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See detailAtmospheric parameters and chemical properties of red giants in the CoRoT asteroseismology fields
Morel, Thierry ULg; Miglio, A.; Lagarde, N. et al

in Astronomy and Astrophysics (2014), 564

A precise characterisation of the red giants in the seismology fields of the CoRoT satellite is a prerequisite for further in-depth seismic modelling. High-resolution FEROS and HARPS spectra were obtained ... [more ▼]

A precise characterisation of the red giants in the seismology fields of the CoRoT satellite is a prerequisite for further in-depth seismic modelling. High-resolution FEROS and HARPS spectra were obtained as part of the ground-based follow-up campaigns for 19 targets holding great asteroseismic potential. These data are used to accurately estimate their fundamental parameters and the abundances of 16 chemical species in a self-consistent manner. Some powerful probes of mixing are investigated (the Li and CNO abundances, as well as the carbon isotopic ratio in a few cases). The information provided by the spectroscopic and seismic data is combined to provide more accurate physical parameters and abundances. The stars in our sample follow the general abundance trends as a function of the metallicity observed in stars of the Galactic disk. After an allowance is made for the chemical evolution of the interstellar medium, the observational signature of internal mixing phenomena is revealed through the detection at the stellar surface of the products of the CN cycle. A contamination by NeNa-cycled material in the most massive stars is also discussed. With the asteroseismic constraints, these data will pave the way for a detailed theoretical investigation of the physical processes responsible for the transport of chemical elements in evolved, low- and intermediate-mass stars. Based on observations collected at La Silla Observatory, ESO (Chile) with the FEROS and HARPS spectrograph at the 2.2 and 3.6-m telescopes under programs LP178.D-0361, LP182.D-0356, and LP185.D-0056.Appendix A is available in electronic form at <A href="http://www.aanda.org/10.1051/0004-6361/201322810/olm">http://www.aanda.org</A>Tables A.2 to A.6 are available at the CDS via anonymous ftp to <A href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A> (ftp://130.79.128.5) or via <A href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/564/A119">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/564/A119</A> [less ▲]

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See detailB fields in OB stars (BOB): The discovery of a magnetic field in a multiple system in the Trifid nebula, one of the youngest star forming regions
Hubrig, S.; Fossati, L.; Carroll, T. A. et al

in Astronomy and Astrophysics (2014), 564

<BR /> Aims: Recent magnetic field surveys in O- and B-type stars revealed that about 10% of the core-hydrogen-burning massive stars host large-scale magnetic fields. The physical origin of these fields ... [more ▼]

<BR /> Aims: Recent magnetic field surveys in O- and B-type stars revealed that about 10% of the core-hydrogen-burning massive stars host large-scale magnetic fields. The physical origin of these fields is highly debated. To identify and model the physical processes responsible for the generation of magnetic fields in massive stars, it is important to establish whether magnetic massive stars are found in very young star-forming regions or whether they are formed in close interacting binary systems. <BR /> Methods: In the framework of our ESO Large Program, we carried out low-resolution spectropolarimetric observations with FORS 2 in 2013 April of the three most massive central stars in the Trifid nebula, HD 164492A, HD 164492C, and HD 164492D. These observations indicated a strong longitudinal magnetic field of about 500-600 G in the poorly studied component HD 164492C. To confirm this detection, we used HARPS in spectropolarimetric mode on two consecutive nights in 2013 June. <BR /> Results: Our HARPS observations confirmed the longitudinal magnetic field in HD 164492C. Furthermore, the HARPS observations revealed that HD 164492C cannot be considered as a single star as it possesses one or two companions. The spectral appearance indicates that the primary is most likely of spectral type B1-B1.5 V. Since in both observing nights most spectral lines appear blended, it is currently unclear which components are magnetic. Long-term monitoring using high-resolution spectropolarimetry is necessary to separate the contribution of each component to the magnetic signal. Given the location of the system HD 164492C in one of the youngest star formation regions, this system can be considered as a Rosetta Stone for our understanding of the origin of magnetic fields in massive stars. Based on observations obtained in the framework of the ESO Prg. 191.D-0255(A,B). [less ▲]

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See detailSeismic analysis of HD 43587Aa, a solar-like oscillator in a multiple system
Boumier, P.; Benomar, O.; Baudin, F. et al

in Astronomy and Astrophysics (2014), 564

Context. The object HD 43587Aa is a G0V star observed during the 145-day LRa03 run of the COnvection, ROtation and planetary Transits space mission (CoRoT), for which complementary High Accuracy Radial ... [more ▼]

Context. The object HD 43587Aa is a G0V star observed during the 145-day LRa03 run of the COnvection, ROtation and planetary Transits space mission (CoRoT), for which complementary High Accuracy Radial velocity Planet Searcher (HARPS) spectra with S/N > 300 were also obtained. Its visual magnitude is 5.71, and its effective temperature is close to 5950 K. It has a known companion in a highly eccentric orbit and is also coupled with two more distant companions. <BR /> Aims: We undertake a preliminary investigation of the internal structure of HD 43587Aa. <BR /> Methods: We carried out a seismic analysis of the star, using maximum likelihood estimators and Markov chain Monte Carlo methods. <BR /> Results: We established the first table of the eigenmode frequencies, widths, and heights for HD 43587Aa. The star appears to have a mass and a radius slightly larger than the Sun, and is slightly older (5.6 Gyr). Two scenarios are suggested for the geometry of the star: either its inclination angle is very low, or the rotation velocity of the star is very low. <BR /> Conclusions: A more detailed study of the rotation and of the magnetic and chromospheric activity for this star is needed, and will be the subject of a further study. New high resolution spectrometric observations should be performed for at least several months in duration. [less ▲]

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See detailSource-position transformation: an approximate invariance in strong gravitational lensing
Schneider, Peter; Sluse, Dominique ULg

in Astronomy and Astrophysics (2014), 564

The main obstacle that gravitational lensing has in determining accurate masses of deflectors, or in determining precise estimates for the Hubble constant, is the degeneracy of lensing observables with ... [more ▼]

The main obstacle that gravitational lensing has in determining accurate masses of deflectors, or in determining precise estimates for the Hubble constant, is the degeneracy of lensing observables with respect to the mass-sheet transformation (MST). The MST is a global modification of the mass distribution which leaves all image positions, shapes, and flux ratios invariant, but which changes the time delay. Here we show that another global transformation of lensing mass distributions exists which leaves image positions and flux ratios almost invariant, and of which the MST is a special case. As is the case for the MST, this new transformation only applies if one considers only those source components that are at the same distance from us. Whereas for axi-symmetric lenses this source position transformation exactly reproduces all strong lensing observables, it does so only approximately for more general lens situations. We provide crude estimates for the accuracy with which the transformed mass distribution can reproduce the same image positions as the original lens model, and present an illustrative example of its performance. This new invariance transformation is most likely the reason why the same strong lensing information can be accounted for with rather different mass models. [less ▲]

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See detailThe yellow hypergiant HR 5171 A: Resolving a massive interacting binary in the common envelope phase
Chesneau, O.; Meilland, A.; Chapellier, E. et al

in Astronomy and Astrophysics (2014), 563

Context. Only a few stars are caught in the very brief and often crucial stages when they quickly traverse the Hertzsprung-Russell diagram, and none has yet been spatially resolved in the mass transfer ... [more ▼]

Context. Only a few stars are caught in the very brief and often crucial stages when they quickly traverse the Hertzsprung-Russell diagram, and none has yet been spatially resolved in the mass transfer phase. Aims: We initiated long-term optical interferometry monitoring of the diameters of massive and unstable yellow hypergiants (YHG) with the goal of detecting both the long-term evolution of their radius and shorter term formation of a possible pseudo-photosphere related to proposed large mass-loss events. Methods: We observed HR 5171 A with AMBER/VLTI. We also examined archival photometric data in the visual and near-IR spanning more than 60 years, as well as sparse spectroscopic data. Results: HR 5171 Aexhibits a complex appearance. Our AMBER data reveal a surprisingly large star for a YHG R∗ = 1315 ± 260R⊙ (or ~6.1 AU) at the distance of 3.6 ± 0.5 kpc. The source is surrounded by an extended nebulosity, and these data also show a large level of asymmetry in the brightness distribution of the system, which we attribute to a newly discovered companion star located in front of the primary star. The companion's signature is also detected in the visual photometry, which indicates an orbital period of Porb = 1304 ± 6 d. Modeling the light curve with the NIGHTFALL program provides clear evidence that the system is a contact or possibly over-contact eclipsing binary. A total current system mass of 39^+40_-22 M⊙ and a high mass ratio q ≥ 10 is inferred for the system. Conclusions: The low-mass companion of HR 5171 is very close to the primary star that is embedded within its dense wind. Tight constraints on the inclination and vsini of the primary are lacking, which prevents us from determining its influence precisely on the mass-loss phenomenon, but the system is probably experiencing a wind Roche-Lobe overflow. Depending on the amount of angular momentum that can be transferred to the stellar envelope, HR 5171 A may become a fast-rotating B[e]/luminous blue variable/Wolf-Rayet star. In any case, HR 5171 A highlights the possible importance of binaries for interpreting the unstable YHGs and for massive star evolution in general. [less ▲]

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See detailTransiting planets from WASP-South, Euler and TRAPPIST: WASP-68 b, WASP-73 b and WASP-88 b, three hot Jupiters transiting evolved solar-type stars
Delrez, Laetitia ULg; Van Grootel, Valérie ULg; Anderson, D. R. et al

in Astronomy and Astrophysics (2014)

Using the WASP transit survey, we report the discovery of three new hot Jupiters, WASP-68 b, WASP-73 b and WASP-88 b. The planet WASP-68 bhas a mass of 0.95 ± 0.03 MJup, a radius of 1.24-0.06+0.10 RJup ... [more ▼]

Using the WASP transit survey, we report the discovery of three new hot Jupiters, WASP-68 b, WASP-73 b and WASP-88 b. The planet WASP-68 bhas a mass of 0.95 ± 0.03 MJup, a radius of 1.24-0.06+0.10 RJup, and orbits a V = 10.7 G0-type star (1.24 ± 0.03 M&sun; 1.69-0.06+0.11 R&sun;, Teff = 5911 ± 60 K) with a period of 5.084298 ± 0.000015 days. Its size is typical of hot Jupiters with similar masses. The planet WASP-73 bis significantly more massive (1.88-0.06+0.07 MJup) and slightly larger (1.16-0.08+0.12 RJup) than Jupiter. It orbits a V = 10.5 F9-type star (1.34-0.04+0.05 M&sun;, 2.07-0.08+0.19 R&sun;, Teff = 6036 ± 120 K) every 4.08722 ± 0.00022 days. Despite its high irradiation (~2.3 × 109 erg s-1 cm-2), WASP-73 b has a high mean density (1.20-0.30+0.26 rhoJup) that suggests an enrichment of the planet in heavy elements. The planet WASP-88 bis a 0.56 ± 0.08 MJuphot Jupiter orbiting a V = 11.4 F6-type star (1.45 ± 0.05 M&sun;, 2.08-0.06+0.12 R&sun;, Teff = 6431 ± 130 K) with a period of 4.954000 ± 0.000019 days. With a radius of 1.70-0.07+0.13 RJup, it joins the handful of planets with super-inflated radii. The ranges of ages we determine through stellar evolution modeling are 4.5-7.0 Gyr for WASP-68, 2.8-5.7 Gyr for WASP-73 and 1.8-4.3 Gyr for WASP-88. The star WASP-73 appears to be significantly evolved, close to or already in the subgiant phase. The stars WASP-68 and WASP-88 are less evolved, although in an advanced stage of core H-burning. [less ▲]

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See detailMode identification based on time-series spectrophotometry for the bright rapid sdB pulsator EC 01541-1409
Randall, Suzanna K; Fontaine, Gilles; Geier, Stephan et al

in Astronomy and Astrophysics (2014), 563

We present an analysis of time-resolved spectrophotometry gathered with FORS/VLT for the rapidly pulsating hot B subdwarf EC 01541-1409 with the aim of identifying the degree index ℓ of the larger ... [more ▼]

We present an analysis of time-resolved spectrophotometry gathered with FORS/VLT for the rapidly pulsating hot B subdwarf EC 01541-1409 with the aim of identifying the degree index ℓ of the larger amplitude modes. This mode identification can be extremely useful in detailed searches for viable asteroseismic models in parameter space, and can be crucial for testing the validity of a solution a posteriori. To achieve it, we exploit the ℓ-dependence of the monochromatic amplitude, phase, and velocity-to-amplitude ratio of a mode as a function of wavelength. We use the ℓ-sensitive phase lag between the flux perturbation and the radial velocity as an additional diagnostic tool. On this basis, we are able to unambiguously identify the dominant 140.5 s pulsation of our target as a radial mode, and the second-highest amplitude periodicity at 145.8 s as an ℓ = 2 mode. We further exploit the exceptionally high-sensitivity data that we gathered for the dominant mode to infer modal properties that are usually quite difficult to estimate in sdB pulsators, namely the physical values of the dimensionless radius, temperature, and surface gravity perturbations. [less ▲]

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See detailA multi-method approach to radial-velocity measurement for single-object spectra
David, M.; Blomme, R.; Frémat, Y. et al

in Astronomy and Astrophysics (2014), 562

Context. The derivation of radial velocities from large numbers of spectra that typically result from survey work, requires automation. However, except for the classical cases of slowly rotating late-type ... [more ▼]

Context. The derivation of radial velocities from large numbers of spectra that typically result from survey work, requires automation. However, except for the classical cases of slowly rotating late-type spectra, existing methods of measuring Doppler shifts require fine-tuning to avoid a loss of accuracy due to the idiosyncrasies of individual spectra. The radial velocity spectrometer (RVS) on the Gaia mission, which will start operating very soon, prompted a new attempt at creating a measurement pipeline to handle a wide variety of spectral types. <BR /> Aims: The present paper describes the theoretical background on which this software is based. However, apart from the assumption that only synthetic templates are used, we do not rely on any of the characteristics of this instrument, so our results should be relevant for most telescope-detector combinations. <BR /> Methods: We propose an approach based on the simultaneous use of several alternative measurement methods, each having its own merits and drawbacks, and conveying the spectral information in a different way, leading to different values for the measurement. A comparison or a combination of the various results either leads to a "best estimate" or indicates to the user that the observed spectrum is problematic and should be analysed manually. <BR /> Results: We selected three methods and analysed the relationships and differences between them from a unified point of view; with each method an appropriate estimator for the individual random error is chosen. We also develop a procedure for tackling the problem of template mismatch in a systematic way. Furthermore, we propose several tests for studying and comparing the performance of the various methods as a function of the atmospheric parameters of the observed objects. Finally, we describe a procedure for obtaining a knowledge-based combination of the various Doppler-shift measurements. [less ▲]

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See detailWind collisions in three massive stars of Cygnus OB2
Cazorla, Constantin ULg; Nazé, Yaël ULg; Rauw, Grégor ULg

in Astronomy and Astrophysics (2014), 561

Aims. We wish to study the origin of the X-ray emission of three massive stars in the CygOB2 association: CygOB2#5, Cyg OB2 #8A, and Cyg OB2 #12. Methods. To this aim, dedicated X-ray observations from ... [more ▼]

Aims. We wish to study the origin of the X-ray emission of three massive stars in the CygOB2 association: CygOB2#5, Cyg OB2 #8A, and Cyg OB2 #12. Methods. To this aim, dedicated X-ray observations from XMM-Newton and Swift are used, as well as archival ROSAT and Suzaku data. Results. Our results on Cyg OB2 #8A improve the phase coverage of the orbit and confirm previous studies: the signature of a wind- wind collision is conspicuous. In addition, signatures of a wind-wind collision are also detected in Cyg OB2 #5, but the X-ray emission appears to be associated with the collision between the inner binary and the tertiary component orbiting it with a 6.7 yr period, without a putative collision inside the binary. The X-ray properties strongly constrain the orbital parameters, notably allowing us to discard some proposed orbital solutions. To improve the knowledge of the orbit, we revisit the light curves and radial velocity of the inner binary, looking for reflex motion induced by the third star. Finally, the X-ray emission of Cyg OB2 #12 is also analyzed. It shows a marked decrease in recent years, compatible with either a wind-wind collision in a wide binary or the aftermath of a recent eruption. [less ▲]

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See detailWASP-103 b: A new planet at the edge of tidal disruption
Gillon, Michaël ULg; Anderson, D. R.; Collier-Cameron, A. et al

in Astronomy and Astrophysics (2014)

We report the discovery of WASP-103b, a new ultra-short-period planet (P=22.2 hr) transiting a 12.1 V-magnitude F8-type main-sequence star (1.22+-0.04 Msun, 1.44-0.03+0.05 Rsun, Teff = 6110+-160 K). WASP ... [more ▼]

We report the discovery of WASP-103b, a new ultra-short-period planet (P=22.2 hr) transiting a 12.1 V-magnitude F8-type main-sequence star (1.22+-0.04 Msun, 1.44-0.03+0.05 Rsun, Teff = 6110+-160 K). WASP-103b is significantly more massive (1.49+-0.09 Mjup) and larger (1.53-0.07+0.05 Rjup) than Jupiter. Its large size and extreme irradiation (around 9 10^9 erg/s/cm^2) make it an exquisite target for a thorough atmospheric characterization with existing facilities. Furthermore, its orbital distance is less than 20% larger than its Roche radius, meaning that it might be significantly distorted by tides and might experience mass loss through Roche-lobe overflow. It thus represents a new key object for understanding the last stage of the tidal evolution of hot Jupiters. [less ▲]

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See detailA search for pulsations in the HgMn star HD 45975 with CoRoT photometry and ground-based spectroscopy
Morel, Thierry ULg; Briquet, Maryline ULg; Auvergne, M. et al

in Astronomy and Astrophysics (2014), 561

The existence of pulsations in HgMn stars is still being debated. To provide the first unambiguous observational detection of pulsations in this class of chemically peculiar objects, the bright star HD ... [more ▼]

The existence of pulsations in HgMn stars is still being debated. To provide the first unambiguous observational detection of pulsations in this class of chemically peculiar objects, the bright star HD 45975 was monitored for nearly two months by the CoRoT satellite. Independent analyses of the light curve provide evidence of monoperiodic variations with a frequency of 0.7572 d[SUP]-1[/SUP] and a peak-to-peak amplitude of ~2800 ppm. Multisite, ground-based spectroscopic observations overlapping the CoRoT observations show the star to be a long-period, single-lined binary. Furthermore, with the notable exception of mercury, they reveal the same periodicity as in photometry in the line moments of chemical species exhibiting strong overabundances (e.g., Mn and Y). In contrast, lines of other elements do not show significant variations. As found in otherHgMn stars, the pattern of variability consists in an absorption bump moving redwards across the line profiles. We argue that the photometric and spectroscopic changes are more consistent with an interpretation in terms of rotational modulation of spots at the stellar surface. In this framework, the existence of pulsations producing photometric variations above the ~50 ppm level is unlikely in HD 45975. This provides strong constraints on the excitation/damping of pulsation modes in this HgMn star. The CoRoT space mission was developed and is operated by the French space agency CNES, with participation of ESA's RSSD and Science Programmes, Austria, Belgium, Brazil, Germany, and Spain. This work is based on observations collected at La Silla and Paranal Observatories, ESO (Chile), with the HARPS and UVES spectrographs at the 3.6-m and very large telescopes, under programmes LP185.D-0056 and 287.D-5066. It is also based on observations made with the Mercator Telescope, operated on the island of La Palma by the Flemish Community, at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias. Based on observations obtained with the HERMES spectrograph, which is supported by the Fund for Scientific Research of Flanders (FWO), Belgium, the Research Council of K.U. Leuven, Belgium, the Fonds National de la Recherche Scientifique (FNRS), Belgium, the Royal Observatory of Belgium, the Observatoire de Genève, Switzerland, and the Thüringer Landessternwarte Tautenburg, Germany. [less ▲]

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See detailTwo spotted and magnetic early B-type stars in the young open cluster NGC2264 discovered by MOST and ESPaDOnS
Fossati, L.; Zwintz, K.; Castro, N. et al

in Astronomy and Astrophysics (2014), 1401

Star clusters are known as superb tools for understanding stellar evolution. In a quest for understanding the physical origin of magnetism and chemical peculiarity in about 7% of the massive main-sequence ... [more ▼]

Star clusters are known as superb tools for understanding stellar evolution. In a quest for understanding the physical origin of magnetism and chemical peculiarity in about 7% of the massive main-sequence stars, we analysed two of the ten brightest members of the ~10 Myr old Galactic open cluster NGC 2264, the early B-dwarfs HD47887 and HD47777. We find accurate rotation periods of 1.95 and 2.64 days, respectively, from MOST photometry. We obtained ESPaDOnS spectropolarimetric observations, through which we determined stellar parameters, detailed chemical surface abundances, projected rotational velocities, and the inclination angles of the rotation axis. Because we found only small (<5 km/s) radial velocity variations, most likely caused by spots, we can rule out that HD47887 and HD47777 are close binaries. Finally, using the least-squares deconvolution technique, we found that both stars possess a large-scale magnetic field with an average longitudinal field strength of about 400 G. From a simultaneous fit of the stellar parameters we determine the evolutionary masses of HD47887 and HD47777 to be 9.4+/-0.7 M0 and 7.6+/-0.5 M0. Interestingly, HD47777 shows a remarkable helium underabundance, typical of helium-weak chemically peculiar stars, while the abundances of HD47887 are normal, which might imply that diffusion is operating in the lower mass star but not in the slightly more massive one. Furthermore, we argue that the rather slow rotation, as well as the lack of nitrogen enrichment in both stars, can be consistent with both the fossil and the binary hypothesis for the origin of the magnetic field. However, the presence of two magnetic and apparently single stars near the top of the cluster mass-function may speak in favour of the latter. [less ▲]

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See detailStellar laboratories. II. New Zn IV and Zn V oscillator strengths and their validation in the hot white dwarfs G191-B2B and RE 0503-289
Rauch, T; Werner, K; Quinet, Pascal ULg et al

in Astronomy and Astrophysics (2014), 564(A41),

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See detailStellar laboratories. III. New Ba V, Ba VI and Ba VII oscillator strengths and the barium abundance in the hot white dwarfs G191-B2B and RE 0503-289
Rauch, T; Werner, K; Quinet, Pascal ULg et al

in Astronomy and Astrophysics (2014), 566(A10),

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See detailEclipsing Am binary systems in the SuperWASP survey
Smalley, B.; Southworth, J.; Pintado, O. I. et al

in Astronomy and Astrophysics (2014), 564

The results of a search for eclipsing Am star binaries using photometry from the SuperWASP survey are presented. The light curves of 1742 Am stars fainter than V = 8.0 were analysed for the presence of ... [more ▼]

The results of a search for eclipsing Am star binaries using photometry from the SuperWASP survey are presented. The light curves of 1742 Am stars fainter than V = 8.0 were analysed for the presence of eclipses. A total of 70 stars were found to exhibit eclipses, with 66 having sufficient observations to enable orbital periods to be determined and 28 of which are newly identified eclipsing systems. Also presented are spectroscopic orbits for 5 of the systems. The number of systems and the period distribution is found to be consistent with that identified in previous radial velocity surveys of "classical" Am stars. [less ▲]

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See detailContinued activity in P/2013 P5 PANSTARRS - The comet that should not be
Hainaut, O. R.; Boehnhardt, H.; Snodgrass, C. et al

in Astronomy and Astrophysics (2014)

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See detailPhysical properties of the WASP-67 planetary system from multi-colour photometry
Mancini, L.; Southworth, J.; Ciceri, S. et al

in Astronomy and Astrophysics (2014), 568

Context. The extrasolar planet WASP-67 b is the first hot Jupiter definitively known to undergo only partial eclipses. The lack of the second and third contact points in this planetary system makes it ... [more ▼]

Context. The extrasolar planet WASP-67 b is the first hot Jupiter definitively known to undergo only partial eclipses. The lack of the second and third contact points in this planetary system makes it difficult to obtain accurate measurements of its physical parameters. [less ▲]

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See detailHerschel observations of gas and dust in comet C/2006 W3 (Christensen) at 5 AU from the Sun
de Val-Borro, M; Bockelée-Morvan, D; Jehin, Emmanuel ULg et al

in Astronomy and Astrophysics (2014), 564

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See detailWR 138: new results from X-ray and optical spectroscopy
Palate, Matthieu ULg; Rauw, Grégor ULg; De Becker, Michaël ULg et al

in Astronomy and Astrophysics (2013), 560

Massive-binary evolution models predict that some systems will go through an evolutionary phase where the original primary has become a supernova and left a compact object behind that then orbits a Wolf ... [more ▼]

Massive-binary evolution models predict that some systems will go through an evolutionary phase where the original primary has become a supernova and left a compact object behind that then orbits a Wolf-Rayet (WR) star. WR 138 is an X-ray bright WR star that has been described as a triple system, including a compact companion in a short-period orbit. Our goal is to search for spectroscopic evidence of a compact companion around WR 138. We used optical and X-ray spectra to search for signatures of a compact companion, which can be revealed by systematic variations in WR optical spectral lines induced by orbital motion of the compact companion or by hard, luminous X-rays from accretion onto this companion. The optical spectra display emission-line profile variations that are most probably caused by clumps inside the stellar winds. The radial velocities do not vary on a short time-scale compatible with the suggested orbital period of a putative compact companion. The X-ray spectra are found to be normal for a WN5-6+OB system with no indication of accretion by a compact companion. There is no evidence for the presence of a compact companion, and we therefore conclude that WR 138 is a normal long-period (P ~ 1521 d) eccentric WR+OB system. [less ▲]

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See detailA Photometric Study of the Hot Exoplanet WASP-19b
Lendl, M.; Gillon, Michaël ULg; Queloz, D. et al

in Astronomy and Astrophysics (2013), 552

Context. The sample of hot Jupiters that have been studied in great detail is still growing. In particular, when the planet transits its host star, it is possible to measure the planetary radius and the ... [more ▼]

Context. The sample of hot Jupiters that have been studied in great detail is still growing. In particular, when the planet transits its host star, it is possible to measure the planetary radius and the planet mass (with radial velocity data). For the study of planetary atmospheres, it is essential to obtain transit and occultation measurements at multiple wavelengths. Aims: We aim to characterize the transiting hot Jupiter WASP-19b by deriving accurate and precise planetary parameters from a dedicated observing campaign of transits and occultations. Methods: We have obtained a total of 14 transit lightcurves in the r'-Gunn, I-Cousins, z'-Gunn, and I + z' filters and 10 occultation lightcurves in z'-Gunn using EulerCam on the Euler-Swiss telescope and TRAPPIST. We also obtained one lightcurve through the narrow-band NB1190 filter of HAWK-I on the VLT measuring an occultation at 1.19 μm. We performed a global MCMC analysis of all new data, together with some archive data in order to refine the planetary parameters and to measure the occultation depths in z'-band and at 1.19 μm. Results: We measure a planetary radius of Rp = 1.376 ± 0.046 RJ, a planetary mass of Mp = 1.165 ± 0.068 MJ, and find a very low eccentricity of e = 0.0077-0.0032+0.0068, compatible with a circular orbit. We have detected the z'-band occultation at 3σ significance and measure it to be δFocc,z' = 352 ± 116 ppm, more than a factor of 2 smaller than previously published. The occultation at 1.19 μm is only marginally constrained at δFocc,NB1190 = 1711-726+745 ppm. Conclusions: We show that the detection of occultations in the visible range is within reach, even for 1 m class telescopes if a considerable number of individual events are observed. Our results suggest an oxygen-dominated atmosphere of WASP-19b, making the planet an interesting test case for oxygen-rich planets without temperature inversion. [less ▲]

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