arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 2102.12558astro-ph.SR
收藏

赫比格Ae星HK猎户座的CO与H的$_2$比为$\approx 10^{-5}$

A CO-to-H$_2$ ratio of $\approx 10^{-5}$ towards the Herbig Ae star HK Ori

P. Wilson Cauley, Kevin France, Gregory J. Herzceg, Christopher M. Johns-Krull

备注：
15 pages, 11 figures. Accepted to AAS journals on 02/24/2021
阅读 PDF
arXiv 页面 ↗HTML 原文 ↗

摘要：

对原行星气盘中气体质量的测量构成了估计行星形成条件的基础。其中最重要的限制来自磁盘诊断是了解磁盘化学关键的气相物种的丰度。为此，我们提出了直接的视线测量H $_{2}$和CO，采用紫外吸收光谱从$HST$ -COS表征磁盘的组成，分子激发温度和空间分布在拱星材料周围的赫比格Ae星HK Ori和T Ori。我们观察到HK Ori对CO（N（CO）= 10 $^{15.5}$ cm $^{-2}$ ; T $_{rot}$（CO）= 19 K）和H $_{2}$（N（H $_{2}$）= 10 $^{20.34}$ cm $^{-2}$ ; T $_{rot}$（H $_{2}$）= 141 K）的强吸收，CO/H $_{2}$比（$\equiv$ N（CO）/N（H $_{2}$））= 1.3 $^{+1.6}_{-0.7}$ ~ $\times$ ~10 $^{-5}$。这些测量放置直接的经验约束的CO到H $_{2}$转换因子在磁盘周围的赫比格Ae星的第一次，虽然有不确定性，关于确切的观察几何的磁盘。T Ori的光谱显示CO（N（CO）= 10 $^{14.9}$ cm $^{-2}$ ; T $_{rot}$（CO）= 124 K）吸收。有趣的是，我们没有检测到任何H $_{2}$对这颗恒星的吸收（N（H $_{2}$）$<$ 10 $^{15.9}$ cm $^{-2}$）。我们讨论了在没有H $_{2}$的情况下检测CO的潜在情况，值得进一步研究。在HK Ori附近测得的低丰度比表明，星周气体中的CO显著耗尽，这与最近在原行星盘中进行的其他几次CO丰度测量相符。

英文摘要：

Measurements of gas mass in protoplanetary gas disks form the basis for estimating the conditions of planet formation. Among the most important constraints derived from disk diagnostics are the abundances of gas-phase species critical for understanding disk chemistry. Towards this end, we present direct line-of-sight measurements of H$_{2}$ and CO, employing UV absorption spectroscopy from $HST$-COS to characterize disk composition, molecular excitation temperatures, and spatial distribution in the circumstellar material around the Herbig Ae stars HK Ori and T Ori. We observe strong CO (N(CO) = 10$^{15.5}$ cm$^{-2}$; T$_{rot}$(CO) = 19 K) and H$_{2}$ (N(H$_{2}$) = 10$^{20.34}$ cm$^{-2}$; T$_{rot}$(H$_{2}$) = 141 K) absorption towards HK Ori with a CO/H$_{2}$ ratio ($\equiv$ N(CO)/N(H$_{2}$)) = 1.3$^{+1.6}_{-0.7}$~$\times$~10$^{-5}$. These measurements place direct empirical constraints on the CO-to-H$_{2}$ conversion factor in the disk around a Herbig Ae star for the first time, although there is uncertainty concerning the exact viewing geometry of the disk. The spectra of T Ori show CO (N(CO) = 10$^{14.9}$ cm$^{-2}$; T$_{rot}$(CO) = 124 K) absorption. Interestingly, we do not detect any H$_{2}$ absorption towards this star (N(H$_{2}$) $<$ 10$^{15.9}$ cm$^{-2}$). We discuss a potential scenario for the detection of CO without H$_{2}$, which deserves further investigation. The low abundance ratio measured around HK Ori suggests significant depletion of CO in the circumstellar gas, which conforms with the handful of other recent CO abundance measurements in protoplanetary disks.

机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。

↑