Barium and related stars, and their white-dwarf companions. III. The masses of the white dwarfs

TL;DR

This study accurately determines the masses of white dwarf companions to Barium stars using combined astrometric and radial-velocity data, providing insights into binary evolution and nucleosynthesis.

Contribution

It introduces a method to derive assumption-free white dwarf masses in Ba star systems by combining Gaia, Hipparcos, and radial-velocity data with advanced statistical modeling.

Findings

Determined new orbital inclinations and masses for 60 Ba star systems.

Unraveled a previously unknown triple system with two companions.

Improved orbital solutions for several long-period systems.

Abstract

Masses are one of the most difficult stellar properties to measure. In the case of the white-dwarf companions of Barium stars, the situation is worse. These stars are dim, cool, and difficult to observe via direct methods. However, Ba stars were polluted by the Asymptotic Giant Branch progenitors of these WDs with matter rich in heavy elements, and the properties of their WD companions contain key information about binary interaction processes involving AGB stars and about the slow-neutron-capture(s)-process of nucleosynthesis. We aim to determine accurate and assumption-free masses for the WD companions of as many Ba stars as possible. We want to provide new observational constraints that can help us learn about the formation and evolution of these post-interaction binary systems and about the nucleosynthesis processes that took place in the interiors of their AGB progenitors. We combined archival radial-velocity data with Hipparcos and Gaia astrometry using the software package orvara, a code designed to simultaneously fit a single Keplerian model to any combination of these types of data using a parallel-tempering Markov chain Monte Carlo method. We adopted Gaussian priors for the Ba star masses and for the parallaxes, and assumed uninformative priors for the orbital elements and the WD masses. We determined new orbital inclinations and companion masses for 60 Ba star systems, including a couple of new orbits and several improved orbits for the longest-period systems. We also unravelled a triple system that was not known before and constrained the orbits and the masses of the two companions. (Continued in the manuscript)