Disk Truncation and Planet Formation in gamma Cephei

TL;DR

This study investigates whether planet formation is feasible in the truncated protoplanetary disk of gamma Cephei A, considering binary truncation effects and disk properties, concluding core accretion remains possible under certain conditions.

Contribution

It provides a detailed analysis of disk truncation in gamma Cephei and identifies conditions under which planet formation via core accretion can still occur.

Findings

Sufficient disk material exists for core accretion at high accretion rates and low viscosity.

Disk instability is unlikely except in extremely massive, high-accretion disks.

Binary truncation limits but does not preclude planet formation in gamma Cephei.

Abstract

The $\gamma$ Cephei system is one of the most closely bound binary planet hosts known to date. The companion ($\gamma$ Cep B) to the planet-hosting star ($\gamma$ Cep A) should have truncated any protoplanetary disk around $\gamma$ Cep A, possibly limiting planet formation in the disk. We explore this problem by calculating the truncation radii of protoplanetary disk models around $\gamma$ Cep A to determine whether or not there is sufficient material remaining in the disk to form a planet. We vary the accretion rate and viscosity parameter of the disk models to cover a range of reasonable possibilities for the disks properties and determine that for accretion rates of $\geq 10^{-7}$ M$_{\sun}$/yr and low viscosity parameter, sufficient material in gas and solids exist for planet formation via core accretion to be possible. Disk instability is less favored, as this can only occur in the most massive disk model with an extremely high accretion rate.