A Survey of Open Clusters in the u′g′r′i′z′ Filter System. I. Results for NGC 2548 (M48)

We present initial results of a photometric survey of open star clusters, primarily in the southern hemisphere, taken in the u′g′r′i′z′ filter system. While our entire observed sample covers more than 100 clusters, here we present data for NGC 2548 (M48), which is a cluster characterized in the UBV and DDO photometric systems. We compare our results to the published values from other observers and to the Padova theoretical isochrones and metallicity curves. These observations demonstrate that the u′g′r′i′z′ filters can play an important role in determining the metallicity of stars and clusters. We begin this series of papers with a study of NGC 2548 because we have obtained data on this cluster not only with our main program telescope, the CTIO Curtis Schmidt, but also with the US Naval Observatory (USNO) 1.0 m telescope (the telescope used to define the u′g′r′i′z′ system), and with the Sloan Digital Sky Survey (SDSS) 0.5 m Photometric Telescope (the photometric monitoring telescope used to calibrate the SDSS 2.5 m telescope imaging data). We have used the data from this study to validate our ability to transform measurements obtained on other telescopes to the standard USNO 1.0 m u′g′r′i′z′ system. This validation is particularly important for very red stars, for which the original u′g′r′i′z′ standard star network is poorly constrained.