HST confirmation of the lensed quasar J03.13.

In order to denitely prove the claim by Claeskens et al. (1996) that J03.13 is a doubly imaged quasar, WFPC2 direct imaging and FOS spectroscopy of this compact system havebeenobtainedwithHST.Thesetextbookcaseobservations clearly show that J03.13 consists of two point-like images sep- arated by 0.849 00 0.001 00 with a magnitude difference of 2.14 0.03 in V and I. We see no trace of a lensing galaxy. From the FOS observations, we nd that J03.13 A and B have identi- cal spectra within the measurement uncertainties. The data also show that spectroscopic contamination of B by A is negligi- ble. We do conrm the redshift z = 2.545 for J03.13 A and B (emission-lines due to Ly 1025 and Ovi 1031, 1037 are also detected), rst derived from an unresolved ground-based spectrumofthetwocomponentsbyClaeskensetal.Wealsond that the absorption line system at z = 2.344 (Civ and Ly ) is present in the spectra of A and B. On the contrary, the ab- sorption line system at z = 1.085 (Mgii) is only present in the spectrum of J03.13 A. If this latter system is associated with the lens, we may expect that image A consists of two radially merging images with a very small angular separation. From the WFPC2imagery,wecanruleoutthepresenceofathirdcompo- nent fainter than A by up to 5.2 mag. with an angular separation 0.13 00 .