ALMA imaging of the M-dwarf Fomalhaut C's debris disc

TL;DR

This study presents high-resolution ALMA observations of Fomalhaut C's debris disc, revealing its size, shape, and lack of certain emissions, and compares it with other debris discs to understand its characteristics and history.

Contribution

First resolved imaging of Fomalhaut C's debris disc with ALMA, providing detailed modeling of its properties and insights into its potential dynamical history.

Findings

Disc radius of 26 au with a narrow width

Eccentricity upper limit of 0.14

No detection of CO emission or scattered light

Abstract

Fomalhaut C (LP 876-10) is a low mass M4V star in the intriguing Fomalhaut triple system and, like Fomalhaut A, possesses a debris disc. It is one of very few nearby M-dwarfs known to host a debris disc and of these has by far the lowest stellar mass. We present new resolved observations of the debris disc around Fomalhaut C with the Atacama Large Millimetre Array which allow us to model its properties and investigate the system's unique history. The ring has a radius of 26 au and a narrow full width at half maximum of at most 4.2 au. We find a 3$\sigma$ upper limit on the eccentricity of 0.14, neither confirming nor ruling out previous dynamic interactions with Fomalhaut A that could have affected Fomalhaut C's disc. We detect no $^{12}$CO J=3-2 emission in the system and do not detect the disc in scattered light with HST/STIS or VLT/SPHERE. We find the original Herschel detection to be consistent with our ALMA model's radial size. We place the disc in the context of the wider debris disc population and find that its radius is as expected from previous disc radius-host luminosity trends. Higher signal-to-noise observations of the system would be required to further constrain the disc properties and provide further insight to the history of the Fomalhaut triple system as a whole.