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In [arXiv: 1312.1118] the author has found the formal series describingradial adiabatic pulsations of polytropes. These series include atime-dependent function, unknown yet. If a polytrope is uniform this functionis obtainable; it is governed by the well-known equation of Bhatnagar andKothari. In the present work it is shown that the pulsations of a polytropewith a near-equilibrium stratification are described by the same equation.These pulsations are nonlinear and their periods do not equal to the periods ofthe standard model. The periods of the vanishingly small pulsations areobtained; using them, the period-mass-radius relation is deduced. This relationis used to estimate masses of 11 chosen Cepheids with firmly known radii; allthe masses found are between 5 and 11 solar masses that correlate well with theresults of the stellar evolution theory.

On Nonlinear Radial Adiabatic Pulsations of Polytropes