Title of Presentation: Improving the Precision of Near-Infrared Stellar Photometry by Modeling the Image Formation Process within a Lossy Detector

Primary (Corresponding) Author: Kenneth J. Mighell

Organization of Primary Author: National Optical Astronomy Observatory


Abstract:  Current near-infrared detector technology can produce astronomical imagers with large intrapixel quantum efficiency variations.  Space-based cameras using such detectors can have large systematic errors in the measurement of the total stellar flux.  Although this problem can be mitigated by oversampling the stellar image, many near-infrared cameras are undersampled in order to achieve a large field of view. The combination of undersampling stellar images with detectors that have non-uniform pixel response functions is currently diminishing the potential science return of some infrared imagers onboard the Hubble Space Telescope and the Spitzer Space Telescope.  Although the recorded flux of point sources is corrupted by using detectors with significant effective intrapixel quantum efficiency variations, it is still possible to achieve excellent stellar photometry -- if the image formation process inside the detector is accurately modeled.  During the past year, I have worked closely with Spitzer Space Telescope's Infrared Array Camera (IRAC) Instrument Team to demonstrate that my NASA-funded MATPHOT algorithm for precision stellar photometry and astrometry using discrete Point Spread Functions can yield an improvement in the precision of bright star stellar photometry, obtained from IRAC Ch1 observations, of more than 100% over the best results obtained with aperture photometry using the recommended calibration procedures in the IRAC Data Handbook.   This collaborative effort will continue over the next year with the goal of developing new calibration procedures for that have the potential of significantly improving the precision of IRAC point-source photometry. This effort is timely because IRAC Ch1 and Ch2 will be the only operational cameras available during Spitzer's warm mission which is nominally scheduled to start about April 2009 after all of the cryogen has been depleted. This work is funded by grants from the Applied Information Systems Research (AISR) Program of NASA's Science Mission Directorate.