Optimal Photometry

How do you go about measuring the flux from stars in a CCD image to get the highest possible signal-to-noise? It turns out there is a much better way than either aperture photometry or profile fitting, called optimal photometry. The basic technique, and its application to time-series photometry is described in Naylor (1998) (pdf version), and its application to colour-magnitude diagrams in Naylor et al (2002). There is also a conference paper, I presented at the 13th North American CV Workshop. You can see the results of using optimal photometry in some of the citatations of the original paper, and on my page of photometric catalogues.

For those of you wanting to use the algorithm, its been implemented in the Starlink PHOTOM package, and hence is also available in GAIA. Tom Marsh has used in his pipeline reduction for ULTRACAM, and it has also been used for SEST mm data ( Carpenter et al, 2005). John Saxton has an implementation specifically designed for amateur astronomers which is available through his Lymm Observatory web pages. Finally, if you want to write your own implementation, here is my Fortran90 code, and associated documentation.

There is also a discussion of the inner radius of the sky box, which was not covered in either paper.

There is also a discussion of the key points of the optimal photometry software we use for colour magnitude diagrams.