifit of those of you who have never ventured
> into this territory.
> 
> This was a recent observation of V371 Per in which I
> had zero-pointed the instrumental magnitudes
> (meaning
> that the IM's would equal the sequence value) of the
> main Comp star; because of this particular action it
> makes it easy to look at this particular Spread
> sheet
> and pull off the following magnitude data.
> 
> Filter - Not Transformed - Transformed - Difference
> 
> V - 10.959 - 11.979 - .020
> 
> B - 11.563 - 11.575 - .012
> 
> R - 10.611 - 10.619 - .008
> 
> I - 10.217 - 10.230 - .013
> 
> It is important for you to understand that other
> systems (scope/ccd/conditions) could have
> significantly larger differences or even
> significantly
> smaller differences (while pesumably the actual
> transformed values would have been quite close) on
> this same target, at the same time, using the same
> comp(s) stars, depending on the calculated
> transformation coefficients for that system.
> 
> Tim Crawford CTX'
> Arch Cape Observatory
> 
> http://homepage.mac.com/windwalker1/ACObserv.htm
> 
> 
> 
> _______________________________________________
> 
> Aavso-photometry mailing list
> Aavso-photometry at mira.aavso.org
>
http://www.aavso.org/mailman/listinfo/aavso-photometry
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------------------------------

Message: 2
Date: Tue, 11 Mar 2008 20:29:56 -0400
From: Steven Orlando 
Subject: Re: [Aavso-photometry] Transformation Coefficients
To: Michael Crook , aavso-photometry at aavso.org
Message-ID: <004801c883d8$3290e3b0$6501a8c0 at YOURB290464667>
Content-Type: text/plain; format=flowed; charset=iso-8859-1;
reply-type=original

Mick,

An excellent software package Canopus:

http://www.minorplanetobserver.com/MPOSoftware/MPOCanopus.htm

Very reasonably priced.

Also, while there look for the link to Brian D. Warner's book on Lightcurve 
Photometry and Analysis. There are spreadsheet instructions in that book
----- Original Message ----- 
From: "Michael Crook" 
To: "Tim Crawford" ; "aavso photometry" 

Sent: Tuesday, March 11, 2008 4:01 PM
Subject: Re: [Aavso-photometry] Transformation Coefficients

> Tim,
>
> I will be observing LPVs and I understand it is
> important to transform in these cases due to the
> colour differences between the red variables and the
> comparisons.
>
> Is there an 'idiots guide' available to transformed
> differential photometry? (I mean a REALLY basic
> guide?)
>
> Cheers,
>
> Mick
>
>
>
>
>
> --- Tim Crawford wrote:
>
>> While we still have somewhat of a related thread
>> going
>> RE this specific topic (Michael Koppelman's last
>> post
>> on the topic: Differential vs. absolute magnitudes)
>> I
>> thought I would post some recent values showing the
>> difference between not transformed differential
>> photometry and transformed differential photometry
>> for
>> the benifit of those of you who have never ventured
>> into this territory.
>>
>> This was a recent observation of V371 Per in which I
>> had zero-pointed the instrumental magnitudes
>> (meaning
>> that the IM's would equal the sequence value) of the
>> main Comp star; because of this particular action it
>> makes it easy to look at this particular Spread
>> sheet
>> and pull off the following magnitude data.
>>
>> Filter - Not Transformed - Transformed - Difference
>>
>> V - 10.959 - 11.979 - .020
>>
>> B - 11.563 - 11.575 - .012
>>
>> R - 10.611 - 10.619 - .008
>>
>> I - 10.217 - 10.230 - .013
>>
>> It is important for you to understand that other
>> systems (scope/ccd/conditions) could have
>> significantly larger differences or even
>> significantly
>> smaller differences (while pesumably the actual
>> transformed values would have been quite close) on
>> this same target, at the same time, using the same
>> comp(s) stars, depending on the calculated
>> transformation coefficients for that system.
>>
>> Tim Crawford CTX'
>> Arch Cape Observatory
>>
>> http://homepage.mac.com/windwalker1/ACObserv.htm
>>
>>
>>
>> _______________________________________________
>>
>> Aavso-photometry mailing list
>> Aavso-photometry at mira.aavso.org
>>
> http://www.aavso.org/mailman/listinfo/aavso-photometry
>>
>
>
>
> __________________________________________________________
> Sent from Yahoo! Mail.
> The World's Favourite Email http://uk.docs.yahoo.com/nowyoucan.html
> _______________________________________________
>
> Aavso-photometry mailing list
> Aavso-photometry at mira.aavso.org
> http://www.aavso.org/mailman/listinfo/aavso-photometry 

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