An ALMA View on Molecular Complexity: Water, Methanol, and Methyl Formate in the HD 100546 and IRS 48 Disks
8 affiliations
- 1Università degli Studi di Milano
- 2European Southern Observatory
- 3Center for Astrophysics—Harvard & Smithsonian
- 4Max-Planck Institute for Astronomy (MPIA)
- 5Universidad de Chile
- 6Joint ALMA Observatory (JAO)
- 7European Southern Observatory (ESO)
- 8Alma Mater Studiorum Università di Bologna
Abstract
Water and methanol are the fundamental constituents of interstellar and cometary ices; understanding their abundances in disks is therefore of high importance to reveal how this ice reservoir evolves across the timeline of star and planet formation. We present Atacama Large Millimeter/submillimeter Array (ALMA) Band 5 line emission observations of water and methanol in the warm Herbig disks of HD 100546 and IRS 48. While the IRS 48 disk is methanol-rich, water vapor is not detected, implying a high methanol-to-water column density ratio of >0.2, possibly reflecting a distinct ice composition. Methanol and water are both detected in the HD 100546 disk, leading to a CH ₃ OH/H ₂ O ratio of ∼0.02, consistent with the median of the cometary distribution and with the lower edge of the distribution of young stellar objects (YSOs). We suggest that the gas-phase methanol-to-water ratio in the HD 100546 disk directly reveals the ice reservoir subsequently sublimated in the warm disk stage. Moreover, we report a methyl formate-to-methanol ratio in the IRS 48 disk of ∼0.2, consistent with the upper edge of the distribution of YSOs. The methyl formate-to-methanol ratio in the HD 100546 disk is ∼2, much higher than in younger and older sources, possibly reflecting a chemical enhancement of gas-phase methyl formate. We additionally constrain non-LTE conditions, optical depths, and emitting regions of the methanol lines in both disks. These results offer a new opportunity to probe the chemical trail of molecular complexity in the intermediate-disk stage, bridging early and late phases of the star and planet formation history.
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BibTeX
@article{rampinelli2026alma,
title = {{An ALMA View on Molecular Complexity: Water, Methanol, and Methyl Formate in the HD 100546 and IRS 48 Disks}},
author = {Luna Rampinelli and Stefano Facchini and Marta De Simone and Margot Leemker and Alice S. Booth and Myriam Benisty and Pietro Curone and Elizabeth Humphreys and Leonardo Testi},
journal = {The Astrophysical Journal},
year = {2026},
month = nov,
doi = {10.3847/1538-4357/aeb11e},
url = {https://iopscience.iop.org/article/10.3847/1538-4357/aeb11e},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - An ALMA View on Molecular Complexity: Water, Methanol, and Methyl Formate in the HD 100546 and IRS 48 Disks
AU - Luna Rampinelli
AU - Stefano Facchini
AU - Marta De Simone
AU - Margot Leemker
AU - Alice S. Booth
AU - Myriam Benisty
AU - Pietro Curone
AU - Elizabeth Humphreys
AU - Leonardo Testi
PY - 2026
DA - 2026/11/06
JO - The Astrophysical Journal
DO - 10.3847/1538-4357/aeb11e
UR - https://iopscience.iop.org/article/10.3847/1538-4357/aeb11e
AB - Water and methanol are the fundamental constituents of interstellar and cometary ices; understanding their abundances in disks is therefore of high importance to reveal how this ice reservoir evolves across the timeline of star and planet formation. We present Atacama Large Millimeter/submillimeter Array (ALMA) Band 5 line emission observations of water and methanol in the warm Herbig disks of HD 100546 and IRS 48. While the IRS 48 disk is methanol-rich, water vapor is not detected, implying a high methanol-to-water column density ratio of >0.2, possibly reflecting a distinct ice composition. Methanol and water are both detected in the HD 100546 disk, leading to a CH ₃ OH/H ₂ O ratio of ∼0.02, consistent with the median of the cometary distribution and with the lower edge of the distribution of young stellar objects (YSOs). We suggest that the gas-phase methanol-to-water ratio in the HD 100546 disk directly reveals the ice reservoir subsequently sublimated in the warm disk stage. Moreover, we report a methyl formate-to-methanol ratio in the IRS 48 disk of ∼0.2, consistent with the upper edge of the distribution of YSOs. The methyl formate-to-methanol ratio in the HD 100546 disk is ∼2, much higher than in younger and older sources, possibly reflecting a chemical enhancement of gas-phase methyl formate. We additionally constrain non-LTE conditions, optical depths, and emitting regions of the methanol lines in both disks. These results offer a new opportunity to probe the chemical trail of molecular complexity in the intermediate-disk stage, bridging early and late phases of the star and planet formation history.
SN - 1538-4357
SN - 0004-637X
ER -