据信，水、氨和甲醛（H2 CO）等物质的邻位与对位（o/p）比编码了有关分子形成历史的信息。因此，对原行星盘中的o/p比的测量可以用来限制它们的物理和化学历史。我们提出了第一次测量的H2 CO o/p比在原行星盘，使用三个ortho和两个para线观察到的亚毫米阵列（SMA）结合一个高分辨率的测量一个单一的H2 CO线ALMA对磁盘周围的赫比格Ae星HD 163296。我们发现盘平均H_2CO的o/p比为1.8-2.8（取决于假设的盘结构），对应于11-22 K的自旋温度。我们还从三条正交线的通量比导出了24 K的转动温度。所观察到的空间分布，如ALMA，以及旋转温度和O/P比，在大尺度的SMA是最敏感的，是一致的低温形成途径，最有可能的晶粒表面化学，在这个磁盘中的H2 CO。
英文摘要：
Ortho-to-para (o/p) ratios of species like water, ammonia and formaldehyde (H2CO) are believed to encode information about the formation history of the molecule. Measurements of o/p ratios in protoplanetary disks could thus be used to constrain their physical and chemical histories. We present the first measurement of the H2CO o/p ratio in a protoplanetary disk, using three ortho and two para lines observed with the Sub-millimeter Array (SMA) combined with one highly resolved measurement of a single H2CO line with ALMA toward the disk around Herbig Ae star HD 163296. We find a disk-averaged H2CO o/p ratio of 1.8-2.8 (depending on the assumed disk structure), corresponding to a spin temperature of 11-22 K. We also derive a rotational temperature of 24 K from the flux ratio of the three ortho lines. The observed spatial distribution, as seen by ALMA, as well as the rotational temperature and the o/p ratio, at the large scales the SMA is most sensitive to, are consistent with a low-temperature formation pathway, most likely grain surface chemistry, of H2CO in this disk.
Ortho-Para Chemistry of H2CO in the Protoplanetary Disk TW Hya
Université Grenoble Alpes（格勒诺布尔阿尔卑斯大学）；CNRS（法国国家科学研究中心）；Korea Astronomy and Space Science Institute（韩国天文学与空间科学研究院）；National Astronomical Observatory of Japan（日本国立天文台）；RIKEN Pioneering Research Institute（理化学研究所前沿研究机构）
We report the first detection of the molecule cyanomethyl, CH$_2$CN, in a protoplanetary disk. Until now, CH$_2$CN had only been observed at earlier evolutionary stages, in the giant molecular clouds TMC-1 and Sgr 2, and the prestellar core L1544. We detect six transitions of ortho-CH$_2$CN towards the disk around nearby T Tauri star TW Hya. An excitation analysis reveals that the disk-averaged column density, $N$, for ortho-CH$_2$CN is $(6.3\pm 0.5)\times10^{12}$ cm$^{-2}$, which is rescaled to reflect a 3:1 ortho-para ratio, resulting in a total column density, $N_{\rm tot}$, of $(8.4\pm 0.7…
Dust continuum emission and the upper limit fluxes of sub-millimeter water lines of the protoplanetary disk around HD 163296 observed by ALMA
本文利用阿塔卡玛大型毫米/亚毫米波阵列（ALMA），分析了Herbig Ae星HD 163296周围原行星盘的亚毫米波正H $_{2}$ $^{16}$ O 321 GHz、paraH $_{2}$ $^{18}$ O 322 GHz和HDO 335 GHz谱线的上限通量。这些水线被认为是最好的候选亚毫米线定位的H $_{2}$ O雪线的位置，在我们以前的模式计算的基础上。我们比较了上限通量与我们的模式计算的值与尘埃排放，我们约束的线发射区域和尘埃不透明度的观测。我们的结论是，如果高水蒸气丰度区的外缘和水雪线的位置也超过8 au，则毫米尘埃不透明度值将大于2.0 cm $^{2}$ g $^{-1}$。此外，如果mm尘埃不透明度为2.0 cm $^{2}$ g $^{-1}$，则水雪线的位置将在20 au以内。未来的观测尘埃连续辐射在更高的角分辨率和亚毫米水线与更长的观测时间需要澄清的详细结构和位置的H $_{2}$ O雪线在磁盘中面。
The role of non-ideal magnetohydrodynamics has been proven critical during the formation of the protoplanetary disk, particularly in regulating its size. We provide a simple model to predict the disk size under the interplay among the ambipolar diffusion, the Hall effect, and the Ohmic dissipation. The model predicts a small disk size of around 20 AU, that depends only sub-linearly on disk parameters, for a wide range of initial conditions of sub-Solar mass and moderate magnetization. It is able to explain phenomena manifested in existing numerical simulations, including the bimodal disk behav…
Scattering of re-emitted flux is considered to be at least partially responsible for the observed polarisation in the (sub-)millimetre wavelength range of several protoplanetary disks. Although the degree of polarisation produced by scattering is highly dependent on the dust model, early studies investigating this mechanism relied on the assumption of single grain sizes and simple density distribution of the dust. However, in the dense inner regions where this mechanism is usually most efficient, the existence of dust grains with sizes ranging from nanometres to millimetres has been confirmed.…
