From the Dynamics of Cepheids to the Milky Way Rotation, and the Distance Scale Calibration

High precision spectroscopic measurements of 10 southern Galactic Cepheids with HARPS allowed us to analyse in detail the dynamical structure of their atmosphere and close environment. Our results have consequences on the distance scale calibration, and show that the rotation of the milky way is probably simpler than previously thought. However, the full understanding of spectral line asymmetries still requires the development of dedicated models.