Probing dust grain evolution in IM Lupi's circumstellar disc. Multi-wavelength observations and modelling of the dust disc

TL;DR

This study combines multi-wavelength observations and detailed modelling to investigate dust grain evolution in the circumstellar disc of IM Lupi, revealing grain growth, stratification, and possible aggregate formation.

Contribution

It provides the first resolved imaging of the disc across optical to millimetre wavelengths and demonstrates the importance of multi-technique data integration for disc modelling.

Findings

Detection of millimetre-sized dust grains indicating grain growth.

Evidence of vertical stratification with small grains near the surface and larger grains settled midplane.

Indications of fluffy aggregates and ice mantles around dust grains.

Abstract

We present a panchromatic study, involving a multiple technique approach, of the circumstellar disc surrounding the T Tauri star IM Lupi (Sz 82). We have undertaken a comprehensive observational study of IM Lupi using photometry, spectroscopy, millimetre interferometry and multi-wavelength imaging. For the first time, the disc is resolved from optical and near-infrared wavelengths in scattered light, to the millimetre regime in thermal emission. Our data-set, in conjunction with existing photometric data, provides an extensive coverage of the spectral energy distribution, including a detailed spectrum of the silicate emission bands. We have performed a simultaneous modelling of the various observations, using the radiative transfer code MCFOST, and analysed a grid of models over a large fraction of the parameter space via Bayesian inference. We have constructed a model that can reproduce all of the observations of the disc. Our analysis illustrates the importance of combining a wide range of observations in order to fully constrain the disc model, with each observation providing a strong constraint only on some aspects of the disc structure and dust content. Quantitative evidence of dust evolution in the disc is obtained: grain growth up to millimetre-sized particles, vertical stratification of dust grains with micrometric grains close to the disc surface and larger grains which have settled towards the disc midplane, and possibly the formation of fluffy aggregates and/or ice mantles around grains.