A STUDY OF GRAVITATIONAL LENS CHROMATICITY WITH THE HUBBLE SPACE TELESCOPE

We report Hubble Space Telescope observations of six gravitational lenses with the Advanced Camera for Surveys. We measured the flux ratios between the lensed images in seven filters from 8140 angstrom to 2200 angstrom. In three of the systems, HE0512-3329, B1600+434, and H1413 + 117, we were able to construct UV extinction curves partially overlapping the 2175 angstrom feature and characterize the properties of the dust relative to the Galaxy and the Magellanic Clouds. In HE1104-1804, we detect chromatic microlensing and use it to study the physical properties of the quasar accretion disk. For a Gaussian model of the disk exp(-r(2)/2r(s)(2) ), scaling with wavelength as r(s) alpha lambda(p), we estimate r(s) (lambda 3363) = 4(-2)(+4) (7 +/- 4) light days and p = 1.1 +/- 0.6 (1.0 +/- 0.6) for a logarithmic (linear) prior on r(s). The remaining two systems, FBQ0951+2635 and SBS1520+530, yielded no useful estimates of extinction or chromatic microlensing.