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

Abstract
Cepheids have been used to determined distance throughout the last century, thanks to the Period-Luminosity (P-L) relation. However, this relation has to be observationally calibrated in order to accurately determined distances. One of the most promising technique to directly measure distances to Cepheids, hence calibrate the P-L relation, is the quasi geometric interferometric parallax pulsation, or Baade-Wesselink (Baade 1926; Wesselink 1946) method hereafter IBWM. We will present here some of the known interferometric biases to the method: the uncertainty related to the knowledge of the center-to-limb darkening of the pulsating Cepheid, and the possible presence of faint circumstellar envelopes (CSE). These two aspects have been or will be studied using observational techniques, but still lack comprehensive modeling, which is mandatory to fully understand and correct for this biases in case of sparse observational material.