HR 4049: A Spectroscopic Analysis of a Post-AGB Object

A new spectroscopic study of HR 4049, a post-AGB star in a binary system, based on échelle spectra taken between 2019 and 2025 with the 0.81 m telescope of the Three College Observatory (North Carolina, USA) at a resolution of R ≈ 12,000 is reported. A cross-correlation analysis of 73 spectra of a single C i multiplet in the 4760–4780 Å range yielded the following orbital parameters: the orbital period P=428.474±0.002 days, eccentricity e=0.29±0.01, argument of periastron ω=242.3∘±0.3∘, epoch of periastron T0=2,458,383.2±0.6, heliocentric systemic radial velocity γ=−30.12±0.09 km s−1, and semi-amplitude of the radial velocity curve K1=15.52±0.13 km s−1. Phase-dependent variations of the Hα line profile indicate dynamic processes in the circumstellar environment. The luminosity of HR 4049 was refined using the Gaia EDR3 parallax (0.71±0.10 mas), corresponding to a distance of 1397±170 pc, and the average visual magnitude in the brightest state (mV=5.35 mag). The derived luminosity, log(L/L⊙)=4.22±0.12, suggests an initial mass of 3.0–4.0 M⊙. Analysis of the mass function and most probable orbital inclinations (60°–75°) leads to current masses of ∼0.75M⊙ for the primary and 0.70–0.82M⊙ for the secondary component. The results confirm the system’s long-term orbital stability and provide further insights for future research into the nature of post-AGB binaries.