Detailed spectroscopy of post-AGB supergiant GSC 04050$-$02366 in IRAS Z02229+6208 IR source system

TL;DR

This study presents detailed optical spectroscopy of the post-AGB supergiant GSC 04050-02366, revealing radial velocity variability, spectral line asymmetries, and circumstellar envelope expansion, contributing new insights into its atmospheric and circumstellar dynamics.

Contribution

First detailed spectroscopic analysis of GSC 04050-02366 highlighting radial velocity changes, spectral line asymmetries, and circumstellar envelope characteristics.

Findings

Radial velocity varies with a standard deviation of ~1.4 km/s.

Spectra show no emission lines, only absorption features.

Detected asymmetry and splitting in spectral lines indicating atmospheric and circumstellar phenomena.

Abstract

In the optical spectra of the cold post-AGB supergiant GSC 04050$-$02366, obtained with the 6-meter BTA telescope with a spectral resolution of R$\ge$60000 on arbitrary dates over 2019$\div$2021, a radial velocity variability is found. Heliocentric Vr based on the positional measurements of numerous absorptions varies from date to date with a standard deviation of $\Delta$Vr$\approx$1.4 km/s about the average value of Vr=24.75 km/s, which may stem out of the low-amplitude pulsations in the atmosphere. The spectra of the star are purely absorption type, there are no obvious emissions. Intensity variability of most of absorptions and Swan bands of the C$_2$ molecule was discovered. A slight asymmetry of the H$\alpha$ profile is observed at some observation dates. The position of H$\alpha$ absorption core varies within 27.3$\div$30.6 km/s. Splitting into two components (or asymmetry) of strong low-excitation absorptions (YII, ZrII, BaII, LaII, CeII, NdII) was found. The position of the long-wavelength component coincides with the position of other photospheric absorptions, which confirms its formation in the atmosphere of the star. The position of the shortwave component is close to the position of the rotational features of Swan bands, which indicates its formation in the circumstellar envelope expanding at a velocity of about Vexp=16 km/s.