Interstellar Extinction Law in the J, H, and KS Bands, toward the Galactic Center

Shogo Nishiyama, Tetsuya Nagata, Nobuhiko Kusakabe, Noriyuki Matsunaga, Takahiro Naoi, Daisuke Kato, Chie Nagashima, Koji Sugitani, Motohide Tamura, Toshihiko Tanabe, and Shuji Sato

Paper: ApJ, Feb 2006, in press

EPrint Server: astro-ph/0601174


We have determined the ratios of total to selective extinction in the near-infrared bands (J, H, KS) toward the Galactic center from the observations of the region |l| < 2.0^o and 0.5^o < |b| < 1.0^o with the IRSF telescope and the SIRIUS camera. Using the positions of red clump stars in color-magnitude diagrams as a tracer of the extinction and reddening, we determine the average of the ratios of total to selective extinction to be A_KS/E_H-KS = 1.44+/-0.01, A_KS/E_J-KS = 0.494+/-0.006, and A_H/E_J-H =1.42+/-0.02, which are significantly smaller than those obtained in previous studies. >From these ratios, we estimate that A_J : A_H : A_KS = 1 : 0.573 +/- 0.009 : 0.331 +/- 0.004 and E_J-H/E_H-KS = 1.72 +/- 0.04, and we find that the power law A_ lambda proportional to lambda -1.99 +/- 0.02 is a good approximation over these wavelengths. Moreover, we find a small variation in A_KS/E_H-KS across our survey. This suggests that the infrared extinction law changes from one line of sight to another, and the so-called ``universality'' does not necessarily hold in the infrared wavelengths.

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