| Issue |
A&A
Volume 667, November 2022
|
|
|---|---|---|
| Article Number | A119 | |
| Number of page(s) | 32 | |
| Section | Interstellar and circumstellar matter | |
| DOI | https://doi.org/10.1051/0004-6361/202243927 | |
| Published online | 17 November 2022 | |
Tracing the contraction of the pre-stellar core L1544 with HC17O+ J = 1–0 emission★
1
Centre for Astrochemical Studies, Max-Planck-Instiut für extraterrestrische Physik,
Giessenbachstr. 1,
85748
Garching, Germany
e-mail: ferrer@mpe.mpg.de
2
Scuola Normale Superiore,
Piazza dei Cavalieri 7,
56126
Pisa, Italy
3
Dipartimento di Chimica “G. Ciamician”,
via F. Selmi 2,
40126
Bologna, Italy
4
IPR, Université de Rennes,
Bât. 11b, Campus de Beaulieu, 263 avenue du Général Leclerc,
35042
Rennes Cedex, France
Received:
2
May
2022
Accepted:
6
September
2022
Context. Spectral line profiles of several molecules observed towards the pre-stellar core L1544 appear double-peaked. For abundant molecular species this line morphology has been linked to self-absorption. However, the physical process behind the double-peaked morphology for less abundant species is still under debate.
Aims. In order to understand the cause behind the double-peaked spectra of optically thin transitions and their link to the physical structure of pre-stellar cores, we present high-sensitivity and high spectral resolution HC17O+ J =1−0 observations towards the dust peak in L1544.
Methods. We observed the HC17O+(1−0) spectrum with the Institut de Radioastronomie Millimétrique (IRAM) 30 m telescope. By using state-of-the-art collisional rate coefficients, a physical model for the core and the fractional abundance profile of HC17O+, the hyperfine structure of this molecular ion is modelled for the first time with the radiative transfer code loc applied to the predicted chemical structure of a contracting pre-stellar core. We applied the same analysis to the chemically related C17O molecule.
Results. The observed HC17O+(1−0) and C17O(1−0) lines were successfully reproduced with a non-local thermal equilibrium (LTE) radiative transfer model applied to chemical model predictions for a contracting pre-stellar core. An upscaled velocity profile (by 30%) is needed to reproduce the HC17O+(1−0) observations.
Conclusions. The double peaks observed in the HC17O+(1−0) hyperfine components are due to the contraction motions at densities close to the critical density of the transition (~105 cm−3) and to the decreasing HCO+ fractional abundance towards the centre.
Key words: ISM: molecules / ISM: clouds / radio lines: ISM / stars: formation / radiative transfer
© J. Ferrer Asensio et al. 2022
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
This article is published in open access under the Subscribe-to-Open model.
Open Access funding provided by Max Planck Society.
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