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

[Greg Crawford]

>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?

Yes, MPO Canopus will work out colour transformation coefficients and first
order extinction and nightly zero points internally. For example, with colour
transformation coefficients, one loads one's images and a star chart on which
the standard stars are marked. The magnitudes of the standard stars are stored
in the program and supplied to the chart. An "automatch" matches the stars in
your image to the stars on the chart. You select which stars on your image you
intend to measure, and measure them for the whole set. Then a single mouse-click
will give you colour transformation coefficients, along with a plot showing how
close to the line each star falls and the standard deviation, so you can get an
idea of the quality of your measurements. The first order extinction routine is
similar, but you require image sets from high and low altitude. There are also
routines for calculating the CIs of comparisons where those are not known.

In a field where the comparison values are known, such as a typical AAVSO
target, the routine is even simpler. Having used the first routine above to
determine your colour transformation coefficients a few times a year, they are
stored in the program. You then use another routine to identify the stars in
your image (comparisons, check and target), and then run them through an
automated matching a measurement process. In this process, the known comparison
values are applied by the program. There is a check box to apply your stored
colour transformation coefficients in the processing. The end result is a table
of transformed measurements in the new AAVSO format.


Greg