Peculiarities of the atmosphere and envelope of a post-AGB star, the optical counterpart of IRAS 23304+6347

Abstract

Based on high-spectral resolution observations performed with the echelle spectrograph NES of the 6-meter telescope, we have studied the peculiarities of the spectrum and the velocity field in the atmosphere and envelope of the optical counterpart of the infrared source IRAS 23304+6347. We have concluded about the absence of significant variations in the radial velocity Vr inferred from atmospheric absorptions and about its coincidence with the systemic velocity deduced from radio data. The envelope expansion velocity Vexp=15.5 km/s has been determined from the positions of rotational band lines of the C$_2$ Swan (0; 0) band. A complex emission-absorption profile of the Swan (0; 1) 5635 \AA{} has been recorded. Analysis of the multicomponent NaI~D doublet line profile has revealed interstellar components V(IS)=$-61.6$ and $-13.2$ km/s as well as a circumstellar component with V(CS)=$-41.0$ km/s whose position corresponds to the velocity inferred from C$_2$ features. The presence of the interstellar component with Vr=$-61.6$ km/s in the spectrum allows d=2.5 kpc to be considered as a lower limit for the distance to the star. A splitting of the profiles for strong absorptions of ionized metals (YII, BaII, LaII, SiII) attributable to the presence of a short-wavelength component originating in the circumstellar envelope has been detected in the optical spectrum of IRAS23304+6347 for the first time.