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See detailEvolution of the Io Footprint Brightness II: Modeling
Hess, Sébastien; Bonfond, Bertrand ULg; Chantry, Virginie ULg et al

in Planetary and Space Science (2013), 88

The interaction of Io with the Jovian magnetosphere creates the best known and brightest satellite-controlled aurorae in our solar system. These aurorae are generated by the precipitation of electrons ... [more ▼]

The interaction of Io with the Jovian magnetosphere creates the best known and brightest satellite-controlled aurorae in our solar system. These aurorae are generated by the precipitation of electrons, which are accelerated by the Alfvén waves carrying the current between the satellite and the planet. A recent study computed the energy deposited on top of Jupiter's ionosphere due to the electron precipitation and retrieved the correct mean brightness of Io-related aurorae. The model developed in this study takes into account the acceleration mechanism and the Alfvén wave propagation effects. We use the same method to investigate the brightness variation of the different components of the Io footprint as a function of longitude. These observations are discussed in a companion paper. We identify several effects that act together to modulate the footprint brightness such as Alfvén wave reflections, magnetic mirroring of the electrons, the local interaction at Io and kinetic effects close to Jupiter. We identify the effects contributing the most to the modulation of the brightnesses of the three brightest components of the Io footprints: the main and reflected Alfvén wing spots and the transhemispheric electron spot. We show in particular that the modulation of the efficiency of the electron acceleration can be of greater importance than the modulation of the power generated at Io. We reproduce the average modulation of the spot brightnesses and present an extensive discussion of possible explanations for the observed features not reproduced by our model. [less ▲]

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See detailEvolution of the Io footprint brightness I: Far-UV observations
Bonfond, Bertrand ULg; Hess, Sébastien; Gérard, Jean-Claude ULg et al

in Planetary and Space Science (2013), 88

The Io footprint (IFP) is a set of auroral spots and an extended tail resulting from the strong interaction between Io and the Jovian magnetosphere. For the first time, we present measurements of the ... [more ▼]

The Io footprint (IFP) is a set of auroral spots and an extended tail resulting from the strong interaction between Io and the Jovian magnetosphere. For the first time, we present measurements of the brightness and precipitated power for each individual spot, using the image database gathered from 1997 to 2009 with the Hubble Space Telescope in the Far-UV domain. We show that the relative brightness of the spots varies with the System III longitude of Io. Moreover, our novel measurement method based on 3D simulations of the auroral features allows to derive the precipitated energy fluxes from images on which the emission region is observed at a slant angle. Peak values as high as 2 W/m² are observed for the main spot, probably triggering a localized and sudden heating of the atmosphere. Additionally, strong brightness differences are observed from one hemisphere to another. This result indicates that the location of Io in the plasma torus is not the only parameter to control the brightness, but that the magnetic field asymmetries also play a key role. Finally, we present new data confirming that significant variations of the spots' brightness on timescales of 2-4 minutes are ubiquitous, which suggests a relationship with intermittent double layers close to Jovian surface. [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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See detailCOSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses X. Modeling based on high-precision astrometry of a sample of 25 lensed quasars: consequences for ellipticity, shear, and astrometric anomalies
Sluse, Dominique ULg; Chantry, Virginie ULg; Magain, Pierre ULg et al

in Astronomy and Astrophysics (2012), 538

Gravitationally lensed quasars can be used as powerful cosmological and astrophysical probes. We can (i) infer the Hubble constant H0 based on the so-called time-delay technique, (ii) unveil substructures ... [more ▼]

Gravitationally lensed quasars can be used as powerful cosmological and astrophysical probes. We can (i) infer the Hubble constant H0 based on the so-called time-delay technique, (ii) unveil substructures along the line-of-sight toward distant galaxies, and (iii) compare the shape and the slope of baryons and dark matter distributions in the inner regions of galaxies. To reach these goals, we need high-accuracy astrometry of the quasar images relative to the lensing galaxy and morphology measurements of the lens. In this work, we first present new astrometry for 11 lenses with measured time delays, namely, JVAS B0218+357, SBS 0909+532, RX J0911.4+0551, FBQS J0951+2635, HE 1104-1805, PG 1115+080, JVAS B1422+231, SBS 1520+530, CLASS B1600+434, CLASS B1608+656, and HE 2149-2745. These measurements proceed from the use of the Magain-Courbin-Sohy (MCS) deconvolution algorithm applied in an iterative way (ISMCS) to near-IR HST images. We obtain a typical astrometric accuracy of about 1-2.5 mas and an accurate shape measurement of the lens galaxy. Second, we combined these measurements with those of 14 other lensing systems, mostly from the COSMOGRAIL set of targets, to present new mass models of these lenses. The modeling of these 25 gravitational lenses led to the following results: 1) in four double-image quasars (HE0047-1746, J1226-006, SBS 1520+530, and HE 2149-2745), we show that the influence of the lens environment on the time delay can easily be quantified and modeled, hence putting these lenses with high priority for time-delay determination; 2) for quadruple-image quasars, the difficulty often encountered in reproducing the image positions to milli-arcsec accuracy (astrometric anomaly problem) is overcome by explicitly including the nearest visible galaxy/satellite in the lens model. However, one anomalous system (RXS J1131-1231) does not show any luminous perturber in its vicinity, and three others (WFI 2026-4536, WFI 2033-4723, and B2045+265) have problematic modeling. These four systems are the best candidates for a pertubation by a dark matter substructure along the line-of-sight; 3) we revisit the correlation between the position angle (PA) and ellipticity of the light and of the mass distribution in lensing galaxies. As in previous studies, we find a significant correlation between the PA of the light and of the mass distributions. However, in contrast with these same studies, we find that the ellipticity of the light and of the mass also correlate well, suggesting that the overall spatial distribution of matter is not very different from the baryon distribution in the inner ~5 kpc of lensing galaxies. This offers a new test for high-resolution hydrodynamical simulations. Based on observations made with the NASA/ESA HST Hubble Space Telescope by the CfA-Arizona Space Telescope Lens Survey (CASTLeS) collaboration, obtained from the data archive at the Space Science Institute, which is operated by AURA, the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS-5-26555. [less ▲]

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See detailCOSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses. IX. Time delays, lens dynamics and baryonic fraction in HE 0435-1223
Courbin, F.; Chantry, Virginie ULg; Revaz, Y. et al

in Astronomy and Astrophysics (2011), 536

We present accurate time delays for the quadruply imaged quasar HE 0435-1223. The delays were measured from 575 independent photometric points obtained in the R-band between January 2004 and March 2010 ... [more ▼]

We present accurate time delays for the quadruply imaged quasar HE 0435-1223. The delays were measured from 575 independent photometric points obtained in the R-band between January 2004 and March 2010. With seven years of data, we clearly show that quasar image A is affected by strong microlensing variations and that the time delays are best expressed relative to quasar image B. We measured ΔtBC = 7.8 ± 0.8 days, ΔtBD = -6.5 ± 0.7 days and ΔtCD = -14.3 ± 0.8 days. We spacially deconvolved HST NICMOS2 F160W images to derive accurate astrometry of the quasar images and to infer the light profile of the lensing galaxy. We combined these images with a stellar population fitting of a deep VLT spectrum of the lensing galaxy to estimate the baryonic fraction, fb, in the Einstein radius. We measured fb = 0.65-0.10+0.13 if the lensing galaxy has a Salpeter IMF and fb = 0.45-0.07+0.04 if it has a Kroupa IMF. The spectrum also allowed us to estimate the velocity dispersion of the lensing galaxy, σap = 222 ± 34 km s-1. We used fb and σap to constrain an analytical model of the lensing galaxy composed of an Hernquist plus generalized NFW profile. We solved the Jeans equations numerically for the model and explored the parameter space under the additional requirement that the model must predict the correct astrometry for the quasar images. Given the current error bars on fb and σap, we did not constrain H0 yet with high accuracy, i.e., we found a broad range of models with χ2 < 1. However, narrowing this range is possible, provided a better velocity dispersion measurement becomes available. In addition, increasing the depth of the current HST imaging data of HE 0435-1223 will allow us to combine ourconstraints with lens reconstruction techniques that make use of the full Einstein ring that is visible in this object. Based on observations made with the 1.2 m Euler Swiss Telescope, the 1.5 m telescope of Maidanak Observatory in Uzbekistan, and with the 1.2 m Mercator Telescope, operated on the island of La Palma by the Flemish Community, at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias. The NASA/ESA Hubble Space Telescope data was obtained from the data archive at the Space Telescope Science Institute, which is operated by AURA, the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS-5-26555.Light curves are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/536/A53 [less ▲]

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See detailTRAPPIST: TRAnsiting Planets and PlanetesImals Small Telescope
Jehin, Emmanuel ULg; Gillon, Michaël ULg; Queloz, D. et al

in The Messenger (2011), 145

TRAPPIST is a 60-cm robotic telescope that was installed in April 2010 at the ESO La Silla Observatory. The project is led by the Astrophysics and Image Processing group (AIP) at the Department of ... [more ▼]

TRAPPIST is a 60-cm robotic telescope that was installed in April 2010 at the ESO La Silla Observatory. The project is led by the Astrophysics and Image Processing group (AIP) at the Department of Astrophysics, Geophysics and Oceanography (AGO) of the University of Liège, in close collaboration with the Geneva Observatory, and has been funded by the Belgian Fund for Scientific Research (F.R.S.-FNRS) and the Swiss National Science Foundation (SNF). It is devoted to the detection and characterisation of exoplanets and to the study of comets and other small bodies in the Solar System. We describe here the goals of the project and the hardware and present some results obtained during the first six months of operation. [less ▲]

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See detailTRAPPIST: a robotic telescope dedicated to the study of planetary systems
Gillon, Michaël ULg; Jehin, Emmanuel ULg; Magain, Pierre ULg et al

in EPJ Web of Conferences (2011, February 01), 11

We present here a new robotic telescope called TRAPPIST<xref ref-type="fn" rid="FN2">1</xref> (TRAnsiting Planets and PlanetesImals Small Telescope). Equipped with a high-quality CCD camera mounted on a 0 ... [more ▼]

We present here a new robotic telescope called TRAPPIST<xref ref-type="fn" rid="FN2">1</xref> (TRAnsiting Planets and PlanetesImals Small Telescope). Equipped with a high-quality CCD camera mounted on a 0.6 meter light weight optical tube, TRAPPIST has been installed in April 2010 at the ESO La Silla Observatory (Chile), and is now beginning its scientific program. The science goal of TRAPPIST is the study of planetary systems through two approaches: the detection and study of exoplanets, and the study of comets. We describe here the objectives of the project, the hardware, and we present some of the first results obtained during the commissioning phase. [less ▲]

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See detailCOSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses VIII. Deconvolution of high resolution near-IR images and simple mass models for 7 gravitationally lensed quasars
Chantry, Virginie ULg; Sluse, Dominique ULg; Magain, Pierre ULg

in Astronomy and Astrophysics (2010), 522

Aims: We attempt to place very accurate positional constraints on seven gravitationally lensed quasars currently being monitored by the COSMOGRAIL collaboration, and shape parameters for the light ... [more ▼]

Aims: We attempt to place very accurate positional constraints on seven gravitationally lensed quasars currently being monitored by the COSMOGRAIL collaboration, and shape parameters for the light distribution of the lensing galaxy. We attempt to determine simple mass models that reproduce the observed configuration and predict time delays. We finally test, for the quads, whether there is evidence of astrometric perturbations produced by substructures in the lensing galaxy, which may preclude a good fit with the simple models. Methods: We apply the iterative MCS deconvolution method to near-IR HST archival data of seven gravitationally lensed quasars. This deconvolution method allows us to differentiate the contributions of the point sources from those of extended structures such as Einstein rings. This method leads to an accuracy of 1-2 mas in the relative positions of the sources and lens. The limiting factor of the method is the uncertainty in the instrumental geometric distortions. We then compute mass models of the lensing galaxy using state-of-the-art modeling techniques. Results: We determine the relative positions of the lensed images and lens shape parameters of seven lensed quasars: HE 0047-1756, RX J1131-1231, SDSS J1138+0314, SDSS J1155+6346, SDSS J1226-0006, WFI J2026-4536, and HS 2209+1914. The lensed image positions are derived with 1-2 mas accuracy. Isothermal and de Vaucouleurs mass models are calculated for the whole sample. The effect of the lens environment on the lens mass models is taken into account with a shear term. Doubly imaged quasars are equally well fitted by each of these models. A large amount of shear is necessary to reproduce SDSS J1155+6346 and SDSS J1226-006. In the latter case, we identify a nearby galaxy as the dominant source of shear. The quadruply imaged quasar SDSS J1138+0314 is reproduced well by simple lens models, which is not the case for the two other quads, RX J1131-1231 and WFI J2026-4536. This might be the signature of astrometric perturbations caused by massive substructures in the galaxy, which are unaccounted for by the models. Other possible explanations are also presented. Based on observations made with the NASA/ESA HST Hubble Space Telescope, obtained from the data archive at the Space Science Institute, which is operated by AURA, the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS-5-26555. [less ▲]

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See detailThe 3/4 July 2010 Pluto Stellar-Occultation Observations
Pasachoff, Jay M; Elliot, J. L.; Souza, S. P. et al

in Bulletin of the American Astronomical Society (2010, October 01), 42

Continuing our monitoring of Pluto's atmospheric temperature and pressure, previously shown by us to be increasing (Elliot et al., Nature 424, 165, 2003; Pasachoff et al., AJ 129, 1718, 2005) and ... [more ▼]

Continuing our monitoring of Pluto's atmospheric temperature and pressure, previously shown by us to be increasing (Elliot et al., Nature 424, 165, 2003; Pasachoff et al., AJ 129, 1718, 2005) and subsequently found by us to be leveling off (Elliot et al., AJ 134, 1, 2007), we report on a stellar occultation by Pluto of UCAC2 mag=15.3, observed from South America and Africa on 4 July 2010 UT. Success was achieved with a 0.45 m at Cerro Calan using one of our POETS (Portable Occultation, Eclipse, and Transit System; Souza et al. PASP 118, 1550, 2006), a 1.0 SMARTS (Small and Medium Aperture Research Telescope System) at Cerro Tololo, four 0.6 m telescopes of PROMPT (Panchromatic Robotic Optical Monitoring and Polarimetry Telescopes) on Cerro Tololo, and TRAPPIST's (TRansiting Planets and Planetesimals Small Telescope) 0.6-m telescope on La Silla in Chile; the 0.35 m telescope of U. Ponta Grossa, Brazil; and the 0.75-m ATOM (Automatic Telescope for Optical Monitoring), Namibia, using POETS. Winds prevented opening the 6.5 m Magellan/Clay telescope on Las Campanas, Chile, with its own frame-transfer camera, and clouds obscured the 1.9 m telescope at Sutherland, South Africa, which had POETS. With shadow velocity 23.6 km/s, it was a rapid event: maximum occultation <2 minutes. The observations were supported in part by grants NNX08AO50G to Williams College and NNX10AB27G to MIT from NASA's Planetary Astronomy Division, and NNH08AI17I to USNO for astrometry. Student participation was supported in part by NASA's Massachusetts Space Grant and NSF's REU. Japan's government donated U. Chile's Cerro Calan Goto telescope. PROMPT observations were made possible by the Robert Martin Ayers Science Fund. TRAPPIST is a project driven by the University of Liège, in close collaboration with the Observatory of Geneva, supported by the Belgian Fund for Scientific Research and the Swiss National Science Foundation. [less ▲]

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See detailTRAPPIST : un télescope liégeois à la découverte des systèmes planétaires
Jehin, Emmanuel ULg; Gillon, Michaël ULg; Chantry, Virginie ULg et al

Article for general public (2010)

Not Available

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See detailGravitationally lensed quasars: light curves, observational constraints, modeling and the Hubble constant.
Chantry, Virginie ULg

Doctoral thesis (2009)

The central topic of this thesis is gravitational lensing, a phenomenon that occurs when light rays from a background source pass near a massive object located on the line of sight and are deflected. It ... [more ▼]

The central topic of this thesis is gravitational lensing, a phenomenon that occurs when light rays from a background source pass near a massive object located on the line of sight and are deflected. It is one of the most wonderful observational fact in favour of the General Theory of Relativity (Einstein, 1916). This phenomenon constitutes a powerful tool to probe different areas in astrophysics, including cosmology, which is our main interest. In particular we study gravitationally lensed quasars. Refsdal (1964) was the first to state that time delays between different lensed images of the same object, if this one is intrisically variable, can lead to the measurement of the Hubble constant H0, which is related the actual expansion rate of the Universe. Up to now, only a few lensed quasars have led to H0 and the precision on it has never reached the one obtained with other methods as the ones based on the Cosmic Distance Ladder. That is why some scientists from around the globe decided to unite their force to measure H0 from about thirty lensed quasars. To reach that goal, these objects are being monitored with some mid-sized ground-based telescopes located in both hemispheres. This thesis is realised in the framework of this collaboration called COSMOGRAIL for COSmological MOnitoring of GRAvItational Lenses. This work focuses on image processing and on several steps mandatory to obtain a measurement of H0 from lensed quasars: the acquisiton of the light curves from which it is possible to extract the time delays and the acquisition of the observational constraints necessary to model the gravitational potential responsible for the observed configura- tion. The central technique of this work is the image deconvolution with the MCS algorithm (Magain, Courbin & Sohy, 1998). The main principle of this algorithm is the non-violation of the sampling theorem in trying to obtain a better resolution in the deconvolved frame instead of an infinite one. The final resolution in the deconvolved frame is chosen by the user and as it is known, every image is decomposed in a contri- bution from the point sources and another one from all the extended structures such as arcs, rings and galaxies. To obtain good light curves from data coming from several telescopes, good reduction procedures are needed. That is why Vuissoz (2008) developed a semi-automated reduc- tion pipeline including deconvolution with the MCS algorithm. In the framework of the i ii Abstract present thesis, we adapt it to one of the telescopes used by the collaboration whose data were never used before, i.e. the Mercator telescope. We also bring some modifications to this pipeline, e.g. concerning the estimation of the error on the magnitudes of the light curves. We apply this revised version of the reduction pipeline to HE 0435-1223, a quadruply imaged quasar with already measured time delays (Kochanek et al., 2006). Another object, the quad WFI J2026-4536, is then investigated: we obtain light curves for each of the four lensed images. Thanks to the CASTLES project (Cfa-Arizona Space Telescope LEns Survey1), many lensed quasars have been observed with the camera 2 of NICMOS (Near Infrared Camera and Multi-Object Spectrometer ) on board the Hubble Space Telescope. With these high resolution images, we can obtain very accurate constraints on the geometry of the lensed systems. But most of the time no star is available in the field of view to obtain a good Point Spread Function (PSF). That is why we develop an iterative strategy combined with the MCS algorithm: we call it ISMCS. This technique allows to use the lensed images themselves to improve the PSFs step by step while simultaneously deconvolving the frame to obtain better estimations of the extended structures in the image. We first test this strategy on a quadruply imaged quasar, the Cloverleaf gravitational lens (H1413+117), and obtain relative positions precise to 1 milliarcsecond (mas). We then apply ISMCS to the quadruply imaged quasar WFI J2033-4723 in order to con- tribute to the estimate of the Hubble constant, as this object was monitored by our team. We then study a sample of seven lensed systems currently monitored by COSMOGRAIL and for which time delays have never been obtained. Here again, we obtain positional constraints with an accuracy of around 1 to 2 mas thanks to the application of ISMCS. We then model these systems with simple mass profiles for the main lens galaxy and obtain an estimation of the values of the time delays. Finally we apply ISMCS to a sample of eleven lensed quasars which already have measured time delays. When the delays have been remeasured by our team, in four cases until now, we also model the potential of the lens with simple mass profiles to estimate H0. 1http://www.cfa.harvard.edu/castles [less ▲]

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See detailMulti-wavelength observations of afterglow of GRB 080319B and the modeling constraints
Pandey, S. B.; Castro-Tirado, A. J.; Jelínek, M. et al

in Astronomy and Astrophysics (2009), 504(1), 45-51

We present observations of the afterglow of GRB 080319B at optical, mm and radio frequencies from a few hours to 67 days after the burst. Present observations along with other published multi-wavelength ... [more ▼]

We present observations of the afterglow of GRB 080319B at optical, mm and radio frequencies from a few hours to 67 days after the burst. Present observations along with other published multi-wavelength data have been used to study the light-curves and spectral energy distributions of the burst afterglow. The nature of this brightest cosmic explosion has been explored based on the observed properties and it's comparison with the afterglow models. Our results show that the observed features of the afterglow fits equally good with the Inter Stellar Matter and the Stellar Wind density profiles of the circum-burst medium. In case of both density profiles, location of the maximum synchrotron frequency $\nu_m$ is below optical and the value of cooling break frequency $\nu_c$ is below $X-$rays, $\sim 10^{4}$s after the burst. Also, the derived value of the Lorentz factor at the time of naked eye brightness is $\sim 300$ with the corresponding blast wave size of $\sim 10^{18}$ cm. The numerical fit to the multi-wavelength afterglow data constraints the values of physical parameters and the emission mechanism of the burst. [less ▲]

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See detailThe QSO HE0450-2958: Scantily dressed or heavily robed? A normal quasar as part of an unusual ULIRG
Jahnke, Knud; Elbaz, David; Pantin, Eric et al

in Astrophysical Journal (2009), 700(2), 1820-1830

(Abridged) The luminous z=0.286 quasar HE0450-2958 is interacting with a companion galaxy at 6.5 kpc distance and the whole system is a ULIRG. A so far undetected host galaxy triggered the hypothesis of a ... [more ▼]

(Abridged) The luminous z=0.286 quasar HE0450-2958 is interacting with a companion galaxy at 6.5 kpc distance and the whole system is a ULIRG. A so far undetected host galaxy triggered the hypothesis of a mostly "naked" black hole (BH) ejected from the companion by three-body interaction. We present new HST/NICMOS 1.6micron imaging data at 0.1" resolution and VLT/VISIR 11.3micron images at 0.35" resolution that for the first time resolve the system in the near- and mid-infrared. We combine these with existing optical HST and CO maps. (i) At 1.6micron we find an extension N-E of the quasar nucleus that is likely a part of the host galaxy, though not its main body. If true, this places HE0450-2958 directly onto the M_BH-M_bulge-relation for nearby galaxies. (ii) HE0450-2958 is consistent with lying at the high-luminosity end of Narrow-Line Seyfert 1 Galaxies, and more exotic explanations like a "naked quasar" are unlikely. (iii) All 11.3micron radiation in the system is emitted by the quasar nucleus, which is radiating at super-Eddington rate, L/L_Edd=6.2+3.8-1.8, or 12 M_sun/yr. (iv) The companion galaxy is covered in optically thick dust and is not a collisional ring galaxy. It emits in the far infrared at ULIRG strength, powered by Arp220-like star formation (strong starburst-like). An M82-like SED is ruled out. (v) With its black hole accretion rate HE0450-2958 produces not enough new stars to maintain its position on the M_BH-M_bulge-relation, and star formation and black hole accretion are spatially disjoint; the bulge has to grow by redistribution of preexisting stars. (vi) Systems similar to HE0450-2958 with spatially disjoint ULIRG-strength star formation and quasar activity are rare. At z<0.43 we only find <4% (3/77) candidates for a similar configuration. [less ▲]

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See detailRedshifts and lens profile for the double quasar QJ 0158-4325
Faure, C.; Anguita, T.; Eigenbrod, A. et al

in Astronomy and Astrophysics (2009), 496(2), 361-364

Aims. We report on the redshift of the lensing galaxy and of the quasar QJ 0158-4325 and on the lens model of the system. Methods. A deep VLT/FORS2 spectrum and HST/NICMOS-F160W images are deconvolved ... [more ▼]

Aims. We report on the redshift of the lensing galaxy and of the quasar QJ 0158-4325 and on the lens model of the system. Methods. A deep VLT/FORS2 spectrum and HST/NICMOS-F160W images are deconvolved. From the images we derive the light profile of the lensing galaxy and an accurate relative astrometry for the system. In addition we measure the flux ratio between the quasar images in the Mg II emission line to constrain the mass model. Results. From the spectrum we measure the redshift of the lensing galaxy (z = 0.317 +/- 0.001) and of the quasar (z = 1.294 +/- 0.008). Using the flux ratio in the lens model allows us to discard the SIE as a suitable approximation of the lens potential. On the contrary the truncated-PIEMD gives a good fit to the lens and leads to a time delay of Delta t(A-B) = -14.5 +/- 0.1 days, with H-0 = 73 km s(-1) Mpc(-1). Conclusions. Using the flux ratio to constrain the mass model favors the truncated-PIEMD over the SIE, while ignoring this constraint leaves the choice open. [less ▲]

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See detailNear-intrared observations of the HE 0450-2958 system: discovery of a second active galactic nucleus?
Letawe, Géraldine ULg; Magain, Pierre ULg; Chantry, Virginie ULg et al

in Monthly Notices of the Royal Astronomical Society (2009), 396(1), 78-84

The quasi-stellar object (QSO) HE 0450−2958 was brought to the front scene by the non-detection of its host galaxy and strong upper limits on the latter's luminosity. The QSO is also a powerful infrared ... [more ▼]

The quasi-stellar object (QSO) HE 0450−2958 was brought to the front scene by the non-detection of its host galaxy and strong upper limits on the latter's luminosity. The QSO is also a powerful infrared emitter, in gravitational interaction with a strongly distorted ultraluminous infrared companion galaxy. We investigate the properties of the companion galaxy, through new near- and mid-infrared observations of the system obtained with Near Infrared Camera and Multi-Object Spectrometer (NICMOS) onboard Hubble Space Telescope, Infrared Spectrometer and Array Camera (ISAAC) and Very Large Telescope Imager and Spectrometer in the Infrared (VISIR) on the European Southern Observatory Very Large Telescope. The companion galaxy is found to harbour a point source revealed only in the infrared, in what appears as a hole or dark patch in the optical images. Various hypotheses on the nature of this point source are analysed and it is found that the only plausible one is that it is a strongly reddened active galactic nucleus hidden behind a thick dust cloud. The hypothesis that the QSO supermassive black hole might have been ejected from the companion galaxy in the course of a galactic collision involving three-body black holes interaction is also reviewed, on the basis of this new insight on a definitely complex system. [less ▲]

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See detailCOSMOGRAIL: the COSmological MOnitoring of GRAvItational lenses - VII. Time delays and the Hubble constant from WFI J2033-4723
Vuissoz, Christel; Courbin, F.; Sluse, Dominique ULg et al

in Astronomy and Astrophysics (2008), 488(2), 481-490

Gravitationally lensed quasars can be used to map the mass distribution in lensing galaxies and to estimate the Hubble constant H-0 by measuring the time delays between the quasar images. Here we report ... [more ▼]

Gravitationally lensed quasars can be used to map the mass distribution in lensing galaxies and to estimate the Hubble constant H-0 by measuring the time delays between the quasar images. Here we report the measurement of two independent time delays in the quadruply imaged quasar WFI J2033-4723 (z = 1.66). Our data consist of R-band images obtained with the Swiss 1.2 m EULER telescope located at La Silla and with the 1.3 m SMARTS telescope located at Cerro Tololo. The light curves have 218 independent epochs spanning 3 full years of monitoring between March 2004 and May 2007, with a mean temporal sampling of one observation every 4th day. We measure the time delays using three different techniques, and we obtain Delta t(B-A) = 35.5 +/- 1.4 days (3.8%) and Delta t(B-C) = 62.6(-2.3)(+4.1) days ((+6.5%)(-3.7%)), where A is a composite of the close, merging image pair. After correcting for the time delays, we find R-band flux ratios of F-A/F-B = 2.88 +/- 0.04, F-A/F-C = 3.38 +/- 0.06, and F-A1/F-A2 = 1.37 +/- 0.05 with no evidence for microlensing variability over a time scale of three years. However, these flux ratios do not agree with those measured in the quasar emission lines, suggesting that longer term microlensing is present. Our estimate of H-0 agrees with the concordance value: non-parametric modeling of the lensing galaxy predicts H-0 = 67(-10)(+13) km s(-1) Mpc(-1), while the Single Isothermal Sphere model yields H-0 = 63(-3)(+7) km s(-1) Mpc(-1) (68% confidence level). More complex lens models using a composite de Vaucouleurs plus NFW galaxy mass profile show twisting of the mass isocontours in the lensing galaxy, as do the non-parametric models. As all models also require a significant external shear, this suggests that the lens is a member of the group of galaxies seen in field of view of WFI J2033-4723. [less ▲]

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See detailGRB 080319B: optical observations.
Jelinek, M.; Castro-Tirado, A. J.; Chantry, Virginie ULg et al

E-print/Working paper (2008)

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See detailGRB 080319B: second epoch imaging from canarias (correction to GCN7469).
Jelinek, M.; Castro-Tirado, A. J.; Chantry, Virginie ULg et al

E-print/Working paper (2008)

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See detailGRB 080315: optical observations.
de Ugarte Postigo, A.; Chantry, Virginie ULg; Castro-Tirado, A. J. et al

E-print/Working paper (2008)

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See detailDECPHOT: An Optimal Deconvolution-based Photometric Reduction Method
Gillon, Michaël ULg; Magain, Pierre ULg; Chantry, Virginie ULg et al

in Transiting Extrapolar Planets Workshop (2007, July 01)

A high accuracy photometric reduction method is needed to take full advantage of the potential of the transit method for the detection and characterization of exoplanets, especially in deep crowded fields ... [more ▼]

A high accuracy photometric reduction method is needed to take full advantage of the potential of the transit method for the detection and characterization of exoplanets, especially in deep crowded fields. In this context, we present DECPHOT, a new deconvolution-based photometry algorithm able to deal with a very high level of crowding and large variations of seeing. It also increases the resolution of astronomical images, an important advantage for the discrimination of false positives in transit photometry. [less ▲]

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