# High sensitivity molecular line observations towards the L1544 pre-stellar core challenge current models

## TL;DR

High-sensitivity molecular line observations of the L1544 pre-stellar core reveal discrepancies with existing models, highlighting the need for improved chemical networks and better understanding of core dynamics.

## Contribution

This study provides detailed radiative transfer modeling of multiple molecular lines towards L1544, challenging current chemical models and emphasizing the importance of S-depletion processes.

## Key findings

- Different molecular transitions trace distinct gas dynamics.
- Current chemical models poorly reproduce sulphur chemistry.
- Single transition modeling is insufficient for accurate abundance profiles.

## Abstract

The increased sensitivity and spectral resolution of observed spectra towards the pre-stellar core L1544 are challenging the current physical and chemical models. With the aim of further constraining the structure of L1544 as well as assessing the completeness of chemical networks, we turn to radiative transfer modelling of observed molecular lines towards this source. We obtained high-sensitivity and high-spectral resolution observations of HCO+ (J = 1 - 0), CS (J = 2 - 1), C34S (J = 2 - 1), H2CO (J ,Ka,Kc = 2,1,2 - 1,1,1), c-C3H2 (J,Ka,Kc = 2,1,2 - 1,0,1), SO (N,J = 2,3 - 1,2) and 34SO (N,J = 2,3 - 1,2) with the IRAM 30m telescope towards the dust peak of L1544. A non-Local Thermodynamic Equilibrium radiative transfer code is coupled to the Markov Chain Monte Carlo method to model the observations. We find that with just one transition for each isotope, the modelling cannot find a global minimum that fits the observations. The derived fractional abundance profiles are compared to those computed with chemical models. The observed transitions trace gas components with distinct dynamics at different distances along the radius of the core. Moreover, the results evidence a poor reproduction of sulphur chemistry by chemical modelling and stresses the need to include a more consistent S-depletion process to accurately reproduce the S-chemistry towards dense cores.