JWST/MIRI Spectroscopy of the Disk of the Young Eruptive Star EX Lup in Quiescence

Abstract

EX Lup is a low-mass pre-main-sequence star that occasionally shows accretion-related outbursts. Here, we present JWST/MIRI medium-resolution spectroscopy obtained for EX Lup 14 yr after its powerful outburst. EX Lup is now in quiescence and displays a Class II spectrum. We detect a forest of emission lines from molecules previously identified in infrared spectra of classical T Tauri disks: H2O, OH, H2, HCN, C2H2, and CO2. The detection of organic molecules demonstrates that they are back after disappearing during the large outburst. Spectral lines from water and OH are for the first time deblended and will provide a much-improved characterization of their distribution and density in the inner disk. The spectrum also shows broad emission bands from warm, submicron-size amorphous silicate grains at 10 and 18 μm. During the outburst, in 2008, crystalline forsterite grains were annealed in the inner disk within 1 au, but their spectral signatures in the 10 μm silicate band later disappeared. With JWST we rediscovered these crystals via their 19.0, 20.0, and 23.5 μm emission, the strength of which implies that the particles are at ∼3 au from the star. This suggests that crystalline grains formed in 2008 were transported outwards and now approach the water snowline, where they may be incorporated into planetesimals. Containing several key tracers of planetesimal and planet formation, EX Lup is an ideal laboratory to study the effects of variable luminosity on the planet-forming material and may provide an explanation for the observed high crystalline fraction in solar system comets.

The Radial Distribution and Excitation of H2 around Young Stars in the HST-ULLYSES Survey

“…Surveys of mid-IR emission from CO (Salyk et al 2009;Brown et al 2013;Banzatti & Pontoppidan 2015;Banzatti et al 2022), H 2 O and organic molecules (Pontoppidan et al 2010;Salyk et al 2011b;Carr & Najita 2011;Banzatti et al 2023), UV emission and absorption of H 2 and CO (Herczeg et al 2004;France et al 2011;Schindhelm et al 2012;France et al 2014a;Arulanantham et al 2021), and spectrally/spatially resolved near-IR observations (Carmona et al 2011;Pontoppidan et al 2011;Brittain et al 2015) have placed constraints on the relative abundance ratios of H 2 , CO, and H 2 O, the evolution of the inner gas disk radius, and the excitation conditions of the molecular gas. The inventory of disk molecules and photochemical studies of the planet-forming environments around young stars is expected to expand rapidly in the era of JWST (Öberg & Bergin 2021;Grant et al 2023;Kóspál et al 2023).…”

“…H 2 is the primary mass component of gas-rich disks, however, the lack of an intrinsic dipole moment and large energy spacing between the rotational levels have traditionally made direct detection of the rovibrational emission lines of the molecule challenging to study in a large number of disks (although see, e.g., Carmona et al 2011;Gangi et al 2020;Kóspál et al 2023). Conversely, the electronic excitation spectrum of H 2 is among the brightest features in the UV spectra of pre-main-sequence stars (France et al 2012), and can serve as a diagnostic of weak mass accretion when traditional accretion diagnostics (e.g., Hα and near-UV Balmer continuum) do not provide clear evidence of active accretion (Ingleby et al 2011;Alcalá et al 2019).…”

The Accretion History of EX Lup: A Century of Bursts, Outbursts, and Quiescence

“…The 2008 outburst led to the depletion of gas in the inner disk (Banzatti et al 2015), moved snowlines to larger radii (White & Kóspál 2020), and created comet-forming materials (Ábrahám et al 2009). Organic molecules reformed after destruction during the outburst, while crystalline grains that formed during the burst were transported outward (Kóspál et al 2023).…”

Inviscid protostellar disc ring formation and high-density ring edges due to the ejection and subsequent infall of material onto a protostellar disc

“…In addition, Spitzer Space Telescope and James Webb Space Telescope observations also demonstrate that crystalline, micronsized particles are ejected from the inner regions of protostars and travel radially across the face of the disc and re-enter the disc some au from the protostar or are completely ejected from the protostellar system (Poteet et al, 2011;Juhász et al, 2012;Ábrahám et al, 2019;Kóspál et al, 2023). These particles from the inner regions of the disc will tend to have little or no angular momentum relative to material in the outer regions of the disc.…”

“…However, this infalling material is observed, at least in one case, to be heterogeneously distributed across the accretion disc (Juhász et al, 2012;Ábrahám et al, 2019;Kóspál et al, 2023). Some theoretical models (e.g., Giacalone et al (2019)) also explicitly predict that disc winds will deposit particulate material outside the outflow region.…”