Precise Fourier parameters of Cepheids RV curves

We subtracted RV modulations caused by binary motion and have removed other residual trends. Uncertainty of Fourier parameters are derived using the covariance matrix. Finally, we have displayed and analyzed qualitatively the progressions found for low- and for high-order Fourier parameters.

We applied a standard identification of their pulsation mode based on their Fourier phase difference {phi}21. We more than doubled the number of Cepheids with published Fourier parameters of their RV curves, determined together with their uncertainties. Our sample includes 178 fundamental-mode and 33 first overtone pulsators, as well as 7 additional Cepheids whose pulsation mode is uncertain or undetermined according to our criteria.

For the fundamental-mode Cepheids, the precision of the obtained low-order Fourier phases is about 7 times better and of the low-order Fourier amplitude ratios about 25% better as compared to precision achieved in previously published Fourier parameter surveys. The precision of the first-overtone Fourier parameters is improved by about 50%.With highly accurate RV Fourier phases {phi}21, we are able to firmly identify V495 Cyg as a new first-overtone Cepheid.

We confirm first-overtone nature of several other stars, tentatively identified as such with the shape of their lightcurves. We also show that {alpha} UMi should be definitely classified as a first-overtone pulsator. In 3 objects (VY Per, AQ Pup and QZ Nor) we found significant {gamma}-velocity variations that we attribute to spectroscopic binarity after careful analysis RV measurements of these stars.

Finally, the analysis of the fundamental mode Fourier parameters up to 7th order reveals very tight progression of Fourier phases for all pulsation periods. They are also tightly correlated with each other. For P<10-day we find a very well defined upper limit for the Fourier amplitude A1.

We have provided new precise Fourier parameters of Cepheid velocity curves, determined from RV measurements available in the literature together with unpublished data. The pulsation period coverage and the precision obtained, in particular for Fourier phase {phi}21, will be useful for studying the dynamics of Cepheid pulsations with the help of hydrodynamical models. Further radial velocity measurements from modern high-resolution spectroscopic instruments will be important to improve these results.