arXiv 1709.047262017-09-14astro-ph.SRastro-ph.GA

HH212原恒星周围太阳系尺度的氘代甲醇

Deuterated methanol on Solar System scale around the HH212 protostar

E. Bianchi, C. Codella, C. Ceccarelli, V. Taquet, S. Cabrit, F. Bacciotti, R. Bachiller, E. Chapillon, F. Gueth, A. Gusdorf, B. Lefloch, S. Leurini, L. Podio, K… 展开作者

E. Bianchi, C. Codella, C. Ceccarelli, V. Taquet, S. Cabrit, F. Bacciotti, R. Bachiller, E. Chapillon, F. Gueth, A. Gusdorf, B. Lefloch, S. Leurini, L. Podio, K. L. J. Rygl, B. Tabone, M. Tafalla

备注：: Astronomy & Astrophysics Letter, in press
发表信息：: A&A 606, L7 (2017)
DOI：: 10.1051/0004-6361/201731404

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摘要：

背景：甲醇被认为主要是在星前阶段形成的，它的氘代形式保留了那个时期的条件记忆。由于ALMA提供的高角分辨率和灵敏度的独特组合，我们希望测量0级原恒星周围行星形成区域的甲醇氘代，并了解其起源。目标：我们绘制了猎户座B中HH 212系统内部区域（$\sim$ 100 au）的$^{13}$ CH $_3$ OH和CH $_2$ DOH分布图。为此，我们在波段7中使用ALMA周期1和周期4观测，角分辨率低至$\sim$ 0.15 $"$。结果如下：我们探测到6条$^{13}$ CH $_3$ OH谱线和13条CH $_2$ DOH谱线，其上能级能量可达438 K（温度单位）。我们推导出的旋转温度为（171 $\pm$ 52）K和柱密度分别为7 $\times$ 10 $^{16}$ cm $^{-2}$（$^{13}$ CH $_3$ OH）和1 $\times$ 10 $^{17}$ cm $^{-2}$（CH $_2$ DOH）。因此，D/H比为（2.4 $\pm$ 0.4）$\times$ 10 $^{-2}$，这个数值比先前使用单碟望远镜对英仙座原恒星测量的数值低了一个数量级。我们的研究结果与猎户座B的尘埃温度高于英仙座云的尘埃温度是一致的。发射是跟踪旋转结构延伸到45 AU从喷流轴和拉长90 AU沿喷流轴。到目前为止，所观察到的发射的起源似乎与吸积盘有关。然而，只有更高的空间分辨率的测量，将能够解开不同的可能的情况：磁盘风，磁盘大气，或吸积冲击。

英文摘要：

Context: Methanol is thought to be mainly formed during the prestellar phase and its deuterated form keeps memory of the conditions at that epoch. Thanks to the unique combination of high angular resolution and sensitivity provided by ALMA, we wish to measure methanol deuteration in the planet formation region around a Class 0 protostar and to understand its origin. Aims: We mapped both the $^{13}$CH$_3$OH and CH$_2$DOH distribution in the inner regions ($\sim$100 au) of the HH212 system in Orion B. To this end, we used ALMA Cycle 1 and Cycle 4 observations in Band 7 with angular resolution down to $\sim$0.15$"$. Results: We detected 6 lines of $^{13}$CH$_3$OH and 13 lines of CH$_2$DOH with upper level energies up to 438 K in temperature units. We derived a rotational temperature of (171 $\pm$ 52) K and column densities of 7$\times$10$^{16}$ cm$^{-2}$ ($^{13}$CH$_3$OH) and 1$\times$10$^{17}$ cm$^{-2}$ (CH$_2$DOH), respectively. Consequently, the D/H ratio is (2.4 $\pm$ 0.4)$\times$10$^{-2}$, a value lower by an order of magnitude with respect to what was previously measured using single dish telescopes toward protostars located in Perseus. Our findings are consistent with the higher dust temperatures in Orion B with respect to that derived for the Perseus cloud. The emission is tracing a rotating structure extending up to 45 au from the jet axis and elongated by 90 au along the jet axis. So far, the origin of the observed emission appears to be related with the accretion disk. Only higher spatial resolution measurements however, will be able to disentangle between different possible scenarios: disk wind, disk atmosphere, or accretion shocks.

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