Evolved stars are expected to rotate, but ALMA observations of a dipolar velocity field at Betelgeuse suggest an extremely rapid rotation rate of 5.47 ± 0.25 km s^-1, which is two orders of magnitude faster than predicted. Ma et al. test whether the dipolar structure could come from a nonrotating star instead. For instance, two large surface convective cells moving in opposite directions could mimic the effect, as would smaller cells moving coherently and starting from greater depths. The authors develop a postprocessing package for synthetic SiO spectra and ALMA images. Their produced radial velocity maps show that 90% of single-epoch observations of a nonrotating star can be falsely interpreted as evidence for rotation rates of 2 km s^-1 or higher.

With the current resolution of ALMA, it is not possible to distinguish between the three cases of rapid rotation, two large convective cells or smaller coherent cells. But a factor of two increase in spatial resolution would be sufficient to do so, especially with additional epochs. It looks like Betelgeuse will remain under watch.

预计演化的恒星会旋转，但 ALMA 对参宿四偶极速度场的观测表明，其旋转速度极快，为 5.47 ± 0.25 km s ^-1，比预测的速度快两个数量级。马等人。测试偶极结构是否可能来自非旋转恒星。例如，两个沿相反方向移动的大型表面对流细胞可以模拟这种效应，较小的细胞从更深处开始连贯地移动也可以模拟这种效应。作者开发了一个用于合成 SiO2 光谱和 ALMA 图像的后处理包。他们制作的径向速度图显示，90% 的非旋转恒星的单历元观测结果都可能被错误地解释为旋转速率为 2 km s ^-1或更高的证据。

以 ALMA 目前的分辨率，无法区分快速旋转、两个大型对流单元或较小的相干单元这三种情况。但空间分辨率增加两倍就足以做到这一点，特别是在额外的历元中。看来参宿四仍将受到监视。