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See detailGravitational Lenses and Damped Ly-alpha Systems
Smette, A.; Claeskens, Jean-François ULg; Surdej, Jean ULg

in Kochanek, C. S.; Hewitt, Jacqueline N (Eds.) Astrophysical applications of gravitational lensing: proceedings of the 173rd Symposium of the International Astronomical Union (1996)

Not Available

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See detail'Gravitational lenses in the Universe', The proceedings of the 31st Liège International Astrophysical Colloquium
Surdej, Jean ULg; Fraipont-Caro, D.; Gosset, Eric ULg et al

Book published by Université de Liège (1993)

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See detailGravitational lenses: observations
Surdej, Jean ULg

in invited talk delivered during the first general meeting of the European Astronomical Society "The impact of space research on astronomy" (1992)

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See detailGravitational lenses: observations, invited talk
Surdej, Jean ULg

in Proceedings of the First general meeting of the European Astronomical Society "The impact of space research on astronomy" (1992)

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See detailGravitational lensing
Surdej, Jean ULg; Claeskens, Jean-François ULg

in Bleeker, J. A.; Geiss, J.; Huber, M. (Eds.) The Century of Space Science, Volume I (2001)

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See detailGravitational Lensing as a Tool: Future Observational Prospects
Surdej, Jean ULg; Refsdal, S.

in Wamsteker, W.; Longair, Malcol S.; Kondo, Y. (Eds.) Frontiers of Space and Ground-Based Astronomy (1994)

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See detailGravitational lensing as a tool: future observational prospects
Surdej, Jean ULg

Conference (1993)

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See detailGravitational Lensing by a Wine Glass
Surdej, Jean ULg

Article for general public (1999)

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See detailGravitational Lensing by Damped LY alpha Absorbers
Smette, A.; Claeskens, Jean-François ULg; Surdej, Jean ULg

in Carilli, C. L.; Radford, S. J. E.; Menten, K. M. (Eds.) et al Highly Redshifted Radio Lines, ASP Conf. Series Vol. 156 (1999)

Spiral galaxies are thought to be the main responsible for the damped Ly-alpha (DLA) systems seen in QSO spectra. They can also act as gravitational lenses, affecting quantities derived in DLA surveys ... [more ▼]

Spiral galaxies are thought to be the main responsible for the damped Ly-alpha (DLA) systems seen in QSO spectra. They can also act as gravitational lenses, affecting quantities derived in DLA surveys. Assuming that z > 0 spiral galaxies are similar to local ones, we find that, at z 0.5, the number density of DLA systems may be over-estimated by up to 90% and the HI cosmological density (Omega[SUB]HI[/SUB]) by up to 170% in a survey using bright b[SUB]q[/SUB] = 16, z[SUB]q[/SUB] ga 2 QSOs and in the absence of important extinction by dust. Applying our model to existing surveys, we find that Omega[SUB]HI[/SUB] is significantly over-estimated only in the z < 1.7 ones (by 34%). Furthermore, statistical tests indicate that these surveys are indeed affected by gravitational lensing at a 2.3% confidence level. If luminosity functions for flat-spectrum radio-sources and optically selected QSOs are similar in shape and slopes, similar Gling effects should affect surveys for 21cm absorbers using bright, high-z flat-spectrum radio-sources. [less ▲]

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See detailGravitational lensing by damped Ly-alpha absorbers
Smette, Alain; Claeskens, Jean-François ULg; Surdej, Jean ULg

in New Astronomy (1997), 2

Assuming that (i) damped Ly-alpha absorbers (DLAs) arise in present-day-like spiral galaxies which are immersed in isothermal dark matter halos, (ii) that these galaxies obey the Tully-Fisher sigma/sigma ... [more ▼]

Assuming that (i) damped Ly-alpha absorbers (DLAs) arise in present-day-like spiral galaxies which are immersed in isothermal dark matter halos, (ii) that these galaxies obey the Tully-Fisher sigma/sigma_* = (L/L_*)^1/alpha_TF and the Holmberg R_L/R_* = (L/L_*)^alpha_H relations, and (iii) that they follow the Schechter luminosity distribution, we describe how their observed number density (dN/dz), distribution of column density (f(N)) as well as inferred cosmological density of HI (Omega_HI) derived from DLA surveys are affected by gravitational lensing (GL). The `by-pass' effect causes the lines-of-sight (LOSs) towards background QSOs to avoid the central parts of galaxies and reduces their effective cross-section for absorption; the `amplification bias' leads observers to select QSOs whose LOSs preferentially cross galaxies close to their Einstein radius. As a consequence, the determination of the quantities dN/dz, f(N) and Omega_HI from DLA surveys does not only depend on the redshift z and luminosity L of galaxies responsible for the absorbers but also on the column density profile of HI within the galaxies and on the redshift z_q and magnitude b_q of the background QSOs. For most of the existing surveys using b_q <~ 19 QSOs, the amplification bias dominates the combined effect resulting in a slight overestimate of dN/dz, f(N) and Omega_HI. We mainly find that observational strategies presently used to produce high-z DLA surveys result in avoiding the signature of significant GL effects: following our model, we determine that an overestimate of Omega_HI by more than 10% is unlikely for the z > 1.7 existing surveys, but may reach ~= 35% for the low redshift ones. However, we show that, in the absence of extinction by dust and micro-lensing effects, surveys ideally designed to enhance GL effects, i.e. to search for DLAs at z ~ 0.5 in front of very bright (b_q ~= 16), high-z (z_q > 1) QSOs, may lead 1) to overestimate by up to ~= 90% the number of DLAs per unit redshift; 2) to bias the survey towards high HI column density systems so that it could contain up to 4 times as many such systems, thus 3) to overestimate by up to ~= 170% the cosmological density of gas associated with those DLAs. Identification of the galaxies responsible for the DLAs may be severely biased towards luminous galaxies if 2/alpha_TF - alpha_H>0 this latter effect is greatly increased for log N_HI > 21 DLAs. Hence, GL effects on the quantities derived from surveys for z ~ 0.5 DLAs are of the same order, but of opposite direction, as the effects of extinction by dust (cf. Fall & Pei, 1993). However, the GL and dust extinction effects do not compensate each other: combining them in a consistent way is necessary to interpret existing DLA surveys. Furthermore, the effects due to micro-lensing should be simultaneously taken into account. We intend to report the results on the complex interplay between macro-lensing, micro-lensing and dust in a subsequent paper. We briefly present statistical tests specifically designed to check whether GL affects existing DLA surveys, and assuming that extinction by dust is negligible. We only find indications of GL effects for the z < 1 ones which, if confirmed, might even be stronger than predicted by our model. We show that an independent work on the same subject by Bartelmann & Loeb (1996) incorrectly treats the inclination effects for the intervening galaxies, thus undermining some of their main results and conclusions. [less ▲]

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See detailGravitational lensing in quasar samples
Claeskens, Jean-François ULg; Surdej, Jean ULg

in Astronomy and Astrophysics Review (2002), 10(4), 263-311

The first cosmic mirage was discovered approximately 20 years ago as the double optical counterpart of a radio source. This phenomenon had been predicted some 70 years earlier as a consequence of General ... [more ▼]

The first cosmic mirage was discovered approximately 20 years ago as the double optical counterpart of a radio source. This phenomenon had been predicted some 70 years earlier as a consequence of General Relativity. We present here a summary of what we have learnt since. The applications are so numerous that we had to concentrate on a few selected aspects of this new field of research. This review is focused on strong gravitational lensing, i.e. the formation of multiple images, in QSO samples. It is intended to give the reader an up-to-date status of the observations and to present an overview of its most interesting potential applications in cosmology and astrophysics, as well as numerous important results achieved so far. The first section follows an intuitive approach to the basics of gravitational lensing and is developed in view of our interest in multiply imaged quasars. The astrophysical and cosmological applications of gravitational lensing are outlined in Sect. 2 and the most important results are presented in Sect. 5. Sections 3 and 4 are devoted to the observations. Finally, conclusions are summarized in the last section. We have tried to avoid duplication with existing (and excellent) introductions to the field of oravitational lensing. For this reason, we did not concentrate on the individual properties of specific lens models, as these are already well presented in Narayan and Bartelmann (1996) and on a more intuitive ground in Refsdal and Surdej (1994). Wambsganss (1998) proposes a broad view on gravitational lensing, in astronomy; the reviews by Fort and Mellier (1994) and Hattori et al. (1999) deal with lensing by galaxy clusters, microlensing in the Galaxy and the local group is reviewed by Paczynski (1996) and a general panorama on weak lensing is given by Bartelmann and Schneider (1999) and Mellier (1999). The monograph on the theory of gravitational lensing by Schneider, Ehlers and Falco (1992) also remains a reference in the field. [less ▲]

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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 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 detailGravitational lensing studies with the 4-m International Liquid Mirror Telescope (ILMT)
Jean, C.; Claeskens, J *-F; Surdej, Jean ULg

Poster (1999, October 01)

A 4-m International Liquid Mirror Telescope (ILMT) is being built in the north of Chile by an international consortium and will become operational in two years from now. We present here a short ... [more ▼]

A 4-m International Liquid Mirror Telescope (ILMT) is being built in the north of Chile by an international consortium and will become operational in two years from now. We present here a short description of the telescope as well as estimates of the microlensing, macrolensing and weak lensing effects expected from a deep, multicolor imaging survey made with such a telescope. [less ▲]

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See detailGravitational lensing studies with the 4-m International Liquid Mirror Telescope (ILMT) (poster contribution)
Jean, C.; Claeskens, Jean-François ULg; Surdej, Jean ULg

in Brainerd, T. G.; Kochanek, C. S. (Eds.) Proceedings of the Conference "Gravitational lensing: recent progress and future goals" (2001, October 01)

A 4-m International Liquid Mirror Telescope (ILMT) is being built in the north of Chile by an international consortium and will become operational in two years from now. We present here a short ... [more ▼]

A 4-m International Liquid Mirror Telescope (ILMT) is being built in the north of Chile by an international consortium and will become operational in two years from now. We present here a short description of the telescope as well as estimates of the microlensing, macrolensing and weak lensing effects expected from a deep, multicolor imaging survey made with such a telescope. [less ▲]

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See detailThe 'Gravitational Lensing' Bibliography
Pospieszalska-Surdej, Anna ULg; Surdej, Jean ULg; Veron, P.

in Kochanek, C. S.; Hewitt, Jacqueline N (Eds.) Astrophysical applications of gravitational lensing, Proceedings of the 173rd Symposium of the International Astronomical Union (1996)

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See detailGravitational Lensing, Dark Matter and the Optical Gravitational Lens Experiment
Surdej, Jean ULg; Claeskens, Jean-François ULg; Delacroix, Christian ULg et al

in Matagne, N.; Cugnon, Joseph; Lansberg, Jean-Philippe (Eds.) American Institute of Physics Conference Proc. Volume 1038 (2008, August 01)

After briefly reviewing the history of gravitational lensing, we recall the basic principles of the theory. We then describe and use a simple optical gravitational lens experiment which has the virtue of ... [more ▼]

After briefly reviewing the history of gravitational lensing, we recall the basic principles of the theory. We then describe and use a simple optical gravitational lens experiment which has the virtue of accounting for all types of image configurations observed so far among the presently known gravitational lens systems. Finally, we briefly present the 4m International Liquid Mirror Telescope project in the context of a photometric monitoring of multiply imaged quasars. [less ▲]

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See detailGravitational lensing, rapport invité
Surdej, Jean ULg

Conference (2005)

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See detailGravitational settling in pulsating subdwarf B stars and their progenitors
Hu, Haili; Glebbeek, E.; Thoul, Anne ULg et al

in Astronomy and Astrophysics (2010), 511

Context. Diffusion of atoms can be important during quiescent phases of stellar evolution. Particularly in the very thin inert envelopes of subdwarf B stars, diffusive movements will considerably change ... [more ▼]

Context. Diffusion of atoms can be important during quiescent phases of stellar evolution. Particularly in the very thin inert envelopes of subdwarf B stars, diffusive movements will considerably change the envelope structure and the surface abundances on a short timescale. Also, the subdwarfs will inherit the effects of diffusion in their direct progenitors, namely giants near the tip of the red giant branch. This will influence the global evolution and the pulsational properties of subdwarf B stars. <BR /> Aims: We investigate the impact of gravitational settling, thermal diffusion and concentration diffusion on the evolution and pulsations of subdwarf B stars. Although radiative levitation is not explicitly calculated, we evaluate its effect by approximating the resulting iron accumulation in the driving region. This allows us to study the excitation of the pulsation modes, albeit in a parametric fashion. Our diffusive stellar models are compared with models evolved without diffusion. <BR /> Methods: We use a detailed stellar evolution code to solve simultaneously the equations of stellar structure and evolution, including the composition changes due to diffusion. The diffusion calculations are performed for a multicomponent fluid using diffusion coefficients derived from a screened Coulomb potential. We constructed subdwarf B models with a mass of 0.465 M[SUB]ȯ[/SUB] from a 1 M[SUB]ȯ[/SUB] and 3 M[SUB]ȯ[/SUB] zero-age main sequence progenitor. The low mass star ignited helium in an energetic flash, while the intermediate mass star started helium fusion gently. For each progenitor type we computed series with and without atomic diffusion. <BR /> Results: Atomic diffusion in red giants causes the helium core mass at the onset of helium ignition to be larger. We find an increase of 0.0015 M[SUB]ȯ[/SUB] for the 1 M[SUB]ȯ[/SUB] model and 0.0036 M[SUB]ȯ[/SUB] for the 3 M[SUB]ȯ[/SUB] model. The effects on the red giant surface abundances are small after the first dredge up. The evolutionary tracks of the diffusive subdwarf B models are shifted to lower surface gravities and effective temperatures due to outward diffusion of hydrogen. This affects both the frequencies of the excited modes and the overall frequency spectrum. Especially the structure and pulsations of the post-non-degenerate sdB star are drastically altered, proving that atomic diffusion cannot be ignored in these stars. Sinking of metals could to some extent increase the gravities and temperatures due to the associated decrease in the stellar opacity. However, this effect should be limited as it is counteracted by radiative levitation. [less ▲]

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See detailGravitationall lensing evidence against extended dark matter halos
Magain, Pierre ULg; Chantry, Virginie ULg

E-print/Working paper (2013)

It is generally thought that galaxies are embedded in dark matter halos extending well beyond their luminous matter. The existence of these galactic halos is mainly derived from the larger than expected ... [more ▼]

It is generally thought that galaxies are embedded in dark matter halos extending well beyond their luminous matter. The existence of these galactic halos is mainly derived from the larger than expected velocities of stars and gas in the outskirts of spiral galaxies. Much less is known about dark matter around early-type (elliptical or lenticular) galaxies. We use gravitational lensing to derive the masses of early-type galaxies deflecting light of background quasars. This provides a robust measurement of the total mass within the Einstein ring, a circle whose diameter is comparable to the separation of the different quasar images. We find that the mass-to-light ratio of the lensing galaxies does not depend on radius, from inner galactic regions out to several half-light radii. Moreover, its value does not exceed the value predicted by stellar population models by more than a factor two, which may be explained by baryonic dark matter alone, without any need for exotic matter. Our results thus suggest that, if dark matter is present in early-type galaxies, its amount does not exceed the amount of luminous matter and its density follows that of luminous matter, in sharp contrast to what is found from rotation curves of spiral galaxies. [less ▲]

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