Evaluations of new atmospheric windows at thirty micron wavelengths for astronomy
Evaluations of new atmospheric windows at thirty micron wavelengths for astronomy
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天文学三十微米波长新大气窗口的评估
DOI：
10.1117/12.925258
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发表时间：
2012
期刊：
影响因子：
--
通讯作者：
N.)
中科院分区：
文献类型：
--
作者：
Miyata;T.;et al. (including Takato;N.)
30微米仍然是地面天文观测尚未开发的前沿领域之一。最近极高地点的发展，包括Chajnantor TAO地点(5640米)，使我们能够从地面访问该波长。对于天文观测来说，预期的透过率似乎足够清楚，但基于天文数据的实际评估尚未进行。我们用安装在微型TAO 1.0米望远镜上的中红外相机MAX38分析了在31.7微米处获得的图像。恒星IRC+10420的109张图像和天空的11,114张图像已被缩减。在测量的光电流和可察觉的水汽之间发现了明确的关系。对ATRAN模式光电流的简单估计与测量结果吻合较好，表明ATRAN模式较好地再现了大气透过率。这也支持了我们的假设，即在Chajnantor TAO位置的PVW的比例因子0.85到APEX处的PWV。当PWV小于0.6 mm时，31.7微米的平均透过率可达到20%以上。在某些情况下，发现透过率明显降低高达10%。它可能是由大小超过10微米的液体或冰水滴引起的，尽管具体原因没有具体说明。文中还研究了天空光电流的日变化。在黄昏的时候，天空有时很明亮，而且通常不稳定。另一方面，中午前后的天空与夜间的天空并没有明显的区别。这可能表明，即使在白天，30微米窗口的观测条件仍然很好。
Thirty micron has remained one of unexplored frontiers of ground-based astronomical observations. Recent developments of extreme high sites including the Chajnantor TAO site (5,640m) enable us to access the this wavelengths from the ground. The expected transmittance seems clear enough for astronomical observations, but practical evaluations based on astronomical data has not been carried out yet. We have analyzed images obtained at the 31.7 micron with a mid-infrared camera MAX38 attached on a mini-TAO 1.0-meter telescope. 109 images of a star IRC+10420 and 11,114 images of the sky have been reduced. Clear relationship between the measured photocurrents and the perceptible water vapor has been found. Simple estimation of the photocurrents with of the ATRAN model gives good agreements with the measurements, indicating that the ATRAN model reproduce the atmospheric transmittance reasonably well. This also supports our assumption that the scaling factor 0.85 of the PVW at the Chajnantor TAO site to the PWV at the APEX. The average transmittance in the 31.7 micron is achieved to be over 20% when the PWV below 0.6 mm. In some cases clear degradation up to 10% in the transmittance is found. It may be caused by droplets of liquid or iced water with a size over 10 micron although the causes are not exactly specified. Diurnal time variations of the sky photocurrents are also investigated. The sky is sometimes bright and usually unstable in the twilight time. On the other hand the sky around the noontime does not show clear difference from the night sky. It may suggest that the observing condition at the thirty micron windows remain good even in the daytime.