SOFIA-EXES Observations of Betelgeuse during the Great Dimming of 2019/2020
SOFIA-EXES Observations of Betelgeuse during the Great Dimming of 2019/2020
复制标题
DOI：
10.3847/2041-8213/ab84e6
复制
发表时间：
2020-04-01
影响因子：
7.9
通讯作者：
Townsend, Amanda J.
中科院分区：
文献类型：
--
作者：
Harper, Graham M.;DeWitt, Curtis N.;Townsend, Amanda J.
2019年10月，参宿四的V波段亮度开始下降，超过了其准周期性（类似于420天周期）的最低预期，成为有记录的光度史上最暗的。2019年12月，甚大望远镜/球体获得的观测结果显示，这颗星星的南半部比2019年1月明显变暗，这表明光球层或附近发生了重大变化。我们提出了红外天文平流层观测站（索菲亚）Echelon Cross Echelle Spectrograph（EXES）在前所未有的2020年2月V波段亮度最小值期间获得的参宿四[Fe II] 25.99 μ m和[SI] 25.25 μ m发射线的高光谱分辨率观测，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，反映了气体速度的任何一条线的轮廓，没有显着的变化，在通量连续比，因此没有显着的变化，在[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]线形成区域，3 R（R-*）< 20。然而，光穿越时间是几个小时的顺序和光度的降低可能会减少尘埃气体加热率和[O I] 63.19 μ m的排放，这有贡献的R > 20 R（*），其中显着的星周富氧尘埃观察。
In 2019 October Betelgeuse began a decline in V-band brightness that went beyond the minimum expected from its quasi-periodic similar to 420 day cycle, becoming the faintest in recorded photometric history. Observations obtained in 2019 December with Very Large Telescope/SPHERE 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 Stratospheric Observatory for Infrared Astronomy (SOFIA) Echelon Cross Echelle Spectrograph (EXES) high spectral-resolution observations of [Fe II] 25.99 mu m and [SI] 25.25 mu m 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 mu m emission, which has contributions from R > 20R(*), where significant circumstellar oxygen-rich dust is observed.