Infrared Surface Brightness Distances to Cepheids: A Comparison of Bayesian and Linear-Bisector Calculations

We have compared the results of Bayesian statistical calculations and linear-bisector calculations for obtaining Cepheid distances and radii by the infrared surface brightness method. We analyzed a set of 38 Cepheids using a Bayesian Markov Chain Monte Carlo method that had been recently studied with a linear-bisector method. The distances obtained by the two techniques agree to 1.5% ± 0.6%, with the Bayesian distances being larger. The radii agree to 1.1% ± 0.7%, with the Bayesian determinations again being larger. We interpret this result as demonstrating that the two methods yield the same distances and radii. This implies that the short distance to the Large Magellanic Cloud found in recent linear-bisector studies of Cepheids is not caused by deficiencies in the mathematical treatment. However, the computed uncertainties in distance and radius for our data set are larger in the Bayesian calculation by factors of 1.4-6.7. We give reasons to favor the Bayesian computations of the uncertainties. The larger uncertainties can have a significant impact on interpretation of Cepheid distances and radii obtained from the infrared surface brightness method.