High-resolution optical spectroscopy of the post-AGB supergiant V340 Ser (=IRAS 17279$-$1119)

TL;DR

This study uses high-resolution optical spectroscopy to analyze the atmospheric dynamics and velocity stratification of the post-AGB supergiant V340 Ser, revealing wind variability and complex line profiles.

Contribution

It provides detailed spectroscopic evidence of wind variability, velocity stratification, and atmospheric structure in V340 Ser, a post-AGB supergiant, using high-resolution spectra.

Findings

Detection of wind variability and velocity stratification.

Identification of multiple components in spectral lines indicating atmospheric layers.

Estimated distance of approximately 2.3 kpc to V340 Ser.

Abstract

Some evidences of wind variability and velocity stratification in the extended atmosphere has been found in the spectra of the supergiant V340 Ser (=IRAS 17279$-$1119) taken at the 6-m BTA telescope with a spectral resolution R$\ge$60000. The H$\alpha$ line has a P Cyg profile whose absorption component (V=+34 km/s) is formed in the upper layers of the expanding atmosphere close to the circumstellar environment. For four dates the mean velocity has been derived from the positions of 300-550 symmetric metal absorptions with an accuracy better than $\pm0.1$ km/s: Vr=59.30, 60.09, 58.46, and 55.78 km/s. A lot of low-excitation metal lines have an inverse P Cyg profile. The mean positions of their emission components, Vr=46.3$\pm$0.4 km/s, differ systematically from the velocity inferred from symmetric absorptions, suggesting the presence of a velocity gradient in the supergiant extended atmosphere. The multicomponent profile of the NaI D-lines contains the interstellar, Vr=-11.2 km/s, and circumstellar, Vr=+10 km/s, components and the component forming in the upper atmospheric layers, Vr=+34.0 km/s. The mean velocity from 20-30 diffuse interstellar bands (DIBs) identified in the spectra, Vr(DIBs)=-11.6$\pm0.2$ km/s, agrees with the velocity from interstellar NaI and KI components. The equivalent width of the oxygen triplet W(7774)=1.25 A corresponds to an absolute magnitude of the star Mv$\approx-4.6^m$, which, taking into account the total (interstellar+circumstellar) extinction, leads to a distance to the star d$\approx$2.3 kpc.