标题： 3I/ATLAS星际物体的初始VLT/MUSE光谱观测 显示英文标题

标题： Initial VLT/MUSE spectroscopy of the interstellar object 3I/ATLAS

摘要： 星际彗星3I/ATLAS是第三个被发现的星际物体。 近日点前的测量提供了一个独特的机会来研究它的活动和成分，这些可能在接下来的几个月中因受热而发生变化。 我们提供了光学光谱观测的初步基准，这些观测是在发现后仅两天使用VLT上的MUSE仪器于2025年7月3日进行的，当时3I距离太阳4.47天文单位，距离地球3.46天文单位。 这些观测证实了3I的彗星性质，并揭示了一个红色的彗发，其光谱斜率为$(18\pm4)\%/1000$~\AA ，比大多数太阳系彗星更红，但与一些太阳系海王星外天体或半人马小行星的表面颜色相似。 我们搜索了C$_2$、NH$_2$、CN和[OI]的气体发射，但未检测到，这与在这一日心距离下太阳系彗星的挥发性物质未检测到一致。 目前，彗发似乎完全是尘埃组成的。 随着3I逐渐接近太阳，未来的观测将提供一个无价的机会来观察其活动性的演变，研究其成分，测试星际物体种群模型的预测，并将3I与太阳系彗星进行比较。 显示英文摘要

摘要： The interstellar comet 3I/ATLAS is only the third interstellar object to be discovered. Pre-perihelion measurements provide a unique opportunity to study its activity and composition, which may alter as it is heated in the coming months. We provide an initial baseline from optical spectroscopic observations obtained only two days after discovery, using the MUSE instrument on the VLT on 2025 July 3, while 3I was at 4.47 au from the Sun and 3.46 au from the Earth. These observations confirm the cometary nature of 3I, and reveal a red coma with a spectral slope of $(18\pm4)\%/1000$~\AA, redder than most Solar System comets but similar to the surface colour of some Solar System Trans-Neptunian Objects or Centaurs. We searched for but did not detect gas emission from C$_2$, NH$_2$, CN, and [OI], which is consistent with volatile non-detections for Solar System comets at this heliocentric distance. At present, the coma appears entirely dusty. Future observations of 3I as it comes closer to the Sun will provide an invaluable opportunity to witness the evolution of its activity, study its composition, test predictions of interstellar object population models, and compare 3I to Solar System comets.