The Panchromatic Hubble Andromeda Treasury XV. The BEAST: Bayesian
  Extinction and Stellar Tool
  We present the Bayesian Extinction And Stellar Tool (BEAST), a probabilistic
approach to modeling the dust extinguished photometric spectral energy
distribution of an individual star while accounting for observational
uncertainties common to large resolved star surveys. Given a set of photometric
measurements and an observational uncertainty model, the BEAST infers the
physical properties of the stellar source using stellar evolution and
atmosphere models and constrains the line of sight extinction using a newly
developed mixture model that encompasses the full range of dust extinction
curves seen in the Local Group. The BEAST is specifically formulated for use
with large multi-band surveys of resolved stellar populations. Our approach
accounts for measurement uncertainties and any covariance between them due to
stellar crowding (both systematic biases and uncertainties in the bias) and
absolute flux calibration, thereby incorporating the full information content
of the measurement. We illustrate the accuracy and precision possible with the
BEAST using data from the Panchromatic Hubble Andromeda Treasury. While the
BEAST has been developed for this survey, it can be easily applied to similar
existing and planned resolved star surveys.
