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Context. Galactic Cepheids in the vicinity of the Sun have a residual line-of-sight velocity, or γ-velocity, which shows a systematic blueshift of about 2 km s-1 compared to an axisymmetric rotation model of the Milky Way. This term is either related to the space motion of the star and, consequently, to the kinematic structure of our Galaxy, or it is the result of the dynamical structure of the Cepheids' atmosphere.
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Nardetto et al. (2008) studied this question.
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