Issue |
A&A
Volume 699, July 2025
|
|
---|---|---|
Article Number | A194 | |
Number of page(s) | 19 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361/202554109 | |
Published online | 08 July 2025 |
MINDS: The very low-mass star and brown dwarf sample
Detections and trends in the inner disk gas
1
Kapteyn Astronomical Institute, Rijksuniversiteit Groningen,
Postbus 800,
9700AV
Groningen,
The Netherlands
2
Max-Planck-Institut für Astronomie (MPIA),
Königstuhl 17,
69117
Heidelberg,
Germany
3
Leiden Observatory, Leiden University,
2300
RA
Leiden,
The Netherlands
4
Max-Planck Institut für Extraterrestrische Physik (MPE),
Giessenbachstr. 1,
85748
Garching,
Germany
5
Department of Astrophysics/IMAPP, Radboud University,
PO Box 9010,
6500
GL
Nijmegen,
The Netherlands
6
SRON Netherlands Institute for Space Research,
Niels Bohrweg 4,
2333
CA
Leiden,
The Netherlands
7
Institute of Astronomy, KU Leuven,
Celestijnenlaan 200D,
3001
Leuven,
Belgium
8
STAR Institute, Université de Liège,
Allée du Six Août 19c,
4000
Liège,
Belgium
9
Department of Planetary Sciences, University of Arizona; 1629 East University Boulevard,
Tucson,
AZ
85721,
USA
10
Niels Bohr Institute, University of Copenhagen,
NBB BA2, Jagtvej 155A,
2200
Copenhagen,
Denmark
11
Earth and Planets Laboratory, Carnegie Institution for Science,
5241 Broad Branch Road, NW,
Washington,
DC,
20015,
USA
12
Dept. of Astrophysics, University of Vienna,
Türkenschanzstr. 17,
1180
Vienna,
Austria
13
ETH Zürich, Institute for Particle Physics and Astrophysics,
Wolfgang-Pauli-Str. 27,
8093
Zürich,
Switzerland
14
Université Paris-Saclay, Université Paris Cité, CEA, CNRS, AIM,
91191
Gif-sur-Yvette,
France
15
Centro de Astrobiología (CAB), CSIC-INTA, ESAC Campus, Camino Bajo del Castillo s/n,
28692
Villanueva de la Cañada, Madrid,
Spain
16
INAF – Osservatorio Astronomico di Capodimonte,
Salita Moiariello 16,
80131
Napoli,
Italy
17
SRON Netherlands Institute for Space Research,
PO Box 800,
9700
AV,
Groningen,
The Netherlands
18
Department of Physics and Astronomy, University of Exeter,
Exeter
EX4 4QL,
UK
19
Space Research Institute, Austrian Academy of Sciences,
Schmiedlstr. 6,
8042
Graz,
Austria
20
TU Graz, Fakultät für Mathematik, Physik und Geodäsie, Petersgasse,
168010
Graz,
Austria
21
Université Paris-Saclay, CNRS, Institut d’Astrophysique Spatiale,
91405
Orsay,
France
★ Corresponding author: arabhavi@astro.rug.nl
Received:
12
February
2025
Accepted:
3
June
2025
Context. Planet-forming disks around brown dwarfs and very low-mass stars (VLMS) are, on average, less massive and are expected to undergo faster radial solid transport than their higher-mass counterparts. Spitzer had detected C2H2, CO2, and HCN around these objects but did not provide a firm detection of water. With a better sensitivity and spectral resolving power than that of Spitzer, the James Webb Space Telescope (JWST) has recently revealed incredibly carbon-rich spectra and only one water-rich spectrum from such disks. A study of a larger sample of objects is necessary to understand how common such carbon-rich inner disk regions are and to put constraints on their evolution.
Aims. We present and analyze JWST MIRI/MRS observations of ten disks around VLMS from the MIRI guaranteed time observations program. This sample is diverse, with the central object ranging in mass from 0.02 to 0.14 M⊙. They are located in three star-forming regions and a moving group (1 to 10 Myr).
Methods. We identified molecular emission in all sources based on recent literature and spectral inspection, and reported detection rates. We compared the molecular flux ratios between different species and to dust emission strengths. We also compared the flux ratios with the stellar and disk properties.
Results. The spectra of these VLMS disks are extremely rich in molecular emission, and we detect the 10 μm silicate dust emission feature in 70% of the sample. We detect C2H2 and HCN in all the sources and find larger hydrocarbons, such as C4H2 and C6H6, in nearly all sources. Among oxygen-bearing molecules, we find firm detections of CO2, H2O, and CO in 90,50, and 20% of the sample, respectively. We find that the detection rates of organic molecules correlate with other organic molecules and anticorrelate with the detection rates of inorganic molecules. Hydrocarbon-rich sources show weaker 10 μm dust strengths, as well as lower disk dust masses (measured from millimeter fluxes) than the oxygen-rich sources. We find evidence for a C/O ratio enhancement with disk age. The observed trends are consistent with models that suggest rapid inward solid material transport and grain growth.
Key words: astrochemistry / protoplanetary disks / stars: low-mass / stars: pre-main sequence / infrared: planetary systems
© The Authors 2025
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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