GROUND-BASED MID-INFRARED SPECTROSCOPY OF FAINT STANDARD STARS IN THE NORTH ECLIPTIC POLAR REGION FOR THE ASTRO-F INFRARED CAMERA1

Faint standard stars in the mid-infrared region (less than a few hundred millijanskys at 9 (mu)m) are required for the on-orbit calibration of the Infrared Camera (IRC) on board ASTRO-F because of its high sensitivity, as well as the small dynamic range. Mid-infrared low-resolution ((lambda)/(delta)(lambda) ~250) spectra of six faint K and M giant stars (70–180 mJy at 9 (mu)m, K1.5–M0 III), which are located in the north ecliptic polar region and are thus suitable for calibrators for the IRC, are obtained by using the Cooled Mid-Infrared Camera and Spectrometer (COMICS) on the Subaru telescope to test the faint-infrared standard-star network recently constructed for space-borne instruments. The spectra are directly calibrated relative to Vega (A0 V). The present results indicate that the spectra of the faint standard K–M0 giant stars show good agreement with those predicted in the standard network within 10% accuracy on average. The overall spectral shapes are also in agreement with the predictions. In particular, the observed SiO absorption feature in the 8 (mu)m region matches well with the prediction for an M0 III star. The present observations directly connect a primary standard calibrator (Vega) to faint K giant calibrators of the network in the 10 (mu)m region and validate several faint (~0.1 Jy) members of the standard-star network for the first time. Absolute calibrations are provided for five of the medium-band filters of the COMICS instrument in the 10 (mu)m window.