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 two-dimensional 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 21-pixel-wide damped sinc function, and position-partial derivatives are computed using a five-point numerical differentiation formula. Precise and accurate stellar photometry and astrometry are achieved with undersampled CCD (charge-coupled 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 c-language 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 space-based discrete PSFs.
Online MNRAS abstract
Online MNRAS article (if a subscriber to MNRAS)
PDF version of article (... if not)
astro-ph/0505455 ( PDF) astro-ph preprint
The National Center for Supercomputer Applications (NCSA) and the Ohio Supercomputer Center (OSC) sponsored the Reconfigurable Systems Summer Institute which was held July 11--13, 2005 at the Beckman Institute for Advanced Science and Technology on the campus of the University of Illinois at Urbana-Champaign.
Volodymyr Kindratenko, a senior research scientist at NCSA,
gave a presentation
First-hand experience on porting MATPHOT code to SRC platform ( PPT) ( PDF)
based on the MATPHOT code for stellar photometry and astrometry with discrete point spread functions.
Dr. Kindratenko analyzed the MATHOT code and determined that the current implementation spends approximately 90% of the total computation time calculating the two-dimensional damped sinc interpolation of PSF models. Kindratenko ported the C implementation of the interpolation algorithm to an SRC MAPstation which is based on SRC's patented MAP processor that has 2 Xilinx Field Programmable Gate Arrays ( FPGAs).
PDF version of the AI2004 poster
Mathematical Challenges of using Point Spread Function
Analysis Algorithms in Astronomical Imaging
Ken Mighell (National Optical Astronomical Observatory)
PDF version of the presentation
MATPHOT release: 2005OCT28
Retrieve the MX source code file:
Build MX (tested on Apple OS X Tiger and RedHat Linux 7.2):CHECK: If the file bin/mx_mpd exists, you have built MATPHOT!
Now try out MATPHOT:
More to come...
Kenneth Mighell Associate Scientist Kitt Peak National Observatory National Optical Astronomy Observatory EMAIL: firstname.lastname@example.org MAIL: P.O. Box 26732, Tucson, AZ 85726-6732 FEDEX: 950 N. Cherry Ave., Tucson, AZ 85719 PHONE: (520) 318-8391 FAX: (520) 318-8360 URL: http://www.noao.edu/staff/mighell/