The unstable fate of the planet orbiting the A-star in the HD 131399 triple stellar system

TL;DR

This paper investigates the long-term stability of the planet HD 131399Ab in a triple star system, revealing that it is likely ejected during stellar evolution, contributing to free-floating planets and polluted white dwarf systems.

Contribution

The study demonstrates that the planet's orbit is unstable during stellar evolution, highlighting the role of triple systems in planet ejection and white dwarf pollution.

Findings

Planet is only stable under specific parameters.

Most scenarios lead to ejection during stellar evolution.

System provides insight into free-floating planets and white dwarf pollution.

Abstract

Validated planet candidates need not lie on long-term stable orbits, and instability triggered by post-main-sequence stellar evolution can generate architectures which transport rocky material to white dwarfs, polluting them. The giant planet HD 131399Ab orbits its parent A star at a projected separation of about 50-100 au. The host star, HD 131399A, is part of a hierarchical triple with HD 131399BC being a close binary separated by a few hundred au from the A star. Here, we determine the fate of this system, and find that (i) stability along the main sequence is achieved only for a favourable choice of parameters within the errors, and (ii) even for this choice, in almost every instance the planet is ejected during the transition between the giant branch and white dwarf phases of HD 131399A. This result provides an example of both how the free-floating planet population may be enhanced by similar systems, and how instability can manifest in the polluted white dwarf progenitor population.