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

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.