Improved photometric calibrations for red stars observed with the SDSS Photometric Telescope

We present a new set of photometric transformations for red stars observed with the Sloan Digital Sky Survey (SDSS) 0.5 m Photometric Telescope (PT) and the SDSS 2.5 m telescope at the Apache Point Observatory in New Mexico. Nightly PT observations of US Naval Observatory standards are used to determine extinction corrections and calibration terms for SDSS 2.5 m photometry. Systematic differences between the PT and native SDSS 2.5 m ugriz photometry require conversions between the two systems which have previously been undefined for the reddest stars. By matching similar to 43,000 stars observed with both the PT and SDSS 2.5 m, we extend the present relations to include low-mass stars with colors 0.6 <= r - i <= 1.7. These corrections will allow us to place photometry of bright, low-mass trigonometric parallax stars previously observed with the PT on the 2.5 m system. We present new transformation equations and discuss applications of these data to future low-mass star studies using the SDSS.