Phase-dependent variation of the fundamental parameters of Cepheids. IV. s-Cepheids

In this fourth of a series of papers presenting the results of a detailed multiphase spectroscopic analysis of classical Cepheids, we report on fundamental parameter variation in a group of so-called s-Cepheids. For each star, we have derived phased values of effective temperature, surface gravity, microturbulent velocity, and elemental abundances. Dependences between these parameters, amplitudes of their variation, and pulsational period are discussed in a framework of such dependences obtained in our previous works for 30 classical Cepheids. Our temperature data reveal that five of the s-Cepheids have mean temperatures that deviate substantially from the remainder of the Cepheid data. The temperature deviations place these s-Cepheids near the edges of the fundamental instability strip. While these deviations cannot differentiate between fundamental and overtone pulsation modes, the deviations are undoubtedly related to the root cause of the small amplitudes found in these stars.