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

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Abstract
We apply the image subtraction method to re-analyze 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 12-55 days, we find 112 Cepheids with periods ranging from 7-91 days, as well as ~60 other variables. These include 2 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, HST observations are necessary to obtain a Cepheid period-luminosity distance not dominated by blending and crowding. We propose a ``hybrid'' approach, where numerous Cepheids are discovered and characterized using large ground-based telescopes and then followed-up with the HST to obtain precise distances.Comment: 10 pages, 4 figures, accepted for publication by ApJL (July 2003). The full version of Figure 1 is available from http://cfa-www.harvard.edu/~abonanos/M83