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

[Lionel Catalan]

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?

Lionel Catalan