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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 detailGRB 080913 at Redshift 6.7
Greiner, J.; Krühler, T.; Fynbo, J. P. U. et al

in Astrophysical Journal (2009), 693

We report on the detection by Swift of GRB 080913, and subsequent optical/near-infrared follow-up observations by GROND, which led to the discovery of its optical/NIR afterglow and the recognition of its ... [more ▼]

We report on the detection by Swift of GRB 080913, and subsequent optical/near-infrared follow-up observations by GROND, which led to the discovery of its optical/NIR afterglow and the recognition of its high-z nature via the detection of a spectral break between the i' and z' bands. Spectroscopy obtained at the ESO-VLT revealed a continuum extending down to λ = 9400 Å, and zero flux for 7500 Å<λ < 9400 Å, which we interpret as the onset of a Gunn-Peterson trough at z = 6.695± 0.025 (95.5% confidence level), making GRB 080913 the highest-redshift gamma-ray burst (GRB) to date, and more distant than the highest-redshift QSO. We note that many redshift indicators that are based on promptly available burst or afterglow properties have failed for GRB 080913. We report on our follow-up campaign and compare the properties of GRB 080913 with bursts at lower redshift. In particular, since the afterglow of this burst is fainter than typical for GRBs, we show that 2 m class telescopes can identify most high-redshift GRBs. [less ▲]

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See detailDust in the inner regions of debris disks around A stars
Akeson, R. L.; Ciardi, D. R.; Millan-Gabet, R. et al

in Astrophysical Journal (2009), 691

We present infrared interferometric observations of the inner regions of two A-star debris disks, beta Leo and zeta Lep, using the FLUOR instrument at the CHARA interferometer on both short (30 m) and ... [more ▼]

We present infrared interferometric observations of the inner regions of two A-star debris disks, beta Leo and zeta Lep, using the FLUOR instrument at the CHARA interferometer on both short (30 m) and long (> 200 m) baselines. For the target stars, the short-baseline visibilities are lower than expected for the stellar photosphere alone, while those of a check star, delta Leo, are not. We interpret this visibility offset of a few percent as a near-infrared (NIR) excess arising from dust grains which, due to the instrumental field of view, must be located within several AU of the central star. For beta Leo, the NIR excess-producing grains are spatially distinct from the dust which produces the previously known mid-infrared (MIR) excess. For zeta Lep, the NIR excess may be spatially associated with the MIR excess-producing material. We present simple geometric models which are consistent with the NIR and MIR excesses and show that for both objects, the NIR-producing material is most consistent with a thin ring of dust near the sublimation radius, with typical grain sizes smaller than the nominal radiation pressure blowout radius. Finally, we discuss possible origins of the NIR-emitting dust in the context of debris disk evolution models. [less ▲]

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See detailWasp-7: A Bright Transiting-Exoplanet System in the Southern Hemisphere
Hellier, Coel; Anderson, D. R.; Gillon, Michaël ULg et al

in Astrophysical Journal (2009), 690

We report that a Jupiter-mass planet, WASP-7b, transits the V = 9.5 star HD 197286 every 4.95 d. This is the brightest discovery from the WASP-South transit survey so far and is currently the brightest ... [more ▼]

We report that a Jupiter-mass planet, WASP-7b, transits the V = 9.5 star HD 197286 every 4.95 d. This is the brightest discovery from the WASP-South transit survey so far and is currently the brightest transiting-exoplanet system in the southern hemisphere. WASP-7b is among the densest of the known Jupiter-mass planets, suggesting that it has a massive core. The planet mass is 0.96[SUP]+0.12[/SUP] [SUB]--0.18[/SUB] M [SUB]Jup[/SUB], the radius is 0.915[SUP]+0.046[/SUP] [SUB]--0.040[/SUB] R [SUB]Jup[/SUB], and the density is 1.26[SUP]+0.25[/SUP] [SUB]--0.21[/SUB] rho[SUB]Jup[/SUB] (1.67[SUP]+0.33[/SUP] [SUB]--0.28[/SUB] g cm[SUP]--3[/SUP]). [less ▲]

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See detailSpectrum synthesis modeling of the X-ray spectrum of GRO J1655-40 during the 2005 outburst
Kallman, T R; Bautista, M A; Goriely, S et al

in Astrophysical Journal (2009), 701

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See detailLarge Excess of Heavy Nitrogen in Both Hydrogen Cyanide and Cyanogen from Comet 17P/Holmes
Bockelée-Morvan, D.; Biver, N.; Jehin, Emmanuel ULg et al

in Astrophysical Journal (2008), 679(Letters), 49-52

From millimeter and optical observations of the Jupiter-family comet 17P/Holmes performed soon after its huge outburst of 2007 October 24, we derive [SUP]14[/SUP]N/[SUP]15[/SUP]N = 139 +/- 26 in HCN and ... [more ▼]

From millimeter and optical observations of the Jupiter-family comet 17P/Holmes performed soon after its huge outburst of 2007 October 24, we derive [SUP]14[/SUP]N/[SUP]15[/SUP]N = 139 +/- 26 in HCN and [SUP]14[/SUP]N/[SUP]15[/SUP]N = 165 +/- 40 in CN, establishing that HCN has the same nonterrestrial isotopic composition as CN. The same conclusion is obtained for the long-period comet C/1995 O1 (Hale-Bopp) after a reanalysis of previously published measurements. These results are compatible with HCN being the prime parent of CN in cometary atmospheres. The [SUP]15[/SUP]N excess relative to the Earth's atmospheric value indicates that N-bearing volatiles in the solar nebula underwent important N isotopic fractionation at some stage of solar system formation. HCN molecules never isotopically equilibrated with the main nitrogen reservoir in the solar nebula before being incorporated in Oort Cloud and Kuiper Belt comets. The [SUP]12[/SUP]C/[SUP]13[/SUP]C ratios in HCN and CN are measured to be consistent with the terrestrial value. [less ▲]

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See detailWASP-4b: A 12th Magnitude Transiting Hot Jupiter in the Southern Hemisphere
Wilson, D. M.; Gillon, Michaël ULg; Hellier, C. et al

in Astrophysical Journal (2008), 675

We report the discovery of WASP-4b, a large transiting gas-giant planet with an orbital period of 1.34 days. This is the first planet to be discovered by the SuperWASP-South observatory and CORALIE ... [more ▼]

We report the discovery of WASP-4b, a large transiting gas-giant planet with an orbital period of 1.34 days. This is the first planet to be discovered by the SuperWASP-South observatory and CORALIE collaboration and the first planet orbiting a star brighter than 16th magnitude to be discovered in the southern hemisphere. A simultaneous fit to high-quality light curves and precision radial velocity measurements leads to a planetary mass of 1.22[SUP]+0.09[/SUP][SUB]-0.08[/SUB] M[SUB]Jup[/SUB] and a planetary radius of 1.42[SUP]+0.07[/SUP][SUB]-0.04[/SUB] R[SUB]Jup[/SUB]. The host star is USNO-B1.0 0479-0948995, a G7 V star of visual magnitude 12.5. As a result of the short orbital period, the predicted surface temperature of the planet is 1761 K, making it an ideal candidate for detections of the secondary eclipse at infrared wavelengths. [less ▲]

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See detailLupus-TR-3b: A Low-Mass Transiting Hot Jupiter in the Galactic Plane?
Weldrake, David T F; Bayliss, Daniel D R; Sackett, Penny D et al

in Astrophysical Journal (2008), 675

We present a strong case for a transiting hot Jupiter planet identified during a single-field transit survey toward the Lupus Galactic plane. The object, Lupus-TR-3b, transits a V=17.4 K1 V host star ... [more ▼]

We present a strong case for a transiting hot Jupiter planet identified during a single-field transit survey toward the Lupus Galactic plane. The object, Lupus-TR-3b, transits a V=17.4 K1 V host star every 3.91405 days. Spectroscopy and stellar colors indicate a host star with effective temperature 5000 +/- 150 K, with a stellar mass and radius of 0.87 +/- 0.04 M[SUB]solar[/SUB] and 0.82 +/- 0.05 R[SUB]solar[/SUB], respectively. Limb-darkened transit fitting yields a companion radius of 0.89+/-0.07 R[SUB]J[/SUB] and an orbital inclination of 88.3[SUP]+1.3[/SUP][SUB]-0.8[/SUB] deg. Magellan 6.5 m MIKE radial velocity measurements reveal a 2.4 sigma K = 114 +/- 25 m s[SUP]-1[/SUP] sinusoidal variation in phase with the transit ephemeris. The resulting mass is 0.81 +/- 0.18 M[SUB]J[/SUB] and density 1.4 +/- 0.4 g cm[SUP]-3[/SUP]. Y-band PANIC image deconvolution reveals a V>=21 red neighbor 0.4[SUP]''[/SUP] away which, although highly unlikely, we cannot conclusively rule out as a blended binary with current data. However, blend simulations show that only the most unusual binary system can reproduce our observations. This object is very likely a planet, detected from a highly efficient observational strategy. Lupus-TR-3b constitutes the faintest ground-based detection to date, and one of the lowest mass hot Jupiters known. [less ▲]

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See detailUnderstanding the relations between QSOs and their host galaxies from combined HST imaging and VLT spectroscopy
Letawe, Yannick ULg; Magain, Pierre ULg; Letawe, Géraldine ULg et al

in Astrophysical Journal (2008), 679(2), 967-983

The host galaxies of six nearby QSOs are studied on the basis of high-resolution HST optical images and spatially resolved VLT slit spectra. The gas ionization and velocity are mapped as a function of the ... [more ▼]

The host galaxies of six nearby QSOs are studied on the basis of high-resolution HST optical images and spatially resolved VLT slit spectra. The gas ionization and velocity are mapped as a function of the distance to the central QSO. In the majority of the cases, the QSO significantly contributes to the gas ionization in its whole host galaxy, and sometimes even outside. Reflection or scattering of the QSO H alpha line from remote regions of the galaxy is detected in several instances. The line shifts show that, in all cases, the matter responsible for the light reflection moves away from the QSO, likely accelerated by its radiation pressure. The two faintest QSOs reside in spirals, with some signs of a past gravitational perturbation. One of the intermediate-luminosity QSOs resides in a massive elliptical containing gas ionized (and probably pushed away) by the QSO radiation. The other medium-power object is found in a spiral galaxy displaying complex velocity structure, with the central QSO moving with respect to the bulge, probably as a result of a galactic collision. The two most powerful objects are involved in violent gravitational interactions, and one of them has no detected host. These results suggest that (1) large-scale phenomena, such as galactic collisions, are closely related to the triggering and the feeding of the QSO and (2) once ignited, the QSO has significant influence on its large-scale neighborhood ( often the whole host and sometimes further away). [less ▲]

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See detailISM Studies of GRB 030329 with High-Resolution Spectroscopy
Thöne, Christina C; Greiner, Jochen; Savaglio, Sandra et al

in Astrophysical Journal (2007), 671

We present early Very Large Telescope UV-Visual Echelle Spectrograph (VLT UVES) high-resolution spectra of the afterglow of GRB 030329 at redshift z=0.16867+/-0.00001. In contrast to other spectra from ... [more ▼]

We present early Very Large Telescope UV-Visual Echelle Spectrograph (VLT UVES) high-resolution spectra of the afterglow of GRB 030329 at redshift z=0.16867+/-0.00001. In contrast to other spectra from this burst, both emission and absorption lines were detected. None of them showed any temporal evolution. From the emission lines, we determine the properties of the host galaxy, which has a star formation rate (SFR) of 0.198 M[SUB]solar[/SUB] yr[SUP]-1[/SUP] and a low metallicity of 0.17 Z[SUB]solar[/SUB]. Given the low total stellar host mass logM[SUB]*[/SUB]=7.75+/-0.15 M[SUB]solar[/SUB] and an absolute luminosity m[SUB]B[/SUB]=-16.29, we derive specific SFRs (SSFR) of logSFR=-8.5 yr[SUP]-1[/SUP] and SFR = 15.1 M[SUB]solar[/SUB] yr[SUP]-1[/SUP] L[SUP]-1[/SUP][SUB]*[/SUB]. This fits well into the picture of GRB hosts as being low-mass, low-metallicity, actively star-forming galaxies. The Mg II and Mg I absorption lines from the host show multiple narrow (Doppler width b=5-12 km s[SUP]-1[/SUP]) components spanning a range of v~230 km s[SUP]-1[/SUP], mainly blueshifted compared to the redshift from the emission lines. These components are likely probing outflowing material of the host galaxy, which could arise from former galactic superwinds, driven by supernovae from star-forming regions. Similar features have been observed in QSO spectra. The outflowing material has high column densities of logN[SUB]MgII[/SUB]=13.99+/-0.04 cm[SUP]-2[/SUP] and logN[SUB]MgI[/SUB]=12.39+/-0.04 cm[SUP]-2[/SUP] and the nonvariability of the column densities implies a distance of at least 560 pc from the burst, further supporting an outflow scenario. Based on ESO proposal 70.D-0087. [less ▲]

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See detailAcceleration and Substructure Constraints in a Quasar Outflow
Hall, Patrick B; Sadavoy, Sarah I; Hutsemekers, Damien ULg et al

in Astrophysical Journal (2007), 665

We present observations of probable line-of-sight acceleration of a broad absorption trough of C IV in the quasar SDSS J024221.87+004912.6. We also discuss how the velocity overlap of two other outflowing ... [more ▼]

We present observations of probable line-of-sight acceleration of a broad absorption trough of C IV in the quasar SDSS J024221.87+004912.6. We also discuss how the velocity overlap of two other outflowing systems in the same object constrains the properties of the outflows. The Si IV doublet in each system has one unblended transition and one transition that overlaps with absorption from the other system. The residual flux in the overlapping trough is well fit by the product of the residual fluxes in the unblended troughs. For these optically thick systems to yield such a result, at least one of them must consist of individual subunits, rather than being a single structure with velocity-dependent coverage of the source. If these subunits are identical, opaque, spherical clouds, we estimate the cloud radius to be r~=3.9×10[SUP]15[/SUP] cm. If they are identical, opaque, linear filaments, we estimate their width to be w~=6.5×10[SUP]14[/SUP] cm. These subunits are observed to cover the Mg II broad emission-line region of the quasar, at which distance from the black hole the above filament width is equal to the predicted scale height of the outer atmosphere of a thin accretion disk. Insofar as that scale height is a natural size scale for structures originating in an accretion disk, these observations are evidence that the accretion disk can be a source of quasar absorption systems. This paper is based on data from ESO program 075.B-0190(A). [less ▲]

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See detailConstraining the fundamental parameters of the O-type binary CPD-41 7733
Sana, H.; Rauw, Grégor ULg; Gosset, Eric ULg

in Astrophysical Journal (2007), 659(2, Part 1), 1582-1591

Using a set of high-resolution spectra, we studied the physical and orbital properties of the O-type binary CPD -41 7733, located in the core of NGC 6231. We report the unambiguous detection of a ... [more ▼]

Using a set of high-resolution spectra, we studied the physical and orbital properties of the O-type binary CPD -41 7733, located in the core of NGC 6231. We report the unambiguous detection of a secondary spectral signature and we derive the first SB2 orbital solution of the system. The period is 5.6815 + 0.0015 days, and the orbit has no significant eccentricity. CPD -41 7733 probably consists of stars of spectral types O8.5 and B3. As for other objects in the cluster, we observe discrepant luminosity classifications while using spectroscopic or brightness criteria. Still, the present analysis suggests that both components display physical parameters close to those of typical O8.5 and B3 dwarfs. We also analyze the X-ray light curves and spectra obtained during six 30 ks XMM-Newton pointings spread over the 5.7 day period. We find no significant variability between the different pointings, nor within the individual observations. The CPD - 41 7733 X- ray spectrum is well reproduced by a three-temperature thermal mekal model with temperatures of 0.3, 0.8, and 2.4 keV. No X-ray overluminosity, resulting, e. g., from a possible wind interaction, is observed. The emission of CPD -41 7733 is thus very representative of typical O-type star X- ray emission. [less ▲]

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See detailFirst detection of phase-dependent colliding wind X-ray emission outside the Milky Way
Nazé, Yaël ULg; Corcoran, M. F.; Koenigsberger, G. et al

in Astrophysical Journal (2007), 658(1, Part 2), 25-28

After having reported the detection of X-rays emitted by the peculiar system HD 5980, we assess here the origin of this high-energy emission from additional X-ray observations obtained with XMM-Newton ... [more ▼]

After having reported the detection of X-rays emitted by the peculiar system HD 5980, we assess here the origin of this high-energy emission from additional X-ray observations obtained with XMM-Newton. This research provides the first detection of apparently periodic X-ray emission from hot gas produced by the collision of winds in an evolved massive binary outside the Milky Way. It also provides the first X-ray monitoring of a luminous blue variable only years after its eruption and shows that the dominant source of the X-rays is not associated with the ejecta. After having reported the detection of X-rays emitted by the peculiar system HD 5980, we assess here the origin of this high-energy emission from additional X-ray observations obtained with XMM-Newton. This research provides the first detection of apparently periodic X-ray emission from hot gas produced by the collision of winds in an evolved massive binary outside the Milky Way. It also provides the first X-ray monitoring of a luminous blue variable only years after its eruption and shows that the dominant source of the X-rays is not associated with the ejecta. [less ▲]

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See detailSpectral Energy Distributions of Hard X-Ray Selected Active Galactic Nuclei in the XMM-Newton Medium Deep Survey
Polletta, M.; Tajer, M.; Maraschi, L. et al

in Astrophysical Journal (2007), 663

We present the SEDs of a hard X-ray selected sample containing 136 sources with F[SUB]2-10keV[/SUB]>10[SUP]-14[/SUP] erg cm[SUP]-2[/SUP] s[SUP]-1[/SUP] 132 are AGNs. The sources are detected in a 1 deg ... [more ▼]

We present the SEDs of a hard X-ray selected sample containing 136 sources with F[SUB]2-10keV[/SUB]>10[SUP]-14[/SUP] erg cm[SUP]-2[/SUP] s[SUP]-1[/SUP] 132 are AGNs. The sources are detected in a 1 deg[SUP]2[/SUP] area of the XMM-Newton Medium Deep Survey where optical data from the VVDS and CFHTLS and infrared data from the SWIRE survey are available. Based on a SED fitting technique we derive photometric redshifts with sigma(1+z)=0.11 and 6% of outliers and identify AGN signatures in 83% of the objects. This fraction is higher than derived when a spectroscopic classification is available. The remaining 17[SUP]+9[/SUP][SUB]-6[/SUB]% of AGNs show star-forming galaxy SEDs (SF class). The sources with AGN signatures are divided in two classes, AGN1 (33[SUP]+6[/SUP][SUB]-1[/SUB]%) and AGN2 (50[SUP]+6[/SUP][SUB]-11[/SUB]%). The AGN1 and AGN2 classes include sources whose SEDs are fitted by type 1 and type 2 AGN templates, respectively. On average, AGN1s show soft X-ray spectra, consistent with being unabsorbed, while AGN2s and SFs show hard X-ray spectra, consistent with being absorbed. The analysis of the average SEDs as a function of X-ray luminosity shows a reddening of the infrared SEDs, consistent with a decreasing contribution from the host galaxy at higher luminosities. The AGNs in the SF classes are likely obscured in the mid-infrared, as suggested by their low L[SUB]3-20mum[/SUB]/L[SUP]corr[/SUP][SUB]0.5-10keV[/SUB] ratios. We confirm the previously found correlation for AGNs between the radio luminosity and the X-ray and the mid-infrared luminosities. The X-ray-radio correlation can be used to identify heavily absorbed AGNs. However, the estimated radio fluxes for the missing AGN population responsible for the bulk of the background at E>10 keV are too faint to be detected even in the deepest current radio surveys. [less ▲]

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See detailGCIRS 16SW: A massive eclipsing binary in the Galactic center
Martins, F.; Trippe, S.; Paumard, T. et al

in Astrophysical Journal (2006), 649(2, Part 2), 103-106

We report on the spectroscopic monitoring of GCIRS 16SW, an Ofpe/WN9 star and LBV candidate in the central parsec of the Galaxy. SINFONI observations show strong daily spectroscopic changes in the K band ... [more ▼]

We report on the spectroscopic monitoring of GCIRS 16SW, an Ofpe/WN9 star and LBV candidate in the central parsec of the Galaxy. SINFONI observations show strong daily spectroscopic changes in the K band. Radial velocities are derived from the He I 2.112 mu m line complex and vary regularly with a period of 19.45 days, indicating that the star is most likely an eclipsing binary. Under various assumptions, we are able to derive a mass of similar to 50 M circle dot for each component. [less ▲]

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See detailOn the nature of the hard X-ray source IGR J2018+4043
Bykov, Andrei Mikhailovich; Krassilchtchikov, Alexandre Mikhailovich; Uvarov, Yuri Alexandrovich et al

in Astrophysical Journal (2006), 649(1, Part 2), 21-24

We found a very likely counterpart to the recently discovered hard X-ray source IGR J2018 + 4043 in the multiwavelength observations of the source field. The source, originally discovered in the 20-40 keV ... [more ▼]

We found a very likely counterpart to the recently discovered hard X-ray source IGR J2018 + 4043 in the multiwavelength observations of the source field. The source, originally discovered in the 20-40 keV band, is now confidently detected also in the 40-80 keV band, with a flux of (1.4 +/- 0.4) x 10(-11) ergs cm(-2) s(-1). A 5 ks Swift observation of the IGR J2018 + 4043 field revealed a hard pointlike source with an observed 0.5-10 keV flux of 3.4(-0.8)(+0.7) x 10(-12) ergs cm(-2) s(-1) (90% confidence level) at alpha = 20(h)18(m)38(s).55, delta = +40 degrees 41'00.4" (with a 4".2 uncertainty). The combined Swift-INTEGRAL spectrum can be described by an absorbed power-law model with photon index Gamma = 1.3 +/- 0.2 and N-H = 6.1(-2.2)(+3.3) x 10(22) cm(-2). In archival optical and infrared data we found a slightly extended and highly absorbed object at the Swift source position. There is also an extended VLA 1.4 GHz source peaked at a beamwidth distance from the optical and X-ray positions. The observed morphology and multiwavelength spectra of IGR J2018 + 4043 are consistent with those expected for an obscured accreting object, i.e., an AGN or a Galactic X-ray binary. The identification suggests possible connection of IGR J2018 + 4043 to the bright gamma-ray source GEV J2020 + 4023 detected by COS B and CGRO EGRET. [less ▲]

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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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