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Published online by Cambridge University Press: 15 August 2009
The link between the dynamical structure of Cepheid atmosphere andthe distance scale calibration in the universe is now clearlyestablished through a period-projection factor relation (Pp).However, to support future observations, we currently need fullyconsistent hydrodynamical models, including pulsating andevolutionary theories, convective energy transport, adaptivenumerical meshes, and a refined calculation of the radiativetransfer within the pulsating atmosphere and the expectedcircumstellar envelope (hereafter CSE). Confronting such models withobservations (spectral line profiles, spatial- and spectral-visibility curves), will permit to resolve and/or strengthen subtlequestions concerning (1) the limb-darkening, (2) the dynamicalstructure of Cepheids' atmosphere, (3) the expected interactionbetween the atmosphere and the CSE, and (4) it will bring newinsights in determining the fundamental parameters of Cepheids. Allthese physical quantities are supposed furthermore to be linked tothe pulsation period of Cepheids. From these studies, it will bepossible to paint a glowing picture of all Cepheids within theinstability strip, allowing an unprecedent calibration of theperiod-luminosity relation, leading to new insights in the fields ofextragalactic distance scales and cosmology.