Planetary Engulfment Prognosis within the $\rho$ CrB System

Abstract

Exoplanets have been detected around stars at various stages of their lives, ranging from young stars emerging from formation, to latter stages of evolution, including white dwarfs and neutron stars. Post main sequence stellar evolution can result in dramatic, and occasionally traumatic, alterations to the planetary system architecture, such as tidal disruption of planets and engulfment by the host star. The $\rho$ CrB system is a particularly interesting case of advanced main sequence evolution, due to the relative late age and brightness of the host star, its similarity to solar properties, and the harboring of four known planets. Here, we use stellar evolution models to estimate the expected trajectory of the $\rho$ CrB stellar properties, especially over the coming 1.0-1.5 billion years as it evolves off the main sequence. We show that the inner three planets (e, b, and c) are engulfed during the red giant phase and asymptotic giant branch, likely destroying those planets via either evaporation or tidal disruption at the fluid body Roche limit. The outer planet, planet d, is briefly engulfed by the star several times toward the end of the asymptotic giant branch, but the stellar mass loss and subsequent changing planetary orbit may allow the survival of the planet into the white dwarf phase of the stellar evolution. We discuss the implications of this outcome for similar systems, and describe the consequences for planets that may lie within the Habitable Zone of the system.