The grain size survival threshold in one-planet post-main-sequence exoplanetary systems

TL;DR

This study models how dust and debris orbiting stars evolve during the giant branch phase, revealing a size threshold (~1 mm to 5 cm) that determines whether particles escape or remain bound, impacting debris observability.

Contribution

It introduces a dynamical framework for understanding grain orbit evolution during stellar giant phases, establishing a size-dependent escape threshold in one-planet systems.

Findings

Particles smaller than ~1 mm tend to escape during giant branch evolution.

Particles larger than ~5 cm generally remain gravitationally bound.

The size threshold for escape is largely independent of planetary location.

Abstract

The size distribution and orbital architecture of dust, grains, boulders, asteroids, and major planets during the giant branch phases of evolution dictate the preponderance and observability of the eventual debris, which have been found to surround white dwarfs and pollute their atmospheres with metals. Here, we utilize the photogravitational planar restricted three-body problem in one-planet giant branch systems in order to characterize the orbits of grains as the parent star luminosity and mass undergo drastic changes. We perform a detailed dynamical analysis of the character of grain orbits (collisional, escape, or bounded) as a function of location and energy throughout giant branch evolution. We find that for stars with main-sequence masses of $2.0M_{\odot}$, giant branch evolution, combined with the presence of a planet, ubiquitously triggers escape in grains smaller than about 1 mm, while leaving grains larger than about 5 cm bound to the star. This result is applicable for systems with either a terrestrial or giant planet, is largely independent of the location of the planet, and helps establish a radiative size threshold for escape of small particles in giant branch planetary systems.