{
  "id": "2201.07315",
  "version": "v1",
  "published": "2022-01-18T21:19:23.000Z",
  "updated": "2022-01-18T21:19:23.000Z",
  "title": "Deuterium chemistry and D/H ratios in Class 0/I proto-brown dwarfs",
  "authors": [
    "B. Riaz",
    "W. -F. Thi"
  ],
  "comment": "Accepted in MNRAS",
  "categories": [
    "astro-ph.GA",
    "astro-ph.SR"
  ],
  "abstract": "We have conducted the first extensive observational survey of several deuterated species in 16 Class 0/I proto-brown dwarfs (proto-BDs) and 4 Class Flat/Class II brown dwarfs. Observations were obtained with the IRAM 30m telescope in the DCO$^{+}$ (3-2), DCN (3-2), DNC (3-2), and N$_{2}$D$^{+}$ (3-2) lines. The DCO$^{+}$/H$^{13}$CO$^{+}$, DCN/H$^{13}$CN, and DNC/HN$^{13}$C ratios are comparatively higher and show a narrower range than the DCO$^{+}$/HCO$^{+}$, DCN/HCN, and DNC/HNC ratios, respectively. The mean D/H ratios for the proto-BDs derived from these molecules are in the range of $\\sim$0.02-3. Both low-temperature gas-phase ion-molecule deuteron transfer and grain surface reactions are required to explain the enhanced deuterium fractionation. The very dense and cold ($n_{H_{2}}$ $\\geq$10$^{6}$ cm$^{-3}$, T $\\leq$10 K) interior of the proto-BDs provide the suitable conditions for efficient deuterium fractionation in these cores. There is no correlation between the D/H ratios and the CO depletion factor, with the exception of the DCN/HCN ratios that show a strong anti-correlation possibly due to the difference in the peak emitting regions of the DCN and HCN molecules. Over a wide range in the bolometric luminosities spanning $\\sim$0.002--40 L$_{\\odot}$, we find a trend of higher DCO$^{+}$/HCO$^{+}$ (r = -0.7) and DCN/HCN (r = -0.6) ratios, nearly constant DNC/HNC (r = -0.4) and DNC/HN$^{13}$C (r = -0.1) ratios, lower N$_{2}$D$^{+}$/N$_{2}$H$^{+}$ ratios (r = 0.6) in the proto-BDs compared to protostars. Only one Class II brown dwarf shows emission in the DCO$^{+}$ (3-2) line. No correlation is seen between the D/H ratios and the evolutionary stage.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2022-01-18T21:19:23.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "d/h ratios",
      "proto-brown dwarfs",
      "deuterium chemistry",
      "low-temperature gas-phase ion-molecule deuteron transfer",
      "grain surface reactions"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 0,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}