Instability in the system of the distant post-AGB star LS III+52 24 (IRAS 22023+5249)

TL;DR

This study analyzes the optical spectra of the post-AGB star LS III+52 24 over a decade, revealing wind variability, possible binarity, and atmospheric pulsations, indicating complex stellar dynamics and its location beyond the Scutum-Crux arm.

Contribution

First detailed spectroscopic analysis of LS III+52 24 showing wind variability, radial velocity changes, and potential binarity or pulsations.

Findings

Wind variability and velocity stratification observed.

Radial velocity variability suggests possible companion or pulsations.

Star located beyond the Scutum-Crux arm at ≥5.3 kpc.

Abstract

The optical spectra of the B-supergiant LS III+52 24 (IRAS 22023+5249) obtained at the 6-meter telescope BTA with a resolution R$\ge$60000 in 2010-2021 revealed signs of wind variability and velocity stratification in the extended atmosphere. The H$\alpha$ and H$\beta$ lines have a P Cyg type profile; their wind absorption changes position in the range from $-270$ to $-290$ km/s. The intensity of the H$\alpha$ emission reaches record values with respect to the local continuum: I/Icont $\approx$70. The stationary radial velocity according to the positions of symmetric forbidden emissions and permitted metal emissions was taken as the systemic velocity Vsys=$-149.6\pm$0.6 km/s. Based on the positions of absorptions of NII and OII ions, a time variability of the radial velocity in the range from $-127.2$ to $-178.3$ km/s was found for the first time for this star. This variability indicates the possible presence of a companion and/or atmospheric pulsations. The change of the oxygen triplet profile OI 7775 A due to the occurrence of unstable emission was registered. The set of interstellar absorptions of the NaI D-lines profile in the range from $-10.0$ to $-167.2$ km/s is formed in the Local Arm and subsequent arms of the Galaxy. The distance to the star, d$\ge$5.3 kpc, combined with the high systemic velocity, indicates that the star is located in the Galaxy beyond the Scutum-Crux arm.