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Astron. Astrophys. 327, L1-L4 (1997)

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1. Introduction

In a search for gravitational lensing within a sample of highly luminous quasars (hereafter HLQs, Surdej et al. 1993), Claeskens et al. (1996, Paper I) have reported the identification of a new candidate for the quasar J03.13. On the basis of direct images obtained with the MPI/ESO 2.2m and NTT telescopes, they found that this high redshift and bright (B = 17.4) quasar consists of two point-like images with magnitude differences [FORMULA] B = 2.15, [FORMULA] R = 2.14 and [FORMULA] i = 2.05 [FORMULA] 0.05, and angular separations of 0.88 [FORMULA], 0.84 [FORMULA] and 0.81 [FORMULA] [FORMULA] 0.02 [FORMULA], in the B, R and Gunn-i passbands, respectively. Because of the too small angular separation, they could only obtain a spatially unresolved low resolution spectrum of J03.13 A and B with the NTT + EMMI in February 1994. They measured a redshift z = 2.55 for the quasar and identified two narrow absorption line systems at z = 2.344 (Ly [FORMULA], CIV) and z = 1.085 (FeII, MgI, MgII). They concluded that it was mandatory to obtain spectra of the two resolved point-like images in order to definitely prove the gravitational lens hypothesis for this system.

Multiple direct CCD frames of J03.13 were obtained on November 28, 1995 through the F555W and F814W filters with the WFPC2 camera onboard HST. Analysis of these observations is described in section 2. From these direct images, it was possible to measure very accurate astrometric positions and brightnesses of the two components. It then became feasible to properly center these targets within the standard 0.5 circular aperture of the Faint Object Spectrograph (FOS). As a result, good S/N low resolution FOS spectra of J03.13 A and B could be obtained on October 28, 1996. These data and their interpretation are presented in section 3.

Finally, a discussion and conclusions form the last section.

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© European Southern Observatory (ESO) 1997

Online publication: April 6, 1998