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See detailHST confirmation of the lensed quasar J03.13.
Surdej, Jean ULg; Claeskens, Jean-François ULg; Remy, M. et al

in Astronomy and Astrophysics (1997), 327

In order to definitely prove the claim by Claeskens et al. (1996A&A...305L...9C) that J03.13 is a doubly imaged quasar, WFPC2 direct imaging and FOS spectroscopy of this compact system have been obtained ... [more ▼]

In order to definitely prove the claim by Claeskens et al. (1996A&A...305L...9C) that J03.13 is a doubly imaged quasar, WFPC2 direct imaging and FOS spectroscopy of this compact system have been obtained with HST. These textbook case observations clearly show that J03.13 consists of two point-like images separated by 0.849"+/-0.001" 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 find that J03.13 A and B have identical spectra within the measurement uncertainties. The data also show that spectroscopic contamination of B by A is negligible. We do confirm the redshift z=2.545 for J03.13 A and B (emission-lines due to Ly-beta lambda1025 and O VI lambdalambda1031, 1037 are also detected), first derived from an unresolved ground-based spectrum of the two components by Claeskens et al. We also find that the absorption line system at z=2.344 (CIV and Ly-alpha) is present in the spectra of A and B. On the contrary, the absorption 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 WFPC2 imagery, we can rule out the presence of a third component fainter than A by up to 5.2mag. with an angular separation >=0.13". [less ▲]

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See detailGround-based and HST Direct Imaging of HLQs
Surdej, Jean ULg; Jaunsen, A. O.; Claeskens, Jean-François ULg et al

in Kochanek, C.; Hewitt, J. (Eds.) Astrophysical Applications of Gravitational Lensing (1996)

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See detailGravitational lensing statistics based on a large sample of highly luminous quasars
Surdej, Jean ULg; Claeskens, Jean-François ULg; Crampton, D. et al

in Astronomical Journal (The) (1993), 105

Results on gravitational lensing statistics applied to a sample of 469 highly luminous quasars are reported. The objects were directly imaged, either from the ground under optimal seeing conditions, or ... [more ▼]

Results on gravitational lensing statistics applied to a sample of 469 highly luminous quasars are reported. The objects were directly imaged, either from the ground under optimal seeing conditions, or using the HST. We have derived values for the effectiveness parameter F of galaxies, modeled by means of singular isothermal spheres, to produce macrolensed images of distant quasars, and upper limits on the density parameter Omega(L) of compact objects with masses between 10 exp 10 and 10 exp 12 solar masses. Adopting H(0)= 50 km/s/Mpc, Omega(0)= 1, and Lambda = 0, we find that at the 99.7 percent confidence level, F is between 0.005 and 0.478 and that Omega(L) is less than 0.02. A critical discussion of these results is presented. Finally, comparing the efficiencies of ground-based and space instruments used to search for gravitational lens systems among highly luminous quasars, we conclude that for the near future, ground-based direct imaging characterized by a good dynamical range still constitutes the best observational strategy. [less ▲]

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See detailErratum - Q:1208+1011 - the Most Distant Multiply Imaged Quasar or a Binary
Magain, Pierre ULg; Surdej, Jean ULg; Vanderriest, C. et al

in Astronomy and Astrophysics (1993), 272

In the title of this Letter, the word "multiply" was accidentally omitted. The correct title is shown above.

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See detailSearch for gravitational lenses in a large sample of highly luminous quasars and statistical determination of cosmological parameters
Claeskens, Jean-François ULg; Crampton, D.; Filippenko, A. V. et al

in Surdej, Jean; Fraipont-Caro, D.; Gosset, Eric (Eds.) et al The proceedings of the 31st Liège International Astrophysical Colloquium "Gravitational lenses in the Universe" (1993)

Results on gravitational lensing statistics applied to a sample of 469 highly luminous quasars are reported.

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See detailThe new gravitational lens candidate Q 1208+1011 and the importance of high quality data.
Magain, Pierre ULg; Surdej, Jean ULg; Vanderriest, C. et al

in The Messenger (1992), 67

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See detailQ 1208 + 1011 - The most distant imaged quasar, or a binary?
Magain, Pierre ULg; Surdej, Jean ULg; Vanderriest, C. et al

in Astronomy and Astrophysics (1992), 253(Letters), 13-16

The paper reports the discovery of a new gravitational lens candidate: the high redshift (z = 3.803) and highly luminous (V = 17.5, M[SUB]V[/SUB] = -30.3) quasar Q 1208 + 1011. As derived from the ... [more ▼]

The paper reports the discovery of a new gravitational lens candidate: the high redshift (z = 3.803) and highly luminous (V = 17.5, M[SUB]V[/SUB] = -30.3) quasar Q 1208 + 1011. As derived from the analysis of direct CCD frames taken with the ESO/MPI 2.2 m telescope, this multiple quasar consists of two pointlike images, separated by 0.45 arcsec and characterized by a brightness ratio of 3.5, in red light. Existing spectroscopic data support the gravitational lens interpretation for this system but cannot exclude the hypothesis of a binary quasar. In the former case, the spectrum suggests that, if the metallic absorption line system reported by Steidel (1990) at a redshift z = 2.9157 is associated with the deflector, the mass of the lens should be of the order of M = 7.8 x 10 exp 11 solar masses. Evaluation of a recent HST PC frame obtained for Q 1208 + 1011 within the snapshot survey for gravitational lenses confirms the above results. [less ▲]

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See detailUsing the HST archive - gravitational lenses from the snapshot survey
Pirenne, B.; Surdej, Jean ULg; Magain, Pierre ULg

Article for general public (1992)

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See detailGravitational lensing statistics based on a large sample of highly luminous quasars observed with ground-based telescopes and HST
Surdej, Jean ULg; Claeskens, Jean-François ULg; Crampton, D. et al

in Benvenuti, Piero; Schreier, Ethan J (Eds.) Proceedings of a ST-ECF/STScI Workshop "Science with the Hubble Space Telescope" (1992)

We present here some recent results on gravitational lensing statistics as applied to a sample of 470 highly luminous quasars.

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See detailOptical observations of gravitational lenses
Surdej, Jean ULg; Claeskens, Jean-François ULg; Hutsemekers, Damien ULg et al

in Kayser, Rainer; Schramm, Thomas; Nieser, Lars (Eds.) Proceedings of the Hamburg conference on ’Gravitational Lenses’, Lecture Notes in Physics 406 (1992)

We report here on some of the major developments achieved on optical observations of gravitational lenses since the last conference devoted to 'Gravitational Lensing'.

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See detailA Search for Gravitational Lenses Using Sky Survey Plate Scans
Meylan, G.; Djorgovski, S.; Surdej, Jean ULg et al

in Kayser, Rainer; Schramm, Thomas; Nieser, Lars (Eds.) Proceedings of the Hamburg conference on ’Gravitational Lenses’, Lecture Notes in Physics 406 (1992)

We used scans of sky survey plates available at STScl to look for the presence of multiple-image QSOs which could be due to gravitational lensing. We extracted about 1500 fields, each having 5 arcmin in ... [more ▼]

We used scans of sky survey plates available at STScl to look for the presence of multiple-image QSOs which could be due to gravitational lensing. We extracted about 1500 fields, each having 5 arcmin in size, around QSOs brighter than m v = 18. No lenses have been found so far. We found several cases of galaxies close in projection (within a few arcsec) from QSOs. [less ▲]

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