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Reanalysis of Very Large Telescope Data for M83 with Image Subtraction—Ninefold Increase in Number of Cepheids

We apply the image-subtraction method in order to reanalyze the ESO Very Large Telescope data on M83 (NGC 5236), obtained and analyzed by Thim et al. Whereas Thim et al. found 12 Cepheids with periods between 12 and 55 days, we find 112 Cepheids with periods ranging from 7 to 91 days as well as ~60 other variables. These include two candidate eclipsing binaries, which, if confirmed, would be the first optically discovered outside the Local Group. We thus demonstrate that the image-subtraction method is much more powerful for detecting variability, especially in crowded fields. However, Hubble Space Telescope observations are necessary to obtain a Cepheid period-luminosity distance not dominated by blending and crowding. We propose a "hybrid" approach, in which numerous Cepheids are discovered and characterized using large ground-based telescopes and then followed up with the Hubble Space Telescope to obtain precise distances.