Line derived infrared extinction towards the Galactic Center
  We derive the extinction curve towards the Galactic Center from 1 to 19
micron. We use hydrogen emission lines of the minispiral observed by ISO-SWS
and SINFONI. The extinction free flux reference is the 2 cm continuum emission
observed by the VLA. Towards the inner 14" * 20" we find an extinction of
A(2.166 micron)=2.62 +/- 0.11, with a power-law slope of alpha=-2.11 +/- 0.06
shortward of 2.8 micron, consistent with the average near infrared slope from
the recent literature. At longer wavelengths, however, we find that the
extinction is grayer than shortward of 2.8 micron. We find it is not possible
to fit the observed extinction curve with a dust model consisting of pure
carbonaceous and silicate grains only, and the addition of composite particles,
including ices, is needed to explain the observations. Combining a distance
dependent extinction with our distance independent extinction we derive the
distance to the GC to be R_0=7.94 +/- 0.65 kpc. Towards Sgr A* (r<0.5") we
obtain A_H=4.21 +/- 0.10, A_Ks=2.42 +/- 0.10 and A_L'=1.09 +/- 0.13.
