[Aavso-photometry] RE: Negative CCD observations

[Tom Krajci]

>From: "Tomas L. Gomez" <tomas.l.gomez at gmail.com>

>To measure the limiting magnitude I do the following:....

See:  http://www.aavso.org/observing/programs/hen/submit.shtml

Important part:  Limiting magnitude:   "M_limiting = M + 2.5 * log10
(SNR/3). where M = Magnitude of star and SNR is the SNR of the star for a 3
sigma LM."

You can measure a star's S/N ratio with your photometry software, then use
the equation above to determine what your limiting magnitude is for 3 sigma
detection.

Here's the interesting "science" part:  take one image (with stars of
various brightness, not saturated)...measure SNR for various brightness
stars, do the math of what your limiting magnitude is 'supposed' to be, and
do an X-Y plot of star SNR versus calculated limiting magnitude.  (If it all
works right...I think you should have the same limiting magnitude, no matter
what star brightness you start with.  But the actual results may be
different.)

I hope this helps.

Tom Krajci
Cloudcroft, New Mexico
http://overton2.tamu.edu/aset/krajci/



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