来自一颗静止红矮星的相干射电辐射指示恒星-行星相互作用
Coherent radio emission from a quiescent red dwarf indicative of star-planet interaction
摘要：
低频（$ν\lesssim 150\,$ MHz）恒星射电辐射预计起源于外日冕，其高度与恒星半径相当或大于恒星半径。这种来自太阳的辐射被用来研究日冕结构，质量喷射，行星周围的空间天气条件（Schwenn 2006）。其他恒星低频发射的探测器只探测到一颗活跃的耀斑星（Lynch et al. 2017），这并不能代表更广泛的恒星星族。在这里，我们报告的低频无线电发射的检测从一个静止的恒星，GJ 1151-在银河系中最常见的恒星类型（红矮星或光谱类M）的成员。发射的特征与行星极光发射的特征相似（Zarka 1998年）（例如木星的十米波发射），表明日冕结构由等离子体密度低的全球磁层主导。我们的研究结果表明，为无线电极光提供动力的大规模电流在质量和大气成分的巨大范围内运作，从类地行星到主序星。GJ 1151的缓慢自转并不能产生坡印廷通量，但它的磁层等离子体与短周期系外行星的次阿尔夫文相互作用可能产生坡印廷通量。发射特性与理论预期一致（Zarka 2007; Lanza 2009; Saur et al. 2013; Turnpenney et al. 2018），与地球大小的行星在$\sim 1-5$一天的轨道上相互作用。
英文摘要：
Low frequency ($ν\lesssim 150\,$MHz) stellar radio emission is expected to originate in the outer corona at heights comparable to and larger than the stellar radius. Such emission from the Sun has been used to study coronal structure, mass ejections, space-weather conditions around the planets (Schwenn 2006). Searches for low-frequency emission from other stars have only detected a single active flare-star (Lynch et al. 2017) that is not representative of the wider stellar population. Here we report the detection of low-frequency radio emission from a quiescent star, GJ 1151--- a member of the most common stellar type (red dwarf or spectral class M) in the Galaxy. The characteristics of the emission are similar to those of planetary auroral emissions (Zarka 1998) (e.g. Jupiter's decametric emission), suggesting a coronal structure dominated by a global magnetosphere with low plasma density. Our results show that large-scale currents that power radio aurorae operate over a vast range of mass and atmospheric composition, ranging from terrestrial planets to main-sequence stars. The Poynting flux required to produce the observed radio emission cannot be generated by GJ 1151's slow rotation, but can originate in a sub-Alfvénic interaction of its magnetospheric plasma with a short-period exoplanet. The emission properties are consistent with theoretical expectations (Zarka 2007; Lanza 2009; Saur et al. 2013; Turnpenney et al. 2018) for interaction with an Earth-size planet in a $\sim 1-5$ day-long orbit.
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