Near-Infrared observations and lens model for UM673

Aims: We perform a detailed photometric analysis of the lensed system UM673 (Q0142-100) and explore possible models of the lens. Methods: We examined high-resolution adaptive optics images of UM673 taken with the Subaru telescope in the H band. We also analysed the J, H and K-band observational data of UM673 obtained with the 1.3-m telescope at the CTIO observatory. Results: We measure properties of the lensing and nearby galaxies in the field of the lensed quasar UM673. In the Subaru H-band images of UM673 we detect a new extended object, presumably a galaxy, which has not been observed in the previous HST observations of the system. Based on the CTIO observations of UM673 we present J and H-band photometry, and estimates of the J, H and K-band flux ratios between the two UM673 components in recent epochs. The near-infrared fluxes of the A and B components of UM673 and their published optical fluxes are analysed to measure extinction properties of the lensing galaxy. We estimate the extinction-corrected flux ratio between components A and B to be about 2.14 mag. We discuss lens models for the UM673 system constrained with the positions of the UM673 components, their flux ratio and the previously measured time delay.