AAS 197, January 2001
Session 17. Frontiers of Astrophysics IV
Display, Monday, January 8, 2001, 9:30am-7:00pm, Exhibit Hall

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[17.05] Background Matching & Subtraction versus PSF Deconvolution: Comparison of Two Photometric Techniques applied to images of High-z SNe

A. Clocchiatti, F. Courbin (Pontificia Universidad Catolica de Chile), High-z Supernova Search Team

High-z Type Ia SNe are too faint for the distances predicted by mass dominated cosmologies, implying that (a) the Universe is accelerating (b) there is a ``grey'' dust undetectable by usual color measurements, or (c) SNe are not redshift independent light sources. Option (a), which has been favorably greeted by an ample portion of astronomers as the missing piece of the cosmological puzzle, implies in the simplest model the existence of a Cosmological Constant. The detection of a Cosmological Constant has far reaching consequences for both cosmology and General Physics at its most basic level, and, hence,the High-Z Supernova Search Team has been committed since 1998 to challenge these early results by application of different tests.

We present here results of the Spring 1999 campaign. Our sets of two color observations of SNe 1999M (z=0.50), 1999N (z=0.54), 1999Q (z=0.46), 1999S (z=0.46), and 1999U (z=0.50), have been analyzed using two different photometric techniques. In one of them, an image taken more than a year after the SN exploded, when the light of the SN itself is negligible in comparison with the sky, is used as a model of the background underneath the SN (template). Each image with the SN is matched to the template in position, PSF shape and flux scale, and then the latter is subtracted from the former. PSF fitting photometry is used to obtain the flux of the SN in the subtracted image. In the other, we use the newly presented MCS deconvolution, a technique that deconvolves the images using a PSF narrower than the observed one, constrained by the requirement that the deconvolved image is compatible with the adopted sampling. All the images of each SN, with its parent galaxy and nearby stars are simultaneously deconvolved (a process that takes maximum benefit from the independent sampling of each image, as similarly done with so-called ``drizzling'' techniques) and taken to a common narrow final PSF with known Gaussian shape. Furthermore, the images are decomposed into a sum of numerical background and analytic point sources, where the background is constant over time and represents the host galaxy and where the point sources are allowed vary from one frame to another, following the light variation of the supernova. The deconvolved image of the constant light distribution underneath the SN is therefore obtained as a byproduct of the deconvolution.

The results obtained by the two different techniques are presented, relative photometric uncertainties compared, and systematic differences discussed.

AC & FC acknowledge the support of CONICYT (Chile) under projects 1000524 and 3990024.

If you would like more information about this abstract, please follow the link to http://cfa-www.harvard.edu/cfa/oir/Research/supernova/HighZ.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.

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