论文标题
侧夜天空温度和望远镜结构的亚冷却
Bolometric Night Sky Temperature and Subcooling of Telescope Structures
论文作者
论文摘要
语境。在不同情况下，文献中使用了一词，通常会导致混乱。在这项工作中，我们研究了$ t_ \ text {sky} $，这是一个有效的辐射天温度，半球形黑体将在地面上与夜空相同的平坦水平结构，在整个热波长范围内集成了$ 1-100 \，μ$ m。然后，我们通过特别关注望远镜的辐射冷却的热物理学分析并讨论缓解策略。 目标。数量$ t_ \ text {sky} $对于量化望远镜中的子冷却很有用，这些子冷却可以通过引入光路差（OPD）来恶化图像质量，并引起对结构的热应力和机械偏转。 方法。我们采用欧洲南方天文台的Cerro Paranal天空模型来得出一个简单的$ T_ \ text {sky} $的公式，作为大气参数的函数。然后将结构子冷却和诱导的OPD表示为表面发射率，天空视图因子，局部空气速度和结构尺寸的函数。 结果。在Atacama沙漠中的Cerro Paranal（2600 m）和Cerro Armazones（3060 m），$ t_ \ text {sky} $ to to Zenith主要在地面附近的环境温度以下$ 20-50 $ kelvin，这取决于大气中的质水蒸气（PWV）列。对于更高的天顶距离，温度差可以降低几个开尔文。子冷操作OPD与望远镜直径线性缩放至二次缩放，并与望远镜结构附近的局部空气速度成反比。
Context. The term sky temperature is used in the literature in different contexts which often leads to confusion. In this work, we study $T_\text{sky}$, the effective bolometric sky temperature at which a hemispherical black body would radiate the same power onto a flat horizontal structure on the ground as the night sky, integrated over the entire thermal wavelength range of $1-100\,μ$m. We then analyze the thermal physics of radiative cooling with special focus on telescopes and discuss mitigation strategies. Aims. The quantity $T_\text{sky}$ is useful to quantify the subcooling in telescopes which can deteriorate the image quality by introducing an Optical Path Difference (OPD) and induce thermal stress and mechanical deflections on structures. Methods. We employ the Cerro Paranal Sky Model of the European Southern Observatory to derive a simple formula of $T_\text{sky}$ as a function of atmospheric parameters. The structural subcooling and the induced OPD are then expressed as a function of surface emissivity, sky view factor, local air speed and structure dimensions. Results. At Cerro Paranal (2600 m) and Cerro Armazones (3060 m) in the Atacama desert, $T_\text{sky}$ towards the zenith mostly lies $20-50$ Kelvin below the ambient temperature near the ground, depending strongly on the precipitable water vapor (PWV) column in the atmosphere. The temperature difference can decrease by several Kelvin for higher zenith distances. The subcooling OPD scales linearly to quadratically with the telescope diameter and is inversely proportional to the local air speed near the telescope structure.
