Deuteration Of HC3N And CH3CCH In The Pre-stellar Core L1544

Deuterated molecules are a useful diagnostic tool to probe the evolution and the kinematics in the earliest stages of star formation.

Due to the low temperatures and high densities in the centre of pre-stellar cores, the deuterium fraction is enhanced by several orders of magnitude. We study the distribution of the emission and the deuteration of the two carbon chains HC₃N and CH₃CCH throughout the pre-stellar core L1544.

We analyse emission maps of CH₃CCH, CH₂DCCH, CH₃CCD, HC₃N, HCC¹³CN, and DC₃N, observed with the IRAM 30m single-dish radio telescope. We use non-LTE radiative transfer calculations, combined with chemical modelling of the molecular abundances, to constrain physical parameters of the observed species. Following this, we derive the column density and deuteration maps. We find D-fractions of N(DC₃N)/N(HC₃N)=0.04-0.07, N(CH₂DCCH)/N(CH₃CCH)=0.09-0.15, and N(CH₃CCD)/N(CH₃CCH)=0.07-0.09.

The deuteration of HC₃N appears homogeneous across the core, with widespread D-fraction values above 0.06, tracing intermediate-density gas in the outer layers of the core. CH₃CCD is most efficiently formed in the higher-density regions towards the core centre, while the D-fraction of CH₂DCCH traces a local density enhancement in the north-east of the core, coinciding with the CH₃OH emission peak.

The results suggest that gas-phase reactions dominate the formation and deuteration of both HC₃N and CH₃CCH in L1544, with spatial variations driven by physical structure, density and external radiation. The significantly higher D-fraction of CH₂DCCH compared to CH₃CCD and a tentative gradient with higher values in the north suggest different deuteration mechanisms for the two functional groups. Similarities between the CH₂DCCH emission and CH₂DOH might indicate an additional deuteration pathway of CH₃CCH on the surfaces of dust grains, as observed for H₂CO.

K. Giers, S. Spezzano, Y. Lin, P. Caselli, O. Sipilä
Comments: 15 pages, 13 figures, accepted for publication in A&A
Subjects: Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2601.15791 [astro-ph.GA] (or arXiv:2601.15791v1 [astro-ph.GA] for this version)
https://doi.org/10.48550/arXiv.2601.15791
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Submission history
From: Katharina Giers
[v1] Thu, 22 Jan 2026 09:27:03 UTC (488 KB)
https://arxiv.org/abs/2601.15791
Astrobiology, Astrochemistry,