Stellar photometry and astrometry with discrete point spread functions
Abstract
The key features of the MATPHOT algorithm for precise and accurate stellar photometry and astrometry using discrete point spread functions (PSFs) are described. A discrete PSF is a sampled version of a continuous PSF, which describes the twodimensional probability distribution of photons from a point source (star) just above the detector. The shape information about the photon scattering pattern of a discrete PSF is typically encoded using a numerical table (matrix) or an FITS (Flexible Image Transport System) image file. Discrete PSFs are shifted within an observational model using a 21pixelwide damped sinc function, and positionpartial derivatives are computed using a fivepoint numerical differentiation formula. Precise and accurate stellar photometry and astrometry are achieved with undersampled CCD (chargecoupled device) observations by using supersampled discrete PSFs that are sampled two, three or more times more finely than the observational data. The precision and accuracy of the MATPHOT algorithm is demonstrated by using the Clanguage MPD code to analyse simulated CCD stellar observations; measured performance is compared with a theoretical performance model. Detailed analysis of simulated Next Generation Space Telescope observations demonstrate that millipixel relative astrometry and mmag photometric precision is achievable with complicated spacebased discrete PSFs.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 August 2005
 DOI:
 10.1111/j.13652966.2005.09208.x
 arXiv:
 arXiv:astroph/0505455
 Bibcode:
 2005MNRAS.361..861M
 Keywords:

 methods: analytical;
 methods: numerical;
 methods: statistical;
 techniques: image processing;
 techniques photometric;
 astrometry;
 Astrophysics
 EPrint:
 19 pages, 22 figures, accepted for publication in MNRAS