期刊
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF THE PACIFIC
卷 134, 期 1042, 页码 -出版社
IOP Publishing Ltd
DOI: 10.1088/1538-3873/acac51
关键词
Atmospheric extinction; Earth atmosphere; Millimeter astronomy; Radio observatories; Radio telescopes; Submillimeter astronomy; Very long baseline interferometers; Water vapor
资金
- Academia Sinica (AS)
- Ministry of Science and Technology (MOST) of Taiwan [MOST 105-2119-M-001-042, MOST 106-2119-M-001-013, MOST 107-2119-M-001-041, MOST 108-2112-M-001-048, MOST 109-2124-M-001-005, MOST 110-2112-M-001-001]
- MoST [MOST 106-2923-M-001-005, MOST 107-2923-M-001-002, MOST 108-2923-M-001-002, MOST 109-2923-M-001-001, MOST 110-2923-M-001-001]
- National Science Foundation (NSF) [MOST 106-2923-M-001-005, MOST 107-2923-M-001-002, MOST 108-2923-M-001-002, MOST 109-2923-M-001-001, MOST 110-2923-M-001-001]
The five-year monitoring results of 225 GHz zenith opacity at Thule Air Base in Greenland show a clear seasonal variation, with lower opacity in winter compared to summer, similar to Greenland Summit. Thule is considered a good site for millimeter astronomy due to its stable opacity conditions, especially in winter.
We present five-year monitoring results of 225 GHz zenith opacity using a tipping radiometer at Thule Air Base (Pituffik), Greenland, where the Greenland Telescope is currently located. The site shows a clear seasonal variation with average opacity lower by a factor of two during winter compared with summer, similar to Greenland Summit. The 25%, 50%, and 75% quartiles of the 225 GHz opacity during the winter months of November through April are 0.14, 0.17, and 0.22, respectively. These values are three times larger than those at the Greenland Summit, and the astronomical observing efficiency in this band is about an order of magnitude better at the Summit than at the Thule Air Base. 225 GHz opacity continuously less than 0.2 for 100-200 hr (i.e., for about a week) occurs about 20 times per year, and on several occasions it even reaches up to 300-400 hr (i.e., about two weeks). These statistics indicate that Thule is a very good site for millimeter astronomy that needs very stable opacity conditions, such as continuum camera observations or VLBI observations that span over several days. Estimated transmission spectra in the winter season show that most of the time (75% quartile) observations at frequencies below 300 GHz are possible with modest atmospheric attenuation (opacities < 0.5), and at frequencies below 350 GHz for a quarter of the time. Although the atmospheric transmission is low (only up to similar to 20%), the 650 GHz and 850 GHz windows are also accessible for 5% of the wintertime. For about 50% of the summertime, it is possible to observe around the frequency of 220 GHz, which overlaps with the current EHT observation frequency of 221.1 GHz, with modest atmospheric attenuation (opacities < 0.5). On the other hand, the 350 GHz window is very difficult to observe in the summertime.
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