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- Title
Revised wavelength and spectral response calibrations for AKARI near-infrared grism spectroscopy: Cryogenic phase.
- Authors
Shunsuke BABA; Takao NAKAGAWA; Mai SHIRAHATA; Naoki ISOBE; Fumihiko USUI; Youichi OHYAMA; Takashi ONAKA; Kenichi YANO; Chihiro KOCHI
- Abstract
We perform revised spectral calibrations for the AKARI near-infrared grism to correct quantitatively for the effect of the wavelength-dependent refractive index. The nearinfrared grism covering the wavelength range of 2.5-5.0μm, with a spectral resolving power of 120 at 3.6μm, is found to be contaminated by second-order light at wavelengths longer than 4.9μm, which is especially serious for red objects. First, we present the wavelength calibration considering the refractive index of the grism as a function of the wavelength for the first time. We find that the previous solution is positively shifted by up to 0.01μm compared with the revised wavelengths at 2.5-5.0μm. In addition, we demonstrate that second-order contamination occurs even with a perfect order-sorting filter owing to the wavelength dependence of the refractive index. Secondly, the spectral responses of the system from the first- and second-order light are simultaneously obtained from two types of standard objects with different colors. The response from the second-order light suggests leakage of the order-sorting filter below 2.5μm. The relations between the output of the detector and the intensities of the first- and second-order light are formalized by a matrix equation that combines the two orders. The removal of the contaminating second-order light can be achieved by solving the matrix equation. The new calibration extends the available spectral coverage of the grism mode from 4.9μm up to 5.0μm. The revision can be used to study spectral features falling in these extended wavelengths, e.g., the carbon monoxide fundamental ro-vibrational absorption within nearby active galactic nuclei.
- Subjects
WAVELENGTH measurement; INFRARED absorption; REFRACTIVE index; ACTIVE galactic nuclei; SPECTRAL sensitivity; DATA analysis
- Publication
Publications of the Astronomical Society of Japan, 2016, Vol 68, Issue 2, p27-1
- ISSN
0004-6264
- Publication type
Article
- DOI
10.1093/pasj/psw013