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How to COAAD Images. I. Optimal Source Detection and Photometry of Point Sources Using Ensembles of Images

Zackay, Barak and Ofek, Eran O. (2017) How to COAAD Images. I. Optimal Source Detection and Photometry of Point Sources Using Ensembles of Images. Astrophysical Journal, 836 (2). Art. No. 187. ISSN 1538-4357.

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Stacks of digital astronomical images are combined in order to increase image depth. The variable seeing conditions, sky background, and transparency of ground-based observations make the coaddition process nontrivial. We present image coaddition methods that maximize the signal-to-noise ratio (S/N) and optimized for source detection and flux measurement. We show that for these purposes, the best way to combine images is to apply a matched filter to each image using its own point-spread function (PSF) and only then to sum the images with the appropriate weights. Methods that either match the filter after coaddition or perform PSF homogenization prior to coaddition will result in loss of sensitivity. We argue that our method provides an increase of between a few and 25% in the survey speed of deep ground-based imaging surveys compared with weighted coaddition techniques. We demonstrate this claim using simulated data as well as data from the Palomar Transient Factory data release 2. We present a variant of this coaddition method, which is optimal for PSF or aperture photometry. We also provide an analytic formula for calculating the S/N for PSF photometry on single or multiple observations. In the next paper in this series, we present a method for image coaddition in the limit of background-dominated noise, which is optimal for any statistical test or measurement on the constant-in-time image (e.g., source detection, shape or flux measurement, or star–galaxy separation), making the original data redundant. We provide an implementation of these algorithms in MATLAB.

Item Type:Article
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URLURL TypeDescription Paper
Ofek, Eran O.0000-0002-6786-8774
Additional Information:© 2017 The American Astronomical Society. Received 2015 December 6; revised 2016 October 21; accepted 2016 December 28; published 2017 February 21. We thank Avishay Gal-Yam, Assaf Horesh, Frank Masci, William Newman, and Ora Zackay for discussions. This paper is based on observations obtained with the Samuel Oschin Telescope as part of the Palomar Transient Factory project, a scientific collaboration between the California Institute of Technology, Columbia University, Las Cumbres Observatory, the Lawrence Berkeley National Laboratory, the National Energy Research Scientific Computing Center, the University of Oxford, and the Weizmann Institute of Science. B.Z. is grateful for receiving the Clore fellowship. E.O.O. is incumbent of the Arye Dissentshik career development chair and is grateful for support by grants from the Willner Family Leadership Institute Ilan Gluzman (Secaucus NJ), Israel Science Foundation, Minerva, Weizmann-UK, and the I-Core program by the Israeli Committee for Planning and Budgeting and the Israel Science Foundation (ISF).
Group:Palomar Transient Factory
Funding AgencyGrant Number
Weizmann Institute of ScienceUNSPECIFIED
Willner Family Leadership Institute Ilan GluzmanUNSPECIFIED
Israel Science FoundationUNSPECIFIED
I-CORE Program of the Planning and Budgeting CommitteeUNSPECIFIED
Subject Keywords:cosmology: observations – gravitational lensing: weak – methods: data analysis – surveys – techniques: image processing – techniques: photometric
Issue or Number:2
Record Number:CaltechAUTHORS:20190529-075432034
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Official Citation:Barak Zackay and Eran O. Ofek 2017 ApJ 836 187
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:95841
Deposited By: Tony Diaz
Deposited On:31 May 2019 16:28
Last Modified:03 Oct 2019 21:17

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