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From: Shogo NISHIYAMA <shogo@kusastro.kyoto-u.ac.jp>
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%astro-ph/0902.3095
%http://www.kusastro.kyoto-u.ac.jp/~shogo/papers/09NishiyamaExlawMIR.pdf

\documentstyle[apjfonts,emulateapj]{article}

\begin{document}

\title{Interstellar Extinction Law toward the Galactic Center I\hspace{-.1em}I\hspace{-.1em}I : \\
$J$, $H$, $K_S$ bands in the 2MASS and the MKO systems, \\
and 3.6, 4.5, 5.8, 8.0 $\mu$m in the {\it Spitzer}/IRAC system}

\author{Shogo Nishiyama(1), Motohide Tamura(2), Hirofumi Hatano(3), Daisuke Kato(4),
Toshihiko Tanabe(5), Koji Sugitani(6), and Tetsuya Nagata(1)
}

\altaffiltext{1}{Department of Astronomy, Kyoto University, 
Kyoto, 606-8502, Japan}
\altaffiltext{2}{National Astronomical Observatory of Japan, 
Mitaka, Tokyo, 181-8588, Japan}
\altaffiltext{3}{Department of Astrophysics, Nagoya University, 
Nagoya, 464-8602, Japan}
\altaffiltext{4}{Department of Astronomy, Graduate School of Science, 
The University of Tokyo, Bunkyo-ku, Tokyo, 113-0033, Japan}
\altaffiltext{5}{Institute of Astronomy, Graduate School of Science, 
The University of Tokyo, Mitaka, Tokyo, 181-0015, Japan}
\altaffiltext{6}{Graduate School of Natural Sciences, Nagoya City University,
Nagoya, 464-8602, Japan}


%------------------------------------------------------

\begin{abstract}
We have determined interstellar extinction law toward the Galactic center (GC) 
at the wavelength from 1.2 to 8.0 $\mu$m,
using point sources detected in the IRSF/SIRIUS near-infrared survey
and those in the 2MASS and {\it Spitzer}/IRAC/GLIMPSE I\hspace{-.1em}I catalogs.
The central region 
$\mid l \mid \la 3\fdg0$ and $\mid b \mid \la 1\fdg0$
has been surveyed in the $J$, $H$ and $K_S$ bands
with the IRSF telescope and the SIRIUS camera whose filters are similar to 
the Mauna Kea Observatories (MKO) near-infrared photometric system.
Combined with the GLIMPSE I\hspace{-.1em}I point source catalog,
we made $K_S$ versus $K_S - \lambda$ color-magnitude diagrams
where $\lambda =$ 3.6, 4.5, 5.8, and 8.0 $\mu$m.
The $K_S$ magnitudes of bulge red clump stars 
and the $K_S - \lambda$ colors of red giant branches
are used as a tracer of the reddening vector in the color-magnitude diagrams.
From these magnitudes and colors, we have obtained 
the ratios of total to selective extinction $A_{K_S}/E_{K_S-\lambda}$
for the four IRAC bands.  
Combined with $A_{\lambda}/A_{K_S}$ for the $J$ and $H$ bands derived by Nishiyama et al.,
we obtain
$A_J : A_H : A_{K_S} : A_{[3.6]} : A_{[4.5]} : A_{[5.8]} : A_{[8.0]}
= 3.02:1.73:1:0.50:0.39:0.36:0.43$ for the line of sight toward the GC.
This confirms the flattening of the extinction curve at $\lambda \ga 3 \mu$m
from a simple extrapolation of the power-law extinction at shorter wavelengths,
in accordance with recent studies.  
The extinction law in the 2MASS $JHK_S$ bands has also been calculated,
and a good agreement with that in the MKO system is found. 
Thus, it is established that 
the extinction in the wavelength range of $J$, $H$, and $K_S$ 
is well fitted by a power law of steep decrease 
$A_\lambda \propto \lambda^{-2.0}$ toward the GC.  
In nearby molecular clouds and diffuse interstellar medium, 
the lack of reliable measurements of the total to selective extinction ratios
hampers unambiguous determination of the extinction law; 
however, observational results toward these lines of sight
cannot be reconciled with a single extinction law.
\end{abstract}

\keywords{infrared: ISM --- dust, extinction --- stars: horizontal-branch --- Galaxy: center}

%------------------------------------------------------

\end{document}