AAS 203rd Meeting, January 2004
Session 46 Instrumentation for HST and Sirtf
Poster, Tuesday, January 6, 2004, 9:20am-6:30pm, Grand Hall

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[46.03] Effects of Precise Astrometry on Photometry: WFPC2

G.B. Brammer, V. Kozhurina-Platais, A.M. Koekemoer, W. Hack, I. Heyer (STScI)

We examine how resampling and stacking WFPC2 observations using the MultiDrizzle software can enhance the spatial resolution and deepen the limiting magnitude of a dithered WFPC2 dataset. For this analysis, multiple observations of the inner calibration field of Omega Cen, offset by 0.25'' and 35'' and exposed through filters F300W, F555W, and F814W, have been 'drizzled' with both old (Trauger, 1995) and new (Anderson & King, 2003; Kozhurina-Platais, 2003) geometric distortion coefficients. Differential photometry on the drizzled images has been done using the IRAF/PSF/ALLSTAR package for all three filters. The results show that if CCD mosaic metrology and distortion-free WCS are neglected, image resampling and stacking will produce an unwanted blurring of and photometric uncertainties of up to 3% for the objects of scientific interest. An absolute comparison of drizzling using the two sets of distortion coefficients was performed using the linear portion of the main sequence in the Omega Cen CMD (V~V-I) that shows that the scatter in (V-I) is reduced by a factor of 3 when the new distortion coefficients are used to drizzle the images. The Yale isochrones have been fit to the main sequence of Omega Cen, and we find that the discrepancy between the theoretical and observed main sequences is less for photometry derived from the images drizzled with the new distortion coefficients.

If you would like more information about this abstract, please follow the link to http://www.stsci.edu/instruments/wfpc2/wfpc2_top.html. This link was provided by the author. When you follow it, you will leave the Web site for this meeting; to return, you should use the Back comand on your browser.

The author(s) of this abstract have provided an email address for comments about the abstract: brammer@stsci.edu

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