Tracing The Sulfur Depletion In Starless And Pre-stellar Cores

Sulfur is one of the most abundant elements in the Universe, yet the sulfur budget inferred from the observed sulfur-bearing molecules in dense cores is significantly lower than expected.

Starless and pre-stellar cores represent the earliest stages of star formation and provide a laboratory for studying the physical and chemical processes that cause sulfur depletion. We aim to constrain sulfur chemistry in dense cores by measuring abundances of sulfur-bearing molecules and how they reflect core evolution and environmental effects. We observed nine cores in the Taurus Molecular Cloud, targeting 13 sulfur-bearing molecules, including CS, CCS, C₃S, OCS, SO, SO₂, H₂CS, and isotopologs.

Molecular abundances and six abundance ratios were compared to three evolutionary tracers: H2 column density, N₂D⁺/N₂H⁺, and the CO depletion factor. We also compared observations with 0D chemical models with different initial sulfur abundances. We find variations in abundances across cores.

L1517B exhibits low abundances and a high depletion factor, whereas L1495B shows enhanced levels in oxygen-bearing species within the L1495 filament. Ratios tracing carbon- and oxygen-bearing species (CCS/³⁴SO and C³⁴S/³⁴SO) decrease with increasing H2 column density and N₂D⁺/N₂H⁺ ratio. Other species and ratios show weak or no correlation with tracers.

Models reproduce OCS, H₂CS, and HDCS reasonably well, but not all species simultaneously, especially between carbon- and oxygen-bearing molecules. The variations and lack of consistent correlations suggest that a single evolutionary parameter cannot describe sulfur chemistry and that the local environmental conditions strongly influence the observed abundances.

Reproducing the full sample of sulfur-bearing molecules would require improved chemical networks and models that account for the core’s physical structure.

L. Schöller, S. Spezzano, O. Sipilä, E. I. Makarenko, P.Caselli, H. A. Bunn, S. S. Jensen

Comments: Accepted for publication in A&A
Subjects: Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2605.13635 [astro-ph.GA] (or arXiv:2605.13635v1 [astro-ph.GA] for this version)
https://doi.org/10.48550/arXiv.2605.13635
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Submission history
From: Laura Schöller
[v1] Wed, 13 May 2026 15:02:07 UTC (4,320 KB)
https://arxiv.org/abs/2605.13635

Astrobiology, Astrochemistry,