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THE MASSIVE POST-RED SUPERGIANTS IRC+10420 AND HD 179821

机译：大型后置红色超人IRC + 10420和HD 179821

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摘要

The transition of a massive post-main-sequence star from red supergiant to luminous blue variable or Wolf-Rayet star is a rapid and therefore rarely observed phase of evolution. We present evidence that the unusual yellow supergiants IRC +10420 and HD 179821 (= AFGL 2343) are undergoing such a transition. Polari-metric, coronagraphic near-infrared images reveal that each star is surrounded by an extended dust reflection nebula. These detections set IRC + 10420 and HD 179821 apart from 89 Her, HD 161796, and several other luminosity class Ⅰ stars that are thought to be descended from low- to intermediate-mass progenitors. The nebulae surrounding IRC +10420 and HD 179821 are very similar; each appears circularly symmetric, is detected out to ～9″ from the central star at 1.25 μm, and is unusually red for reflection nebulosity. The last result suggests that the dust grains in these envelopes are larger than is typical of grains in the dust envelopes of low- and intermediate-mass evolved stars. Under the assumption that both stars lie at their kinematic distances (～6 kpc in each case), our images suggest that each circumstellar envelope has a dynamical lifetime of ～ 5000 yr, contains ～ 5 solar mass of gas and dust, and was likely ejected during a prior OH/IR supergiant phase. Thus, in addition to bolstering the post-red supergiant classification of both stars, these imaging results appear to place strong constraints on the evolutionary and mass-loss histories of supernova progenitors.
机译：大主序后恒星从红色超巨星到发光的蓝色变星或Wolf-Rayet星的过渡是快速的，因此很少观察到演化阶段。我们提供的证据表明，异常黄色超级巨人IRC +10420和HD 179821（= AFGL 2343）正在经历这种过渡。极化的日冕近红外图像显示，每颗恒星都被一个扩展的尘埃反射星云包围。这些探测使IRC + 10420和HD 179821与89 Her，HD 161796和其他几类Ⅰ级光度星相距甚远，这些恒星被认为是从低质量祖先到中等质量祖先的。 IRC +10420和HD 179821周围的星云非常相似。每个都呈圆形对称，从中心星以1.25μm的距离被探测到〜9英寸，并且对于反射雾状来说异常红色。最后的结果表明，这些包层中的尘埃颗粒比低质量和中等质量的恒星的尘埃中典型的尘埃颗粒大。假设两个恒星都处于运动距离（每种情况下约为6 kpc），我们的图像表明每个星际包壳的动态寿命为〜5000 yr，包含约5个太阳质量的气体和尘埃，并可能被抛射在先前的OH / IR超级阶段中。因此，除了支持两颗恒星的红色后超巨星分类外，这些成像结果似乎对超新星祖先的演化和质量损失历史施加了强大的约束。

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