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Precision Stellar Photometry and Astrometry with Discrete Point Spread Functions

Dr. Kenneth Mighell, National Optical Astronomy Observatory (KPNO) Friday, May 22, 2009 (Note the date!)
When May 22, 2009
from 02:30 PM to 04:00 PM
Where Building 56, Large Conference Room
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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 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 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 observations demonstrate that millipixel relative astrometry and millimag photometric precision is achievable with complicated space-based discrete PSFs --- even with lossy detectors that exhibit nonuniform intrapixel quantum efficiency variations.


Dr. Kenneth Mighell is an Associate Scientist at the National Optical Astronomy Observatory in Tucson, Arizona where he studies the star-formation and chemical-enrichment histories of resolved stellar populations in nearby galaxies. He also develops parallel-processing astrophysical image-analysis applications for the Hubble and Spitzer Space Telescopes as part of his research efforts for the Applied Information Systems Research (AISR) program of NASA's Science Mission Directorate. Dr. Mighell has a B.S. in Physics and Astronomy from the University of Washington (1982), and a Ph.D. in Astrophysics from the University of Groningen in the Netherlands (1990). He was an Australian National University Research Fellow at Mount Stromlo and Siding Spring Observatories (1989-1992) and an Associate Research Scientist at Columbia University (1992-1996) before moving to NOAO in 1996. Besides his research for NASA, Dr. Mighell has run the NSF-funded REU (Research Experiences for Undergraduates) program for the Kitt Peak National Observatory since 2000; during that time he has managed 57 bright undergraduates in the KPNO REU program which is now being underwritten by the U.S. Air Force Office of Scientific Research through the DoD ASSURE program.

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