Atmospheric conditions at a site for submillimeter-wavelength astronomy
Atmospheric conditions at a site for submillimeter-wavelength astronomy
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亚毫米波长天文学地点的大气条件
DOI：
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发表时间：
1998
期刊：
影响因子：
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通讯作者：
M. Holdaway
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文献类型：
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作者：
Simon J. E. Radford;M. Holdaway
在毫米波和亚毫米波波长下，压力加宽的分子光谱线使大气层成为天文观测灵敏度和分辨率的天然限制。对流层水汽是罪魁祸首。半透明的大气层既通过衰减入射辐射来降低信号，又通过热辐射来增加噪声。此外，水蒸气分布的不均匀性导致通过大气的电路径长度的变化。这些变化导致相位误差，降低了用干涉仪和填充孔径望远镜拍摄的图像的灵敏度和分辨率。为了评估毫米波阵列的可能位置，NRAO进行了广泛的测试活动。在智利北方Cerro Chajnantor附近海拔5000米的候选地点，我们于1995年4月部署了一套自主仪器。其中包括一个测量大气透明度和瞬时发射波动的225千兆赫倾斜辐射计和一个测量大气相位波动的12千兆赫干涉仪。最近又增加了一台用于测量350微米波长大气透明度的亚毫米倾翻光度计和一台亚毫米傅里叶变换光谱仪。NRAO和其他团体也在其他地点部署了类似的仪器，特别是莫纳克亚山、夏威夷和南极。这些测量表明Chajnantor是毫米和亚毫米波长天文学的绝佳场所。225 GHz的透明度比莫纳克亚山更好。在Chajnantor和在南极测量的225 GHz频率中值相当。
At millimeter and submillimeter wavelengths, pressure broadened molecular spectral lines make the atmosphere a natural limitation to the sensitivity and resolution of astronomical observations. Tropospheric water vapor is the principal culprit. The translucent atmosphere both decreases the signal, by attenuating incoming radiation, and increases the noise, by radiating thermally. Furthermore, inhomogeneities in the water vapor distribution cause variations in the electrical path length through the atmosphere. These variations result in phase errors that degrade the sensitivity and resolution of images made with both interferometers and filled aperture telescopes. To evaluate possible sites for the Millimeter Array, NRAO has carried out an extensive testing campaign. At a candidate site at 5000 m altitude near Cerro Chajnantor in northern Chile, we deployed an autonomous suite of instruments in 1995 April. These include a 225 GHz tipping radiometer that measures atmospheric transparency and temporal emission fluctuations and a 12 GHz interferometer that measures atmospheric phase fluctuations. A sub-millimeter tipping photometer to measure the atmospheric transparency at 350 micrometer wavelength and a submillimeter Fourier transform spectrometer have recently been added. Similar instruments have been deployed at other sites, notably Mauna Kea, Hawaii, and the South Pole, by NRAO and other groups. These measurements indicate Chajnantor is an excellent site for millimeter and submillimeter wavelength astronomy. The 225 GHz transparency is better than on Mauna Kea. The median 225 GHz transparencies measured at Chajnantor and at the South Pole are comparable.