太空生命种子（SOLIS）。III。放大前恒星核心L1544的甲醇峰
Seeds of Life in Space (SOLIS). III. Zooming into the methanol peak of the pre-stellar core L1544
摘要：
在前星核L1544附近，甲醇（CH $_3$ OH）的辐射在核中心周围形成一个不对称的环，其中CH $_3$ OH主要以固体形式存在，在尘埃连续谱峰的东北方向有一个清晰的4000 au的峰。作为NOEMA大型项目SOLIS（太空生命种子）的一部分，CH $_3$ OH峰已被空间解析，以研究其运动学和物理结构，并调查局部增强背后的原因。我们发现，甲醇排放分布在一个脊平行于主轴的致密核心。中心速度增加约0.2 km s $^{-1}$，速度频散由亚音速向跨音速逐渐增大，速度场也呈现复杂结构。这可能是物质在核心上的缓慢堆积或两个细丝的相互作用的迹象，产生了缓慢的冲击。我们测量的旋转温度，并表明，甲醇是在当地的热力学平衡（LTE）仅接近尘埃峰，在那里它是显着耗尽。CH $_3$ OH柱密度，$N_{tot}({\rm CH_3OH})$，配置文件已被推导出与非LTE辐射转移建模，并与化学模型的静态核心。测得的$N_{tot}({\rm CH_3OH})$配置文件与模型预测一致，但总柱密度比模型预测的低一个数量级，这表明模型中采用的反应解吸或原子氢隧道效应的效率可能被高估;或者需要一个进化模型来更好地再现甲醇丰度。
英文摘要：
Towards the pre-stellar core L1544, the methanol (CH$_3$OH) emission forms an asymmetric ring around the core centre, where CH$_3$OH is mostly in solid form, with a clear peak 4000~au to the north-east of the dust continuum peak. As part of the NOEMA Large Project SOLIS (Seeds of Life in Space), the CH$_3$OH peak has been spatially resolved to study its kinematics and physical structure and to investigate the cause behind the local enhancement. We find that methanol emission is distributed in a ridge parallel to the main axis of the dense core. The centroid velocity increases by about 0.2~km~s$^{-1}$ and the velocity dispersion increases from subsonic to transonic towards the central zone of the core, where the velocity field also shows complex structure. This could be indication of gentle accretion of material onto the core or interaction of two filaments, producing a slow shock. We measure the rotational temperature and show that methanol is in local thermodynamic equilibrium (LTE) only close to the dust peak, where it is significantly depleted. The CH$_3$OH column density, $N_{tot}({\rm CH_3OH})$, profile has been derived with non-LTE radiative transfer modelling and compared with chemical models of a static core. The measured $N_{tot}({\rm CH_3OH})$ profile is consistent with model predictions, but the total column densities are one order of magnitude lower than those predicted by models, suggesting that the efficiency of reactive desorption or atomic hydrogen tunnelling adopted in the model may be overestimated; or that an evolutionary model is needed to better reproduce methanol abundance.
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