------------------------------------------------------------------------
 sskim.tex 2005 PASP, 117, 445
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\documentclass[preprint]{aastex}
\slugcomment{To appear in PASP (2005, v. 117, p. 445)}
\shorttitle{Theoretical Isochrones near the K Band}
\shortauthors{KIM, FIGER, LEE, \& OH}
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\begin{document}
\title{Theoretical Isochrones with Extinction in the K-Band}
\author{Sungsoo S. Kim\altaffilmark{1}, Donald F. Figer\altaffilmark{2},
Myung Gyoon Lee\altaffilmark{3}, and Seungkyung Oh\altaffilmark{1}}
\altaffiltext{1}{Dept. of Astronomy \& Space Science, Kyung Hee University,
Yongin-shi, Kyungki-do 449-701, Korea; sskim@ap.khu.ac.kr}
\altaffiltext{2}{Space Telescope Science Institute, 3700 San Martin Drive,
Baltimore, MD 21218; figer@stsci.edu}
\altaffiltext{3}{Astronomy Program, SEES, Seoul National University,
Seoul 151-742, Korea; mglee@astrog.snu.ac.kr}

We calculate theoretical isochrones, in a consistent way, for five
filters in the atmospheric window between $1.9 \, {\rm \mu m}$ and
$2.5 \, {\rm \mu m}$, $K$, $K'$, $K_s$, F205W, and F222M, using
the Padova stellar evolutionary models by Girardi et al.
Even when displayed in the same Vega magnitude system, the near-infrared
colors of the same isochrone can differ by up to 0.18 mag at its
bright end, depending on the filter.  We present magnitude transformations
between $K$-band filters as a function of color from $H$ \& $K$
band filters. Isochrones with extinction at $K$
of up to 6 mag are also presented.  We find that care is needed
when comparing extinction values that are estimated using different
filter sets in the $K$-band, in particular when comparing those
between atmospheric and space filter sets: extinction values for
space filters can be in error by up to 0.3 mag.
To reduce this error, we introduce an ``effective extinction slope''
for each filter set and isochrone model, which describes the extinction
behaviour of isochrones in the color-magnitude diagram more correctly
than the actual extinction law.  Our calculation also suggests that
the extinction law implied by the observations of Rieke, Rieke, \& Paul
for wavelengths between $H$ and $K$ bands is better described by a
power-law function with an exponent of 1.61, instead of 1.55, which is
commonly used with an assumption that the transmission functions of $H$
and $K$ filters are Dirac delta functions.
\end{abstract}
\keywords{Hertzsprung-Russell diagram --- techniques: photometric ---
stars: fundamental parameters --- infrared: stars}

\end{document}