Japan Geoscience Union Meeting 2014

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[U-06_28AM1] New Progress toward the Understanding of Small Solar System Bodies

Mon. Apr 28, 2014 9:00 AM - 10:45 AM 503 (5F)

Convener:*Masahiko Arakawa(Graduate School of Science, Kobe University), Taishi Nakamoto(Tokyo Institute of Technology), Sei-ichiro WATANABE(Division of Earth and Planetary Sciences, Graduate School of Science, Nagoya University), Masanao Abe(Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency), MASATERU ISHIGURO(Department of Physics and Astronomy, Seoul National University), Chair:Masahiko Arakawa(Graduate School of Science, Kobe University)

10:30 AM - 10:45 AM

[U06-P21_PG] Development of a wide-band optical filter optimized for deep imaging of small solar-system bodies

3-min talk in an oral session

*Shin-ichiro OKUMURA1, Kota NISHIYAMA1, Seitaro URAKAWA1, Tsuyoshi SAKAMOTO1, Noritsugu TAKAHASHI1, Makoto YOSHIKAWA2 (1.Japan Spaceguard Association, 2.JAXA)

Keywords:optical, small solar system body, light pollution, wide-band filter

We developed a newly designed wide-band optical filter and evaluated its performance. It is optimized for deep imaging of small solar-system bodies. The new filter, which we denote as Wi, is designed to reduce contamination by light pollution from street lamps, especially strong mercury and sodium emission lines. For the reasons that (1) much of artificial light pollution concentrates in the V band, (2) the photon numbers peak at a wavelength of 6350 Å in the spectrum of sunlight, and (3) many asteroids have their peak/plateau reflectance at around 7000 Å in the optical range, the new filter's cut-on wavelength is set to 5880 Å by using an OG590 Schott color glass filter. On the other hand, the cut-off wavelength, which is achieved by a short-pass interference coating, is set to 9380 Å in consideration of worst of the OH night sky emission and the atmospheric water vapor absorption band at 9400 Å.Compared with the use of a commercially available long-wave cut wide-band filter (W filter, 4900-9100 Å), the sky brightness is 10-20 % reduced by the Wi filter under bright-sky conditions by not only artificial light pollution but scattered moonlight. In the detection of asteroids, the detected total flux of an asteroid through the Wi filter has been 3% larger than that through the W filter, though the width of the Wi filter response function is 16% narrower than that of the W filter. By using the Wi filter, the S/N ratios in the detection of asteroids were improved by about 6%, on average, compared with the use of the W filter, and the improvements were slightly larger in a brighter sky. The use of the CCD with high sensitivity at longer wavelength, such as the back-illuminated, fully-depleted CCD, will show a larger improvement in the S/N ratio by using the Wi filter.Reference: Wide-Band Optical Filter Optimized for Deep Imaging of Small Solar-System Bodies, Okumura et al. Publications of the Astronomical Society of Japan, 64, 47 (2012)