The Night Sky at the Calar Alto Observatory II: The Sky at the Near-infrared
The Night Sky at the Calar Alto Observatory II: The Sky at the Near-infrared
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DOI：
10.1086/593981
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发表时间：
2008-09
影响因子：
3.5
通讯作者：
Sebastián F. Sánchez;U. Thiele;J. Aceituno;D. Cristobal;J. Perea;João Alves
中科院分区：
文献类型：
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作者：
Sebastián F. Sánchez;U. Thiele;J. Aceituno;D. Cristobal;J. Perea;João Alves
在2007年Sánchez等人开始的研究之后，我们展示了Calar Alto天文台夜空的其他特性。我们这里关注的是近红外夜空亮度，望远镜观测，以及天文台有用时间的部分。在这项研究中，我们收集了7311张近红外图像的大型数据集，这些图像是在过去四年中为ALHAMBRA调查（J， H和Ks波段）定期拍摄的，以及为当前研究拍摄的额外近红外图像的更精简的数据集。此外，我们收集了天文台气象站近10年的资料，以及云传感器近2年的结果。我们分析了近红外夜空亮度与气团和季节的关系，研究了它的起源，并提出了天顶校正。在Ks波段的夜空亮度与气温之间有很强的相关性，梯度为每1°C -0.08等。J、H和ks波段典型的（最暗的）夜空亮度分别为15.95（16.95等）、13.99（14.98等）和12.39（13.55等）。这些数值是第一次为这个天文台得出的，表明Calar Alto在近红外波段和世界上大多数可以与之比较的天文站点一样暗。只有莫纳克亚山在Ks波段明显更暗，但不仅与卡拉阿尔托相比，而且与世界上任何其他天文台相比。根据所考虑的近红外图像中探测到的恒星的FWHM，推导出典型的望远镜观测值及其分布。当转换为V波段时，该值为~ 1.0”，仅略大于观测监测器在同一时间测量到的大气观测值~ 0.9”。因此，不同于大气的影响对望远镜的观测产生了较小的影响，约为10%。最后，我们根据相对湿度、阵风风速和云的存在来估计有用时间的比例。这一比例，约72%，与2007年得出的结果非常相似，这是基于灭绝监视器工作的时间比例得出的。
We present the characterization of additional properties of the night sky at the Calar Alto observatory, following the study started by Sánchez et al. in 2007. We focus here on the night-sky brightness at the near-infrared, the telescope seeing, and the fraction of useful time at the observatory. For this study we have collected a large data set comprising 7311 near-infrared images taken regularly along the last four years for the ALHAMBRA survey (J, H, and Ks bands), together with a more reduced data set of additional near-infrared images taken for the current study. In addition, we collected the information derived by the meteorological station at the observatory during the last 10 yar, together with the results from the cloud sensor for the last ∼2 yr. We analyze the dependency of the near-infrared night-sky brightness with the air mass and the seasons, studying its origins and proposing a zenithal correction. A strong correlation is found between the night-sky brightness in the Ks band and the air temperature, with a gradient of ∼-0.08 mag per 1°C. The typical (darkest) night-sky brightness in the J, H, and Ks-band are 15.95 mag (16.95 mag), 13.99 mag (14.98 mag), and 12.39 mag (13.55 mag), respectively. These values have been derived for the first time for this observatory, showing that Calar Alto is as dark in the near-infrared as most of the other astronomical sites in the world with which we could compare it. Only Mauna Kea is clearly darker in the Ks band, but not only compared to Calar Alto but to any other observatory in the world. The typical telescope seeing and its distribution were derived on the basis of the FWHM of the stars detected in the considered near-infrared images. This value, ∼1.0′′ when converted to the V band, is only slightly larger than the atmospheric seeing measured at the same time by the seeing monitor, ∼0.9′′. Therefore, the effects different from the atmosphere produce a reduced degradation on the telescope seeing, of the order of ∼10%. Finally we estimate the fraction of useful time based on the relative humidity, gust wind speed, and presence of clouds. This fraction, ∼72%, is very similar to the one derived in 2007, based on the fraction of time when the extinction monitor is working.