Issue |
A&A
Volume 692, December 2024
|
|
---|---|---|
Article Number | A197 | |
Number of page(s) | 24 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361/202451967 | |
Published online | 13 December 2024 |
JWST Observations of Young protoStars (JOYS)
Overview of gaseous molecular emission and absorption in low-mass protostars
1
Leiden Observatory, Leiden University,
PO Box 9513,
2300RA
Leiden,
The Netherlands
2
Max Planck Institut für Extraterrestrische Physik (MPE),
Giessenbachstrasse 1,
85748
Garching,
Germany
3
School of Cosmic Physics, Dublin Institute for Advanced Studies,
31 Fitzwilliam Place,
D02 XF86,
Dublin,
Ireland
4
Max Planck Institute for Astronomy,
Königstuhl 17,
69117
Heidelberg,
Germany
5
INAF-Osservatorio Astronomico di Capodimonte,
Salita Moiariello 16,
80131
Napoli,
Italy
6
Department of Space, Earth and Environment, Chalmers University of Technology,
Onsala Space Observatory,
439 92
Onsala,
Sweden
7
Department of Experimental Physics, Maynooth University,
Maynooth,
Co Kildare,
Ireland
8
European Southern Observatory (ESO),
Karl-Schwarzschild-Strasse 2,
1780 85748
Garching,
Germany
9
Laboratory for Astrophysics, Leiden Observatory, Leiden University,
PO Box 9513,
2300 RA
Leiden,
The Netherlands
10
Department of Astrophysics, University of Vienna,
Türkenschanzstrasse 17,
1180
Vienna,
Austria
11
ETH Zürich, Institute for Particle Physics and Astrophysics,
Wolfgang-Pauli-Strasse 27,
8093
Zürich,
Switzerland
12
Université Paris-Saclay, Université Paris Cité, CEA, CNRS, AIM,
91191
Gif-sur-Yvette,
France
13
UK Astronomy Technology Centre, Royal Observatory Edinburgh,
Blackford Hill,
Edinburgh
EH9 3HJ,
UK
★ Corresponding author; vgelder@strw.leidenuniv.nl
Received:
23
August
2024
Accepted:
2
October
2024
Context. The Mid-InfraRed Instrument (MIRI) on board the James Webb Space Telescope (JWST) allows one to probe the molecular gas composition at mid-infrared (mid-IR) wavelengths with unprecedented resolution and sensitivity. It is important to study these features in low-mass embedded protostellar systems, since the formation of planets is thought to start in this phase. Previous studies were sensitive primarily to high-mass protostars.
Aims. The aim of this paper is to derive the physical conditions of all gas-phase molecules detected toward a sample of 18 low-mass protostars as part of the JWST Observations of Young protoStars (JOYS) program and to determine the origin of the molecular emission and absorption features. This includes molecules such as CO2, C2H2, and CH4 that cannot be studied at millimeter wavelengths.
Methods. We present JWST/MIRI data taken with the Medium Resolution Spectrometer (MRS) of 18 low-mass protostellar systems, focusing on gas-phase molecular lines in spectra extracted from the central protostellar positions. The column densities and excitation temperatures were derived for each molecule using local thermodynamic equilibrium (LTE) slab models. Ratios of the column densities (absorption) or total number of molecules (emission) were taken with respect to H2O in order to compare these to ratios derived in interstellar ices.
Results. Continuum emission is detected across the full MIRI-MRS wavelength toward 16/18 sources; the other two sources (NGC 1333 IRAS 4B and Ser-S68N-S) are too embedded to be detected. The MIRI-MRS spectra show a remarkable richness in molecular features across the full wavelength range, in particular toward B1-c (absorption) and L1448-mm (emission). Besides H2, which is not considered here, water is the most commonly detected molecule (12/16) toward the central continuum positions followed by CO2 (11/16), CO (8/16), and OH (7/16). Other molecules such as 13CO2, C2H2, 13CCH2, HCN, C4H2, CH4, and SO2 are detected only toward at most three of the sources, particularly toward B1-c and L1448-mm. The JOYS data also yield the surprising detection of SiO gas toward two sources (BHR71-IRS1, L1448-mm) and for the first time CS and NH3 at mid-IR wavelengths toward a low- mass protostar (B1-c). The temperatures derived for the majority of the molecules are 100–300 K, much lower than what is typically derived toward more evolved Class II sources (≳500 K). Toward three sources (e.g., TMC1-W), hot (∼1000–1200 K) H2O is detected, indicative of the presence of hot molecular gas in the embedded disks, but such warm emission from other molecules is absent. The agreement in abundance ratios with respect to H2O between ice and gas points toward ice sublimation in a hot core for a few sources (e.g., B1-c), whereas their disagreement and velocity offsets hint at high-temperature (shocked) conditions toward other sources (e.g., L1448-mm, BHR71-IRS1).
Conclusions. Molecular emission and absorption features trace various warm components in young protostellar systems, from the hot core regions to shocks in the outflows and disk winds. The typical temperatures of the gas-phase molecules of 100–300 K are consistent with both ice sublimation in hot cores as well as high-temperature gas phase chemistry. Molecular features originating from the inner embedded disks are not commonly detected, likely because they are too extincted even at mid-IR wavelengths by small, unsettled dust grains in upper layers of the disk.
Key words: astrochemistry / stars: formation / stars: low-mass / stars: protostars / ISM: molecules
© The Authors 2024
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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