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arXiv 2201.07315astro-ph.SRastro-ph.GA
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0/I类原棕矮星中的氘化学和D/H比

Deuterium chemistry and D/H ratios in Class 0/I proto-brown dwarfs

B. Riaz, W. -F. Thi

备注：
Accepted in MNRAS
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摘要：

我们对16颗0/I类原棕矮星和4颗平类/II类棕矮星中的几种氘代物质进行了首次广泛的观测调查。用IRAM 30米望远镜在DCO $^{+}$（3-2）、DCN（3-2）、DNC（3-2）和N $_{2}$ D $^{+}$（3-2）谱线上进行了观测。DCO $^{+}$ /H $^{13}$ CO $^{+}$、DCN/H $^{13}$ CN和DNC/HN $^{13}$ C比值相对较高，并且分别显示出比DCO $^{+}$ /HCO $^{+}$、DCN/HCN和DNC/HNC比值更窄的范围。衍生自这些分子的原BD的平均D/H比在$\sim$ 0.02-3的范围内。低温气相离子分子氘转移和粮食表面反应需要解释增强氘分馏。原始BD的非常致密和寒冷的内部（$n_{H_{2}}$ $\geq$ 10 $^{6}$ cm $^{-3}$，T $\leq$ 10 K）为这些核心中的有效氘分馏提供了合适的条件。D/H比和CO消耗因子之间没有相关性，除了DCN/HCN比显示出可能由于DCN和HCN分子的峰值发射区域的差异而导致的强反相关性。在$\sim$ 0.002- 40 L $_{\odot}$的较宽范围内，我们发现DCO $^{+}$ /HCO $^{+}$有升高的趋势（r = -0.7）和DCN/HCN（r = -0.6）比值，几乎恒定的DNC/HNC（r = -0.4）和DNC/HN $^{13}$ C（r = -0.1）的比值，与原恒星相比，原BD中较低的N $_{2}$ D $^{+}$ /N $_{2}$ H $^{+}$比值（r = 0.6）。在DCO $^{+}$（3-2）线中，只有一颗II类棕矮星显示出辐射。D/H比值与进化阶段之间没有相关性。

英文摘要：

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.

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