TEMPLATE K LIGHT CURVES FOR RR-LYRAE STARS

We discuss a technique to compute [K] using templates developed by fit ting a Fourier series to existing high-quality K light curves of field RR Lyraes. We find that a series of order 2 is sufficient to model th e light curves of first-overtone RRc variables, but four different six th-order templates are needed for the fundamental RRab stars due to ch anges in the light curves that appear to correlate with the B amplitud e. Applying the appropriate template to single-phase observations yiel d estimated [K] values whose deviation from the true [K] is randomly d istributed over phase, and is of the same order of magnitude as the ob servational uncertainty, as long as the ephemeris phase is accurate. T he addition of a second point, separated by at least 0.2 in phase from the first, allows the use of template shifting to remove deviations t hat may arise from uncertainties in the ephemeris phase, and template and scaling factor selection, with final systematic errors reduced to less than 0.03 mag. We find that the use of templates yield superior r esults to those derived using other techniques, which can produce [K] values that show systematic deviations over phase.