Evaluations of new atmospheric windows at thirty micron wavelengths for astronomy

Takashi Miyata; Shigeyuki Sako; Takafumi Kamizuka; Tomohiko Nakamura; Kentaro Asano; Mizuho Uchiyama; Masahiro Konishi; Mizuki Yoneda; Naruhisa Takato; Yuzuru Yoshii; Mamoru Doi; Kotaro Kohno; Kimiaki Kawara; Masuo Tanaka; Kentaro Motohara; Takeo Minezaki; Toshihiko Tanabe; Tomoki Morokuma; Yoichi Tamura; Tsutomu Aoki; Takao Soyano; Ken'ichi Tarusawa; Hidenori Takahashi; Shintaro Koshida; Natsuko M. Kato

doi:10.1117/12.925258

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17 September 2012 Evaluations of new atmospheric windows at thirty micron wavelengths for astronomy

Takashi Miyata, Shigeyuki Sako, Takafumi Kamizuka, Tomohiko Nakamura, Kentaro Asano, Mizuho Uchiyama, Masahiro Konishi, Mizuki Yoneda, Naruhisa Takato, Yuzuru Yoshii, Mamoru Doi, Kotaro Kohno, Kimiaki Kawara, Masuo Tanaka, Kentaro Motohara, Takeo Minezaki, Toshihiko Tanabe, Tomoki Morokuma, Yoichi Tamura, Tsutomu Aoki, Takao Soyano, Ken'ichi Tarusawa, Hidenori Takahashi, Shintaro Koshida, Natsuko M. Kato

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Proceedings Volume 8444, Ground-based and Airborne Telescopes IV; 84446B (2012) https://doi.org/10.1117/12.925258
Event: SPIE Astronomical Telescopes + Instrumentation, 2012, Amsterdam, Netherlands

Abstract

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.

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Takashi Miyata, Shigeyuki Sako, Takafumi Kamizuka, Tomohiko Nakamura, Kentaro Asano, Mizuho Uchiyama, Masahiro Konishi, Mizuki Yoneda, Naruhisa Takato, Yuzuru Yoshii, Mamoru Doi, Kotaro Kohno, Kimiaki Kawara, Masuo Tanaka, Kentaro Motohara, Takeo Minezaki, Toshihiko Tanabe, Tomoki Morokuma, Yoichi Tamura, Tsutomu Aoki, Takao Soyano, Ken'ichi Tarusawa, Hidenori Takahashi, Shintaro Koshida, and Natsuko M. Kato "Evaluations of new atmospheric windows at thirty micron wavelengths for astronomy", Proc. SPIE 8444, Ground-based and Airborne Telescopes IV, 84446B (17 September 2012); https://doi.org/10.1117/12.925258

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