中国西南天文研究所基于大科学装置LAMOST发现S147尘埃云
Discovery of S147 dust cloud from the LAMOST Spectroscopic Surveys
近日，云南大学中国西南天文研究所陈丙秋博士和刘晓为教授基于LAMOST的海量巡天数据，对近邻超新星遗迹S147进行了详细研究，首次发现了与S147成协的尘埃云，并将其命名为S147尘埃云。
质量超过8个太阳质量的大质量恒星在演化晚期中心核能耗尽后，将发生塌缩并引发超新星爆炸。爆炸抛出的物质向外极速膨胀并与周边星际介质发生作用，形成延展的超新星遗迹。超新星遗迹包含了超新星爆发释放的巨大能量和大量重元素（天文学家将重于氢、氦的元素统称为重元素或金属元素），对星际介质的物理、化学性质产生重要影响，是恒星形成及星系化学动力学演化的重要驱动因素。事实上，有关超新星遗迹的众多观测现象都源于其与不均匀星周/星际介质间的相互作用。不仅如此，超新星遗迹还被认为是宇宙高能粒子（如宇宙线）的重要加速场所，超新星遗迹及其与星际介质相互作用的研究因此成为阐释宇宙高能粒子起源的重要一环。
超新星遗迹S147（G180.0-1.7）是银河系反银心方向一个年老的壳状超新星遗迹，角直径约200角分，是研究超新星遗迹及其与星际介质作用的良好实验室。2012年，天文学家利用费米伽马射线太空望远镜发现在S147区域有一个延展的伽马射线源可能与超新星遗迹成协，表明S147可能正在与其周边大型分子云相互作用。然而传统的、基于一氧化碳（CO）分子辐射的搜寻并没有找到与该超新星遗迹成协并与之发生相互作用的分子云。云南大学中国西南天文研究所团组基于盱眙反银心方向测光巡天数据，结合2MASS和WISE红外测光巡天数据以及LAMOST大规模银河系光谱巡天数据，精确测量和描绘了S147区域星际尘埃的三维分布，首次发现了与S147成协的尘埃云。该尘埃云的形态与伽马射线源十分一致，从而在观测上证实了该超新星遗迹正在与周边分子云发生相互作用。分析还给出了S147的距离约3800光年。这一估计与国际上基于其它分析方法得到的最新结果非常一致。
图. 与超新星遗迹S147成协的尘埃云分布图（红色等高线），图的背景是S147的Hα发射线图。
本项工作在国际上开辟了一条通过测量和分析星际尘埃三维消光分布来搜寻与超新星遗迹成协分子云的新路径。相较于传统的基于CO分子辐射的方法，该方法避免了CO分子光解效应及探测极限带来的局限，可以有效地搜寻和发现与超新星遗迹产生相互作用的分子云。此外，该方法克服了银河系外区域分子云距离难以测定的困难，能够给出分子云的精确距离。本项工作已被国际专业学术期刊《皇家天文学月刊》（Monthly Notices of the Royal Astronomical Society）接受，将于近期发表（预印本文库链接https://arxiv.org/abs/1709.01065）。
Supernova (SN) explosion is one of the most energetic events in a galaxy. It usually occurs near its maternal molecular cloud (MC). As such, MCs generally play a critical role in the evolution of the supernova remnants (SNRs). There are now ~300 SNRs identified in our Milky Way. About 70 of them are known to be or possibly be interacting with MCs. And SNR S147 (G180.0--1.7; hereafter referred to as S147), is claimed to be not one of those MC-interacting SNRs.
S147 is one of the most evolved SNRs in the Milky Way. It falls near the Galactic anticentre and has a large angular size of about 200. It shows a complex network of long filaments in the optical and radio bands. The pulsar PSR J0538+2817, located near the center of S147, is suggested to be plausibly associated with S147. X-ray emission has been detected from the pulsar by ROSAT All Sky Survey. In gamma-ray, an extended source is found to coincide with S147. The gamma-ray emission surrounding the SNR is expected to be primarily emitted via the pion decay produced by the interaction between CR protons and dense medium (p–p interaction), while the leptonic origin is unlikely for such an old SNR.
We present a three-dimensional (3D) extinction analysis in the region towards the SNR S147 using multiband photometric data from the Xuyi Schmidt Telescope Photometric Survey of the Galactic Anticentre (XSTPS-GAC), 2MASS and WISE. We isolate a previously unrecognized dust structure likely to be associated with SNR S147. The structure, which we term as ‘S147 dust cloud’, is estimated to have a distance d = 1.22 +/- 0.21 kpc, consistent with the conjecture that S147 is associated with pulsar PSR J0538 + 2817. The cloud includes several dense clumps of relatively high extinction that locate on the radio shell of S147 and coincide spatially with the CO and gamma-ray emission features. We conclude that the usage of CO measurements to trace the SNR associated MCs is unavoidably limited by the detection threshold, dust depletion and the difficulty of distance estimates in the outer Galaxy. 3D dust extinction mapping may provide a better way to identify and study SNR–MC interactions.
