Determining Accurate Distances to Cepheids Using the Interferometric Baade-Wesselink Method: Possible Interferometric Biases

Abstract

Cepheids have been used to determined distance throughout the lastcentury, thanks to the Period-Luminosity (P-L) relation. However, thisrelation has to be observationally calibrated in order to accuratelydetermined distances. One of the most promising technique to directlymeasure distances to Cepheids, hence calibrate the P-L relation, isthe quasi geometric interferometric parallax pulsation, orBaade-Wesselink (Baade 1926; Wesselink 1946) method hereafter IBWM. Wewill present here some of the known interferometric biases to themethod: the uncertainty related to the knowledge of the center-to-limbdarkening of the pulsating Cepheid, and the possible presence of faintcircumstellar envelopes (CSE). These two aspects have been or will bestudied using observational techniques, but still lack comprehensivemodeling, which is mandatory to fully understand and correct for thisbiases in case of sparse observational material.