{
  "id": "2209.02489",
  "version": "v1",
  "published": "2022-09-06T13:34:17.000Z",
  "updated": "2022-09-06T13:34:17.000Z",
  "title": "Tracing the contraction of the pre-stellar core L1544 with HC$^{17}$O$^+$ $J$ = 1-0 emission",
  "authors": [
    "J. Ferrer Asensio",
    "S. Spezzano",
    "P. Caselli",
    "F. O. Alves",
    "O. Sipilä",
    "E. Redaelli",
    "L. Bizzocchi",
    "F. Lique",
    "A. Mullins"
  ],
  "categories": [
    "astro-ph.GA"
  ],
  "abstract": "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. 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 HC$^{17}$O$^+$ $J =$1-0 observations towards the dust peak in L1544. We observed the HC$^{17}$O$^+$ (1-0) spectrum with the Institut de Radioastronomie Millim\\'etrique (IRAM) 30m telescope. By using new state-of-the-art collisional rate coefficients, a physical model for the core and the fractional abundance profile of HC$^{17}$O$^+$, 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 C$^{17}$O molecule. The observed HC$^{17}$O$^+$(1-0) and C$^{17}$O(1-0) lines have been 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 HC$^{17}$O$^+$(1-0) observations. The double peaks observed in the HC$^{17}$O$^+$(1-0) hyperfine components are due to the contraction motions at densities close to the critical density of the transition ($\\sim$10$^{5}$ cm$^{-3}$) and to the fact that the HCO$^{+}$ fractional abundance decreases toward the centre.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2022-09-06T13:34:17.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "contraction",
      "contracting pre-stellar core",
      "state-of-the-art collisional rate coefficients",
      "pre-stellar core l1544 appear",
      "fractional abundance"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 0,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}