Pristine composition or size evolution: Can current dust models reproduce emissivities observed in nearby protostars?
Abstract
Context. Interstellar medium dust is a crucial asset in many astronomical observations, as its emission permits the retrieval of the physical properties of astrophysical structures. Characterising dust grains present in the dense gas and in star-forming environments is also key to constrain the pristine conditions for planetary formation. However, dust properties, especially in young protostars, remain poorly characterised and are still debated: low dust emissivities observed in nearby protostars are, for example, not completely explained to this day. Aims. In this study, we aim to determine (i) whether it is possible to retrieve the dust properties from multi-wavelength observations of the dust emission towards embedded protostars, and (ii) the extent to which current dust models should be excluded from or can reproduce the observed values of the dust emissivity index in young embedded protostars. Methods. We perform radiative transfer computations of the thermal dust emission from a model protostellar envelope, considering different dust optical properties commonly used in the community. This allows us to explore the effects of dust composition on the spectral index, and compare these synthetic observations to literature data of dust emission in nearby protostars, to try and explain the variation in the emissivity index in observations. Results. We find a large variation in the spectral index as the sole result of different dust models, without the need for dust grain size evolution. However, our work does not allow us to reproduce the lowest emissivity index values found in some protostellar envelopes without including unexpectedly large millimetre-sized processed grains. We show a tentative clustering of the emissivity index values depending on the star-forming region these protostars belong to, suggesting a potential relationship with the pristine dust reservoir at cloud scales. Conclusions. We show that appropriate methods, tested on theoretical models, allow us to measure the dust emissivity from observations of the spectral index at millimetre wavelengths with very little uncertainty, despite the large temperature and density gradients present in star-forming cores. Comparing the large magnitude of variation in emissivity index between the different observed sources with the dust models most commonly used by the community implies that the intrinsic composition of dust and its associated optical properties are not sufficient to explain the lowest spectral index values. Thus, early dust evolution producing larger dust grains in a dense medium may have to be taken into account to obtain a complete picture.
Related
- Carbon distribution in planet Mercury from magma ocean evolution to graphite crust and core composition
- Elemental Composition Evolution during the 2024 September 30 Solar Eruption: A Comparison of Hot and Cool Plasma Components with Solar Orbiter/SPICE, Hinode/EIS, and Chandrayaan-2/XSM
- Complex Organic Molecules in Protostars with ALMA Spectral Surveys (COMPASS). VIII. First interstellar detection of fully deuterated methyl cyanide
- Can coupled thawing quintessence reproduce DESI DR2? A test with two potentials
- Fermentation heterotrophy can reproduce Enceladus's plume H2 and CH4 under limited serpentinization
BibTeX
@article{carpine2026pristine,
title = {{Pristine composition or size evolution: Can current dust models reproduce emissivities observed in nearby protostars?}},
author = {M.-A. Carpine and A. Maury and N. Ysard and L. Cacciapuoti},
journal = {Astronomy \& Astrophysics - A\&A},
year = {2026},
month = aug,
doi = {10.1051/0004-6361/202556551},
eprint = {2606.29895},
archivePrefix = {arXiv},
url = {https://hal.science/hal-05761953v1},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Pristine composition or size evolution: Can current dust models reproduce emissivities observed in nearby protostars?
AU - M.-A. Carpine
AU - A. Maury
AU - N. Ysard
AU - L. Cacciapuoti
PY - 2026
DA - 2026/08/11
JO - Astronomy & Astrophysics - A&A
DO - 10.1051/0004-6361/202556551
UR - https://hal.science/hal-05761953v1
AB - Context. Interstellar medium dust is a crucial asset in many astronomical observations, as its emission permits the retrieval of the physical properties of astrophysical structures. Characterising dust grains present in the dense gas and in star-forming environments is also key to constrain the pristine conditions for planetary formation. However, dust properties, especially in young protostars, remain poorly characterised and are still debated: low dust emissivities observed in nearby protostars are, for example, not completely explained to this day. Aims. In this study, we aim to determine (i) whether it is possible to retrieve the dust properties from multi-wavelength observations of the dust emission towards embedded protostars, and (ii) the extent to which current dust models should be excluded from or can reproduce the observed values of the dust emissivity index in young embedded protostars. Methods. We perform radiative transfer computations of the thermal dust emission from a model protostellar envelope, considering different dust optical properties commonly used in the community. This allows us to explore the effects of dust composition on the spectral index, and compare these synthetic observations to literature data of dust emission in nearby protostars, to try and explain the variation in the emissivity index in observations. Results. We find a large variation in the spectral index as the sole result of different dust models, without the need for dust grain size evolution. However, our work does not allow us to reproduce the lowest emissivity index values found in some protostellar envelopes without including unexpectedly large millimetre-sized processed grains. We show a tentative clustering of the emissivity index values depending on the star-forming region these protostars belong to, suggesting a potential relationship with the pristine dust reservoir at cloud scales. Conclusions. We show that appropriate methods, tested on theoretical models, allow us to measure the dust emissivity from observations of the spectral index at millimetre wavelengths with very little uncertainty, despite the large temperature and density gradients present in star-forming cores. Comparing the large magnitude of variation in emissivity index between the different observed sources with the dust models most commonly used by the community implies that the intrinsic composition of dust and its associated optical properties are not sufficient to explain the lowest spectral index values. Thus, early dust evolution producing larger dust grains in a dense medium may have to be taken into account to obtain a complete picture.
SN - 0004-6361
SN - 1432-0746
ER -