Instabilities of the Kinematic State of the Atmospheres of Single C-Rich Post-AGB Stars

To search for and study the instabilities in the atmospheres of selected post-AGB stars, we have performed a long-term high-resolution spectroscopy ( $$R\geq 60\,000$$ ) with the NES spectrograph of the 6-m BTA telescope. Low-amplitude pulsations, splitting and/or asymmetry of the absorption profiles with a low excitation potential (mainly absorptions of $$s$$ -process metals), as well as variability of a complex $$H_{\alpha}$$ profile have been registered in the optical spectra of single stars associated with the IR sources IRASz02229+6208, IRAS 04296+3429, IRAS 07134+1005, IRAS 07430+1115, IRAS 19500 $$-$$ 1709, IRAS 22223+4327, and IRAS 23304+6147 that had previously undergone the third mixing. The maximum pulsation amplitude $$A_{V_{r}}$$ was detected for the stars in the IRAS 07134+1005 and IRAS 19500 $$-$$ 1709 systems, which have the maximum temperatures among the stars in the studied sample. Stratification of radial velocity in the atmosphere was found for two stars in the sample. The luminosity of the studied stars was estimated based on the intensity of the IR oxygen triplet O I $$\lambda$$ 7774. Moreover, a luminosity of $$\log L/L_{\odot}\approx 3.1$$ was obtained for the star in the IRAS 07430+1115 system within the range of typical post-AGB star luminosity values, which eliminates the paradox of the luminosity and the initial mass of this object.