6.8 Autosimulation vs. Aperture Photometry

The performance of the autosimulation technique for flux determination described in Section 4.10 was also assessed comparing the total fluxes obtained with this procedure with those obtained by means of ordinary aperture photometry. Potentially extended sources in our catalogue were identified through both visual inspection of sky maps and calculation of parameters connected to source extension. Sources flagged by these criteria (totalling 67 out of 1923 making up the catalogue, or 3.5%) were then individually treated, aperture photometry with a suitable aperture radius was carried out on a case-by-case basis and the result was adopted as their most reliable flux estimate.

As to the overall performance of aperture photometry when compared with the autosimulation process, autosimulated fluxes and their counterparts calculated through aperture photometry are compared for all sources in Section 6.8. The relation between these two quantities shows a good linearity for most sources, as it is shown for simulated sources in Figure 6.17. Plotted aperture fluxes were computed adopting an aperture of 6 arcsec radius and correcting both for the transients and for the 40% of the instrumental PSF falling beyond this aperture. Such an aperture was chosen as the most reliable trade-off allowing to reliably include most of the source flux and lest of the background. Only a few sources depart substantially from the 1:1 relation, with 94% sources with fluxes in accordance within 20% and an overall rms deviation of 12%. On the whole, our flux determination procedure is therefore consistent with conventional aperture photometry, provided proper correction for PSF effects is applied.

Figure 6.17: Autosimulated Fluxes vs. Aperture Fluxes