TYC 8606-2025-1: a mild barium star surrounded by the ejecta of a very late thermal pulse

TL;DR

This paper reports the discovery of a mild barium star with a spiral nebula likely ejected by a companion during a very late thermal pulse, revealing new insights into stellar evolution and circumstellar phenomena.

Contribution

It identifies a new mild barium star with a circumstellar nebula, linking the nebula's origin to a very late thermal pulse in a binary system.

Findings

The star is a G8 III with s-process element overabundance.

The nebula has a spiral shape and no optical counterpart.

Radial velocity suggests an unseen binary companion.

Abstract

We report the discovery of a spiral-like nebula with the Wide-field Infrared Survey Explorer (WISE) and the results of optical spectroscopy of its associated star TYC 8606-2025-1 with the Southern African Large Telescope (SALT). We find that TYC 8606-2025-1 is a G8 III star of $\approx3$ M$_\odot$, showing a carbon depletion by a factor of two and a nitrogen enhancement by a factor of three. We also derived an excess of s-process elements, most strongly for barium, which is a factor of three overabundant, indicating that TYC 8606-2025-1 is a mild barium star. We thereby add a new member to the small group of barium stars with circumstellar nebulae. Our radial velocity measurements indicate that TYC 8606-2025-1 has an unseen binary companion. The advanced evolutionary stage of TYC 8606-2025-1, together with the presence of a circumstellar nebula, implies an initial mass of the companion of also about 3 M$_\odot$. We conclude that the infrared nebula, due to its spiral shape, and because it has no optical counterpart, was ejected by the companion as a consequence of a very late thermal pulse, during about one orbital rotation.