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

[Michael Newberry]

Be careful about interpolation according to the kind of science you are 
trying to do. There's no patent answer for this.

First of all, a general rule would be to interpolate only if the timescale 
of what you are studying does not vary significantly on the timescale of 
your observations. You want the data points to conincide with what is 
happening on the star. For example, if doing RR Lyr, UV Ceti flare stars 
asteroid rotation, etc., then I would use the actual observation times and 
not interpolated ones (but see item 2, below). OTOH, if you are doing Mira 
variables, etc., having a very slow rate of change, then I don't think 
anyone would care about interpolating near the time of observation.

Second, what kind of interpolation would you use? Would you thread the 
points, do a piece-wide linear interpolation, cubic spline, etc.? Each will 
give you a different magnitude value at whatever interpolated time you 
choose. Be sure you understand the effects of the method you use so that you 
get numbers that are scientifically defendable.

Michael Newberry

----- Original Message ----- 
From: "Lionel Catalan" <lcatalan at lakeheadu.ca>
To: <aavso-photometry at mira.aavso.org>
Sent: Friday, September 05, 2008 12:49 PM
Subject: [Aavso-photometry] Software for combining time series data 
takenwith different filters to calculate transformed magnitudes


>I have times series data for B,V, and I filters that I would like to 
>combine
> to calculate transformed magnitudes using transformation equations. I use 
> a
> filter wheel to change filters between images, so I have sequences of 
> images
> such as bvibvibvibvi etc.  Some images have to be rejected from time to 
> time
> due to wind or clouds, so the sequences are not exactly regular. I already
> have determined the transformation coefficients for my system. 
> Essentially,
> 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.
>
> Lionel CTE
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