We combined sensitive near-infrared data obtained with ground-based imagers on the ESO NTT and VLT telescopes with space mid-infrared data acquired with the IRAC imager on the Spitzer Space Telescope to calculate the extinction law A _ { \lambda } / A _ { K _ { S } } as a function of \lambda between 1.25 and 7.76 \mu m to an unprecedented depth in ( catalog Barnard 59 ) , a star forming , dense core located in the Pipe Nebula .
The ratios A _ { \lambda } / A _ { K _ { S } } were calculated from the slopes of the distributions of sources in color-color diagrams \lambda - K _ { S } vs . H - K _ { S } .
The distributions in the color-color diagrams are fit well with single slopes to extinction levels of A _ { K _ { S } } \approx 7 ( A _ { V } \approx 59 mag ) .
Consequently , there appears to be no significant variation of the extinction law with depth through the B59 line of sight .
However , when slopes are translated into the relative extinction coefficients A _ { \lambda } / A _ { K _ { S } } , we find an extinction law which departs from the simple extrapolation of the near-infrared power law extinction curve , and agrees more closely with a dust extinction model for a cloud with a total to selective absorption R _ { V } =5.5 and a grain size distribution favoring larger grains than those in the diffuse ISM .
Thus , the difference we observe could be possibly due to the effect of grain growth in denser regions .
Finally , the slopes in our diagrams are somewhat less steep than those from the study of Indebetouw et al .
( 13 ) for clouds with lower column densities , and this indicates that the extinction law between 3 and 8 \mu m might vary slightly as a function of environment .