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See detailFirst Results from the CHARA Array. VII. Long-Baseline Interferometric Measurements of Vega Consistent with a Pole-On, Rapidly Rotating Star
Aufdenberg, J. P.; Mérand, A.; Coudé du Foresto, V. et al

in Astrophysical Journal (2006), 645

We have obtained high-precision interferometric measurements of Vega with the CHARA Array and FLUOR beam combiner in the K' band at projected baselines between 103 and 273 m. The measured visibility ... [more ▼]

We have obtained high-precision interferometric measurements of Vega with the CHARA Array and FLUOR beam combiner in the K' band at projected baselines between 103 and 273 m. The measured visibility amplitudes beyond the first lobe are significantly weaker than expected for a slowly rotating star characterized by a single effective temperature and surface gravity. Our measurements, when compared to synthetic visibilities and synthetic spectrophotometry from a Roche-von Zeipel gravity-darkened model atmosphere, provide strong evidence for the model of Vega as a rapidly rotating star viewed very nearly pole-on. Our best-fitting model indicates that Vega is rotating at ~91% of its angular break-up rate with an equatorial velocity of 275 km s[SUP]-1[/SUP]. Together with the measured vsini, this velocity yields an inclination for the rotation axis of 5deg. For this model the pole-to-equator effective temperature difference is ~2250 K, a value much larger than previously derived from spectral line analyses. A polar effective temperature of 10,150 K is derived from a fit to ultraviolet and optical spectrophotometry. The synthetic and observed spectral energy distributions are in reasonable agreement longward of 140 nm, where they agree to 5% or better. Shortward of 140 nm, the model is up to 10 times brighter than observed. The model has a luminosity of ~37 L[SUB]solar[/SUB], a value 35% lower than Vega's apparent luminosity based on its bolometric flux and parallax, assuming a slowly rotating star. Our model predicts the spectral energy distribution of Vega as viewed from its equatorial plane, and it may be employed in radiative models for the surrounding debris disk. [less ▲]

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See detailDeep Impact: High-Resolution Optical Spectroscopy with the ESO VLT and the Keck I Telescope
Jehin, Emmanuel ULg; Manfroid, Jean ULg; Hutsemekers, Damien ULg et al

in Astrophysical Journal (2006), 641(Letters), 145-148

We report on observations of comet 9P/Tempel 1 carried out before, during, and after the NASA Deep Impact event (UT July 4), with the optical spectrometers UVES and HIRES mounted on the telescopes Kueyen ... [more ▼]

We report on observations of comet 9P/Tempel 1 carried out before, during, and after the NASA Deep Impact event (UT July 4), with the optical spectrometers UVES and HIRES mounted on the telescopes Kueyen of the ESO VLT (Chile) and Keck I on Mauna Kea (Hawaii), respectively. A total observing time of about 60 hr, distributed over 15 nights around the impact date, allowed us (1) to find a periodic variation of 1.709 +/- 0.009 days in the CN and NH flux, explained by the presence of two major active regions; (2) to derive a lifetime >~5 × 10[SUP]4[/SUP] s (at 1.5 AU) for the parent of the CN radical from a simple modeling of the CN light curve after the impact; (3) to follow the gas and dust spatial profiles' evolution during the 4 hr following the impact and derive the projected velocities (400 and 150 m s[SUP]-1[/SUP], respectively); and (4) to show that the material released by the impact has the same carbon and nitrogen isotopic composition as the surface material ([SUP]12[/SUP]C/[SUP] 13[/SUP]C = 95 +/- 15 and [SUP]14[/SUP]N/[SUP]15[/SUP]N = 145 +/- 20). [less ▲]

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See detailAnnular Groove Phase Mask Coronagraph
Mawet, D.; Riaud, Pierre ULg; Absil, Olivier ULg et al

in Astrophysical Journal (2005), 633

We present a new phase mask coronagraph consisting in an optical vortex induced by a space-variant surface relief subwavelength grating. Phase mask coronagraphy is a recent technique aiming at ... [more ▼]

We present a new phase mask coronagraph consisting in an optical vortex induced by a space-variant surface relief subwavelength grating. Phase mask coronagraphy is a recent technique aiming at accommodating both high dynamic and high angular resolution imaging of faint sources around bright objects such as exoplanets orbiting their parent stars or host galaxies of active galactic nuclei. Subwavelength gratings are known to be artificially birefringent. Their unique dispersive characteristics can be controlled through the grating geometry in order to synthesize achromatic phase shifters. We show that implementing them in a ring-shaped way produces a fully symmetric and achromatic coronagraph without any gap or ``dead zone.'' The practical manufacturing of the device is also discussed. [less ▲]

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See detailThe massive runaway stars HD 14633 and HD 15137
Boyajian, T. S.; Beaulieu, T. D.; Gies, D. R. et al

in Astrophysical Journal (2005), 621(2, Part 1), 978-984

We present results from a radial velocity study of two runaway O-type stars, HD14633 (ON8.5V) and HD 15137 [O9.5 III(n)]. We find that HD 14633 is a single-lined spectroscopic binary with an orbital ... [more ▼]

We present results from a radial velocity study of two runaway O-type stars, HD14633 (ON8.5V) and HD 15137 [O9.5 III(n)]. We find that HD 14633 is a single-lined spectroscopic binary with an orbital period of 15.4083 days. The second target, HD 15137, is a radial velocity variable and a possible single-lined spectroscopic binary with a period close to 1 month. Both binaries have large eccentricity, small semiamplitude, and a small mass function. We show the trajectories of the stars in the sky based on an integration of motion in the Galactic potential, and we suggest that both stars were ejected from the vicinity of the open cluster NGC 654 in the Perseus spiral arm. The binary orbital parameters and runaway velocities are consistent with the idea that both these stars were ejected by supernova explosions in binaries and that they host neutron star companions. We find that the time of flight since ejection is longer than the predicted evolutionary timescales for the stars. This discrepancy may indicate that the stars have a lower mass than normally associated with their spectral classifications, that they were rejuvenated by mass transfer prior to the supernova, or that their lives have been extended through rapid rotation. [less ▲]

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See detailA period and a prediction for the Of ? p spectrum alternator HD 191612
Walborn, Nolan R.; Howarth, Ian D.; Rauw, Grégor ULg et al

in Astrophysical Journal (2004), 617(1, Part 2), 61-64

The observational picture of the enigmatic O-type spectrum variable HD 191612 has been sharpened substantially. A symmetrical, low-amplitude light curve with a period near 540 days has recently been ... [more ▼]

The observational picture of the enigmatic O-type spectrum variable HD 191612 has been sharpened substantially. A symmetrical, low-amplitude light curve with a period near 540 days has recently been reported from Hipparcos photometry. This period satisfies all of the spectroscopy since at least 1982, including extensive new observations during 2003 and 2004, and it has predicted the next transition during 2004 September - October. Measurements of the Ha equivalent width reveal a sharp emission peak in the phase diagram, in contrast to the apparently sinusoidal light curve. The He II absorption-line strength is essentially constant, while He I varies strongly, possibly filled in by emission in the O6 state, thus producing the apparent spectral type variations. The O8 state appears to be the "normal" one. Two intermediate O7 observations have been obtained, which fall at the expected phases, but these are the only modern observations of the transitions so far. The period is too long for rotation or pulsation; although there is no direct evidence as yet for a companion, a model in which tidally induced oscillations drive an enhanced wind near periastron of an eccentric orbit appears promising. Further observations during the now predictable transitions may provide a critical test. Ultraviolet and X-ray observations during both states will likely also prove illuminating. [less ▲]

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See detailThe Anomalous 14N/15N Ratio in Comets 122P/1995 S1 (de Vico) and 153P/2002 C1 (Ikeya-Zhang)
Jehin, Emmanuel ULg; Manfroid, Jean ULg; Cochran, A. L. et al

in Astrophysical Journal (2004), 613(Letters), 161-164

High-resolution (R~60,000) spectra of the CN B[SUP]2[/SUP]Sigma[SUP]+[/SUP]-X[SUP]2[/SUP]Sigma[SUP]+[/SUP] (0, 0) band (near 3880 Å) in the Halley-type comet 122P/1995 S1 de Vico (with a period of 74 yr ... [more ▼]

High-resolution (R~60,000) spectra of the CN B[SUP]2[/SUP]Sigma[SUP]+[/SUP]-X[SUP]2[/SUP]Sigma[SUP]+[/SUP] (0, 0) band (near 3880 Å) in the Halley-type comet 122P/1995 S1 de Vico (with a period of 74 yr) and the ``intermediate-period'' comet 153P/2002 C1 Ikeya-Zhang (P~370 yr) were obtained with the 2dcoudé spectrograph at the 2.7 m Harlan J. Smith telescope of the McDonald Observatory. The comets were within 1 AU from the Sun (0.66 and 0.92 AU, respectively) at the time of the observations. While the measured [SUP]12[/SUP]C/[SUP]13[/SUP]C isotope ratios of both comets (90+/-10 and 90+/-25, respectively) are in very good agreement with the solar system value, the [SUP]14[/SUP]N/[SUP]15[/SUP]N ratios (140+/-20 and 170+/-50, respectively) are approximately half the value in Earth's atmosphere. The similarity is striking between these ratios and those obtained recently for two other long-period Oort Cloud comets, C/1995 O1 (Hale-Bopp) and C/2000 WM1 (LINEAR). While these optical determinations of [SUP]14[/SUP]N/[SUP]15[/SUP]N are consistent with each other, they disagree with those obtained in comet Hale-Bopp from submillimeter measurements of HCN, generally believed to be the main parent of CN. This puzzling difference points toward the existence of (an)other unknown parent(s) of CN, with an even higher [SUP]15[/SUP]N excess. Organic compounds like those found in interplanetary dust particles are good candidates. [less ▲]

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See detailAn x-ray investigation of the NGC 346 field in the small Magellanic Cloud. III. XMM-Newton data
Nazé, Yaël ULg; Manfroid, Jean ULg; Stevens, I. R. et al

in Astrophysical Journal (2004), 608(1, Part 1), 208-219

We present new XMM-Newton results on the field around the NGC 346 star cluster in the SMC. This continues and extends previously published work on Chandra observations of the same field. The two XMM ... [more ▼]

We present new XMM-Newton results on the field around the NGC 346 star cluster in the SMC. This continues and extends previously published work on Chandra observations of the same field. The two XMM-Newton observations were obtained, respectively, 6 months before and 6 months after the previously published Chandra data. Of the 51 X-ray sources detected with XMM-Newton, 29 were already detected with Chandra. Comparing the properties of these X-ray sources in each of our three data sets has enabled us to investigate their variability on timescales of a year. Changes in the flux levels and/or spectral properties were observed for 21 of these sources. In addition, we discovered long-term variations in the X-ray properties of the peculiar system HD 5980, a luminous blue variable star that is likely to be a colliding wind binary system, which displayed the largest luminosity during the first XMM-Newton observation. [less ▲]

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See detailVLT+UVES Spectroscopy of the Ca II Low-Ionization Broad Absorption Line Quasar SDSS J030000.56+004828.0
Hall, Patrick B; Hutsemekers, Damien ULg; Anderson, Scott F et al

in Astrophysical Journal (2003), 593

We study high-resolution spectra of the ``overlapping-trough'' low-ionization broad absorption line (LoBAL) quasar SDSS J030000.56+004828.0. The Ca II, Mg II, and Mg I column densities in this object are ... [more ▼]

We study high-resolution spectra of the ``overlapping-trough'' low-ionization broad absorption line (LoBAL) quasar SDSS J030000.56+004828.0. The Ca II, Mg II, and Mg I column densities in this object are the largest reported to date for any BAL outflow. The broad Ca II absorption is mildly blended, but the blending can be disentangled to measure the Ca II column density, which is large enough that the outflow must include a strong hydrogen ionization front. The outflow begins at a blueshift of ~1650 km s[SUP]-1[/SUP] from the systemic redshift. The lowest velocity BAL region produces strong Ca II absorption but does not produce significant excited Fe II absorption, while the higher velocity excited Fe II absorption region produces very little Ca II absorption. We have found that only a disk wind outflow can explain this segregation. Whether the outflow is smooth or clumpy, we conclude that the Ca II BAL region has a density high enough to populate excited levels of Fe II but a temperature low enough to prevent them from being significantly populated. This requirement means the Ca II BAL region has T<~1100 K, and perhaps even T<~550 K. This quasar also has an associated absorption line system (AAL) that exhibits partial covering and therefore is likely located near the central engine. Its association with the BAL outflow is unclear. Blending of the AAL with the BAL trough shows that the spatial region covered by the BAL outflow can vary over velocity differences of ~1700 km s[SUP]-1[/SUP]. Based on observations from ESO Director's Discretionary Time program 267.A-5698. [less ▲]

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See detailAn X-ray investigation of the NGC 346 field in the Small Magellanic Cloud. II. The field population
Nazé, Yaël ULg; Hartwell, J. M.; Stevens, I. R. et al

in Astrophysical Journal (2003), 586(2, Part 1), 983-995

We present results from a Chandra observation of the NGC 346 cluster, which is the ionizing source of N66, the most luminous H II region and the largest star formation region in the SMC. In the first part ... [more ▼]

We present results from a Chandra observation of the NGC 346 cluster, which is the ionizing source of N66, the most luminous H II region and the largest star formation region in the SMC. In the first part of this investigation, we have analyzed the X-ray properties of the cluster itself and the remarkable star HD 5980, but the field contains additional objects of interest. In total, 75 X-ray point sources were detected in the Chandra observation: this is 5 times the number of sources detected by previous X-ray surveys. We investigate here their characteristics in detail. Because of high foreground absorption, the sources possess rather high hardness ratios. Their cumulative luminosity function appears generally steeper than that for the rest of the SMC at higher luminosities. Their absorption columns suggest that most of the sources belong to NGC 346. Using Digitized Sky Survey data and new UBVRI imaging with the ESO 2.2 m telescope, we also discovered possible counterparts for 32 of these X-ray sources and estimated a B spectral type for a large number of these counterparts. This tends to suggest that most of the X-ray sources in the field are in fact X-ray binaries. Finally, some objects show X-ray and/or optical variability, with a need for further monitoring. [less ▲]

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See detailAn X-ray investigation of the NGC 346 field in the Small Magellanic Cloud - I. The luminous blue variable HD 5980 and the NGC 346 cluster
Nazé, Yaël ULg; Hartwell, J. M.; Stevens, I. R. et al

in Astrophysical Journal (2002), 580(Part 1), 225-234

We present results from a Chandra observation of the NGC 346 cluster. This cluster contains numerous massive stars and is responsible for the ionization of N66, the most luminous H II region and the ... [more ▼]

We present results from a Chandra observation of the NGC 346 cluster. This cluster contains numerous massive stars and is responsible for the ionization of N66, the most luminous H II region and the largest star formation region in the SMC. In this first paper we will focus on the characteristics of the main objects of the field. The NGC 346 cluster itself shows only relatively faint X-ray emission (with L-X(unabs) similar to 1.5x10(34) ergs s(-1)), tightly correlated with the core of the cluster. In the field also lies HD 5980, a luminous blue variable star in a binary (or possibly a triple) system that is detected for the first time at X-ray energies. The star is X-ray bright, with an unabsorbed luminosity of L-X(unabs) similar to 1.7x10(34) ergs s(-1), but needs to be monitored further to investigate its X-ray variability over a complete 19 day orbital cycle. The high X-ray luminosity may be associated either with colliding winds in the binary system or with the 1994 eruption. HD 5980 is surrounded by a region of diffuse X-ray emission, which is a supernova remnant. While it may be only a chance alignment with HD 5980, such a spatial coincidence may indicate that the remnant is indeed related to this peculiar massive star. [less ▲]

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See detailThe Quadruple Wolf-Rayet System GP Cephei: Spectral Types, Masses, Mass-Loss Rate, and Colliding Winds
Demers, H.; Moffat, A. F. J.; Marchenko, S. V. et al

in Astrophysical Journal (2002), 577

We have reevaluated the orbital elements for each pair of the quadruple (W-R+O) + (O+O) stellar system GP Cep and propose new spectral types WN6o/WCE + O3-6, B0: I + B1: V-III. It is shown that there is ... [more ▼]

We have reevaluated the orbital elements for each pair of the quadruple (W-R+O) + (O+O) stellar system GP Cep and propose new spectral types WN6o/WCE + O3-6, B0: I + B1: V-III. It is shown that there is only one Wolf-Rayet (W-R) star in GP Cep, contrary to a previous claim. A rate of change P=1.3+/-0.2 s yr[SUP]-1[/SUP] is determined for the W-R+O pair, which leads to a new period of 6.6887 days and to a W-R mass-loss rate of (0.8-3.0)à 10[SUP]-5[/SUP] M[SUB]solar[/SUB] yr[SUP]-1[/SUP]. Masses for this pair are estimated to be M[SUB]W-R[/SUB]>~6 M[SUB]solar[/SUB] and M[SUB]O[/SUB]>~21 M[SUB]solar[/SUB]. The effects of wind-wind collision in the W-R+O pair are studied. It is shown that even after allowing for dilution by the OB components of the quadruple system, these effects are not as strong as in the binary V444 Cygni (WN5+O6, P=4.212 days). In GP Cep, the phase-dependent, relatively weak excess emission does not originate in the arms of the bow shock cone. Rather, it emerges from the extra heated portion of the W-R wind facing the hot O companion. The trailing bow shock arm is clearly seen, however, as an enhanced He I absorption component near quadrature at phase ~0.73. An anomalous blueshifted He I absorption is present at phase ~0.9, as is also seen in V444 Cyg, in the WC8+O9 I/O8 III binary γ Velorum and in the LBV-cotype binary R81 (B2.5 Iab:e). A 3.5 day orbit for the eclipsing B star pair is confirmed. [less ▲]

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See detailQSO 2237+0305 VR light curves from Gravitational Lenses International Time Project optical monitoring
Alcalde, D.; Mediavilla, E.; Moreau, O. et al

in Astrophysical Journal (2002), 572(2, Part 1), 729-734

We present VR observations of QSO 2237+ 0305 conducted by the Gravitational Lensing International Time Project collaboration from 1999 October 1 to 2000 February 3. The observations were made with the 2 ... [more ▼]

We present VR observations of QSO 2237+ 0305 conducted by the Gravitational Lensing International Time Project collaboration from 1999 October 1 to 2000 February 3. The observations were made with the 2.56 m Nordic Optical Telescope at Roque de los Muchachos Observatory, La Palma ( Spain). The pointspread function ( PSF) fitting method and an adapted version of the ISIS subtraction method have been used to derive the VR light curves of the four components ( A D) of the quasar. The mean errors range in the intervals 0.01-0.04 mag ( PSF fitting) and 0.01-0.02 mag ( ISIS subtraction), with the faintest component ( D) having the largest uncertainties. We address the relatively good agreement between the A and D light curves derived using different filters, photometric techniques, and telescopes. The new VR light curves of component A extend the time coverage of a high-magnification microlensing peak, which was discovered by the OGLE team. [less ▲]

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See detailRecurring Outbursts and Nuclear Fragmentation of Comet C/2001 A2 (LINEAR)
Sekanina, Zdenek; Jehin, Emmanuel ULg; Boehnhardt, Hermann et al

in Astrophysical Journal (2002), 572

Analysis of the visual light curve and fragmentation sequence of comet C/2001 A2 (LINEAR) shows a strong temporal correlation between the onset of outbursts and separation of companion nuclei. This ... [more ▼]

Analysis of the visual light curve and fragmentation sequence of comet C/2001 A2 (LINEAR) shows a strong temporal correlation between the onset of outbursts and separation of companion nuclei. This scenario conforms to Sekanina's conceptual model for the release of sizable fragments of an inert dust mantle from the nucleus surface: an outburst is triggered as some of the mass rapidly disintegrates into fine dust. [less ▲]

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See detailDoubly ionized thorium: Laser lifetime measurements and transition probability determination of interest in cosmochronology
Biémont, Emile ULg; Palmeri, P.; Quinet, Pascal ULg et al

in Astrophysical Journal (2002), 567(2, Part 1), 1276-1283

The first lifetime measurements have been performed for six levels of doubly ionized thorium, an important cosmochronometer in astrophysics for estimating the age of the Galaxy. The levels, belonging to ... [more ▼]

The first lifetime measurements have been performed for six levels of doubly ionized thorium, an important cosmochronometer in astrophysics for estimating the age of the Galaxy. The levels, belonging to the 5f(2), 5f7p, 7s7p, and 6d7p configurations of Th III, have been measured by the time-resolved laser-induced fluorescence method and compared with relativistic Hartree-Fock calculations including configuration interaction and core-polarization effects. Taking advantage of the excellent agreement between theory and experiment, a first set of transition probabilities of astrophysical interest has been deduced for this ion from a combination of the experimental lifetimes and of the theoretical branching fractions. [less ▲]

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See detailDiscovery of soft X-ray emission from Io, Europa, and the Io Plasma Torus
Elsner, Ronald F.; Gladstone, G. Randall; Waite, J. Hunter et al

in Astrophysical Journal (2002), 572(2), 1077-1082

We report the discovery of soft (0.25-2 keV) X-ray emission from the Galilean satellites Io and Europa, probably Ganymede, and from the Io Plasma Torus (IPT). Bombardment by energetic (greater than 10 keV ... [more ▼]

We report the discovery of soft (0.25-2 keV) X-ray emission from the Galilean satellites Io and Europa, probably Ganymede, and from the Io Plasma Torus (IPT). Bombardment by energetic (greater than 10 keV) H, O, and S ions from the region of the IPT seems to be the likely source of the X-ray emission from the Galilean satellites. According to our estimates, fluorescent X-ray emission excited by solar X-rays, even during flares from the active Sun, charge-exchange processes, previously invoked to explain Jupiter's X-ray aurora and cometary X-ray emission, and ion stripping by dust grains fail to account for the observed emission. On the other hand, bremsstrahlung emission of soft X-rays from nonthermal electrons in the few hundred to few thousand eV range may account for a substantial fraction of the observed X-ray flux from the IPT. [less ▲]

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See detailHelioseismic Tests of the New Los Alamos LEDCOP Opacities
Neuforge-Verheecke, C.; Guzik, J. A.; Keady, J. J. et al

in Astrophysical Journal (2001), 561(1), 450-454

We compare the helioseismic properties of two solar models, one calibrated with the OPAL opacities and the other with the recent Los Alamos LEDCOP (Light Element Detailed Configuration Opacity) opacities ... [more ▼]

We compare the helioseismic properties of two solar models, one calibrated with the OPAL opacities and the other with the recent Los Alamos LEDCOP (Light Element Detailed Configuration Opacity) opacities. We show that, in the radiative interior of the Sun, the small differences between the two sets of opacities (up to 6% near the base of the convection zone) lead to noticeable differences in the solar structure (up to 0.3% in sound speed), with the OPAL model being the closest to the helioseismic data. More than half of the difference between the two opacity sets results from the interpolation scheme and from the relatively widely spaced temperature grids used in the tables. The remaining 3% intrinsic difference between the OPAL and the LEDCOP opacities in the radiative interior of the Sun is well within the error bars on the opacity calculations resulting from the uncertainties on the physics. We conclude that both the OPAL and LEDCOP opacities produce solar models in close agreement with helioseismic inferences, but discrepancies still persist at the level of 0.6% between the calculated and inferred sound speed in the radiative interior of the Sun. [less ▲]

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See detailAn Optical Time Delay Estimate for the Double Gravitational Lens System B1600+434
Burud, I.; Hjorth, J.; Jaunsen, A. O. et al

in Astrophysical Journal (2000), 544

We present optical I-band light curves of the gravitationally lensed double QSO B1600+434 from observations obtained at the Nordic Optical Telescope (NOT) between 1998 April and 1999 November. The ... [more ▼]

We present optical I-band light curves of the gravitationally lensed double QSO B1600+434 from observations obtained at the Nordic Optical Telescope (NOT) between 1998 April and 1999 November. The photometry has been performed by simultaneous deconvolution of all the data frames, involving a numerical lens galaxy model. Four methods have been applied to determine the time delay between the two QSO components, giving a mean estimate of Deltat=51+/-4 days (95% confidence level). This is the fourth optical time delay ever measured. Adopting a Omega=0.3, Lambda=0 universe and using the mass model of Maller et al., this time delay estimate yields a Hubble parameter of H[SUB]0[/SUB]=52[SUP]+14[/SUP][SUB]-8[/SUB] km s[SUP]-1[/SUP] Mpc[SUP]-1[/SUP] (95% confidence level), where the errors include time delay as well as model uncertainties. There are time-dependent offsets between the two (appropriately shifted) light curves that indicate the presence of external variations due to microlensing. Based on observations made with the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. [less ▲]

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See detailA Method for Spatial Deconvolution of Spectra
Courbin, F.; Magain, Pierre ULg; Kirkove, Murielle ULg et al

in Astrophysical Journal (2000), 529

A method for spatial deconvolution of spectra is presented. It follows the same fundamental principles as the ``MCS image deconvolution algorithm'' recently developed by Magain, Courbin, & Sohy and uses ... [more ▼]

A method for spatial deconvolution of spectra is presented. It follows the same fundamental principles as the ``MCS image deconvolution algorithm'' recently developed by Magain, Courbin, & Sohy and uses information contained in the spectrum of a reference point-spread function to spatially deconvolve spectra of very blended sources. An improved resolution rather than an infinite one is aimed at, overcoming the well-known problem of ``deconvolution artifacts.'' As in the MCS algorithm, the data are decomposed into a sum of analytical point sources and a numerically deconvolved background so that the spectrum of extended sources in the immediate vicinity of bright point sources may be accurately extracted and sharpened. The algorithm has been tested on simulated data including seeing variation as a function of wavelength and atmospheric refraction. It is shown that the spectra of severely blended point sources can be resolved while fully preserving the spectrophotometric properties of the data. Extended objects ``hidden'' by bright point sources (up to 4-5 mag brighter) can be accurately recovered as well, provided the data have a sufficiently high total signal-to-noise ratio (200-300 per spectral resolution element). Such spectra are relatively easy to obtain, even down to faint magnitudes, within a few hours of integration time with 10 m class telescopes. [less ▲]

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See detailExperimental and theoretical radiative lifetimes, branching fractions, and oscillator strengths for Lu I and experimental lifetimes for Lu II and Lu III
Fedchak, J. A.; Den Hartog, E. A.; Lawler, J. E. et al

in Astrophysical Journal (2000), 542

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See detailDeep Imaging of AX J2019+112: The Luminosity of a ``Dark Cluster''
Benítez, Narciso; Broadhurst, Tom; Rosati, Piero et al

in Astrophysical Journal (1999), 527

We detect a distant cluster of galaxies centered on the QSO lens and luminous X-ray source AX J2019+112, a.k.a. the ``Dark Cluster.'' Using deep V and I Keck images and wide-field K[SUB]s[/SUB] imaging ... [more ▼]

We detect a distant cluster of galaxies centered on the QSO lens and luminous X-ray source AX J2019+112, a.k.a. the ``Dark Cluster.'' Using deep V and I Keck images and wide-field K[SUB]s[/SUB] imaging from the New Technology Telescope (NTT), a tight red sequence of galaxies is identified within a radius of 0.2 h[SUP]-1[/SUP] Mpc of the known z=1.01 elliptical lensing galaxy. The sequence, which includes the central elliptical galaxy, has a slope in good agreement with the model predictions of Kodama et al. for z~1. We estimate the integrated rest-frame luminosity of the cluster to be L[SUB]V[/SUB]>=3.2x10[SUP]11[/SUP] h[SUP]-2[/SUP] L[SUB]solar[/SUB] (after accounting for significant extinction at the low latitude of this field), more than an order of magnitude higher than previous estimates. The central region of the cluster is deconvolved using the technique of Magain, Courbin, & Sohy, revealing a thick central arc coincident with an extended radio source. All the observed lensing features are readily explained by differential magnification of a radio-loud active galactic nucleus by a shallow elliptical potential. The QSO must lie just outside the diamond caustic, producing two images; the arc is a highly magnified image formed from a region close to the center of the host galaxy, projecting inside the caustic. The mass-to-light ratio within an aperture of 0.4 h[SUP]-1[/SUP] Mpc is M[SUB]X[/SUB]/L[SUB]V[/SUB]=224[SUP]+112[/SUP][SUB]- 78[/SUB]h(M/L[SUB]V[/SUB])[SUB]solar[/SUB], using the X-ray temperature. The strong lens model yields a compatible value, M/L[SUB]V[/SUB]=372[SUP]+94[/SUP][SUB]- 94[/SUB]h(M/L[SUB]V[/SUB])[SUB]solar[/SUB], whereas an independent weak-lensing analysis sets an upper limit of M/L[SUB]V[/SUB]<520h(M/L[SUB]V[/SUB])[SUB]solar[/SUB], typical of massive clusters. [less ▲]

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