SOFIA-EXES在2019/2020年大调光期间对参宿四的观测
SOFIA-EXES Observations of Betelgeuse during the Great Dimming of 2019/2020
摘要：
2019年10月，参宿四的V波段亮度开始下降，超过了其准周期约420天周期的最低预期，成为有记录的光度史上最暗的。VLT/SPHERE（Montarges 2020）在2019年12月获得的观测结果表明，该恒星的南半部比2019年1月明显变暗，这表明光球层或附近发生了重大变化。我们提出了SOFIA-EXES高光谱分辨率观测的[Fe II] 25.99 mic和[S I] 25.25 mic发射线从参宿四在前所未有的2020年2月V波段亮度最低期间获得，以调查拱星流的潜在变化。这些光谱与2015年和2017年获得的观测结果进行了比较，当时V星等是较亮相位的典型代表。我们发现只有很小的变化，在气体速度反映的任何一条线的配置文件，没有显着的变化，在通量连续比，因此没有显着的变化[Fe II]/[S I]通量比。有证据表明，在2020年连续统中出现了吸收特征。阿尔芬波从上层光球穿越的时间足够长，人们不会期望大尺度磁场的变化到达星周[Fe II]和[S I]线形成区，3 < R（R*）< 20。然而，光穿越时间是几个小时的数量级，光度的降低可能会降低尘埃-气体加热速率和[O I] 63.19 mic的发射，其中有R > 20 R * 的贡献，在那里观察到显着的星周富氧尘埃。
英文摘要：
In 2019 October Betelgeuse began a decline in V-band brightness that went beyond the minimum expected from its quasi-periodic ~420 day cycle, becoming the faintest in recorded photometric history. Observations obtained in 2019 December with VLT/SPHERE (Montarges 2020) have shown that the southern half of the star has become markedly fainter than in 2019 January indicating that a major change has occurred in, or near, the photosphere. We present SOFIA-EXES high spectral-resolution observations of [Fe II] 25.99 mic and [S I] 25.25 mic emission lines from Betelgeuse obtained during the unprecedented 2020 February V-band brightness minimum to investigate potential changes in the circumstellar flow. These spectra are compared to observations obtained in 2015 and 2017 when the V magnitude was typical of brighter phases. We find only very small changes in the gas velocities reflected by either of the line profiles, no significant changes in the flux to continuum ratios, and hence no significant changes in the [Fe II]/[S I] flux ratios. There is evidence that absorption features have appeared in the 2020 continuum. The Alfven wave-crossing time from the upper-photosphere is sufficiently long that one would not expect a change in the large scale magnetic field to reach the circumstellar [Fe II] and [S I] line forming regions, 3 < R(R*) < 20. However, the light-crossing time is of order a few hours and a reduction in luminosity may reduce the dust-gas heating rate and [O I] 63.19 mic emission which has contributions from R > 20R*, where significant circumstellar oxygen-rich dust is observed.
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