MINDS: The very low-mass star and brown dwarf sample

Astronomy and Astrophysics, vol. 703, pp. A53

Abstract

Context . Disks around very low-mass stars (VLMSs) provide environments for the formation of Earth-like planets. Mid-infrared observations have revealed that these disks often exhibit weak silicate features and prominent hydrocarbon emissions. Aims . This study aims to characterize the dust properties and geometrical structures of VLMS and brown dwarf (BD) disks, observed by the James Webb Space Telescope (JWST)/Mid-Infrared Instrument (MIRI). We investigate how these properties relate to gas column density and potential evolutionary stages. Methods . We analyzed mid-infrared spectra of ten VLMSs and BD disks from the JWST/MIRI observations as part of the MIRI mid-Infrared Disk Survey (MINDS) program. Spectral slopes and silicate band strengths were measured and compared with hydrocarbon emission line ratios, which probe the gas column density. Moreover, the Dust Continuum Kit with Line emission from Gas (DuCKLinG) was used to quantify grain sizes, dust compositions, and crystallinity on the disk surface. Results . The disks are classified into less, more, and fully settled geometries based on their mid-infrared spectral slopes and silicate band strengths. Less settled disks show a relatively strong silicate band, high spectral slopes, and low crystallinity and are dominated by 5 µm-sized grains. More settled disks have weaker silicate bands, low spectral slopes, enhanced crystallinity, and higher mass fractions of smaller grains (<5 µm). Fully settled disks exhibit little or no silicate emission and negative spectral slopes. An overall trend of increasing gas column density with decreasing spectral slope suggests that more molecular gas is exposed when the dust opacity decreases with increasing dust settling. Conclusions . Our findings indicate that our sample shows dust processing signatures of grain growth and crystallization. These characteristics may reflect possible evolutionary pathways with disk turbulence, dust settling, and thermal processing or may alternatively point to inner-disk clearing or a collisional cascade. These results highlight the need for broader samples to understand the link between dust and gas appearance in regions where Earth-like planets form.

Authors 13

1. Hyerin Jang

   Radboud University Nijmegen

   Affiliation as printed

   Department of Astrophysics/IMAPP, Radboud University

2. Aditya M. Arabhavi

   University of Groningen

   Affiliation as printed

   Kapteyn Astronomical Institute, Rijksuniversiteit Groningen

3. Till Kaeufer

   University of Exeter

   Affiliation as printed

   Department of Physics and Astronomy, University of Exeter

4. Rens Waters Aachen SRON Netherlands Institute for Space Research

   Radboud University Nijmegen · Space Research Organisation Netherlands

   Affiliation as printed

   Department of Astrophysics/IMAPP, Radboud University

   SRON Netherlands Institute for Space Research

5. I. Kamp

   University of Groningen

   Affiliation as printed

   Kapteyn Astronomical Institute, Rijksuniversiteit Groningen

6. Thomas K. Henning

   Max Planck Institute for Astronomy

   Affiliation as printed

   Max-Planck-Institut für Astronomie (MPIA)

7. A. Caratti o Garatti

   Astronomical Observatory of Capodimonte · National Institute for Astrophysics

   Affiliation as printed

   INAF – Osservatorio Astronomico di Capodimonte

8. Ewine F. van Dishoeck Aachen Leiden Observatory

   Leiden University · Max Planck Society · Max Planck Institute for Extraterrestrial Physics · Leiden Observatory

   Affiliation as printed

   Leiden Observatory, Leiden University

   Max-Planck Institut für Extraterrestrische Physik (MPE)

9. Giulia Perotti

   University of Copenhagen · Max Planck Institute for Astronomy

   Affiliation as printed

   Max-Planck-Institut für Astronomie (MPIA)

   Niels Bohr Institute, University of Copenhagen

10. M. Guêdel

    University of Vienna · ETH Zurich · Institute for Particle Physics and Astrophysics

    Affiliation as printed

    Dept. of Astrophysics, University of Vienna

    ETH Zürich, Institute for Particle Physics and Astrophysics

11. M. Morales‐Calderón

    Centro de Astrobiología

    Affiliation as printed

    Centro de Astrobiología (CAB), CSIC-INTA, ESAC Campus

12. Sierra L. Grant

    Carnegie Institution for Science · Earth and Planets Laboratory

    Affiliation as printed

    Earth and Planets Laboratory, Carnegie Institution for Science

13. Valentin Christiaens

    University of Liège · KU Leuven

    Affiliation as printed

    Institute of Astronomy, KU Leuven

    STAR Institute, Université de Liège