References of "Astronomy and Astrophysics"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailTowards consistent mapping of distant worlds: secondary eclipse scanning of HD189733b
de Wit, Julien; Gillon, Michaël ULg; Demory, Brice-Olivier et al

in Astronomy and Astrophysics (2012), 548

Context. Mapping the brightness distribution of exoplanets is the next frontier for exoplanet infrared photometry studies. For tidally-locked hot Jupiters that transit and are eclipsed by their host star ... [more ▼]

Context. Mapping the brightness distribution of exoplanets is the next frontier for exoplanet infrared photometry studies. For tidally-locked hot Jupiters that transit and are eclipsed by their host star with non-zero impact parameter, the first steps are now possible. Aims. The aim is to use eclipse scanning from occultation ingress/egress and phase curve measurements to constrain exoplanet large-scale brightness structure. Methods. We use archived Spitzer/IRAC 8 {\mu}m data of HD189733 in a global MCMC procedure encompassing six transits, eight secondary eclipses, and a phase curve in a two-step analysis. The first step derives the planet-star system parameters. The second step investigates the structure found in eclipse scanning, using the previous planet-star system parameter derivation as Gaussian priors. Results. We find a 5-sigma deviation from the expected occultation ingress/egress shape for a uniform brightness disk, and demonstrate that this is dominated by large-scale brightness structure and not an occultation timing offset due to a non-zero eccentricity. Our analysis yields a 2D brightness temperature distribution showing a large-scale asymmetric hot spot whose finer structure is limited by the data quality and planet orbit geometry. We also present an improved upper limit for eccentricity, e<0.0081 (95% confidence). Conclusions. Reanalysis of archived HD 189733 data revealed brightness structure by using global analysis that mitigated systematics. Future eclipse scanning observations of the same exoplanet at other wavelengths will probe different atmosphere layers, ultimately generating a large-scale 3D map. [less ▲]

Detailed reference viewed: 25 (5 ULg)
Full Text
Peer Reviewed
See detailMagnetic fields of HgMn stars
Hubrig, S.; González, J. F.; Ilyin, I. et al

in Astronomy and Astrophysics (2012), 547

Context. The frequent presence of weak magnetic fields on the surface of spotted late-B stars with HgMn peculiarity in binary systems has been controversial during the two last decades. Recent studies of ... [more ▼]

Context. The frequent presence of weak magnetic fields on the surface of spotted late-B stars with HgMn peculiarity in binary systems has been controversial during the two last decades. Recent studies of magnetic fields in these stars using the least-squares deconvolution (LSD) technique have failed to detect magnetic fields, indicating an upper limit on the longitudinal field between 8 and 15 G. In these LSD studies, assumptions were made that all spectral lines are identical in shape and can be described by a scaled mean profile. <BR /> Aims: We re-analyse the available spectropolarimetric material by applying the moment technique on spectral lines of inhomogeneously distributed elements separately. Furthermore, we present new determinations of the mean longitudinal magnetic field for the HgMn star HD 65949 and the hotter analog of HgMn stars, the PGa star HD 19400, using FORS 2 installed at the VLT. We also give new measurements of the eclipsing system AR Aur with a primary star of HgMn peculiarity, which were obtained with the SOFIN spectropolarimeter installed at the Nordic Optical Telescope. <BR /> Methods: We downloaded from the European Southern Observatory (ESO) archive the publically available HARPS spectra for eight HgMn stars and one normal and one superficially normal B-type star obtained in 2010. Out of this sample, three HgMn stars belong to spectroscopic double-lined systems. The application of the moment technique to the HARPS and SOFIN spectra allowed us to study the presence of the longitudinal magnetic field, the crossover effect, and quadratic magnetic fields. Results for the HgMn star HD 65949 and the PGa star HD 19400 are based on a linear regression analysis of low-resolution spectra obtained with FORS 2 in spectropolarimetric mode. <BR /> Results: Our measurements of the magnetic field with the moment technique using spectral lines of several elements separately reveal the presence of a weak longitudinal magnetic field, a quadratic magnetic field, and the crossover effect on the surface of several HgMn stars as well as normal and superficially normal B-type stars. Furthermore, our analysis suggests the existence of intriguing correlations between the strength of the magnetic field, abundance anomalies, and binary properties. The results are discussed in the context of possible mechanisms responsible for the development of the element patches and complex magnetic fields on the surface of late B-type stars. Based on observations obtained at the European Southern Observatory (ESO programmes 076.D-0169(A), 076.D-0172(A), 084.D-0338(A), 085.D-0296(A), 085.D-0296(B), 087.D-0049(A), 088.D-0284(A)), SOFIN observations at the 2.56 m Nordic Optical Telescope on La Palma, and observations obtained with the CORALIE Echelle Spectrograph on the 1.2 m Euler Swiss telescope on La Silla, Chile.Tables 2-7, 9, 10 are only available in electronic form at <A href="http://www.aanda.org">http://www.aanda.org</A> [less ▲]

Detailed reference viewed: 11 (1 ULg)
Full Text
Peer Reviewed
See detailPulsations of rapidly rotating stars. I. The ACOR numerical code
Ouazzani, Rhita-Maria ULg; Dupret, Marc-Antoine ULg; Reese, Daniel ULg

in Astronomy and Astrophysics (2012), 547

Context. Very high precision seismic space missions such as CoRoT and Kepler provide the means of testing the modeling of transport processes in stellar interiors. For some stars, such as solar-like and ... [more ▼]

Context. Very high precision seismic space missions such as CoRoT and Kepler provide the means of testing the modeling of transport processes in stellar interiors. For some stars, such as solar-like and red giant stars, a rotational splitting is measured. However, to fully exploit these splittings and constrain the rotation profile, one needs to be able to calculate them accurately. For some other stars, such as δ Scuti and Be stars, for instance, the observed pulsation spectra are modified by rotation to such an extent that a perturbative treatment of the effects of rotation is no longer valid. <BR /> Aims: We present here a new two-dimensional non-perturbative code called ACOR (adiabatic code of oscillation including rotation) that allows us to compute adiabatic non-radial pulsations of rotating stars without making any assumptions on the sphericity of the star, the fluid properties (i.e., baroclinicity) or the rotation profile. <BR /> Methods: The 2D non-perturbative calculations fully take into account the centrifugal distortion of the star and include the full influence of the Coriolis acceleration. The numerical method is based on a spectral approach for the angular part of the modes and a fourth-order finite differences approach for the radial part. <BR /> Results: We test and evaluate the accuracy of the calculations by comparing them with those coming from the TOP (two-dimensional oscillation program) for the same polytropic models. We illustrate the effects of rapid rotation on stellar pulsations through the phenomenon of avoided crossings. <BR /> Conclusions: As shown by the comparison with the TOP for simple models, the code is stable, and gives accurate results up to near-critical rotation rates. [less ▲]

Detailed reference viewed: 20 (5 ULg)
Full Text
Peer Reviewed
See detailA hot Uranus transiting the nearby M dwarf GJ 3470. Detected with HARPS velocimetry. Captured in transit with TRAPPIST photometry
Bonfils, X.; Gillon, Michaël ULg; Udry, S. et al

in Astronomy and Astrophysics (2012), 546

We report on the discovery of GJ 3470 b, a transiting hot Uranus of mass m[SUB]p[/SUB] = 14.0 ± 1.8 M[SUB]⊕[/SUB], radius R[SUB]p[/SUB] = 4.2 ± 0.6 R[SUB]⊕[/SUB] and period P = 3.3371 ± 0.0002 day. Its ... [more ▼]

We report on the discovery of GJ 3470 b, a transiting hot Uranus of mass m[SUB]p[/SUB] = 14.0 ± 1.8 M[SUB]⊕[/SUB], radius R[SUB]p[/SUB] = 4.2 ± 0.6 R[SUB]⊕[/SUB] and period P = 3.3371 ± 0.0002 day. Its host star is a nearby (d = 25.2 ± 2.9 pc) M1.5 dwarf of mass M[SUB]⋆[/SUB] = 0.54 ± 0.07 M[SUB]&sun;[/SUB] and radius R[SUB]⋆[/SUB] = 0.50 ± 0.06 R[SUB]&sun;[/SUB]. The detection was made during a radial-velocity campaign with Harps that focused on the search for short-period planets orbiting M dwarfs. Once the planet was discovered and the transit-search window narrowed to about 10% of an orbital period, a photometric search started with Trappist and quickly detected the ingress of the planet. Additional observations with Trappist, EulerCam and Nites definitely confirmed the transiting nature of GJ 3470b and allowed the determination of its true mass and radius. The star's visible or infrared brightness (V[SUP]mag[/SUP] = 12.3, K[SUP]mag[/SUP] = 8.0), together with a large eclipse depth D = 0.57 ± 0.05%, ranks GJ 3470 b among the most suitable planets for follow-up characterizations. Based on observations made with the HARPS instrument on the ESO 3.6 m telescope under the program IDs 183.C-0437 at Cerro La Silla (Chile).Our radial-velocity and photometric time series are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via <A href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/546/A27">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/546/A27</A> [less ▲]

Detailed reference viewed: 16 (0 ULg)
Full Text
Peer Reviewed
See detailThe nature of the high Galactic latitude O-star HD 93521: new results from X-ray and optical spectroscopy
Rauw, Grégor ULg; Morel, Thierry ULg; Palate, Matthieu ULg

in Astronomy and Astrophysics (2012), 546

Context. Owing to its unusual location and its isolation, the nature of the high Galactic latitude O9.5 Vp object HD 93521 is still uncertain. <BR /> Aims: We have collected X-ray and optical observations ... [more ▼]

Context. Owing to its unusual location and its isolation, the nature of the high Galactic latitude O9.5 Vp object HD 93521 is still uncertain. <BR /> Aims: We have collected X-ray and optical observations to characterize the star and its surroundings. <BR /> Methods: X-ray images and spectra are analysed to search for traces of a recent star formation event around HD 93521 and to search for the signature of a possible compact companion. Optical echelle spectra are analysed with plane-parallel model atmosphere codes, assuming either a spherical star or a gravity darkened rotationally flattened star, to infer the effective temperature and surface gravity, and to derive the He, C, N and O abundances of HD 93521. <BR /> Results: The X-ray images reveal no traces of a population of young low-mass stars coeval with HD 93521. The X-ray spectrum of HD 93521 is consistent with a normal late O-type star although with subsolar metallicity. No trace of a compact companion is found in the X-ray data. In the optical spectrum, He and N are found to be overabundant, in line with the effect of rotational mixing in this very fast rotator, whilst C and O are subsolar. A critical comparison with the properties of subdwarf OB stars, indicates that, despite some apparent similarities, HD 93521 does not belong to this category. <BR /> Conclusions: Despite some ambiguities on the runaway status of the star, the most likely explanation is that HD 93521 is a Population I massive O-type star that was ejected from the Galactic plane either through dynamical interactions or a result of a supernova event in a binary system. Based on observations collected at the Observatoire de Haute Provence (France) and with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA member states and the USA (NASA).Hα images are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via <A href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/546/A77">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/546/A77</A> [less ▲]

Detailed reference viewed: 29 (3 ULg)
Full Text
Peer Reviewed
See detailRegular oscillation sub-spectrum of rapidly rotating stars
Pasek, M.; Lignières, F.; Georgeot, B. et al

in Astronomy and Astrophysics (2012), 546

<BR /> Aims: We present an asymptotic theory that describes regular frequency spacings of pressure modes in rapidly rotating stars. <BR /> Methods: We use an asymptotic method based on an approximate ... [more ▼]

<BR /> Aims: We present an asymptotic theory that describes regular frequency spacings of pressure modes in rapidly rotating stars. <BR /> Methods: We use an asymptotic method based on an approximate solution of the pressure wave equation constructed from a stable periodic solution of the ray limit. The approximate solution has a Gaussian envelope around the stable ray, and its quantization yields the frequency spectrum. <BR /> Results: We construct semi-analytical formulas for regular frequency spacings and mode spatial distributions of a subclass of pressure modes in rapidly rotating stars. The results of these formulas are in good agreement with numerical data for oscillations in polytropic stellar models. The regular frequency spacings depend explicitly on internal properties of the star, and their computation for different rotation rates gives new insights on the evolution of mode frequencies with rotation. [less ▲]

Detailed reference viewed: 12 (1 ULg)
Full Text
Peer Reviewed
See detailPlanetary transit candidates in the CoRoT LRa01 field
Carone, L.; Gandolfi, D.; Cabrera, J. et al

in Astronomy and Astrophysics (2012), 538

Context: CoRoT is a pioneering space mission whose primary goals are stellar seismology and extrasolar planets search. Its surveys of large stellar fields generate numerous planetary candidates whose ... [more ▼]

Context: CoRoT is a pioneering space mission whose primary goals are stellar seismology and extrasolar planets search. Its surveys of large stellar fields generate numerous planetary candidates whose lightcurves have transit-like features. An extensive analytical and observational follow-up effort is undertaken to classify these candidates. Aims: The list of planetary transit candidates from the CoRoT LRa01 star field in the Monoceros constellation towards the Galactic anti-center is presented. The CoRoT observations of LRa01 lasted from 24 October 2007 to 3 March 2008. Methods: 7470 chromatic and 3938 monochromatic lightcurves were acquired and analysed. Instrumental noise and stellar variability were treated with several filtering tools by different teams from the CoRoT community. Different transit search algorithms were applied to the lightcurves. Results: Fifty-one stars were classified as planetary transit candidates in LRa01. Thirty-seven (i.e., 73 % of all candidates) are "good" planetary candidates based on photometric analysis only. Thirty-two (i.e., 87 % of the "good" candidates) have been followed-up. At the time of this writing twenty-two cases have been solved and five planets have been discovered: three transiting hot-Jupiters (CoRoT-5b, CoRoT-12b, and CoRoT-21b), the first terrestrial transiting planet (CoRoT-7b), and another planet in the same system (CoRoT-7c, detected by radial velocity survey only). Evidences of another non-transiting planet in the CoRoT-7 system, namely CoRoT-7d, have been recently found. [less ▲]

Detailed reference viewed: 14 (1 ULg)
Full Text
Peer Reviewed
See detailAn upper limit for the water outgassing rate of the main-belt comet 176P/LINEAR observed with Herschel/HIFI
de Val-Borro, M.; Rezac, L.; Hartogh, P. et al

in Astronomy and Astrophysics (2012), 546

176P/LINEAR is a member of the new cometary class known as main-belt comets (MBCs). It displayed cometary activity shortly during its 2005 perihelion passage, which may be driven by the sublimation of ... [more ▼]

176P/LINEAR is a member of the new cometary class known as main-belt comets (MBCs). It displayed cometary activity shortly during its 2005 perihelion passage, which may be driven by the sublimation of subsurface ices. We have therefore searched for emission of the H[SUB]2[/SUB]O 1[SUB]10[/SUB]-1[SUB]01[/SUB] ground state rotational line at 557 GHz toward 176P/LINEAR with the Heterodyne Instrument for the Far Infrared (HIFI) onboard the Herschel Space Observatory on UT 8.78 August 2011, about 40 days after its most recent perihelion passage, when the object was at a heliocentric distance of 2.58 AU. No H[SUB]2[/SUB]O line emission was detected in our observations, from which we derive sensitive 3-σ upper limits for the water production rate and column density of <4 × 10[SUP]25[/SUP] mol s[SUP]-1[/SUP] and of <3 × 10[SUP]10[/SUP] cm[SUP]-2[/SUP], respectively. From the peak brightness measured during the object's active period in 2005, this upper limit is lower than predicted by the relation between production rates and visual magnitudes observed for a sample of comets at this heliocentric distance. Thus, 176P/LINEAR was most likely less active at the time of our observation than during its previous perihelion passage. The retrieved upper limit is lower than most values derived for the H[SUB]2[/SUB]O production rate from the spectroscopic search for CN emission in MBCs. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. [less ▲]

Detailed reference viewed: 4 (0 ULg)
Full Text
Peer Reviewed
See detailImproved precision on the radius of the nearby super-Earth 55 Cnc e
Gillon, Michaël ULg; Demory, B.-O.; Benneke, B. et al

in Astronomy and Astrophysics (2012), 539

We report on new transit photometry for the super-Earth 55 Cnc e obtained with Warm Spitzer/IRAC at 4.5 microns. An individual analysis of these new data leads to a planet radius of 2.21-0.16+0.15 Rearth ... [more ▼]

We report on new transit photometry for the super-Earth 55 Cnc e obtained with Warm Spitzer/IRAC at 4.5 microns. An individual analysis of these new data leads to a planet radius of 2.21-0.16+0.15 Rearth, in good agreement with the values previously derived from the MOST and Spitzer transit discovery data. A global analysis of both Spitzer transit time-series improves the precision on the radius of the planet at 4.5 microns to 2.20+-0.12 Rearth. We also performed an independent analysis of the MOST data, paying particular attention to the influence of the systematic effects of instrumental origin on the derived parameters and errors by including them in a global model instead of performing a preliminary detrending-filtering processing. We deduce from this reanalysis of MOST data an optical planet radius of 2.04+-0.15 Rearth that is consistent with our Spitzer infrared radius. Assuming the achromaticity of the transit depth, we performed a global analysis combining Spitzer and MOST data that results in a planet radius of 2.17+-0.10 Rearth (13,820+-620 km). These results confirm that the most probable composition of 55 Cnc e is an envelope of supercritical water above a rocky nucleus. [less ▲]

Detailed reference viewed: 14 (6 ULg)
Full Text
Peer Reviewed
See detailStochastic gravito-inertial modes discovered by CoRoT in the hot Be star HD 51452
Neiner, C.; Floquet, M.; Samadi, R. et al

in Astronomy and Astrophysics (2012), 546

Context. Be stars are rapidly rotating stars with a circumstellar decretion disk. They usually undergo pressure and/or gravity pulsation modes excited by the κ-mechanism, i.e. an effect of the opacity of ... [more ▼]

Context. Be stars are rapidly rotating stars with a circumstellar decretion disk. They usually undergo pressure and/or gravity pulsation modes excited by the κ-mechanism, i.e. an effect of the opacity of iron-peak elements in the envelope of the star. In the Milky Way, p-modes are observed in stars that are hotter than or equal to the B3 spectral type, while g-modes are observed at the B2 spectral type and cooler. <BR /> Aims: We observed a B0IVe star, HD 51452, with the high-precision, high-cadence photometric CoRoT satellite and high-resolution, ground-based HARPS and SOPHIE spectrographs to study its pulsations in great detail. We also used the lower resolution spectra available in the BeSS database. <BR /> Methods: We analyzed the CoRoT and spectroscopic data with several methods: Clean-NG, FreqFind, and a sliding window method. We also analyzed spectral quantities, such as the violet over red (V/R) emission variations, to obtain information about the variation in the circumstellar environment. We calculated a stellar structure model with the ESTER code to test the various interpretation of the results. <BR /> Results: We detect 189 frequencies of variations in the CoRoT light curve in the range between 0 and 4.5 c d[SUP]-1[/SUP]. The main frequencies are also recovered in the spectroscopic data. In particular we find that HD 51452 undergoes gravito-inertial modes that are not in the domain of those excited by the κ-mechanism. We propose that these are stochastic modes excited in the convective zones and that at least some of them are a multiplet of r-modes (i.e. subinertial modes mainly driven by the Coriolis acceleration). Stochastically excited gravito-inertial modes had never been observed in any star, and theory predicted that their very low amplitudes would be undetectable even with CoRoT. We suggest that the amplitudes are enhanced in HD 51452 because of the very rapid stellar rotation. In addition, we find that the amplitude variations of these modes are related to the occurrence of minor outbursts. <BR /> Conclusions: Thanks to CoRoT data, we have detected a new kind of pulsations in HD 51452, which are stochastically excited gravito-inertial modes, probably due to its very rapid rotation. These modes are probably also present in other rapidly rotating hot Be stars. The CoRoT space mission, launched on December 27, 2006, has been developed and is operated by CNES, with the contribution of Austria, Belgium, Brazil, ESA (RSSD, and Science Programs), Germany, and Spain. This work uses observations partly made with the HARPS instrument at the 3.6-m ESO telescope (La Silla, Chile) in the framework of the LP182.D-0356, as well as data obtained with Sophie at OHP and from the BeSS database.Table 3 is available in electronic form at <A href="http://www.aanda.org">http://www.aanda.org</A> [less ▲]

Detailed reference viewed: 29 (4 ULg)
Full Text
Peer Reviewed
See detailThe 2.35 year itch of Cygnus OB2 #9. I. Optical and X-ray monitoring
Nazé, Yaël ULg; Mahy, Laurent ULg; Damerdji, Yassine ULg et al

in Astronomy and Astrophysics (2012), 546

Context. Nonthermal radio emission in massive stars is expected to arise in wind-wind collisions occurring inside a binary system. One such case, the O-type star Cyg OB2 #9, was proven to be a binary only ... [more ▼]

Context. Nonthermal radio emission in massive stars is expected to arise in wind-wind collisions occurring inside a binary system. One such case, the O-type star Cyg OB2 #9, was proven to be a binary only four years ago, but the orbital parameters remained uncertain. The periastron passage of 2011 was the first one to be observable under good conditions since the discovery of binarity. <BR /> Aims: In this context, we have organized a large monitoring campaign to refine the orbital solution and to study the wind-wind collision. <BR /> Methods: This paper presents the analysis of optical spectroscopic data, as well as of a dedicated X-ray monitoring performed with Swift and XMM-Newton. <BR /> Results: In light of our refined orbital solution, Cyg OB2 #9 appears as a massive O+O binary with a long period and high eccentricity; its components (O5-5.5I for the primary and O3-4III for the secondary) have similar masses and similar luminosities. The new data also provide the first evidence that a wind-wind collision is present in the system. In the optical domain, the broad Hα line varies, displaying enhanced absorption and emission components at periastron. X-ray observations yield the unambiguous signature of an adiabatic collision, because as the stars approach periastron, the X-ray luminosity closely follows the 1/D variation expected in that case. The X-ray spectrum appears, however, slightly softer at periastron, which is probably related to winds colliding at slightly lower speeds at that time. <BR /> Conclusions: It is the first time that such a variation has been detected in O+O systems, and the first case where the wind-wind collision is found to remain adiabatic even at periastron passage. [less ▲]

Detailed reference viewed: 64 (10 ULg)
Full Text
Peer Reviewed
See detailHot circumstellar material resolved around β Pic with VLTI/PIONIER
Defrère, D.; Lebreton, J.; Le Bouquin, J.-B. et al

in Astronomy and Astrophysics (2012), 546

Aims: We aim at resolving the circumstellar environment around β Pic in the near-infrared in order to study the inner planetary system (<200 mas, i.e., ~4 AU). Methods: Precise interferometric fringe ... [more ▼]

Aims: We aim at resolving the circumstellar environment around β Pic in the near-infrared in order to study the inner planetary system (<200 mas, i.e., ~4 AU). Methods: Precise interferometric fringe visibility measurements were obtained over seven spectral channels dispersed across the H band with the four-telescope VLTI/PIONIER interferometer. Thorough analysis of interferometric data was performed to measure the stellar angular diameter and to search for circumstellar material. Results: We detected near-infrared circumstellar emission around β Pic that accounts for 1.37% ± 0.16% of the near-infrared stellar flux and that is located within the field-of-view of PIONIER (i.e., ~200 mas in radius). The flux ratio between this excess and the photosphere emission is shown to be stable over a period of 1 year and to vary only weakly across the H band, suggesting that the source is either very hot (≳1500 K) or dominated by the scattering of the stellar flux. In addition, we derive the limb-darkened angular diameter of β Pic with an unprecedented accuracy (θLD= 0.736 ± 0.019 mas). Conclusions: The presence of a small H-band excess originating in the vicinity of β Pic is revealed for the first time thanks to the high-precision visibilities enabled by VLTI/PIONIER. This excess emission is likely due to the scattering of stellar light by circumstellar dust and/or the thermal emission from a yet unknown population of hot dust, although hot gas emitting in the continuum cannot be firmly excluded. [less ▲]

Detailed reference viewed: 12 (2 ULg)
Full Text
Peer Reviewed
See detailGalaxy counterparts of intervening high-z sub-DLAs/DLAs and Mg ii absorbers towards gamma-ray bursts
Schulze, steve; Letawe, Géraldine ULg

in Astronomy and Astrophysics (2012), 546(A20),

We present the first search for galaxy counterparts of intervening high-z (2 < z < 3.6) sub-damped Lyα absorbers (sub-DLAs) and DLAs towards gamma-ray bursts (GRBs). Our final sample comprises five ... [more ▼]

We present the first search for galaxy counterparts of intervening high-z (2 < z < 3.6) sub-damped Lyα absorbers (sub-DLAs) and DLAs towards gamma-ray bursts (GRBs). Our final sample comprises five intervening sub-DLAs and DLAs in four GRB fields. To identify candidate galaxy counterparts of the absorbers we used deep optical- and near-infrared imaging, and low-, mid- and high-resolution spectroscopy acquired with 6-m to 10-m class telescopes, the Hubble and the Spitzer Space Telescopes. Furthermore, we used the spectroscopic information and spectral-energy-distribution fitting techniques to study them in detail. Our main result is the detection and spectroscopic confirmation of the galaxy counterpart of the intervening DLA at z = 3.096 in the field of GRB 070721B (zGRB = 3.6298) as proposed by other authors. We also identify good candidates for the galaxy counterparts of the two strong Mg ii absorbers at z = 0.6915 and 1.4288 towards GRB 050820A (zGRB = 2.615). The properties of the detected DLA galaxy are typical for Lyman-break galaxies (LBGs) at similar redshifts; a young, highly star-forming galaxy that shows evidence for a galactic outflow. This supports thehypothesis that a DLA can be the gaseous halo of an LBG. In addition, we report a redshift coincidence of different objects associated with metal lines in the same field, separated by 130–161 kpc. The high detection rate of three correlated structures on a length scale as short as ~150 kpc in two pairs of lines of sight is intriguing. The absorbers in each of these are most likely not part of the same gravitationally bound structure. They more likely represent groups of galaxies. [less ▲]

Detailed reference viewed: 15 (1 ULg)
Full Text
Peer Reviewed
See detailXX. CoRoT-20b: A very high density, high eccentricity transiting giant planet
Deleuil, M.; Bonomo, A. S.; Ferraz-Mello, S. et al

in Astronomy and Astrophysics (2012), 538

We report the discovery by the CoRoT space mission of a new giant planet, CoRoT-20b. The planet has a mass of 4.24 +/- 0.23 MJ and a radius of 0.84 +/- 0.04 RJ. With a mean density of 8.87 +/- 1.10 g/cm^3 ... [more ▼]

We report the discovery by the CoRoT space mission of a new giant planet, CoRoT-20b. The planet has a mass of 4.24 +/- 0.23 MJ and a radius of 0.84 +/- 0.04 RJ. With a mean density of 8.87 +/- 1.10 g/cm^3, it is among the most compact planets known so far. Evolution models for the planet suggest a mass of heavy elements of the order of 800 ME if embedded in a central core, requiring a revision either of the planet formation models or of planet evolution and structure models. We note however that smaller amounts of heavy elements are expected from more realistic models in which they are mixed throughout the envelope. The planet orbits a G-type star with an orbital period of 9.24 days and an eccentricity of 0.56. The star's projected rotational velocity is vsini = 4.5 +/- 1.0 km/s, corresponding to a spin period of 11.5 +/- 3.1 days if its axis of rotation is perpendicular to the orbital plane. In the framework of Darwinian theories and neglecting stellar magnetic breaking, we calculate the tidal evolution of the system and show that CoRoT-20b is presently one of the very few Darwin-stable planets that is evolving towards a triple synchronous state with equality of the orbital, planetary and stellar spin periods. [less ▲]

Detailed reference viewed: 16 (5 ULg)
Full Text
Peer Reviewed
See detailThe 12C2/12C13C isotopic ratio in comets C/2001 Q4 (NEAT) and C/2002 T7 (LINEAR)
Rousselot, P.; Jehin, Emmanuel ULg; Manfroid, Jean ULg et al

in Astronomy and Astrophysics (2012), 545

Context. Measuring the carbon isotope abundance ratio in comets allows one to constrain the conditions in the outer protosolar nebula. Different measurements of the [SUP]12[/SUP]C/[SUP]13[/SUP]C ratio ... [more ▼]

Context. Measuring the carbon isotope abundance ratio in comets allows one to constrain the conditions in the outer protosolar nebula. Different measurements of the [SUP]12[/SUP]C/[SUP]13[/SUP]C ratio, using various molecules, have already been published for different solar system objects, such as the Sun, the Earth, the Moon, asteroids, planets, or comets. So far, all these measurements are consistent with [SUP]12[/SUP]C/[SUP]13[/SUP]C ~ 90, but significant differences have been observed. This ratio is remarkably constant in comets (91.0 ± 3.6) for studies based on the CN radical, but it presents stronger variations in studies based on other radicals. <BR /> Aims: This paper aims at measuring the [SUP]12[/SUP]C/[SUP]13[/SUP]C ratio in two bright Oort cloud comets using the [SUP]12[/SUP]C_2 and [SUP]12[/SUP]C[SUP]13[/SUP]C emission lines and an improved method. The ratios will be compared to those obtained for the same comets with another radical, CN. <BR /> Methods: We used the (2,1) and (1,0) bandheads of the [SUP]12[/SUP]C[SUP]13[/SUP]C, near 4723 and 4745 Å to measure the [SUP]12[/SUP]C/[SUP]13[/SUP]C ratio and compared their intensity to the [SUP]12[/SUP]C_2 lines of the same bands. We developed a model for interpreting observational data obtained at high resolution (~70 000) using the 8.2-m Kueyen telescope (UT2) of the Very Large Telescope (VLT) with the Ultraviolet and Visual Echelle Spectrograph (UVES) in two comets: C/2001 Q4 (NEAT) and C/2002 T7 (LINEAR). <BR /> Results: Our modeling has provided [SUP]12[/SUP]C/[SUP]13[/SUP]C = 85 ± 20 for C/2002 T7 (LINEAR) and 80 ± 20 for C/2001 Q4 (NEAT). These values are compatible with previous measurements performed with the CN radical. Based on observations made with ESO Telescopes at the Paranal Observatory under programmes ID 073.C-0525. [less ▲]

Detailed reference viewed: 26 (5 ULg)
Full Text
Peer Reviewed
See detailTransiting exoplanets from the CoRoT space mission. XXIII. CoRoT-21b: a doomed large Jupiter around a faint subgiant star
Pätzold, M.; Endl, M.; Csizmadia, Sz et al

in Astronomy and Astrophysics (2012), 545

CoRoT-21, a F8IV star of magnitude V = 16 mag, was observed by the space telescope CoRoT during the Long Run 01 (LRa01) in the first winter field (constellation Monoceros) from October 2007 to March 2008 ... [more ▼]

CoRoT-21, a F8IV star of magnitude V = 16 mag, was observed by the space telescope CoRoT during the Long Run 01 (LRa01) in the first winter field (constellation Monoceros) from October 2007 to March 2008. Transits were discovered during the light curve processing. Radial velocity follow-up observations, however, were performed mainly by the 10-m Keck telescope in January 2010. The companion CoRoT-21b is a Jupiter-like planet of 2.26 ± 0.33 Jupiter masses and 1.30 ± 0.14 Jupiter radii in an circular orbit of semi-major axis 0.0417 ± 0.0011 AU and an orbital period of 2.72474 ± 0.00014 days. The planetary bulk density is (1.36 ± 0.48) × 10[SUP]3[/SUP] kg m[SUP]-3[/SUP], very similar to the bulk density of Jupiter, and follows an M[SUP]1/3[/SUP] - R relation like Jupiter. The F8IV star is a sub-giant star of 1.29 ± 0.09 solar masses and 1.95 ± 0.2 solar radii. The star and the planet exchange extremetidal forces that will lead to orbital decay and extreme spin-up of the stellar rotation within 800 Myr if the stellar dissipation is Q[SUB]∗[/SUB]/k[SUB]2∗[/SUB] ≤ 10[SUP]7[/SUP]. The CoRoT space mission, launched on December 27th 2006, has been developed and is operated by CNES, with the contribution of Austria, Belgium, Brazil, ESA (RSSD and Science Programme), Germany and Spain. [less ▲]

Detailed reference viewed: 16 (0 ULg)
Full Text
Peer Reviewed
See detailWASP-42 b and WASP-49 b: two new transiting sub-Jupiters
Lendl, M; Anderson, D R; Collier-Cameron, A et al

in Astronomy and Astrophysics (2012), 544

We report the discovery of two new transiting planets from the WASP survey. WASP-42 b is a 0.500 +- 0.035 M_J planet orbiting a K1 star at a separation of 0.0548 +- 0.0017 AU with a period of 4.9816872 ... [more ▼]

We report the discovery of two new transiting planets from the WASP survey. WASP-42 b is a 0.500 +- 0.035 M_J planet orbiting a K1 star at a separation of 0.0548 +- 0.0017 AU with a period of 4.9816872 +- 0.0000073 days. The radius of WASP-42 is 1.080 +- 0.057 R_J while its equilibrium temperature is T_eq = 995 +- 34 K. We detect some evidence of a small but non-zero eccentricity of e = 0.060 +- 0.013. WASP-49 b is a 0.378 +- 0.027 M_J planet around an old G6 star. It has a period of 2.7817387 +- 5.6 x 10-6 days and a separation of 0.0379 +- 0.0011 AU. This planet is slightly bloated, having a radius of 1.115 +- 0.056 R_J and an equilibrium temperature of T_eq = 1369 +- 42 K. Both planets have been followed up intensively in photometry, in total we have obtained 5 full and one partial transit light curves of WASP-42 and 4 full and one partial light curves of WASP-49 using the Euler-Swiss, TRAPPIST and Faulkes South telescopes. [less ▲]

Detailed reference viewed: 14 (0 ULg)
Full Text
Peer Reviewed
See detailAngular momentum transport in stellar interiors constrained by rotational splittings of mixed modes in red giants
Eggenberger, P.; Montalban Iglesias, Josefa ULg; Miglio, A.

in Astronomy and Astrophysics (2012), 544

Context. Recent asteroseismic observations have led to the determination of rotational frequency splittings for ℓ = 1 mixed modes in red giants. <BR /> Aims: We investigate how these observed splittings ... [more ▼]

Context. Recent asteroseismic observations have led to the determination of rotational frequency splittings for ℓ = 1 mixed modes in red giants. <BR /> Aims: We investigate how these observed splittings can constrain the modelling of the physical processes transporting angular momentum in stellar interiors. <BR /> Methods: We first compare models including a comprehensive treatment of shellular rotation only, with the rotational splittings observed for the red giant <ASTROBJ>KIC 8366239</ASTROBJ>. We then study how these asteroseismic constraints can give us information about the efficiency of an additional mechanism for the internal transport of angular momentum. This is done by computing rotating models of <ASTROBJ>KIC 8366239</ASTROBJ> that include a constant viscosity corresponding to this physical process, in addition to the treatment of shellular rotation. <BR /> Results: We find that models of red giant stars including shellular rotation only predict steep rotation profiles, which are incompatible with the measurements of rotational splittings in the red giant <ASTROBJ>KIC 8366239</ASTROBJ>. Meridional circulation and shear mixing alone are found to produce an insufficient internal coupling so that an additional mechanism for the internal transport of angular momentum is needed during the post-main sequence evolution. We show that the viscosity ν[SUB]add[/SUB] corresponding to this mechanism is strongly constrained to be ν[SUB]add[/SUB] = 3 × 10[SUP]4[/SUP] cm[SUP]2[/SUP] s[SUP]-1[/SUP] thanks to the observed ratio of the splittings for modes in the wings to those at the centre of the dipole forests. Such a value of viscosity may suggest that the same unknown physical process is at work during the main sequence and the post-main sequence evolution. [less ▲]

Detailed reference viewed: 12 (5 ULg)
Full Text
Peer Reviewed
See detailMicrolensing of the broad line region in 17 lensed quasars
Sluse, D.; Hutsemekers, Damien ULg; Courbin, F. et al

in Astronomy and Astrophysics (2012), 544

When an image of a strongly lensed quasar is microlensed, the different components of its spectrum are expected to be differentially magnified owing to the different sizes of the corresponding emitting ... [more ▼]

When an image of a strongly lensed quasar is microlensed, the different components of its spectrum are expected to be differentially magnified owing to the different sizes of the corresponding emitting region. Chromatic changes are expected to be observed in the continuum while the emission lines should be deformed as a function of the size, geometry and kinematics of the regions from which they originate. Microlensing of the emission lines has been reported only in a handful of systems so far. In this paper we search for microlensing deformations of the optical spectra of pairs of images in 17 lensed quasars with bolometric luminosities between 10[SUP]44.7 - 47.4[/SUP] erg/s and black hole masses 10[SUP]7.6 - 9.8[/SUP] M[SUB]&sun;[/SUB]. This sample is composed of 13 pairs of previously unpublished spectra and four pairs of spectra from literature. Our analysis is based on a simple spectral decomposition technique which allows us to isolate the microlensed fraction of the flux independently of a detailed modeling of the quasar emission lines. Using this technique, we detect microlensing of the continuum in 85% of the systems. Among them, 80% show microlensing of the broad emission lines. Focusing on the most common emission lines in our spectra (C III] and Mg II) we detect microlensing of either the blue or the red wing, or of both wings with the same amplitude. This observation implies that the broad line region is not in general spherically symmetric. In addition, the frequent detection of microlensing of the blue and red wings independently but not simultaneously with a different amplitude, does not support existing microlensing simulations of a biconical outflow. Our analysis also provides the intrinsic flux ratio between the lensed images and the magnitude of the microlensing affecting the continuum. These two quantities are particularly relevant for the determination of the fraction of matter in clumpy form in galaxies and for the detection of dark matter substructures via the identification of flux ratio anomalies. Based on observations made with the ESO-VLT Unit Telescope # 2 Kueyen (Cerro Paranal, Chile; Proposals 074.A-0563, 075.A-0377, 077.A-0155, PI: G. Meylan).Figure 1 and the new spectra presented in this paper are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via <A href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/544/A62">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/544/A62</A> and via the German virtual observatory <A href="http://dc.g-vo.org/mlqso/q/web/form">http://dc.g-vo.org/mlqso/q/web/form</A>Appendices are available in electronic form at <A href="http://www.aanda.org">http://www.aanda.org</A> [less ▲]

Detailed reference viewed: 36 (4 ULg)
Full Text
Peer Reviewed
See detailEstimating the p-mode frequencies of the solar twin 18 Scorpii
Bazot, M.; Campante, T.L.; Chaplin, W.J. et al

in Astronomy and Astrophysics (2012), 544

Solar twins have been a focus of attention for more than a decade, because their structure is extremely close to that of the Sun. Today, thanks to high-precision spectrometers, it is possible to use ... [more ▼]

Solar twins have been a focus of attention for more than a decade, because their structure is extremely close to that of the Sun. Today, thanks to high-precision spectrometers, it is possible to use asteroseismology to probe their interiors. Our goal is to use time series obtained from the HARPS spectrometer to extract the oscillation frequencies of 18 Sco, the brightest solar twin. We used the tools of spectral analysis to estimate these quantities. We estimate 52 frequencies using an MCMC algorithm. After examination of their probability densities and comparison with results from direct MAP optimization, we obtain a minimal set of 21 reliable modes. The identification of each pulsation mode is straightforwardly accomplished by comparing to the well-established solar pulsation modes. We also derived some basic seismic indicators using these values. These results offer a good basis to start a detailed seismic analysis of 18 Sco using stellar models. [less ▲]

Detailed reference viewed: 10 (0 ULg)