Aperture Photometry Tool Versus SExtractor for Noncrowded Fields

July 2012 • 2012PASP..124..764L

Authors • Laher, Russ R. • Rebull, Luisa M. • Gorjian, Varoujan • Masci, Frank J. • Fowler, John W. • Grillmair, Carl • Surace, Jason • Mattingly, Sean • Jackson, Ed • Hacopeans, Eugean • Hamam, Nouhad • Groom, Steve • Teplitz, Harry • Mi, Wei • Helou, George • van Eyken, Julian C. • Law, Nicholas M. • Dekany, Richard G. • Rahmer, Gustavo • Hale, David • Smith, Roger • Quimby, Robert M. • Ofek, Eran O. • Kasliwal, Mansi M. • Zolkower, Jeff • Velur, Viswa • Walters, Richard • Henning, John • Bui, Khahn • McKenna, Dan • Kulkarni, Shrinivas R.

Abstract • Outputs from new software program Aperture Photometry Tool (APT) are compared with similar outputs from SExtractor for sources extracted from R-band optical images acquired by the Palomar Transient Factory (PTF), infrared mosaics constructed from Spitzer Space Telescope images, and a processed visible/near-infrared image from the Hubble Legacy Archive (HLA). Two large samples from the PTF images are studied, each containing around 3 × 10³ sources from noncrowded fields. The median values of source-intensity relative percentage differences between the two software programs, computed separately for two PTF samples, are +0.13% and +0.17%, with corresponding statistical dispersions of 1.43% and 1.84%, respectively. For the Spitzer mosaics, a similar large sample of extracted sources for each of channels 1-4 of Spitzer’s Infrared Array Camera (IRAC) are analyzed with two different sky annulus sizes, and we find that the median and modal values of source-intensity relative percentage differences between the two software programs are between -0.5% and +2.0%, and the corresponding statistical dispersions range from 1.4 to 6.7%, depending on the Spitzer IRAC channel and sky annulus. The results for the HLA image are mixed, as might be expected for a moderately crowded field. The comparisons for the three different kinds of images show that there is generally excellent agreement between APT and SExtractor. Differences in source-intensity uncertainty estimates for the PTF images amount to less than 3% for the PTF sources, and these are potentially caused by SExtractor’s omission of the sky background uncertainty term in the formula for source-intensity uncertainty, as well as differing methods of sky background estimation.

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