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The distance of the long period Cepheid RS Puppis from its remarkable light echoes

The Milky Way Cepheid RS Puppis is a particularly important calibrator for the Leavitt law (the Period-Luminosity relation). It is a rare, long period pulsator (P=41.5 days), and a good analog of the Cepheids observed in distant galaxies. It is the only known Cepheid to be embedded in a large (~0.5 pc) dusty nebula, that scatters the light from the pulsating star. Due to the light travel time delay introduced by the scattering on the dust, the brightness and color variations of the Cepheid imprint spectacular light echoes on the nebula. I here present a brief overview of the studies of this phenomenon, in particular through polarimetric imaging obtained with the HST/ACS camera. These observations enabled us to determine the geometry of the nebula and the distance of RS Pup. This distance determination is important in the context of the calibration of the Baade-Wesselink technique and of the Leavitt law.