About the origin of extinction in the gravitational lens system MG J0414+0534

Photometric measurements of the highly reddened gravitational mirage MG J04 14+0534 have been carried out either by PSF subtraction or by applying accu rate deconvolution algorithms to optical (R, I) and near-infrared (K) image s obtained at CFHT and NOT under sub-arcsecond seeing conditions. It is con firmed that the close pair of images A1-A2 suffers a larger extinction than B and C. While the colours of image A2 obtained from ground-based data see m inconsistent with a simple reddening law, higher resolution images availa ble from HST archives reveal an additional extended component (arc) which i ntroduces significant errors in the photometric decomposition. When the are component is properly taken into account, the colours of the 4 nucleus ima ges do agree with a classical reddening law, with A2 being by far the most obscured component. Such a differential extinction (maximum difference Delt a E(R-I) similar or equal to 0.6) is likely due to the tensing galaxy. This does not mean that all the extinction occurs into the lens. Indeed, the fa ct that the are is much less red than the images of the nucleus suggests th at an important part of the reddening is intrinsic to the source. Finally, no significant variability is observed within this data set, i.e. between 1 994 and 1997, while a discrepancy from earlier data is noticed for (A1 + A2 ).