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Panning for RRL Nuggets in the SDSS-DR9, Single Epoch Spectra

The SDSS has been a gold mine for understanding properties of the Milky Way. Below, in the watershed, there remain small nuggets to be found flowing from the deepest recesses of the mine. The SDSS-DR9 included the release of the flux- and wavelength-calibrated, individual spectra which were subsequently combined to form the composite spectra found in previous SDSS data releases. These single-epoch spectra (SES) can be analyzed to find flux and spectral line variability, and to probe aspects of phase variations for objects such as RRL stars. For $\sim 45%$ of the spectra in the RRL color range, SES were taken on separate nights, sometimes weeks apart. The remaining dataset have a time baseline of 0.75 to 1.5 hours and consist of 4-7 separate exposures. In my talk I will present details of our project to detect variability and to constrain the pulsation phase at the time of observation. I will discuss our auto-detection technique that uses division of all SES for a given star to search for variations in the flux, the hydrogen Balmer lines and the CaII K line. This procedure is being tested against known variables and non-variable stars within Stripe 82 to determine the identification effectiveness as a function of signal-to-noise, RRL type, and time baseline length. I will also discuss the use of empirical standard star templates to predict pulsation phase from the combination of hydrogen line strengths and radial velocity variations. Our ultimate goal is to combine the SES analysis with our new metallicity calibration in order to increase the number of RRL stars that have reliable metallicity determinations and which can then be used to probe the structure of the Milky Way halo.