[Aavso-photometry] Why bother to calibrate?

[Tom Richards]

Hi all

It's cat-amongst-the-pigeons time. I think I know some answers to the
following, but I'd like to get a discussion going.

I just did an unfiltered time series on T Pyx, V~15.5, 216 images. I
measured the images in MaxIm, first without calibrating them, then
calibrating them (the full bottle: bias, bias-subtracted dark, and
bias-and-dark-subtracted flat). And it's a horrible-looking flat thanks to
numerous chip blemishes.

Uncalibrated, the sigma on the check star (V~15.40) was 0.0128 mag. For the
calibrated images this improved all of 1.5 % to 0.0126 mag, a negligible
change. And the standard error on the absolute difference in measured
magnitudes for T Pyx frame by frame, was 0.0011 mag, again negligible. The
maximum difference was 0.010 mag.

So, for simple time-series work, just finding light curves, why bother to
calibrate? And a relevant second question: who does not bother to calibrate
for simple time-series work? Be honest now!

Cheers

Tom Richards

Woodridge Observatory

Melbourne, AU

 <http://www.woodridgeobsy.org/> http://www.woodridgeobsy.org

Carpe noctem!