Distances and extinction values are usually degenerate .
To refine the distance to the general Galactic Center region , a carefully determined extinction law ( taking into account the prevailing systematic errors ) is urgently needed .
We collected data for 55 classical Cepheids projected toward the Galactic Center region to derive the near- to mid-infrared extinction law using three different approaches .
The relative extinction values obtained are A _ { J } / A _ { K _ { s } } = 3.005 ,A _ { H } / A _ { K _ { s } } = 1.717 ,A _ { [ 3.6 ] } / A _ { K _ { s } } = 0. % 478 ,A _ { [ 4.5 ] } / A _ { K _ { s } } = 0.341 ,A _ { [ 5.8 ] } / A _ { K _ { s } } = 0.234 ,A _ { [ 8.0 ] } / A _ { K% _ { s } } = 0.321 ,A _ { W 1 } / A _ { K _ { s } } = 0.506 , and A _ { W 2 } / A _ { K _ { s } } = 0.340 .
We also calculated the corresponding systematic errors .
Compared with previous work , we report an extremely low and steep mid-infrared extinction law .
Using a seven-passband ‘ optimal distance ’ method , we improve the mean distance precision to our sample of 55 Cepheids to 4 % .
Based on four confirmed Galactic Center Cepheids , a solar Galactocentric distance of R _ { 0 } = 8.10 \pm 0.19 \pm 0.22 kpc is determined , featuring an uncertainty that is close to the limiting distance accuracy ( 2.8 % ) for Galactic Center Cepheids .