1. Tracing the contraction of the pre-stellar core L1544 with HC17O+ J = 1–0 emission
- Author
-
Asensio, J. Ferrer, Spezzano, S., Caselli, P., Alves, F. O., Sipilä, O., Redaelli, E., Bizzocchi, L., Lique, F., Mullins, A., Max-Planck-Institut für Extraterrestrische Physik (MPE), Scuola Normale Superiore di Pisa (SNS), Institut de Physique de Rennes (IPR), Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS), and J.F.A., S.S., P.C., F.O.A., O.S, E.R. and L.B. gratefully acknowledge the support of the Max Planck Society.
- Subjects
[PHYS]Physics [physics] ,radio lines: ISM ,stars: formation ,radiative transfer ,Space and Planetary Science ,Astrophysics of Galaxies (astro-ph.GA) ,FOS: Physical sciences ,Astronomy and Astrophysics ,Quantum dynamics ,Molecular physics ,Astrophysics - Astrophysics of Galaxies ,ISM: clouds ,ISM: molecules - Abstract
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.
- Published
- 2022