ALMA observations of the $\eta$ Corvi debris disc: inward scattering of CO-rich exocomets by a chain of 3-30 M$_\oplus$ planets?

TL;DR

This study uses ALMA observations to analyze the $ta$ Corvi debris disc, suggesting a stable planetary configuration may be responsible for inward scattering of CO-rich exocomets, explaining the hot dust presence.

Contribution

First ALMA high-resolution imaging of $ta$ Corvi's outer belt, constraining planetary parameters and proposing a stable planetary system as the source of inward-scattered exocomets.

Findings

The outer belt is axisymmetric with a radius of 152au and a narrow width.

Detection of CO gas at approximately 20au suggests in situ release from icy planetesimals.

A potential planet of 3-30 M$_\u2297$ at 75-100au could be responsible for disc sculpting and inward scattering.

Abstract

While most of the known debris discs present cold dust at tens of AU, a few young systems exhibit hot dust analogous to the Zodiacal dust. $\eta$ Corvi is particularly interesting as it is old and it has both, with its hot dust significantly exceeding the maximum luminosity of an in-situ collisional cascade. Previous work suggested that this system could be undergoing an event similar to the Late Heavy Bombardment (LHB) soon after or during a dynamical instability. Here we present ALMA observations of $\eta$ Corvi with a resolution of 1."2 (~22au) to study its outer belt. The continuum emission is consistent with an axisymmetric belt, with a mean radius of 152au and radial FWHM of 46au, which is too narrow compared to models of inward scattering of an LHB-like scenario. Instead, the hot dust could be explained as material passed inwards in a rather stable planetary configuration. We also report a 4sigma detection of CO at ~ 20au. CO could be released in situ from icy planetesimals being passed in when crossing the H$_2$O or CO$_2$ ice lines. Finally, we place constraints on hidden planets in the disc. If a planet is sculpting the disc's inner edge, this should be orbiting at 75-100au, with a mass of 3-30 M$_\oplus$ and an eccentricity < 0.08. Such a planet would be able to clear its chaotic zone on a timescale shorter than the age of the system and scatter material inwards from the outer belt to the inner regions, thus feeding the hot dust.