Variable Stars and Quasars in the Canada-France-Hawaii Telescope Legacy Survey Deep Fields*

Studies of the substructure of the Milky Way’s stellar halo provide a window into our galaxy’s accretion history. RR Lyrae are arguably the most reliable tracers of the Milky Way’s stellar halo for two reasons: (1) their periodic pattern of photometric variation makes them relatively easy to identify; (2) they are excellent standard candles. AGNs/quasars are the most significant source of contamination when identifying RR Lyrae. The Canada-France-Hawaii Telescope Legacy Survey (CFHTLS) is a deep, multi-epoch (~300 epochs per filter), multi-band (ugriz filters) photometric survey. Its depth and exquisite cadence allow for accurate identification of RR Lyrae and quantifying degrees of incompleteness and contamination in other time domain surveys. In this work we analyze the CFHTLS data to: (1) identify candidate variable objects; (2) classify variable objects. We fit polynomials to the ridge line of log(RMS) vs. median ugriz magnitude to find the measurement error. We sum the intrinsic RMS of the 5 bands for each object weighted by the measurement error in each band. Objects are categorized as “marginal,” “intermediate” or “extreme” variable candidates based on their weighted intrinsic RMS. The Lomb-Scargle periodogram helps create phase-folded light curves to classify variables.