AI 中文总结
本研究利用VLA和ALMA对参宿四开展多频率空间分辨观测，发现其大气亮温度分布演化、温度极小值等特征，并证实近距伴星对大气存在周期性扰动。
AI 中文摘要
我们利用Karl G. Jansky甚大阵（VLA）与阿塔卡马大型毫米/亚毫米波阵（ALMA），对红超巨星参宿四（猎户座α）开展了7个频率的新空间分辨观测，频率分别为22 GHz（波长1.36厘米）、44 GHz（波长6.8毫米）、107 GHz（波长2.8毫米）、136 GHz（波长2.2毫米）、224 GHz（波长1.3毫米）、338 GHz（波长0.89毫米）及485 GHz（波长0.62毫米）。这些观测的时间跨度为2021-2026年，可用于表征该恒星延展大气的平均亮温度（$T_B$）、形状与对称性。在22 GHz和44 GHz频段，$T_B$在2019年观测到的历史低值后有所上升，该时间点恰好处于2019年末/2020年初的“大变暗”事件前夕。我们发现，与2016年之前的测量结果相比，$T_B$的峰值出现在更大的投影半径（$r\thicksim2.7R_{\rm star}$）处，这与大气密度剖面可能发生的演化相符。此外，我们还发现$T_B$从$\thicksim2.7R_{\rm star}$处的约3500开尔文系统性下降至$\thicksim1.2R_{\rm star}$处的约2220开尔文，证实了此前报道的光球层与色球层之间存在温度极小值的结论。在所有观测频率下，对应半径处的$T_B$均低于紫外测量推断的温度，表明较冷等离子体（温度$T\thicksim T_{\rm eff}$）与较暖色球物质混合的状态持续存在。新测量得到的全局谱指数$\thicksim=1.35\thicksim0.03$，且在超过二十年的频率观测中未发现$\thicksim$发生变化的证据。近期有研究报道了参宿四存在近距伴星的证据，其轨道间距约为$2.3R_{\rm star}$。我们识别出射电测量得到的参宿四椭率与伴星轨道相位之间存在相关性，该结果与伴星对大气的周期性扰动相一致。
英文摘要
We present new spatially resolved observations of the red supergiant Betelgeuse ($α$ Orionis) at seven frequencies: 22 GHz ($λ$1.36cm); 44 GHz ($λ$6.8mm); 107 GHz ($λ$2.8mm); 136 GHz ($λ$2.2mm); 224 GHz ($λ$1.3mm); 338 GHz ($λ$0.89mm); and 485 GHz ($λ$0.62mm) using the Karl G. Jansky Very Large Array and the Atacama Large Millimeter/submillimeter Array. These observations (spanning 2021-2026) enable a characterization of the mean brightness temperature ($T_B$), shape, and symmetry of the star's extended atmosphere. At 22 GHz and 44 GHz $T_B$ has increased following the historic lows observed in 2019, just prior to the Great Dimming of late 2019/early 2020. We find that $T_B$ peaks at a larger projected radius ($r\sim2.7R_{\star}$) compared with measurements prior to 2016, consistent with a possible evolution in the atmospheric density profile. In addition we find a systematic decrease in $T_B$ from $\approx3500$K at $\sim2.7R_{\star}$ to $T_{B}\approx$2220K at $\sim1.2R_{\star}$, confirming a previously reported temperature minimum between the photosphere and chromosphere. At all observed frequencies $T_B$ is lower than temperatures inferred from ultraviolet measurements at comparable radii, indicating the continued presence of cooler plasma ($T\le T_{\rm eff}$) mixed with the warmer chromospheric material. The new measurements yield a global spectral index $α=1.35\pm$0.03, with no evidence for a change in $α$ over more than two decades in frequency. Recently, evidence of a close-in companion to Betelgeuse has been reported, with an orbital separation $r\sim2.3R_{\star}$. We have identified a correlation between the ellipticity of Betelgeuse, as obtained from radio measurements, and the companion's orbital phase. The results are consistent with periodic perturbations of the atmosphere by the companion.
Comments23 pages, 13 figures, 6 tables. Accepted to the Astronomical Journal
