Infrared Survey of the Galactic Center with the 1.4-m IRSF telescope at SAAO

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Infrared survey of the Galactic center has been performed in the J, H, and K bands with the high resolution of 0.45"/pix. The observed area covers ±1 deg (±150 pc) in the Galactic latitude and ±10 deg (±1.5 kpc) in the Galactic longitude. We used Simultaneous Infrared Imager for Unbiased Survey (SIRIUS) with three 1024x1024 HgCdTe arrays, which were attached to the IRSF 1.4-m telescope placed at South African Astronomical Observatory by Nagoya University. The array read-out has been improved and the efficiency of the observation is now extremely high.First, using the detected red clump stars in the central degree, which are in the core He burning phase, we determined the interstellar reddening law ; this is different from the color-excess method in the literature, and much more accurate. The interstellar extinction is deviated from the Rieke-Lebofsky law (proportional to the -1.6th order of the wavelength), and rather follows to the -2nd order of the wavelength. It has been sometimes argued that the infrared extinction is "universal" in the various lines of sight, but this result has presented clear evidence against it. The determined index itself is also important in dereddening the observed spectra.Then, we derived the peak of distribution of red clump stars in the ±1.5 kpc region around the Galactic center. The apparent magnitude peak changes continuously along the Galactic plane, from K=13.4 mag to 12.2 mag after dereddening. This variation is explained by the bar-like structure found in previous studies, but we find an additional inner structure within the region of 1.2 kpc in diameter, where the apparent magnitude peak changes by only 0.1 mag.