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See detailHigh angular resolution imaging and infrared spectroscopy of CoRoT candidates
Guenther, E. W.; Fridlund, M.; Alonso, R. et al

in Astronomy and Astrophysics (2013), 556

Context. Studies of transiting extrasolar planets are of key importance for understanding the nature of planets outside our solar system because their masses, diameters, and bulk densities can be measured ... [more ▼]

Context. Studies of transiting extrasolar planets are of key importance for understanding the nature of planets outside our solar system because their masses, diameters, and bulk densities can be measured. An important part of transit-search programmes is the removal of false-positives. In the case of the CoRoT space mission, the majority of the false-positives are removed by a detailed analysis of the light curves and by seeing-limited imaging in- and out-of-transit. However, the critical question is how many of the candidates that passed all these tests are false-positives. Such false-positives can be caused by eclipsing binaries, which are either related or unrelated to the targets. <BR /> Aims: For our study we selected 25 CoRoT candidates that have already been screened against false-positives using detailed analysis of the light curves and seeing-limited imaging, which has transits that are between 0.7 and 0.05% deep. Our aim is to search for companion candidates that had not been recognized in previous observations. <BR /> Methods: We observed 20 candidates with the adaptive optics imager NaCo and 18 with the high-resolution infrared spectrograph CRIRES. <BR /> Results: We found previously unknown stars within 2'' of the targets in seven of the candidates. All of these are too faint and too close to the targets to have been previously detected with seeing-limited telescopes in the optical. Our study thus leads to the surprising results that if we remove all candidates excluded by the sophisticated analysis of the light-curve, as well as carrying out deep imaging with seeing-limited telescopes, still 28-35% of the remaining candidates are found to possess companions that are bright enough to be false-positives. <BR /> Conclusions: Given that the companion candidates cluster around the targets and that the J - K colours are consistent with physical companions, we conclude that the companion candidates are more likely to be physical companions rather than unrelated field stars. Based on observations obtained at the European Southern Observatory at Paranal, Chile in programmes 282.C-5015A, 282.C-5015B, 282.C-5015C, 285.C-5045A, and 285.C-5045B, 086.C-0235A, 086.C-0235B, 088.C-0707A, 088.C-0707B, 090.C-0251A, 090.C-0251B, and 091.C-203(A).Appendices A and B are available in electronic form at <A href="http://www.aanda.org">http://www.aanda.org</A> [less ▲]

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See detailSpectral modelling of the α Virginis (Spica) binary system
Palate, Matthieu ULg; Koenigsberger, G.; Rauw, Grégor ULg et al

in Astronomy and Astrophysics (2013), 556

Context. The technique of matching synthetic spectra computed with theoretical stellar atmosphere models to the observations is widely used in deriving fundamental parameters of massive stars. When ... [more ▼]

Context. The technique of matching synthetic spectra computed with theoretical stellar atmosphere models to the observations is widely used in deriving fundamental parameters of massive stars. When applied to binaries, however, these models generally neglect the interaction effects present in these systems. <BR /> Aims: The aim of this paper is to explore the uncertainties in binary stellar parameters that are derived from single-star models. <BR /> Methods: Synthetic spectra that include the tidal perturbations and irradiation effects are computed for the binary system α Virginis (Spica) using our recently-developed CoMBiSpeC model. The synthetic spectra are compared to S/N ~ 2000 observations and optimum values of T[SUB]eff[/SUB] and log g are derived. <BR /> Results: The binary interactions have only a small effect on the strength of the photospheric absorption lines in Spica (<2% for the primary and <4% for the secondary). These differences are comparable to the uncertainties inherent to the process of matching synthetic spectra to the observations and thus the derived values of T[SUB]eff[/SUB] and log g are unaffected by the binary perturbations. On the other hand, the interactions do produce significant phase-dependent line profile variations in the primary star, leading to systematic distortions in the shape of its radial velocity curve. Migrating sub-features ("bumps") are predicted by our model to be present in the same photospheric lines as observed, and their appearance does not require any a priori assumptions regarding non-radial pulsation modes. Matching the strength of lines in which the most prominent "bumps" occur requires synthetic spectra computed with larger "microturbulence" than that required by other lines. [less ▲]

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See detailAn interferometric study of the Fomalhaut inner debris disk. III. Detailed models of the exozodiacal disk and its origin
Lebreton, J; van Lieshout, R; Augereau, J-C et al

in Astronomy and Astrophysics (2013), 555

Context. Debris disks are thought to be extrasolar analogues to the Solar System planetesimal belts. The star Fomalhaut harbors a cold debris belt at 140AU comparable to the Edgeworth-Kuiper belt, as well ... [more ▼]

Context. Debris disks are thought to be extrasolar analogues to the Solar System planetesimal belts. The star Fomalhaut harbors a cold debris belt at 140AU comparable to the Edgeworth-Kuiper belt, as well as evidence for a warm dust component, unresolved by single-dish telescopes, that is suspected to be a bright analogue to the Solar System's zodiacal dust. Aims. Interferometric observations obtained with the VLTI/VINCI instrument and the Keck Interferometer Nuller have identi fied near- and mid-infrared excesses attributed respectively to hot and warm exozodiacal dust residing in the inner few AU of the Fomalhaut environment. We aim to characterize the properties of this double inner dust belt and to unveil its origin. Methods.We perform parametric modelling of the exozodiacal disk ("exozodi") using the GRaTer radiative transfer code in order to reproduce the interferometric data, complemented by mid- to far-infrared photometric measurements from Spitzer and Herschel. A detailed treatment of sublimation temperatures is introduced to explore the hot population at the size-dependent sublimation rim. We then use an analytical approach to test successively several source mechanisms for the dust and suspected parent bodies. Results. A good fi t to the multi-wavelength data is found by two distinct dust populations: (1) a population of very small (0.01 to 0.5 µ m) and therefore unbound, hot dust grains con ned in a narrow region ( ~0.1 - 0.3 AU) at the sublimation rim of carbonaceous material; (2) a population of bound grains at 2AU that is protected from sublimation and has a larger mass despite its fainter flux level. We propose that the hot dust is produced by the release of small carbon grains following the disruption of dust aggregates that originate from the warm component. A mechanism such as gas braking is required to further con ne the small grains for long enough. In situ dust production could hardly be ensured for the age of the star and we conclude that the observed amount of dust is triggered by intense dynamical activity. Conclusions. Fomalhaut may be representative of exozodis that are currently being surveyed at near and mid-infrared wavelengths worldwide. We propose a framework for reconciling the "hot exozodi phenomenon" with theoretical constraints: the hot component of Fomalhaut is likely the "tip of the iceberg" as it could derive from the more massive, but fainter, warm dust component residing near the ice line. This inner disk exhibits interesting morphology and can be considered a prime target for future exoplanet research. [less ▲]

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See detailA near-infrared interferometric survey of debris disc stars. III. First statistics based on 42 stars observed with CHARA/FLUOR
Absil, Olivier ULg; Defrère, Denis; Coudé du Foresto, Vincent et al

in Astronomy and Astrophysics (2013), 555

Context. Dust is expected to be ubiquitous in extrasolar planetary systems due to the dynamical activity of minor bodies. Inner dust populations are, however, still poorly known due to the high contrast ... [more ▼]

Context. Dust is expected to be ubiquitous in extrasolar planetary systems due to the dynamical activity of minor bodies. Inner dust populations are, however, still poorly known due to the high contrast and small angular separation with respect to their host star. Yet, a proper characterisation of exozodiacal dust is mandatory for the design of future Earth-like planet imaging missions. Aims. We aim to determine the level of near-infrared exozodiacal dust emission around a sample of 42 nearby main sequence stars with spectral types ranging from A to K, and to investigate its correlation with various stellar parameters and with the presence of cold dust belts. Methods. We use high-precision K-band visibilities obtained with the FLUOR interferometer on the shortest baseline of the CHARA array. The calibrated visibilities are compared with the expected visibility of the stellar photosphere to assess the presence of an additional, fully resolved circumstellar emission source. Results. Near-infrared circumstellar emission amounting to about 1% of the stellar flux is detected around 13 of our 42 target stars. Follow-up observations showed that one of them (eps Cep) is associated with a stellar companion, while another one was detected around what turned out to be a giant star (kap CrB). The remaining 11 excesses found around single main sequence stars are most probably due to the presence of hot circumstellar dust, yielding an overall occurrence rate of 28+8-6% for our (biased) sample. We show that the occurrence rate of bright exozodiacal discs correlates with spectral type, K-band excesses being more frequent around A-type stars. It also correlates with the presence of detectable far-infrared excess emission in the case of solar-type stars. Conclusions. This study provides new insights regarding the phenomenon of bright exozodiacal disc, showing that hot dust populations are probably linked to outer dust reservoirs in the case of solar-type stars. In the case of A-type stars, no clear conclusion can be made regarding the origin of the detected near-infrared excesses. [less ▲]

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See detailTransiting exoplanets from the CoRoT space mission. XXIV. CoRoT-25b and CoRoT-26b: two low-density giant planets
Almenara, J. M.; Bouchy, F.; Gaulme, P. et al

in Astronomy and Astrophysics (2013), 555

We report the discovery of two transiting exoplanets, CoRoT-25b and CoRoT-26b, both of low density, one of which is in the Saturn mass-regime. For each star, ground-based complementary observations ... [more ▼]

We report the discovery of two transiting exoplanets, CoRoT-25b and CoRoT-26b, both of low density, one of which is in the Saturn mass-regime. For each star, ground-based complementary observations through optical photometry and radial velocity measurements secured the planetary nature of the transiting body and allowed us to fully characterize them. For CoRoT-25b we found a planetary mass of 0.27 ± 0.04 M[SUB]Jup[/SUB], a radius of 1.08[SUB]-0.10[/SUB][SUP]+0.3[/SUP] R[SUB]Jup[/SUB] and hence a mean density of 0.15[SUB]-0.06[/SUB][SUP]+0.15[/SUP] g cm[SUP]-3[/SUP]. The planet orbits an F9 main-sequence star in a 4.86-day period, that has a V magnitude of 15.0, solar metallicity, and an age of 4.5[SUB]-2.0[/SUB][SUP]+1.8[/SUP]-Gyr. CoRoT-26b orbits a slightly evolved G5 star of 9.06 ± 1.5-Gyr age in a 4.20-day period that hassolar metallicity and a V magnitude of 15.8. With a mass of 0.52 ± 0.05 M[SUB]Jup[/SUB], a radius of 1.26[SUB]-0.07[/SUB][SUP]+0.13[/SUP] R[SUB]Jup[/SUB], and a mean density of 0.28[SUB]-0.07[/SUB][SUP]+0.09[/SUP] g cm[SUP]-3[/SUP], it belongs to the low-mass hot-Jupiter population. Planetary evolution models allowed us to estimate a core mass of a few tens of Earth mass for the two planets with heavy-element mass fractions of 0.52[SUB]-0.15[/SUB][SUP]+0.08[/SUP] and 0.26[SUB]-0.08[/SUB][SUP]+0.05[/SUP], respectively, assuming that a small fraction of the incoming flux is dissipated at the center of the planet. In addition, these models indicate that CoRoT-26b is anomalously large compared with what standard models could account for, indicating that dissipation from stellar heating could cause this size. 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. Partly based on observations obtained at the European Southern Observatory at Paranal and La Silla, Chile in programs 083.C-0690(A), 184.C-0639. [less ▲]

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See detailHD 45314: a new γ Cassiopeiae analog among Oe stars
Rauw, Grégor ULg; Nazé, Yaël ULg; Spano, M. et al

in Astronomy and Astrophysics (2013), 555

Context. Oe stars possibly form an extension to higher temperatures of the Be phenomenon, but it is still unclear whether these stars have disks. <BR /> Aims: X-ray spectra could provide hints for ... [more ▼]

Context. Oe stars possibly form an extension to higher temperatures of the Be phenomenon, but it is still unclear whether these stars have disks. <BR /> Aims: X-ray spectra could provide hints for interactions of the star with a putative surrounding disk. <BR /> Methods: We obtained XMM-Newton observations of two Oe stars, HD 45314 and HD 60848. Spectra and light curves were extracted and analysed. Optical spectra were also obtained to support the X-ray observations. <BR /> Results: We find that both stars display very different X-ray properties. Whilst HD 60848 has an X-ray spectrum and emission level typical for its spectral type, HD 45314 displays a very hard X-ray emission, dominated by a thermal plasma with kT ~ 21 keV. Furthermore, HD 45314 displays count rate variations by a factor 2 on timescales of ~ 10[SUP]3[/SUP] s and a high log (L[SUB]X[/SUB]/L[SUB]bol[/SUB]) = -6.10 ± 0.03. <BR /> Conclusions: The X-ray properties of HD 45314 indicate that this star is a new member of the class of γ Cas analogs, the first one among the original category of Oe stars. Based on observations collected with XMM-Newton, an ESA Science Mission with instruments and contributions directly funded by ESA Member States and the USA (NASA), and observations collected at the European Southern Observatory (La Silla, Chile) and the Observatoire de Haute Provence (France). [less ▲]

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See detailX-ray properties of the young open clusters HM1 and IC 2944/2948
Nazé, Yaël ULg; Rauw, Grégor ULg; Sana, H. et al

in Astronomy and Astrophysics (2013), 555

Using XMM-Newton data, we study for the first time the X-ray emission of HM1 and IC 2944/2948. Low-mass, pre-main-sequence objects with an age of a few Myr are detected, as well as a few background or ... [more ▼]

Using XMM-Newton data, we study for the first time the X-ray emission of HM1 and IC 2944/2948. Low-mass, pre-main-sequence objects with an age of a few Myr are detected, as well as a few background or foreground objects. Most massive stars in both clusters display the usual high-energy properties of that type of objects, though with log [L[SUB]X[/SUB]/L[SUB]BOL[/SUB]] apparently lower in HM1 than in IC 2944/2948. Compared with studies of other clusters, it seems that a low signal-to-noise ratio at soft energies, due to the high extinction, may be the main cause of this difference. In HM1, the two Wolf-Rayet stars show contrasting behaviors: WR89 is extremely bright, but much softer than WR87. It remains to be seen whether wind-wind collisions or magnetically confined winds can explain these emissions. In IC 2944/2948, the X-ray sources concentrate around HD 101205; a group of massive stars to the north of this object is isolated, suggesting that there exist two subclusters in the field-of-view. Tables 2, 5, and Figs. 5, 9 are available in electronic form at <A href="http://www.aanda.org">http://www.aanda.org</A>Based on observations collected with XMM-Newton, an ESA Science Mission with instruments and contributions directly funded by ESA Member States and the USA (NASA).Tables 1, 3 and 4 are only 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/555/A83">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/555/A83</A> [less ▲]

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See detailEstimating the parameters of globular cluster M 30 (NGC 7099) from time-series photometry
Kains, N.; Bramich, D. M.; Arellano Ferro, A. et al

in Astronomy and Astrophysics (2013), 555

<BR /> Aims: We present the analysis of 26 nights of V and I time-series observations from 2011 and 2012 of the globular cluster M 30 (NGC 7099). We used our data to search for variable stars in this ... [more ▼]

<BR /> Aims: We present the analysis of 26 nights of V and I time-series observations from 2011 and 2012 of the globular cluster M 30 (NGC 7099). We used our data to search for variable stars in this cluster and refine the periods of known variables; we then used our variable star light curves to derive values for the cluster's parameters. <BR /> Methods: We used difference image analysis to reduce our data to obtain high-precision light curves of variable stars. We then estimated the cluster parameters by performing a Fourier decomposition of the light curves of RR Lyrae stars for which a good period estimate was possible. We also derived an estimate for the age of the cluster by fitting theoretical isochrones to our colour-magnitude diagram (CMD). <BR /> Results: Out of 13 stars previously catalogued as variables, we find that only 4 are bona fide variables. We detect two new RR Lyrae variables, and confirm two additional RR Lyrae candidates from the literature. We also detect four other new variables, including an eclipsing blue straggler system, and an SX Phoenicis star. This amounts to a total number of confirmed variable stars in M 30 of 12. We perform Fourier decomposition of the light curves of the RR Lyrae stars to derive cluster parameters using empirical relations. We find a cluster metallicity [Fe/H][SUB]ZW[/SUB] = -2.01 ± 0.04, or [Fe/H][SUB]UVES[/SUB] = -2.11 ± 0.06, and a distance of 8.32 ± 0.20 kpc (using RR0 variables), 8.10 kpc (using one RR1 variable), and 8.35 ± 0.42 kpc (using our SX Phoenicis star detection in M 30). Fitting isochrones to the CMD, we estimate an age of 13.0 ± 1.0 Gyr for M 30. This work is based on data collected by MiNDSTEp with the Danish 1.54 m telescope at the ESO La Silla Observatory.The full light curves, an extract of which is shown in Table 2 are only 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/555/A36">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/555/A36</A>Tables 8-10, and Figs. 6 and 9 are available in electronic form at <A href="http://www.aanda.org">http://www.aanda.org</A> [less ▲]

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See detailForbidden oxygen lines in comets at various heliocentric distances
Decock, Alice ULg; Jehin, Emmanuel ULg; Hutsemekers, Damien ULg et al

in Astronomy and Astrophysics (2013), 555

We present a study of the three forbidden oxygen lines [OI] located in the optical region - i.e., 5577.339 Å (the green line), 6300.304 Å and 6363.776 Å (the two red lines) - in order to better understand ... [more ▼]

We present a study of the three forbidden oxygen lines [OI] located in the optical region - i.e., 5577.339 Å (the green line), 6300.304 Å and 6363.776 Å (the two red lines) - in order to better understand the production of these atoms in cometary atmospheres. The analysis is based on 48 high-resolution and high signal-to-noise spectra collected with UVES at the ESO VLT between 2003 and 2011 referring to 12 comets of different origins observed at various heliocentric distances. The flux ratio of the green line to the sum of the two red lines is evaluated to determine the parent species of the oxygen atoms by comparison with theoretical models. This analysis confirms that, at about 1 AU, H[SUB]2[/SUB]O is the main parent molecule producing oxygen atoms. At heliocentric distances >2.5 AU, this ratio changes rapidly, an indication that other molecules are starting to contribute. The most abundant species after H[SUB]2[/SUB]O in the coma, CO and CO[SUB]2[/SUB], are good candidates, and the ratio is used to estimate their abundances. We found that the CO[SUB]2[/SUB] abundance relative to H[SUB]2[/SUB]O in comet C/2001 Q4 (NEAT) observed at 4 AU can be as high as ~70%. The intrinsic widths of the oxygen lines were also measured. The green line is on average about 1 km s[SUP]-1[/SUP] broader than the red lines, while the theory predicts that the red lines are broader. This might be due to the nature of the excitation source or to a contribution of CO[SUB]2[/SUB] as the parent molecule of the 5577.339 Å line. At 4 AU, we found that the width of the green and red lines in comet C/2001 Q4 are the same, which could be explained if CO[SUB]2[/SUB] becomes the main contributor to the three [OI] lines at high heliocentric distances. Based on observations made with ESO Telescope at the La Silla Paranal Observatory under programs ID 268.C-5570, 270.C-5043, 073.C-0525, 274.C-5015, 075.C-0355, 080.C-0615, 280.C-5053, 086.C-0958, and 087.C-0929. [less ▲]

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See detailFast-evolving weather for the coolest of our two new substellar neighbours
Gillon, Michaël ULg; Triaud, A. H. M. J.; Jehin, Emmanuel ULg et al

in Astronomy and Astrophysics (2013), 555

We present the results of an intense photometric monitoring in the near-infrared (~0.9 microns) with the TRAPPIST robotic telescope of the newly discovered binary brown dwarf WISE J104915.57-531906.1, the ... [more ▼]

We present the results of an intense photometric monitoring in the near-infrared (~0.9 microns) with the TRAPPIST robotic telescope of the newly discovered binary brown dwarf WISE J104915.57-531906.1, the third closest system to the Sun at a distance of only 2 pc. Our twelve nights of photometric time-series reveal a quasi-periodic (P = 4.87+-0.01 h) variability with a maximal peak-peak amplitude of ~11% and strong night-to-night evolution. We attribute this variability to the rotational modulation of fast-evolving weather patterns in the atmosphere of the coolest component (~T1-type) of the binary. No periodic signal is detected for the hottest component (~L8-type). For both brown dwarfs, our data allow us to firmly discard any unique transit during our observations for planets >= 2 Rearth. For orbital periods smaller than ~9.5 h, transiting planets are excluded down to an Earth-size. [less ▲]

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See detailStable higher order finite-difference schemes for stellar pulsation calculations
Reese, Daniel ULg

in Astronomy and Astrophysics (2013), 555

Context: Calculating stellar pulsations requires a sufficient accuracy to match the quality of the observations. Many current pulsation codes apply a second order finite-difference scheme, combined with ... [more ▼]

Context: Calculating stellar pulsations requires a sufficient accuracy to match the quality of the observations. Many current pulsation codes apply a second order finite-difference scheme, combined with Richardson extrapolation to reach fourth order accuracy on eigenfunctions. Although this is a simple and robust approach, a number of drawbacks exist thus making fourth order schemes desirable. A robust and simple finite-difference scheme, which can easily be implemented in either 1D or 2D stellar pulsation codes is therefore required. Aims: One of the difficulties in setting up higher order finite-difference schemes for stellar pulsations is the so-called mesh-drift instability. Current ways of dealing with this defect include introducing artificial viscosity or applying a staggered grids approach. However these remedies are not well-suited to eigenvalue problems, especially those involving non-dissipative systems, because they unduly change the spectrum of the operator, introduce supplementary free parameters, or lead to complications when applying boundary conditions. Methods: We propose here a new method, inspired from the staggered grids strategy, which removes this instability while bypassing the above difficulties. Furthermore, this approach lends itself to superconvergence, a process in which the accuracy of the finite differences is boosted by one order. Results: This new approach is successfully applied to stellar pulsation calculations, and is shown to be accurate, flexible with respect to the underlying grid, and able to remove mesh-drift. Conclusions: Although specifically designed for stellar pulsation calculations, this method can easily be applied to many other physical or mathematical problems. [less ▲]

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See detailDUst Around NEarby Stars. The survey observational results
Eiroa, C; Marshall, J; Mora, A et al

in Astronomy and Astrophysics (2013), 555

Context. Debris discs are a consequence of the planet formation process and constitute the fingerprints of planetesimal systems. Their solar system's counterparts are the asteroid and Edgeworth-Kuiper ... [more ▼]

Context. Debris discs are a consequence of the planet formation process and constitute the fingerprints of planetesimal systems. Their solar system's counterparts are the asteroid and Edgeworth-Kuiper belts. Aims. The DUNES survey aims at detecting extra-solar analogues to the Edgeworth-Kuiper belt around solar-type stars, putting in this way the solar system into context. The survey allows us to address some questions related to the prevalence and properties of planetesimal systems. Methods. We used Herschel/PACS to observe a sample of nearby FGK stars. Data at 100 and 160 μm were obtained, complemented in some cases with observations at 70 μm, and at 250, 350 and 500 μm using SPIRE. The observing strategy was to integrate as deep as possible at 100 μm to detect the stellar photosphere. Results. Debris discs have been detected at a fractional luminosity level down to several times that of the Edgeworth-Kuiper belt. The incidence rate of discs around the DUNES stars is increased from a rate of ∼ 12.1% ± 5% before Herschel to ∼ 20.2% ± 2%. A significant fraction (∼ 52%) of the discs are resolved, which represents an enormous step ahead from the previously known resolved discs. Some stars are associated with faint far-IR excesses attributed to a new class of cold discs. Although it cannot be excluded that these excesses are produced by coincidental alignment of background galaxies, statistical arguments suggest that at least some of them are true debris discs. Some discs display peculiar SEDs with spectral indexes in the 70–160 μm range steeper than the Rayleigh-Jeans one. An analysis of the debris disc parameters suggests that a decrease might exist of the mean black body radius from the F-type to the K-type stars. In addition, a weak trend is suggested for a correlation of disc sizes and an anticorrelation of disc temperatures with the stellar age. [less ▲]

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See detailNon-perturbative effect of rotation on dipolar mixed modes in red giant stars
Ouazzani, R.-M.; Goupil, M. J.; Dupret, Marc-Antoine ULg et al

in Astronomy and Astrophysics (2013), 554

Context. The space missions CoRoT and Kepler provide high-quality data that allow us to test the transport of angular momentum in stars by the seismic determination of the internal rotation profile. <BR ... [more ▼]

Context. The space missions CoRoT and Kepler provide high-quality data that allow us to test the transport of angular momentum in stars by the seismic determination of the internal rotation profile. <BR /> Aims: Our aim is to test the validity of seismic diagnostics for red giant rotation that are based on a perturbative method and to investigate the oscillation spectra when the validity does not hold. <BR /> Methods: We use a non-perturbative approach implemented in the ACOR code that accounts for the effect of rotation on pulsations and solves the pulsation eigenproblem directly for dipolar oscillation modes. <BR /> Results: We find that the limit of the perturbation to first order can be expressed in terms of the rotational splitting compared to the frequency separation between consecutive dipolar modes. Above this limit, non-perturbative computations are necessary, but only one term in the spectral expansion of modes is sufficient as long as the core rotation rate remains significantly smaller than the pulsation frequencies. Each family of modes with different azimuthal symmetry, m, has to be considered separately. In particular, in case of rapid core rotation, the density of the spectrum differs significantly from one m-family of modes to another, so that the differences between the period spacings associated with each m-family can constitute a promising guideline toward a proper seismic diagnostic for rotation. [less ▲]

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See detailThree-dimensional orbits of the triple-O stellar system HD 150136
Sana, H.; Le Bouquin, J.-B.; Mahy, Laurent et al

in Astronomy and Astrophysics (2013), 553

Context. HD 150136 is a triple hierarchical system and a non-thermal radio emitter. It is formed by an O3-3.5 V + O5.5-6 V close binary and a more distant O6.5-7 V tertiary. So far, only the inner orbital ... [more ▼]

Context. HD 150136 is a triple hierarchical system and a non-thermal radio emitter. It is formed by an O3-3.5 V + O5.5-6 V close binary and a more distant O6.5-7 V tertiary. So far, only the inner orbital properties have been reliably constrained. Aims. To quantitatively understand the non-thermal emission process, accurate knowledge of the physical and orbital properties of the object is crucial. Here, we aim to investigate the orbital properties of the wide system and to constrain the inclinations of the inner and outer binaries, and with these the absolute masses of the system components. Methods. We used the PIONIER combiner at the Very Large Telescope Interferometer to obtain the very first interferometric measurements of HD 150136. We combined the interferometric observations with new and existing high resolution spectroscopic data to derive the orbital solution of the outer companion in the three-dimensional space. Results. The wide system is clearly resolved by PIONIER, with a projected separation on the plane of the sky of about 9 milli-arcsec. The best-fit orbital period, eccentricity, and inclination are 8.2 yr, 0.73 and 108 degr. We constrain the masses of the three stars of the system to 63 +/- 10, 40 +/- 6, and 33 +/- 12 Msun for the O3-3.5 V, O5.5-6 V and O6.5-7 V components. Conclusions. The dynamical masses agree within errors with the evolutionary masses of the components. Future interferometric and spectroscopic monitoring of HD 150136 should allow one to reduce the uncertainties to a few per cent only and to accurately constrain the distance to the system. This makes HD 150136 an ideal system to quantitatively test evolutionary models of high-mass stars as well as the physics of non-thermal processes occurring in O-type systems. [less ▲]

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See detailCOSMOGRAIL XIII: Time delays and 9-yr optical monitoring of the lensed quasar RX J1131-1231
Tewes, M.; Courbin, F.; Meylan, G. et al

in Astronomy and Astrophysics (2013)

We present the results from 9 years of optically monitoring the gravitationally lensed z=0.658 quasar RX J1131-1231. The R band light curves of the 4 individual images of the quasar are obtained using ... [more ▼]

We present the results from 9 years of optically monitoring the gravitationally lensed z=0.658 quasar RX J1131-1231. The R band light curves of the 4 individual images of the quasar are obtained using deconvolution photometry, for a total of 707 epochs. Several sharp quasar variability features strongly constrain the time delays between the quasar images. Using three different numerical techniques, we measure these delays for all possible pairs of quasar images, while always processing the 4 light curves simultaneously. For all three methods, the delays between the 3 close images A, B and C are compatible with being 0, while we measure the delay of image D to be 91 days, with a fractional uncertainty of 1.5% (1 sigma), including systematic errors. Our analysis of random and systematic errors accounts in a realistic way for the observed quasar variability, fluctuating microlensing magnification over a broad range of temporal scales, noise properties, and seasonal gaps. Finally, we find that our time delay measurement methods yield compatible results when applied to subsets of the data. [less ▲]

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See detailCOSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses: XII. Time delays of the doubly lensed quasars SDSS~J1206+4332 and HS~2209+1914
Eulaers, Eva ULg; Tewes, Malte; Magain, Pierre ULg et al

in Astronomy and Astrophysics (2013)

Aims. Within the framework of the COSMOGRAIL collaboration we present 7- and 8.5-year-long light curves and time-delay esti- mates for two gravitationally lensed quasars: SDSS J1206+4332 and HS 2209+1914 ... [more ▼]

Aims. Within the framework of the COSMOGRAIL collaboration we present 7- and 8.5-year-long light curves and time-delay esti- mates for two gravitationally lensed quasars: SDSS J1206+4332 and HS 2209+1914. Methods. We monitored these doubly lensed quasars in the R-band using four telescopes: the Mercator, Maidanak, Himalayan Chandra, and Euler Telescopes, together spanning a period of 7 to 8.5 observing seasons from mid-2004 to mid-2011. The pho- tometry of the quasar images was obtained through simultaneous deconvolution of these data. The time delays were determined from these resulting light curves using four very different techniques: a dispersion method, a spline fit, a regression difference technique, and a numerical model fit. This minimizes the bias that might be introduced by the use of a single method. Results. The time delay for SDSS J1206+4332 is ∆tAB = 111.3 ± 3 days with A leading B, confirming a previously published result within the error bars. For HS 2209+1914 we present a new time delay of ∆tBA = 20.0 ± 5 days with B leading A. Conclusions. The combination of data from up to four telescopes have led to well-sampled and nearly 9-season-long light curves, which were necessary to obtain these results, especially for the compact doubly lensed quasar HS 2209+1914. [less ▲]

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See detailLaboratory demonstration of a mid-infrared AGPM vector vortex coronagraph
Delacroix, Christian ULg; Absil, Olivier ULg; Forsberg, Pontus et al

in Astronomy and Astrophysics (2013), 553

Coronagraphy is a powerful technique to achieve high contrast imaging and hence to image faint companions around bright targets. Various concepts have been used in the visible and near-infrared regimes ... [more ▼]

Coronagraphy is a powerful technique to achieve high contrast imaging and hence to image faint companions around bright targets. Various concepts have been used in the visible and near-infrared regimes, while coronagraphic applications in the mid-infrared remain nowadays largely unexplored. Vector vortex phase masks based on concentric subwavelength gratings show great promise for such applications. We aim at producing and validating the first high-performance broadband focal plane phase mask coronagraphs for applications in the mid-infrared regime, and in particular the L band with a fractional bandwidth of ~16% (3.5-4.1 \mu m). Based on rigorous coupled wave analysis, we designed an annular groove phase mask (AGPM) producing a vortex effect in the L band, and etched it onto a series of diamond substrates. The grating parameters were measured by means of scanning electron microscopy. The resulting components were then tested on a mid-infrared coronagraphic test bench. A broadband raw null depth of 2 x 10^{-3} was obtained for our best L-band AGPM after only a few iterations between design and manufacturing. This corresponds to a raw contrast of about 6 x 10^{-5} (10.5 mag) at 2\lambda/D. This result is fully in line with our projections based on rigorous coupled wave analysis modeling, using the measured grating parameters. The sensitivity to tilt and focus has also been evaluated. After years of technological developments, mid-infrared vector vortex coronagraphs finally become a reality and live up to our expectations. Based on their measured performance, our L-band AGPMs are now ready to open a new parameter space in exoplanet imaging at major ground-based observatories. [less ▲]

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See detailEMCCD photometry reveals two new variable stars in the crowded central region of the globular cluster NGC 6981
Skottfelt, J.; Bramich, D. M.; Figuera Jaimes, R. et al

in Astronomy and Astrophysics (2013), 553

Two previously unknown variable stars in the crowded central region of the globular cluster NGC 6981 are presented. The observations were made using the electron multiplying CCD (EMCCD) camera at the ... [more ▼]

Two previously unknown variable stars in the crowded central region of the globular cluster NGC 6981 are presented. The observations were made using the electron multiplying CCD (EMCCD) camera at the Danish 1.54 m Telescope at La Silla, Chile. The two variableswere not previously detected by conventional CCD imaging because of their proximity to a bright star. This discovery demonstrates that EMCCDs are a powerful tool for performing high-precision time-series photometry in crowded fields and near bright stars, especially when combined with difference image analysis. Based on data collected by MiNDSTEp with the Danish 1.54 m telescope. [less ▲]

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See detailTwo new SB2 binaries with main sequence B-type pulsators in the Kepler field
Pápics, P. I.; Tkachenko, A.; Aerts, C. et al

in Astronomy and Astrophysics (2013), 553(127),

Context: OB stars are important in the chemistry and evolution of the Universe, but the sample of targets well understood from an asteroseismological point of view is still too limited to provide feedback ... [more ▼]

Context: OB stars are important in the chemistry and evolution of the Universe, but the sample of targets well understood from an asteroseismological point of view is still too limited to provide feedback on the current evolutionary models. Our study extends this sample with two spectroscopic binary systems. AIMS. Our goal is to provide orbital solutions, fundamental parameters and abundances from disentangled high-resolution high signal-to-noise spectra, as well as to analyse and interpret the variations in the Kepler light curve of these carefully selected targets. This way we continue our efforts to map the instability strips of beta Cep and SPB stars using the combination of high-resolution ground-based spectroscopy and uninterrupted space-based photometry. Methods: We fit Keplerian orbits to radial velocities measured from selected absorption lines of high-resolution spectroscopy using synthetic composite spectra to obtain orbital solutions. We use revised masks to obtain optimal light curves from the original pixel-data from the Kepler satellite, which provided better long term stability compared to the pipeline processed light curves. We use various time-series analysis tools to explore and describe the nature of variations present in the light curve. Results: We find two eccentric double-lined spectroscopic binary systems containing a total of three main sequence B-type stars (and one F-type component) of which at least one in each system exhibits light variations. The light curve analysis (combined with spectroscopy) of the system of two B stars points towards the presence of tidally excited g modes in the primary component. We interpret the variations seen in the second system as classical g mode pulsations driven by the kappa mechanism in the B type primary, and explain the unexpected power in the p mode region as a result of nonlinear resonant mode excitation. [less ▲]

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See detailChemical surface inhomogeneities in late B-type stars with Hg and Mn peculiarity: I. Spot evolution in HD 11753 on short and long time scales
Korhonen, Heidi; Gonzalez, J.F.; Briquet, Maryline ULg et al

in Astronomy and Astrophysics (2013), 553

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