Peculiarities and variations in the optical spectrum of the post-AGB star V448Lac=IRAS22223+4327

TL;DR

This study analyzes high-resolution spectral observations of the post-AGB star V448Lac over a decade, revealing spectral line asymmetries, shell emissions, and velocity variations that inform understanding of its atmospheric and circumstellar dynamics.

Contribution

It provides the first detection of C2 Swan band emission and details the temporal behavior of spectral line profiles and velocity fields in V448Lac.

Findings

Detection of asymmetrical line profiles and their variations.

First observation of C2 Swan band emission in V448Lac.

Constant expansion velocity of the circumstellar shell at 15.2 km/s.

Abstract

Repeated observations with high spectral resolution acquired in 1998-2008 are used to study the temporal behavior of the spectral line profiles and velocity field in the atmosphere and circumstellar envelope of the post-AGB star V448Lac. Asymmetry of the profiles of the strongest absorption lines with low-level excitation potentials less 1eV and time variations of these profiles have been detected, most prominently the profiles of the resonance lines of BaII, YII, LaII, SiII. The peculiarity of these profiles can be explained using a superposition of stellar absorption line and shell emission lines. Emission in the (0;1) 5635A Swan band of the C2 molecule has been detected in the spectrum of V448Lac for the first time. The core of the Halpha line displays radial velocity variations with an amplitude ~8 km/s. Radial velocity variations displayed by weakest metallic lines with lower amplitudes, 1-2 km/s, may be due to atmospheric pulsations. Differential line shifts, 0 -- 8 km/s, have been detected on various dates. The position of the molecular spectrum is stationary in time, indicating a constant expansion velocity of the circumstellar shell, Vexp=15.2 km/s, as derived from the C2 and NaI lines.