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Absolute Photometric Calibration of the Infrared Camera (IRC) aboard AKARI
The absolute photometric calibration of imaging observations with theInfrared Camera (IRC) aboard the AKARI satellite was performed bymonitoring the same stars regularly and by observing aset of standardstars. By our monitoring observations, we confirmed that all channels ofthe IRC were stable to within 4% and that their sensitivities wereconstant until the liquid helium was exhausted. Using the data of theserepeated observations, we evaluated the intrinsic errors as afunction ofthe brightnesses of objects and found that the errors increase rapidlytoward fainter objects. We also checked the consistency between shortand long exposure times, and confirmed that the data sampling had beenexecuted as designed. Finally, by comparing the estimated in-band fluxdensities and the observed data values of standard stars, we obtainedconversion factors to the absolute flux densities of all theband/exposure configurations. Their absolute uncertainties are estimatedto be less than 6%.
| Ground-based Mid-Infrared Spectroscopy of Faint Standard Stars in the North Ecliptic Polar Region for the ASTRO-F Infrared Camera
Faint standard stars in the mid-infrared region (less than a few hundredmillijanskys at 9 μm) are required for the on-orbit calibration ofthe Infrared Camera (IRC) on board ASTRO-F because of its highsensitivity, as well as the small dynamic range. Mid-infraredlow-resolution (λ/Δλ~250) spectra of six faint K andM giant stars (70-180 mJy at 9 μm, K1.5-M0 III), which are located inthe north ecliptic polar region and are thus suitable for calibratorsfor the IRC, are obtained by using the Cooled Mid-Infrared Camera andSpectrometer (COMICS) on the Subaru telescope to test the faint-infraredstandard-star network recently constructed for space-borne instruments.The spectra are directly calibrated relative to Vega (A0 V). The presentresults indicate that the spectra of the faint standard K-M0 giant starsshow good agreement with those predicted in the standard network within10% accuracy on average. The overall spectral shapes are also inagreement with the predictions. In particular, the observed SiOabsorption feature in the 8 μm region matches well with theprediction for an M0 III star. The present observations directly connecta primary standard calibrator (Vega) to faint K giant calibrators of thenetwork in the 10 μm region and validate several faint (~0.1 Jy)members of the standard-star network for the first time. Absolutecalibrations are provided for five of the medium-band filters of theCOMICS instrument in the 10 μm window.Based on data collected at the Subaru Telescope, which is operated bythe National Astronomical Observatory of Japan.
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