Peculiar Disk Substructures Associated with the Young Eruptive Star EX Lupi

TL;DR

This study uses high-resolution ALMA and SPHERE observations to reveal complex disk substructures around the young eruptive star EX Lupi, linking these features to episodic accretion events potentially caused by a massive companion.

Contribution

First high-resolution imaging of EX Lupi's disk revealing distinct substructures and their potential role in episodic accretion mechanisms.

Findings

Inner crescent-shaped arc within 10 au of the star

Outer ring at 30 au with a width matching pressure scale height

Disk shows signs of dynamical perturbations possibly from a massive companion

Abstract

Young eruptive stars such as EXors undergo dramatic accretion outbursts characterized by sudden optical brightenings, yet the underlying physical mechanism remains uncertain. We present high-resolution Atacama Large Millimeter/submillimeter Array (ALMA) Band 3 and 4 continuum observations of EX Lupi, the prototypical EXor-type variable, reconstructed using super-resolution imaging with sparse modeling. Our images reveal, for the first time, two distinct substructures: a compact, crescent-shaped inner arc within 10 au of the star, and a narrow outer ring at 30 au. The inner arc is strongly elongated and casts a shadow observed in the Very Large Telescope/SPHERE near-infrared scattered light. The outer ring exhibits a radial width comparable to the local pressure scale height, consistent with moderately efficient dust trapping. Geometric and thermal analysis of the disk surface, based on combined ALMA and SPHERE data, indicates that the disk is moderately flared with an average disk temperature consistent with that of classical T Tauri disks. The observed substructures suggest dynamical perturbations-plausibly induced by a massive companion companion-that may modulate accretion rates through gravitational interaction with the inner arc. These findings provide morphological evidence linking disk substructure to episodic accretion in the structurally mature disk.