References for data used in current DOLPHOT module

- Zero Points: Taken from the FITS headers.  For NISP, the ZPAB and ZPVEGA keywords are used, depending on how NISPvega variable is set.  For VIS, the MAGZEROP keyword is used.
- The NISP PSFs were derived using the photutils 1.11.10 implementation of the Anderson & King (2000) algorithm with minor modifications.  PSF stars were selected from all 124 Euclid pointings released in Q1, with detection quality and isolation criteria yielding approximately 12000 stars per detector.  The PSF was extracted on a 55x55 physical pixel region, with a 5x oversampling.  Currently there is no spatial variability, so it is recommended to allow DOLPHOT to solve for that using PSFresSpatial=3 or 5 (depending on the number of good PSF stars in your field).
- NISP Encircled Energy is calculated from the mean encircled encircled energy of the three filters and 16 detectors, between the 1.5" aperture used for aperture corrections and full 55x55 pixel empirical effective PSF.
- There are no Vis library PSFs currently available for Euclid.  It is recommended to use the DOLPHOT "Lorentz2" PSF models with approximately a 1-pixel FWHM, and DOLPHOT can frequently solve for an empirical PSF.  For the mosaic images I have viewed, which are approximately at the VIS pixel scale, similar PSFs can be used for VIS mosaics;
- Vis Encircled Energy: At this point, no encircled energy corrections are applied, so effectively photometry assumes 100% of starlight is within the 1.0" aperture used for aperture corrections.
- Distortions: Computed from the FITS files.  UseWCS=2 is required to make use of this.  Note that the pipeline processed FITS files use a non-standard distortion correction, so the nispmask / vismask utilities convert to SIP polynomials.
- Pixel Area: Applied by default by nispmask / vismask.
- Gain, readout noise: Using values from the FITS files keywords.
- Data quality: Provided in the processed FITS files, using published data quality / flag definitions.
