HST Observations of the Gravitationally Lensed Cloverleaf Broad   Absorption Line QSO H1413+1143: Modeling the Lens
  We investigate gravitational lens models for the quadruply-lensed Cloverleaf BAL QSO H1413+1143 based on the HST WFPC/WFPC2 astrometric and photometric data of the system by Turnshek et al. and the HST NICMOS-2 data by Falco et al. The accurate image positions and the dust-extinction-corrected relative amplifications, along with a possible detection of the lensing galaxy in the infrared, permit more accurate lens models than were previously possible. While more recent models are qualitatively consistent with the HST data, none of the previous models considered the dust-extinction-corrected relative amplifications of the image components. We use the power-law elliptical mass model to fit the HST data. We find that a single elliptical galaxy perturbed by an external shear can fit the image positions within the observational uncertainties; however, the predicted relative magnifications are only roughly consistent with the observational relative amplifications. We find that a primary galaxy combined with a secondary galaxy in the vicinity of the Cloverleaf or a cluster centered (south-)west of the Cloverleaf can fit both the image positions and relative amplifications within the observational uncertainties. We discuss future observations which could be used to test and/or further constrain lens models of the Cloverleaf. 
Kyu-Hyun Chae, David A. Turnshek