标题： 斯特芬森2 DFK 52：在大质量恒星团RSGC2中发现一种奇特的红超巨星 显示英文标题

标题： Stephenson 2 DFK 52: Discovery of an exotic red supergiant in the massive stellar cluster RSGC2

摘要： 阿塔卡马大型毫米/亚毫米阵列（ALMA）在1.3毫米处的观测最近揭示了DFK 52周围恒星环境的惊人复杂性，DFK 52是一个位于斯蒂芬森2大质量开放星团中的红超巨星（RSG）。 我们通过研究其连续谱、$^{12}$CO、$^{13}$CO和SiO旋转线的周围恒星辐射，提供了对该恒星质量损失特性的初步表征。 我们发现DFK 52被一个极其大的流出物（半径高达50,000天文单位）包围，其分子和尘埃辐射中显示出复杂的形态。 周围的介质尺寸前所未有，即使与其他已知的极端RSG相比也是如此，其较低的光度表明其质量喷射机制可能在这个群体中是独特的。 分子辐射可以部分由一个由快速（27公里/秒）分离的赤道成分（带有$M{\sim}0.05$ $M_{\odot}$ ）和一个缓慢（10公里/秒）的球形包层（带有$\dot{M}\sim3\times10^{-6}$ $M_{\odot}$ 年$^{-1}$）组成的两组分模型来再现。 这表明 DFK 52 在大约 4000 年前经历了一次剧烈的质量损失事件，但此后转变为更缓慢、更对称的质量损失。 我们保守估计，在复杂的外流延伸区域，其总质量为 $0.1-1$ $M_{\odot}$。 剧烈质量损失的不确定性使得对这颗可能的超新星前身星进行广泛的跟踪成为必要。 显示英文摘要

摘要： Atacama Large Millimeter/submillimeter Array (ALMA) observations at 1.3mm have recently revealed surprising complexity in the circumstellar environment of DFK 52, a red supergiant (RSG) located in the Stephenson 2 massive open cluster. We provide an initial characterisation of the star's mass-loss properties by studying its circumstellar emission in continuum, $^{12}$CO, $^{13}$CO, and SiO rotational lines. We find that DFK 52 is surrounded by an extremely large outflow (up to 50,000 au in radius) that shows complex morphologies in both its molecular and dust emission. The size of the circumstellar medium is unprecedented, even when compared with other known extreme RSGs, and its lower luminosity indicates that its mass ejection mechanism may be unique among this population. The molecular emission can be partially reproduced by a two-component model consisting of a fast (27 km/s) detached equatorial component with $M{\sim}0.05$ $M_{\odot}$ and a slow (10 km/s) spherical envelope with $\dot{M}\sim3\times10^{-6}$ $M_{\odot}$ yr$^{-1}$. This suggests that DFK 52 underwent a dramatic mass-loss event $\sim$4000 years ago, but has since transitioned into having a slower more symmetric mass loss. We conservatively estimate a total mass of $0.1-1$ $M_{\odot}$ in the complex extended regions of the outflow. The uncertain nature of the dramatic mass loss warrants extensive follow-up of this likely supernova progenitor.