Mergers prompted by dynamics in compact, multiple-star systems: a stellar-reduction case for the massive triple TIC 470710327

TL;DR

This paper proposes a scenario where dynamics in a quadruple-star system lead to the merger of a massive binary, explaining the formation of the compact triple TIC 470710327 and shedding light on massive-star formation processes.

Contribution

It introduces a progenitor scenario involving 2+2 quadruple dynamics and Zeipel-Lidov-Kozai resonances that result in binary mergers, a novel explanation for TIC 470710327's formation.

Findings

TIC 470710327 likely formed through binary merger triggered by quadruple dynamics.

The scenario explains the system's current configuration and suggests mergers reduce inclined systems into coplanar ones.

Evidence of a highly-magnetised tertiary star would support a quadruple origin.

Abstract

TIC 470710327, a massive compact hierarchical triple-star system, was recently identified by NASA's Transiting Exoplanet Survey Satellite (TESS). TIC 470710327 is comprised of a compact (1.10 d) circular eclipsing binary, with total mass $\approx 10.9-13.2\ \rm{M_{\odot}}$, and a more massive ($\approx 14-17\ \rm{M_{\odot}}$) eccentric non-eclipsing tertiary in a $52.04$ d orbit. Here we present a progenitor scenario for TIC 470710327 in which '2+2' quadruple dynamics result in Zeipel-Lidov-Kozai (ZLK) resonances that lead to a contact phase of the more massive binary. In this scenario, the two binary systems should form in a very similar manner, and dynamics trigger the merger of the more massive binary either during late phases of star formation or several Myr after the zero-age main sequence (ZAMS), when the stars begin to expand. Any evidence that the tertiary is a highly-magnetised ($\sim 1-10$ kG), slowly-rotating blue main-sequence star would hint towards a quadruple origin. Finally, our scenario suggests that the population of inclined, compact multiple-stellar systems is reduced into co-planar systems, via mergers, late during star formation or early in the main sequence. The elucidation of the origin of TIC 470710327 is crucial in our understanding of multiple massive-star formation and evolution.