Nardetto, NicolasNicolasNardettoPORETTI, EnnioEnnioPORETTIMérand, AntoineAntoineMérandAnderson, Richard I.Richard I.AndersonFokin, AndreiAndreiFokinFouqué, PascalPascalFouquéGallenne, AlexandreAlexandreGallenneGieren, WolfgangWolfgangGierenGraczyk, DariuszDariuszGraczykKervella, PierrePierreKervellaMathias, PhilippePhilippeMathiasMourard, DenisDenisMourardNeilson, HildingHildingNeilsonPietrzynski, GrzegorzGrzegorzPietrzynskiPilecki, BogumilBogumilPileckiRAINER, MonicaMonicaRAINERStorm, JesperJesperStorm2020-08-242020-08-242017978-2-7598-9024-82101-6275http://hdl.handle.net/20.500.12386/26768Even ≃ 16000 cycles after its discovery by John Goodricke in 1783, δ Cep, the prototype of classical Cepheids, is still studied intensively in order to better understand its atmospheric dynamical structure and its environment. Using HARPS-N spectroscopic measurements, we have measured the atmospheric velocity gradient of δ Cep for the first time and we confirm the decomposition of the projection factor, a subtle physical quantity limiting the Baade-Wesselink (BW) method of distance determination. This decomposition clarifies the physics behind the projection factor and will be useful to interpret the hundreds of p-factors that will come out from the next Gaia release. Besides, VEGA/CHARA interferometric observations of the star revealed a bright visible circumstellar environment contributing to about 7% to the total flux. Better understanding the physics of the pulsation and the environment of Cepheids is necessary to improve the BW method of distance determination, a robust tool to reach Cepheids in the MilkyWay, and beyond, in the Local Group.STAMPAenConference paper10.1051/epjconf/2017152070032-s2.0-85029542449000426610100089https://www.epj-conferences.org/articles/epjconf/abs/2017/21/epjconf_puls2017_07003/epjconf_puls2017_07003.html2017EPJWC.15207003NFIS/05 - ASTRONOMIA E ASTROFISICA