[Aavso-photometry] Software for combining time series data taken with different filters to calculate transformed magnitudes

[Michael Newberry]

----- Original Message ----- 
From: "Dirk Terrell" <terrell at boulder.swri.edu>
To: <aavso-photometry at mira.aavso.org>
Sent: Friday, September 05, 2008 1:16 PM
Subject: Re: [Aavso-photometry] Software for combining time series data 
taken with different filters to calculate transformed magnitudes


> On 9/5/2008 Lionel Catalan wrote:
>> I think that I need a program (or perhaps an excel macro) that can
>> interpolate instrumental magnitudes for each filter to common times
>> so that
>> consistent values of b-v and v-i can be calculated.  I would
>> appreciate any
>> suggestion.
>
> I agree with Michael's comments about timescales. If the variable
> changes on timescales similar to your observing cadence, you'll get
> misleading results by interpolation. In the future, I would alter your
> observing sequence to be ivbbvi and then average the pairs in each
> filter. When you do that, you will have observation pairs for all
> filters centered on the same time. By putting the longer wavelength
> filters on the ends of the observing sequence, you minimize problems
> with varying extinction since the variation is slower at longer 
> wavelengths.
>
Hi Dirk,

And I agree with yout excellent advice. But I would add one caveat: Don't do 
it when observing transients (e.g., UV Cet stars, etc.) or other rapidly 
varying objects. Averaging symmetrically paired observations, you still are 
assuming that the variation is linear between the points. And, of course, 
the length of time between the middle of the paired exposures can be 
important too.

Michael

> Dirk
>
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