test data - synthetic images



   Lymm Observatory

     optimal photometry

     how it works

     test data 1

     test data 2

     real data

    I created synthetic images, containing stars corresponding to those studied with the Excel spreadsheet, for the two cases: FWHM =1.50 pixels (case A) and FWHM = 3.0 pixels (case D). I also created a test image for FWHM = 1.16 pixels. Camera gain was assumed to be 1 (so one ADC unit = one photon).

    Here are the synthetic images: FWHM = 1.16 pixels, FWHM = 1.5 pixels and FWHM = 3.0 pixels.

    Use of synthetic images allows us to study the effects of poor sampling, in which the stellar flux varies signifcantly across individual pixels. This causes a problem for aperture photometry when the FWHM is small: how does one handle pixels, which are partly within the (imaginary) aperture? A common solution (and the one used here) is to compute the fraction of the pixel within the aperture, and count this fraction of the signal from that pixel. However, this does not simulate the effects of a true aperture if the flux is not constant across the pixel. In these tests, pixel sensitivity is assumed to be uniform.

    Here is a summary of the star parameters and the S/N obtained.