Spectral evolution and radial dust transport in the prototype young eruptive system EX Lup

TL;DR

This study investigates the spectral evolution of dust in the eruptive star EX Lup, revealing the disappearance of crystalline silicates from the inner disk over five years, and models dust transport processes during outbursts.

Contribution

It provides new observational evidence of dust crystal dispersal in a young eruptive star and introduces radiative transfer models of dust cloud expansion during outbursts.

Findings

Crystalline silicates vanished from the inner disk within five years.

Dust transport models suggest outward movement of crystals during outbursts.

Future JWST observations could constrain dust cloud locations.

Abstract

EX Lup is the prototype of a class of pre-main sequence eruptive stars defined by their repetitive outbursts lasting several months. In 2008 January-September EX Lup underwent its historically largest outburst, brightening by about 4 magnitudes in visual light. In previous studies we discovered on-going silicate crystal formation in the inner disk during the outburst, but also noticed that the measured crystallinity fraction started decreasing after the source returned to the quiescent phase. Here we present new observations of the 10 $\mu$m silicate feature, obtained with the MIDI and VISIR instruments at Paranal Observatory. The observations demonstrate that within five years practically all crystalline forsterite disappeared from the surface of the inner disk. We reconstruct this process by presenting a series of parametric axisymmetric radiative transfer models of an expanding dust cloud that transports the crystals from the terrestrial zone to outer disk regions where comets are supposed to form. Possibly the early Sun also experienced similar flare-ups, and the forming planetesimals might have incorporated crystalline silicate material produced by such outbursts. Finally, we discuss how far the location of the dust cloud could be constrained by future JWST observations.