AAS 207th Meeting, 8-12 January 2006
Session 133 The Milky Way
Poster, Wednesday, 9:20am-6:30pm, January 11, 2006, Exhibit Hall

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[133.12] Nonlinear Reddening Behavior in the Near-Infrared Color-Magnitude Diagram

S. S. Kim (Kyung Hee University), D. F. Figer (STScI), M. G. Lee (Seoul National University)

We calculate theoretical isochrones in a consistent way for five filters (K, K', Ks, F205W, F222M) in the K band using the Padova stellar evolutionary models by Girardi et al. We present magnitude transformations between K-band filters as a function of color. Isochrones with extinction of up to 6 magnitudes in the K band are also presented. We find that the reddened isochrones of different filter pairs behave as if they follow different extinction laws and that the extinction curves of HST/NICMOS filter pairs in the color-magnitude diagram are considerably nonlinear. Because of these problems, extinction values estimated with NICMOS filters can be in error by up to 1.3 mag. Our calculations find that it is not desirable to infer extinction law from observations with an assumption that the filter transmission functions are Dirac delta functions.

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