[论文解读] Atacama Large Aperture Submillimeter Telescope (AtLAST) Science: Solar and stellar observations

Sven Wedemeyer, M. Bárta+36 more|arXiv (Cornell University)|Mar 1, 2024

Spacecraft Design and Technology被引用 4

一句话总结

本文提出在智利的阿塔卡马沙漠建造阿塔卡马大型孔径亚毫米波望远镜（AtLAST），这是一台50米口径的单镜面望远镜，旨在实现对太阳和恒星的高时间分辨率、全波段、偏振亚毫米波观测。研究证明，AtLAST的宽频率覆盖范围（90–660 GHz）、多像素成像能力以及高时间分辨率，将使太阳色球层的三维大气测绘成为可能，并实现对太阳活动周期和恒星磁活动的前所未有的监测。

ABSTRACT

Observations at (sub-)millimeter wavelengths offer a complementary perspective on our Sun and other stars, offering significant insights into both the thermal and magnetic composition of their chromospheres. Despite the fundamental progress in (sub-)millimeter observations of the Sun, some important aspects require diagnostic capabilities that are not offered by existing observatories. In particular, simultaneous observations of the radiation continuum across an extended frequency range would facilitate the mapping of different layers and thus ultimately the 3D structure of the solar atmosphere. Mapping large regions on the Sun or even the whole solar disk at a very high temporal cadence would be crucial for systematically detecting and following the temporal evolution of flares, while synoptic observations, i.e., daily maps, over periods of years would provide an unprecedented view of the solar activity cycle in this wavelength regime. As our Sun is a fundamental reference for studying the atmospheres of active main sequence stars, observing the Sun and other stars with the same instrument would unlock the enormous diagnostic potential for understanding stellar activity and its impact on exoplanets. The Atacama Large Aperture Submillimeter Telescope (AtLAST), a single-dish telescope with 50\,m aperture proposed to be built in the Atacama desert in Chile, would be able to provide these observational capabilities. Equipped with a large number of detector elements for probing the radiation continuum across a wide frequency range, AtLAST would address a wide range of scientific topics including the thermal structure and heating of the solar chromosphere, flares and prominences, and the solar activity cycle. In this white paper, the key science cases and their technical requirements for AtLAST are discussed.

研究动机与目标

• 确定AtLAST在太阳与恒星亚毫米波观测方面的科学潜力。
• 解决当前望远镜的局限性，例如频率覆盖范围狭窄，以及对动态太阳现象的时间或空间分辨率不足。
• 定义仪器需求——如全波段覆盖、高时间分辨率和偏振灵敏度——以实现最优的太阳与恒星科学研究。
• 证明AtLAST可通过覆盖广泛的频率范围，同时映射太阳的多个大气层。
• 探索使用AtLAST对太阳活动周期进行同步监测的可行性，以及对恒星磁活动的研究。

提出的方法

• 提出在智利阿塔卡马沙漠建造一台50米口径的单镜面亚毫米波望远镜AtLAST，专为太阳与恒星观测优化。
• 采用快速“飞行观测”扫描模式与多像素探测器，实现亚分钟级的高时间分辨率与大空间覆盖范围。
• 利用从90 GHz到660 GHz的宽（准）同时频率覆盖，实现对太阳大气中较大高度范围的映射。
• 实现全偏振能力，通过亚毫米波辐射探测色球层中的磁场。
• 利用高动态范围与亮度温度精度（≤100 K）以应对太阳极端的亮度变化，尤其是在耀斑期间。
• 探索本振下混频IFU系统在太阳亚毫米波谱中检测谱线的潜力。

Figure 1: ALMA Total Power (TP) maps in Band 6 (230 GHz) obtained by double-circle scanning at two different times capturing a very quiescent state (left) and a more active state with clearly visible Active Regions including sunspots (right). (ALMA project IDs: 2017.1.00009.S, 2011.0.00020.SV.)

实验结果

研究问题

• RQ1 AtLAST如何通过全波段、同时的亚毫米波观测实现太阳色球层的三维映射？
• RQ2 为实现多年连续、高时间分辨率的全盘太阳成像，需要何种仪器配置？
• RQ3 AtLAST能否探测到太阳的亚毫米波谱线？其诊断价值如何，对太阳大气结构有何帮助？
• RQ4 AtLAST的偏振能力如何提升我们对色球层磁场的理解？
• RQ5 AtLAST在多大程度上可作为太阳与恒星亚毫米波科学的统一平台？

主要发现

• AtLAST的宽频率覆盖范围（90–660 GHz）可实现对太阳色球层多个大气层的同步映射，这对三维大气重建至关重要。
• 配备大瞬时视场的多像素探测器对于在高时间分辨率下高效覆盖太阳圆面至关重要。
• 高时间分辨率（亚分钟级）是解析快速演变的太阳现象（如耀斑和动态色球层结构）所必需的。
• 全偏振能力对于通过亚毫米波辐射诊断色球层磁场至关重要。
• 太阳的极端亮度要求探测器具备高动态范围与亮度温度精度（100 K或更好），以确保耀斑期间测量的可靠性。
• 尽管具有挑战性，太阳亚毫米波谱线的探测可显著增强诊断能力，特别是采用IFU型本振下混频系统时。

Figure 2: Evolution of a synthetic sub-mm and IR flare $T_{b}$ spectrum from RHD modelling (from Simões et al. 2017 ) . From these simulations, for $\lambda>50\mu$ m, $T_{b}$ should provide the electron temperature in the optically-thick upper chromosphere.