Nardetto, NicolasNicolasNardettoPORETTI, EnnioEnnioPORETTIAnderson, Richard I.Richard I.AndersonFokin, AndreiAndreiFokinGallenne, AlexandreAlexandreGallenneGieren, WolfgangWolfgangGierenGraczyk, DariuszDariuszGraczykKervella, PierrePierreKervellaMathias, PhilippePhilippeMathiasMérand, AntoineAntoineMérandMourard, DenisDenisMourardNeilson, HildingHildingNeilsonPietrzyński, GrzegorzGrzegorzPietrzyńskiPilecki, BogumiłBogumiłPileckiRAINER, MonicaMonicaRAINERStorm, JesperJesperStorm2020-11-062020-11-062018978-83-938279-9-22545-1022http://hdl.handle.net/20.500.12386/28177Probing the dynamical structure of Cepheid atmospheres is of primary importance in order to better constrain the cosmic distance ladder. It is indeed now well-known that the projection factor (or p-factor), that is used in the Baade-Wesselink method of distance determination of Cepheids, is sensitive to the atmospheric velocity gradient and other subtle dynamical effects. Relying on HARPS-N high resolution spectroscopic observations, we have measured the atmospheric velocity gradient of δ Cep for the first time, and we found an agreement with the hydrodynamical model of the star. Besides, the mysterious k-term, a residual γ-velocity of the order of 1-2 km s^{-1}, seen in HARPS-N data of δ Cep, is now physically understood thanks to recently published predicted spectroscopic properties of two-dimensional time-dependent Cepheid models.ELETTRONICOenConference paperhttps://www.pta.edu.pl/proc/v6p1https://indico.camk.edu.pl/event/3/2018pas6.conf..217NFIS/05 - ASTRONOMIA E ASTROFISICA