Most stars and planetary systems form in environments where the UV radiation from massive stars is very strong. In order to really understand the observed demographics of planetary systems it is important to study the effect that these environments have on planet-forming disks. The problem is that massive star forming regions are rare, distant, and obscured by gas and dust making it difficult to detect the inner regions (< 10 au) of disks around solar-like stars, where planets like Earth are expected to form. Thanks to the unprecedented sensitivity of JWST, we are now able to do those very challenging observations. Within the eXtreme UV Environments (XUE) collaboration (PIs: Ramírez-Tannus & Bik) we aim to determine the physical and chemical properties of planet-forming disks in extreme environments.

Results

MGC6357 XUE Sample Overview
This paper presents the overview of the full XUE sample. The sample contains 12 disks around stars of masses between 1 and 4 solar masses in NGC6357. Despite being more massive, the XUE stars host disks with molecular richness comparable to isolated T Tauri systems. Most disks display water emission from the inner disk. The absence of strong line fluxes and other irradiation signatures suggests that the XUE disks have been truncated by external UV photons. However, this truncation does not appear to significantly impact the chemical richness of their inner regions. These findings indicate that even in extreme environments, IMTT disks can retain the ingredients necessary for rocky planet formation.

XUE10 Image The CO2-rich terrestrial planet-forming region of an externally irradiated Herbig disk
In this paper, our PhD student Jenny Frediani presents the spectrum of XUE10. A Herbig disk with a very unusual inner disk. Jenny discovered strong CO2 gas signatures, including four distinct isotopologues, which is a first in such a disk. We propose that the mid-infrared spectrum of XUE 10 is explained by H2O removal either via advection or strong photo-dissociation by stellar UV irradiation, and enhanced local CO2 gas-phase production. Outer disk truncation supports the observed CO2-H2O dichotomy. A CO2 vapor enrichment in 18O and 17O can be explained by means of external UV irradiation and early on delivery of isotopically anomalous water ice to the inner disk.

XUE1 Image Thermochemical Modeling Suggests a Compact and Gas-Depleted Structure for a Distant, Irradiated Protoplanetary Disk
In this paper our postdoc Bayron Portilla-Revelo presents the first full thermochemical model of XUE1. We found that the XUE 1 disk must be small and severely depleted of gas due to the UV-driven photoevaporation. Nevertheless, there should be enough material left to form the equivalent of, at least, ten Mercury-like planets! Our findings imply that the innermost regions of protoplanetary disks are resilient to external irradiation and capable of retaining the basic ingredients needed for planet formation.

XUE Image First Molecular inventory of an extremely irradiated Protoplanetary Disk
In the first paper of our collaboration, we present the detection of water, carbon dioxide and other complex molecules in the terrestrial planet-forming zone of a solar-like star located next to some of the most massive stars in the Galaxy. This is the first time that such molecules are detected under these conditions. This is unexpected and exciting, because it tells us that the conditions for planet formation and the ingredients for life are present even under these extreme conditions!
Image credit: Fortuna & Ramírez-Tannus 2023

News

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