MINDS. Hydrocarbons detected by JWST/MIRI in the inner disk of Sz28 consistent with a high C/O gas-phase chemistry

Autor(en): Jayatee Kanwar, Inga Kamp, Hyerin Jang, Laurens B.F.M. Waters, Ewine F. Van Dishoeck, Valentin Christiaens, Aditya M. Arabhavi, Thomas Henning, Manuel Güdel, Peter Woitke, Olivier Absil, David Barrado, Alessio Caratti O Garatti, Adrian M. Glauser, Fred Lahuis, Silvia Scheithauer, Bart Vandenbussche, Danny Gasman, Sierra L. Grant, Nicolas T. Kurtovic, Giulia Perotti, Benoît Tabone, Milou Temmink
Abstrakt: Context. With the advent of JWST, we are acquiring unprecedented insights into the physical and chemical structure of the inner regions of planet-forming disks where terrestrial planet formation occurs. Very low-mass stars (VLMSs) are known to have a high occurrence of the terrestrial planets orbiting them. Exploring the chemical composition of the gas in these inner disk regions can help us better understand the connection between planet-forming disks and planets. Aims. The MIRI mid-Infrared Disk Survey (MINDS) project is a large JWST guaranteed time program whose aim is to characterise the chemistry and physical state of planet-forming and debris disks. We used the JWST-MIRI/MRS spectrum to investigate the gas and dust composition of the planet-forming disk around the VLMS Sz28 (M5.5, 0.12 M_⊙). Methods. We used the dust-fitting tool DuCK to determine the dust continuum and to place constraints on the dust composition and grain sizes. We used 0D slab models to identify and fit the molecular spectral features, which yielded estimates on the temperature, column density, and emitting area. To test our understanding of the chemistry in the disks around VLMSs, we employed the thermochemical disk model P_ROD_IM_O and investigated the reservoirs of the detected hydrocarbons. We explored how the C/O ratio affects the inner disk chemistry. Results. JWST reveals a plethora of hydrocarbons, including CH₃, CH₄, C₂H₂ ¹³CCH₂, C₂H₆, C₃H₄, C₄H₂ and C₆H₆ which suggests a disk with a gaseous C/O > 1. Additionally, we detect CO₂ ¹³CO₂, HCN, and HC₃N. H₂O and OH are absent from the spectrum. We do not detect polycyclic aromatic hydrocarbons. Photospheric stellar absorption lines of H₂O and CO are identified. Notably, our radiation thermo-chemical disk models are able to produce these detected hydrocarbons in the surface layers of the disk when C/O > 1. The presence of C, C⁺, H, and H₂ is crucial for the formation of hydrocarbons in the surface layers, and a C/O ratio larger than 1 ensures the surplus of C needed to drive this chemistry. Based on this, we predict a list of additional hydrocarbons that should also be detectable. Both amorphous and crystalline silicates (enstatite and forsterite) are present in the disk and we find grain sizes of 2 and 5 μm. Conclusions. The disk around Sz28 is rich in hydrocarbons, and its inner regions have a high gaseous C/O ratio. In contrast, it is the first VLMS disk in the MINDS sample to show both distinctive dust features and a rich hydrocarbon chemistry. The presence of large grains indicates dust growth and evolution. Thermo-chemical disk models that employ an extended hydrocarbon chemical network together with C/O >1 are able to explain the hydrocarbon species detected in the spectrum.
Organisation(en): Institut für Astrophysik
Externe Organisation(en): University of Groningen, Österreichische Akademie der Wissenschaften (ÖAW), Technische Universität Graz, Radboud University, SRON Netherlands Institute for Space Research , Leiden University, Max-Planck-Institut für extraterrestrische Physik, Katholieke Universiteit Leuven, Université de Liège, Max-Planck-Institut für Astronomie, Eidgenössische Technische Hochschule Zürich, Centro de Astrobiología (CSIC-INTA), INAF-Osservatorio Astronomico di Capodimonte, Dublin Institute for Advanced Studies, Université Paris Saclay
Journal: Astronomy and Astrophysics
Band: 689
Anzahl der Seiten: 21
ISSN: 0004-6361
DOI: https://doi.org/10.1051/0004-6361/202450078
Publikationsdatum: 09-2024
Peer-reviewed: Ja
ÖFOS 2012: 103003 Astronomie, 103004 Astrophysik
Schlagwörter
ASJC Scopus Sachgebiete: Astronomy and Astrophysics, Space and Planetary Science
Link zum Portal: https://ucrisportal.univie.ac.at/de/publications/b33f1ff8-5812-4e53-9c5a-233ffed6f2ca

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