A sunspot is an ideal waveguide for a variety of magnetohydrodynamic waves, which carry a significant amount of energy to the upper atmosphere and could be used as a tool to probe magnetic and thermal structure of a sunspot. In this study, we used the New Vacuum Solar Telescope and took high-resolution image sequences simultaneously in both TiO (7058$\pm$10 A) and H$_\alpha$ (6562$\pm$2.5 A) bandpasses. We extracted the area and total emission intensity variations of sunspot umbra and analyzed the signals with synchrosqueezing transform. We found that the area and emission intensity varied with both three and five minute periodicity. Moreover, the area and intensity oscillated in phase with each other, this fact hold in both TiO and H$_\alpha$ data. We interpret this oscillatory signal as propagating slow sausage wave. The propagation speed is estimated at about 8 km$\cdot$s$^{-1}$. We infer that this sunspot's umbra could have temperature as low as 2800--3500 K.

中文翻译：

---

在新真空太阳望远镜观测到的太阳黑子中传播慢香肠波

太阳黑子是各种磁流体动力波的理想波导，它携带大量能量到高层大气，可用作探测太阳黑子磁和热结构的工具。在这项研究中，我们使用了新型真空太阳望远镜，并在 TiO (7058$\pm$10 A) 和 H$_\alpha$ (6562$\pm$2.5 A) 带通中同时拍摄了高分辨率图像序列。我们提取了太阳黑子本影的面积和总发射强度变化，并用同步压缩变换分析了信号。我们发现面积和发射强度以三分钟和五分钟的周期变化。此外，面积和强度彼此同相振荡，这一事实在 TiO 和 H$_\alpha$ 数据中都成立。我们将此振荡信号解释为传播缓慢的香肠波。传播速度估计约为 8 km$\cdot$s$^{-1}$。我们推断这个太阳黑子的本影温度可能低至 2800--3500 K。