An ALMA view on molecular complexity: water, methanol, and methyl formate in the HD 100546 and IRS 48 disks
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 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 >0.2, possibly reflecting a distinct ice composition. Methanol and water are both detected in the HD 100546 disk, leading to a CH3OH/H2O ratio of ~0.02, consistent with the median of the cometary distribution and with the lower edge of the distribution of Young Stellar Objects. 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 Young Stellar Objects. 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
@misc{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},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.22503},
eprint = {2610.22503},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.22503},
note = {CC BY 4.0},
}
RIS
TY - UNPB
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 - 2026/10/15
PB - arXiv
DO - 10.48550/arxiv.2610.22503
UR - https://arxiv.org/abs/2610.22503
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 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 >0.2, possibly reflecting a distinct ice composition. Methanol and water are both detected in the HD 100546 disk, leading to a CH3OH/H2O ratio of ~0.02, consistent with the median of the cometary distribution and with the lower edge of the distribution of Young Stellar Objects. 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 Young Stellar Objects. 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.
ER -