We investigate the observable characteristics of the extended atmospheres of asymptotic giant branch (AGB) stars across a wide range of radio and (sub-)millimeter wavelengths using state-of-the-art 1D dynamical atmosphere and wind models over one pulsation period. We also study the relationships between the observable features and model properties. We further study practical distance ranges for observable sources assuming the capabilities of current and upcoming observatories. We present time-variable, frequency-dependent profiles of pulsating AGB stars’ atmospheres, illustrating observable features in resolved and unresolved observations, including disk brightness temperature, photosphere radius, and resolved and unresolved spectral indices. Notably, temporal variations in disk brightness temperature closely mirror the temperature variability of the stellar atmosphere. We find that while the photospheric radius decreases due to gas dilution in the layers between consecutive shocks, the increase in the observed stellar radius reflects shock propagation through the atmosphere during the expansion phase, providing a direct measurement method for the shock velocity. Furthermore, our models indicate that enhanced gas temperatures after the passage of a strong shock might be observable in the high-frequency Atacama Large Millimeter/submillimeter Array (ALMA) bands as a decrease in the brightness temperature with increasing frequency. We demonstrate that synthetic observations based on state-of-the-art dynamical atmosphere and wind models are necessary for proper interpretations of current (ALMA and Very Large Array (VLA)) and future (Square Kilometre Array and next-generation VLA) observations and that multiwavelength observations of AGB stars are crucial for empirical studies of their extended atmospheres.

中文翻译：

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探测 AGB 恒星的扩展大气层。I. 无线电和（亚）毫米波长的一维流体动力学模型合成成像


我们使用最先进的 1D 动力学大气和风模型在一个脉动周期内研究了渐近巨分支 （AGB） 星在宽范围无线电和（亚）毫米波长上的扩展大气的可观测特性。我们还研究了可观察特征和模型属性之间的关系。我们进一步研究了假设当前和即将到来的天文台能力的可观测源的实际距离范围。我们提供了脉动 AGB 星大气的时间可变、频率依赖性剖面，说明了已分辨和未分辨观测中的可观测特征，包括圆盘亮度温度、光球半径以及分辨和未分辨的光谱指数。值得注意的是，盘亮度温度的时间变化与恒星大气的温度变化密切相关。我们发现，虽然光球半径由于连续冲击之间层中的气体稀释而减小，但观测到的恒星半径的增加反映了膨胀阶段冲击在大气中的传播，为冲击速度提供了一种直接的测量方法。此外，我们的模型表明，在高频阿塔卡马大型毫米/亚毫米阵列 （ALMA） 波段中，可能会观察到强冲击后气体温度升高，因为亮度温度随着频率的增加而降低。 我们证明，基于最先进的动力大气和风模型的合成观测对于正确解释当前（ALMA 和甚大型阵列 （VLA））和未来（平方公里阵列和下一代 VLA）观测是必要的，并且 AGB 恒星的多波长观测对于其扩展大气的实证研究至关重要。