中等质量（IM）原恒星的解剖：IC1396N的化学分化
Dissecting an intermediate-mass (IM) protostar: Chemical differentiation in IC1396N
摘要：
我们利用PdBI对中等质量原恒星IRAS 21391 +5802（IC 1396 N）进行了3.1mm连续谱线和N_2H + 1-0、CH_3CN 5_k-4_k和~（13）CS 2-1谱线的高角分辨率（1.4”）观测。此外，我们将PdBI图像与之前的BIMA（1.2mm和3.1mm的连续数据）和单碟（N2 H + 1-0）数据合并，以全面描述该区域。结合我们的数据与BIMA和30米的数据表明，双极外流相关联的已完全侵蚀了初始的分子球。1.2mm和3.1mm的连续辐射沿流出轴延伸，追踪双锥腔的热壁。然而，大多数分子气体位于垂直于流出方向的细长特征中。分子环上存在强烈的化学差异，内部区域不存在N2 H + 1-0发射，这种化学差异可以根据不同的气体动力学温度来理解。在20 ~ 100 K的温度范围内，[CH_3CN]/[N_2H ~+]比随气体温度的升高而增加5个数量级。IRAM 2A是最大的原恒星核心，它的CH 3CN丰度与热Corinos中发现的相似，低于IM和高质量热核心的预期。这可能表明IRAM 2A是一颗低质量或至多是Herbig Ae星（IRAM 2A），而不是大质量Be星的前身。或者，低CH 3CN丰度也可能是IRAM 2A是已经形成小的光解离区域（PDR）的0/I类过渡物体的结果。
英文摘要：
We have carried out high-angular resolution (1.4") observations in the continuum at 3.1mm and in the N2H+ 1-0, CH3CN 5_k-4_k and 13CS 2-1 lines using the Plateau de Bure Interferometer (PdBI) towards the intermediate mass (IM) protostar IRAS21391+5802 (IC1396N). In addition, we have merged the PdBI images with previous BIMA (continuum data at 1.2mm and 3.1mm) and single-dish (N2H+ 1-0) data to have a comprehensive description of the region. The combination of our data with BIMA and 30m data show that the bipolar outflow associated has completely eroded the initial molecular globule. The 1.2mm and 3.1mm continuum emissions are extended along the outflow axis tracing the warm walls of the biconical cavity. Most of the molecular gas, however, is located in an elongated feature in the direction perpendicular to the outflow. A strong chemical differentiation is detected across the molecular toroid, with the N2H+ 1-0 emission absent in the inner region.This chemical differentiation can be understood in terms of the different gas kinetic temperature. The [CH3CN]/[N2H+] ratio increases by 5 orders of magnitude with gas temperature, for temperatures between 20K and 100K. The CH3CN abundance towards IRAM 2A, the most massive protostellar core, is similar to that found in hot corinos and lower than that expected towards IM and high mass hot cores. This could indicate that IRAM 2A is a low mass or at most Herbig Ae star (IRAM 2A) instead of the precursor of a massive Be star. Alternatively, the low CH3CN abundance could also be the consequence of IRAM 2A being a Class 0/I transition object which has already formed a small photodissociation region (PDR).
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