Cepheids at high angular resolution: recent results obtained by stellar interferometry

Abstract

We present the latest results obtained by stellar interferometry (SI) in the field of pulsating Cephieds stars. The SI technique is particularly well suited to measure distances using the quasi-geometric pulsation parallax method known as the Baade-Wesselink (BW) method. The improvements in angular resolution and precision in the measurements have led to high precision calibration of the Cepheids period luminosity relation. On the other hand, the assumptions of the BW method can be investigated using SI: we present a calibration of the spectroscopic projection factor and the study of center to limb darkening and circumstellar envelopes. These later studies clearly demonstrate that SI has recently entered a regime where the BW implemetation is no longer limited by the precision of the angular diameter measurements but by the classical assumptions underlying the method itself. This calls for a better understanding of Cepheids, using numerical models and diverse observation techniques, including SI.