A magnetic tertiary in the most massive compact triple-star system

TL;DR

This paper reports the discovery of a highly massive, magnetized tertiary star in a compact triple system, providing insights into the formation and magnetic properties of massive stellar systems.

Contribution

It confirms the presence of a strong magnetic field in the tertiary and discusses the formation scenario involving stellar mergers in compact triples.

Findings

The tertiary has a magnetic field of the order of kilogauss.

The system is the most massive compact triple known.

The tertiary exhibits slow rotation typical of magnetic massive stars.

Abstract

The system TIC 470710327 is comprised of three main-sequence OB stars, with an inner compact 1.10 d eclipsing binary and a non-eclipsing tertiary on a 52.04 d orbit. With the tertiary mass of 14.5-16 $M_{\odot}$ and both components in the inner eclipsing binary with individual masses of 6--7 and 5.5-6.3 $M_{\odot}$, it is currently the most massive compact system known. The formation scenario of such a compact triple is uncertain. It has been suggested that `2 + 2' quadruple dynamics can lead to a stellar merger in the initially more massive binary and finally result in a highly magnetised tertiary. Our study confirms the presence of a kG-order magnetic field in the tertiary and the slow rotation typical for massive magnetic stars. We conclude that finding massive merger candidates by studies of dynamics in compact, multiple-star systems is an efficient way to understand the evolution of massive stellar multiplicity and the generation of magnetic fields.