年轻恒星PDS 70周围可能正在升华的系外彗星
Potential sublimating exocomets around the young star PDS 70
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中文总结 AI 辅助
该研究通过HARPS光谱发现PDS 70的中性钠可变吸收线，推断其源于高椭圆轨道凌星星子的升华，认为这类系外彗星可能为PDS 70内区提供水。
中文摘要 AI 辅助
詹姆斯·韦布空间望远镜（JWST）的最新观测表明，原恒星PDS 70的气体盘内区存在水，但该水的起源尚不明确。本文报告在PDS 70存档的高精度径向速度行星搜索器（HARPS）光谱中发现了中性钠的可变吸收线，这些吸收线在每日的振幅、数量和视向速度上表现出强烈且随机的变化。测量显示该气体倾向于光学厚，且部分覆盖恒星盘，意味着这种高速运动的气体通常在空间上受限。我们对这些吸收线的起源提出了多个假设，最终得出结论：观测到的钠很可能源于沿高椭圆轨道凌星的星子的升华，类似其他太阳系外系统中观测到的系外彗星现象。这些正在升华的系外彗星可能对PDS 70系统内类地行星形成区域的水的来源有贡献。
英文摘要
Recent observations by the James Webb Space Telescope (JWST) have indicated the presence of water in the inner regions of the disc around the young protostar PDS 70, but the origin of this water remains unclear. Here we report the discovery of variable absorption lines of neutral sodium in archival High Accuracy Radial velocity Planet Searcher (HARPS) spectra of PDS 70. These lines vary strongly and stochastically on a daily basis, in amplitude, number, and radial velocity. Our measurements indicate that this gas tends to be optically thick, and partially cover the stellar disc, meaning this fast-moving gas is often spatially confined. We explore several hypotheses for the origin of these lines, and conclude that a likely source of the observed sodium is sublimation of planetesimals that transit the star on highly elliptical orbits, reminiscent of the exocomet phenomenon seen in other seen in other extrasolar systems. These sublimating exocomets could play a role in sourcing the previously observed water in the inner, terrestrial-planet forming region of the PDS 70 system.
