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See detailγ Doradus stars as test of angular momentum transport models
Ouazzani, R-M; Marques, J P; Goupil, M-J et al

in Astronomy and Astrophysics (in press)

Helioseismology and asteroseismology of red giant stars have shown that the distribution of angular momentum in stellar interiors, and its evolution with time remains an open issue in stellar physics ... [more ▼]

Helioseismology and asteroseismology of red giant stars have shown that the distribution of angular momentum in stellar interiors, and its evolution with time remains an open issue in stellar physics. Owing to the unprecedented quality of Kepler photometry, we are able to seismically infer internal rotation rates in γDoradus stars, which provide the MS counterpart to the red-giants puzzle. We confront these internal rotation rates to stellar evolution models with rotationally induced transport of angular momentum, in order to test angular momentum transport mechanisms. We used a stellar model-independent method developed by Christophe et al. in order to obtain seismically inferred, buoyancy radii and near-core rotation for 37 γ Doradus stars observed by Kepler. We show that the buoyancy radius can be used as a reliable evolution indicator for field stars on the MS. We computed rotating evolutionary models including transport of angular momentum in radiative zones, following Zahn and Maeder, with the CESTAM code. This code calculates the rotational history of stars from the birth line to the tip of the RGB. The initial angular momentum content has to be set initially, which is done by fitting rotation periods in young stellar clusters. We show a clear disagreement between the near-core rotation rates measured in the sample and the rotation rates obtained from evolutionary models including rotationally induced transport following Zahn (1992). These results show a disagreement similar to that of the Sun and red giant stars. This suggests the existence of missing mechanisms responsible for the braking of the core before and along the MS. The efficiency of the missing mechanisms is investigated. The transport of angular momentum as formalized by Zahn and Maeder cannot explain the measurements of near-core rotation in main-sequence intermediate-mass stars we have at hand. [less ▲]

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See detailLower atmosphere and pressure evolution on Pluto from ground-based stellar occultations, 1988-2016
Meza, E.; Sicardy, B.; Assafin, M. et al

in Astronomy and Astrophysics (2019), 625(A42), 21

Context. The tenuous nitrogen (N[SUB]2[/SUB]) atmosphere on Pluto undergoes strong seasonal effects due to high obliquity and orbital eccentricity, and has recently (July 2015) been observed by the New ... [more ▼]

Context. The tenuous nitrogen (N[SUB]2[/SUB]) atmosphere on Pluto undergoes strong seasonal effects due to high obliquity and orbital eccentricity, and has recently (July 2015) been observed by the New Horizons spacecraft. <BR /> Aims: The main goals of this study are (i) to construct a well calibrated record of the seasonal evolution of surface pressure on Pluto and (ii) to constrain the structure of the lower atmosphere using a central flash observed in 2015. <BR /> Methods: Eleven stellar occultations by Pluto observed between 2002 and 2016 are used to retrieve atmospheric profiles (density, pressure, temperature) between altitude levels of 5 and 380 km (i.e. pressures from 10 μbar to 10 nbar). <BR /> Results: (i) Pressure has suffered a monotonic increase from 1988 to 2016, that is compared to a seasonal volatile transport model, from which tight constraints on a combination of albedo and emissivity of N[SUB]2[/SUB] ice are derived. (ii) A central flash observed on 2015 June 29 is consistent with New Horizons REX profiles, provided that (a) large diurnal temperature variations (not expected by current models) occur over Sputnik Planitia; and/or (b) hazes with tangential optical depth of 0.3 are present at 4-7 km altitude levels; and/or (c) the nominal REX density values are overestimated by an implausibly large factor of 20%; and/or (d) higher terrains block part of the flash in the Charon facing hemisphere. [less ▲]

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See detailThe shape of (7) Iris as evidence of an ancient large impact?
Hanuš, J.; Marsset, M.; Vernazza, P. et al

in Astronomy and Astrophysics (2019), 624(A121), 17

Context. Asteroid (7) Iris is an ideal target for disk-resolved imaging owing to its brightness (V 7-8) and large angular size of 0.33'' during its apparitions. Iris is believed to belong to the category ... [more ▼]

Context. Asteroid (7) Iris is an ideal target for disk-resolved imaging owing to its brightness (V 7-8) and large angular size of 0.33'' during its apparitions. Iris is believed to belong to the category of large unfragmented asteroids that avoided internal differentiation, implying that its current shape and topography may record the first few 100 Myr of the solar system's collisional evolution. <BR /> Aims: We recovered information about the shape and surface topography of Iris from disk-resolved VLT/SPHERE/ZIMPOL images acquired in the frame of our ESO large program. <BR /> Methods: We used the All-Data Asteroid Modeling (ADAM) shape reconstruction algorithm to model the 3D shape of Iris, using optical disk-integrated data and disk-resolved images from SPHERE and earlier AO systems as inputs. We analyzed the SPHERE images and our model to infer the asteroid's global shape and the morphology of its main craters. <BR /> Results: We present the 3D shape, volume-equivalent diameter D[SUB]eq[/SUB] = 214 ± 5 km, and bulk density ρ = 2.7 ± 0.3 g cm[SUP]-3[/SUP] of Iris. Its shape appears to be consistent with that of an oblate spheroid with a large equatorial excavation. We identified eight putative surface features 20-40 km in diameter detected at several epochs, which we interpret as impact craters, and several additional crater candidates. Craters on Iris have depth-to-diameter ratios that are similar to those of analogous 10 km craters on Vesta. <BR /> Conclusions: The bulk density of Iris is consistent with that of its meteoritic analog based on spectroscopic observations, namely LL ordinary chondrites. Considering the absence of a collisional family related to Iris and the number of large craters on its surface, we suggest that its equatorial depression may be the remnant of an ancient (at least 3 Gyr) impact. Iris's shape further opens the possibility that large planetesimals formed as almost perfect oblate spheroids. Finally, we attribute the difference in crater morphology between Iris and Vesta to their different surface gravities, and the absence of a substantial impact-induced regolith on Iris. The reduced images 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/624/A121">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/624/A121</A>Based on observations made with ESO Telescopes at the Paranal Observatory under programme ID 199.C-0074 (PI: P. Vernazza) and 086.C-0785 (PI: B. Carry). [less ▲]

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See detailHigh resolution optical spectroscopy of the N2-rich comet C/2016 R2 (PanSTARRS)
Opitom, C.; Hutsemekers, Damien ULiege; Jehin, Emmanuel ULiege et al

in Astronomy and Astrophysics (2019), 624

Context. Early observations of comet C/2016 R2 (PanSTARRS) have shown that the composition of this comet is very peculiar. Radio observations have revealed a CO-rich and HCN-poor comet and an optical coma ... [more ▼]

Context. Early observations of comet C/2016 R2 (PanSTARRS) have shown that the composition of this comet is very peculiar. Radio observations have revealed a CO-rich and HCN-poor comet and an optical coma dominated by strong emission bands of CO[SUP]+[/SUP] and, more surprisingly, N[SUB]2[/SUB][SUP]+[/SUP]. <BR /> Aims: The strong detection of N[SUB]2[/SUB][SUP]+[/SUP] in the coma of C/2016 R2 provided an ideal opportunity to measure the [SUP]14[/SUP]N/[SUP]15[/SUP]N isotopic ratio directly from N[SUB]2[/SUB][SUP]+[/SUP] for the first time, and to estimate the N[SUB]2[/SUB]/CO ratio, which is an important diagnostic to constrain formation models of planetesimals, in addition to the more general study of coma composition. <BR /> Methods: We obtained high resolution spectra of the comet in February 2018 when it was at 2.8 au from the Sun. We used the UVES spectrograph of the European Southern Observatory Very Large Telescope, complemented with narrowband images obtained with the TRAPPIST telescopes. <BR /> Results: We detect strong emissions from the N[SUB]2[/SUB][SUP]+[/SUP] and CO[SUP]+[/SUP] ions, but also CO[SUB]2[/SUB][SUP]+[/SUP], emission lines from the CH radical, and much fainter emissions of the CN, C[SUB]2[/SUB], and C[SUB]3[/SUB] radicals that were not detected in previous observations of this comet. We do not detect OH or H[SUB]2[/SUB]O[SUP]+[/SUP], and we derive an upper limit of the H[SUB]2[/SUB]O[SUP]+[/SUP]/CO[SUP]+[/SUP] ratio of 0.4, implying that the comet has a low water abundance. We measure a N[SUB]2[/SUB][SUP]+[/SUP]/CO[SUP]+[/SUP] ratio of 0.06 ± 0.01. The non-detection of NH[SUB]2[/SUB] indicates that most of the nitrogen content of the comet is in N[SUB]2[/SUB]. Together with the high N[SUB]2[/SUB][SUP]+[/SUP]/CO[SUP]+[/SUP] ratio, this could indicate a low formation temperature of the comet or that the comet is a fragment of a large differentiated Kuiper Belt object. The CO[SUB]2[/SUB][SUP]+[/SUP]/CO[SUP]+[/SUP] ratio is 1.1 ± 0.3. We do not detect [SUP]14[/SUP]N[SUP]15[/SUP]N[SUP]+[/SUP] lines and can only put a lower limit on the [SUP]14[/SUP]N/[SUP]15[/SUP]N ratio (measured from N[SUB]2[/SUB][SUP]+[/SUP]) of about 100, which is compatible with measurements of the same isotopic ratio for NH[SUB]2[/SUB] and CN in other comets. Finally, in addition to the [OI] and [CI] forbidden lines, we detect for the first time the forbidden nitrogen lines [NI] doublet at 519.79 and 520.03 nm in the coma of a comet. [less ▲]

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See detailClosing the gap between Earth-based and interplanetary mission observations: Vesta seen by VLT/SPHERE
Fétick, R. J. L.; Jorda, L.; Vernazza, P. et al

in Astronomy and Astrophysics (2019), 623

Context. Over the past decades, several interplanetary missions have studied small bodies in situ, leading to major advances in our understanding of their geological and geophysical properties. These ... [more ▼]

Context. Over the past decades, several interplanetary missions have studied small bodies in situ, leading to major advances in our understanding of their geological and geophysical properties. These missions, however, have had a limited number of targets. Among them, the NASA Dawn mission has characterised in detail the topography and albedo variegation across the surface of asteroid (4) Vesta down to a spatial resolution of 20 m pixel[SUP]-1[/SUP] scale. <BR /> Aims: Here our aim was to determine how much topographic and albedo information can be retrieved from the ground with VLT/SPHERE in the case of Vesta, having a former space mission (Dawn) providing us with the ground truth that can be used as a benchmark. <BR /> Methods: We observed Vesta with VLT/SPHERE/ZIMPOL as part of our ESO large programme (ID 199.C-0074) at six different epochs, and deconvolved the collected images with a parametric point spread function (PSF). We then compared our images with synthetic views of Vesta generated from the 3D shape model of the Dawn mission, on which we projected Vesta's albedo information. <BR /> Results: We show that the deconvolution of the VLT/SPHERE images with a parametric PSF allows the retrieval of the main topographic and albedo features present across the surface of Vesta down to a spatial resolution of 20-30 km. Contour extraction shows an accuracy of 1 pixel (3.6 mas). The present study provides the very first quantitative estimate of the accuracy of ground-based adaptive-optics imaging observations of asteroid surfaces. <BR /> Conclusions: In the case of Vesta, the upcoming generation of 30-40 m telescopes (ELT, TMT, GMT) should in principle be able to resolve all of the main features present across its surface, including the troughs and the north-south crater dichotomy, provided that they operate at the diffraction limit. Reduced images of Table A.1 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/623/A6">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/623/A6</A>Based on observations made with ESO Telescopes at the Paranal Observatory under programme ID 199.C-0074 (PI: P. Vernazza). [less ▲]

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See detailHints about the multiplicity of WR 133 based on multiepoch radio observations
De Becker, Michaël ULiege; Isequilla, Natacha L.; Benaglia, Paula

in Astronomy and Astrophysics (2019), 623

Several tens of massive binary systems display indirect, or even strong evidence for non-thermal radio emission, hence their particle accelerator status. These objects are referred to as particle ... [more ▼]

Several tens of massive binary systems display indirect, or even strong evidence for non-thermal radio emission, hence their particle accelerator status. These objects are referred to as particle-accelerating colliding-wind binaries (PACWBs). WR 133 is one of the shortest period Wolf-Rayet + O systems in this category, and is therefore critical to characterize the boundaries of the parameter space adequate for particle acceleration in massive binaries. Our methodology consists in analyzing JVLA observations of WR 133 at different epochs to search for compelling evidence for a phase-locked variation attributable to synchrotron emission produced in the colliding-wind region. New data obtained during two orbits reveal a steady and thermal emission spectrum, in apparent contradiction with the previous detection of non-thermal emission. The thermal nature of the radio spectrum along the 112.4-d orbit is supported by the strong free-free absorption by the dense stellar winds, and shows that the simple binary scenario cannot explain the non-thermal emission reported previously. Alternatively, a triple system scenario with a wide, outer orbit would fit with the observational facts reported previously and in this paper, albeit no hint for the existence of a third component exists to date. The epoch-dependent nature of the identification of synchrotron radio emission in WR 133 emphasizes the issue of observational biases in the identification of PACWBs, that undoubtedly affect the present census of PACWB among colliding-wind binaries. [less ▲]

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See detailThe Solar Orbiter Heliospheric Imager (SoloHI)
Howard, R.A.; Rochus, Pierre ULiege

in Astronomy and Astrophysics (2019)

Aims. We present the design and pre-launch performance of the Solar Orbiter Heliospheric Imager (SoloHI) which is an instrument prepared for inclusion on the ESA/NASA Solar Orbiter mission, currently ... [more ▼]

Aims. We present the design and pre-launch performance of the Solar Orbiter Heliospheric Imager (SoloHI) which is an instrument prepared for inclusion on the ESA/NASA Solar Orbiter mission, currently scheduled for launch in 2020. Methods. The goal of this paper is to provide details of the SoloHI instrument concept, design and pre-flight performance to give a potential user of the data a better understanding of how the observations are collected and the sources that contribute to the signal. Results. The paper discusses the science objectives, including the SoloHI-specific aspects, before presenting the design concepts, including the optics, mechanical, thermal, electrical, and ground processing. Finally, the list of planned data products is also presented. Conclusions. The performance measurements of the various instrument parameters meet or exceed the requirements derived from the mission science objectives. SoloHI is poised to take its place as a vital contributor to the science success of the Solar Orbiter mission. [less ▲]

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See detailCombining multiple structural inversions to constrain the solar modelling problem
Buldgen, Gaël ULiege; Salmon, Sébastien ULiege; Noels-Grötsch, Arlette ULiege et al

in Astronomy and Astrophysics (2019), 621

Context. The Sun is the most studied of all stars, which serves as a reference for all other observed stars in the Universe. Furthermore, it also serves the role of a privileged laboratory of fundamental ... [more ▼]

Context. The Sun is the most studied of all stars, which serves as a reference for all other observed stars in the Universe. Furthermore, it also serves the role of a privileged laboratory of fundamental physics and can help us better understand processes occuring in conditions irreproducible on Earth. However, our understanding of our star is currently lessened by the so-called solar modelling problem, resulting from comparisons of theoretical solar models to helioseismic constraints. These discrepancies can stem from various causes, such as the radiative opacities, the equation of state as well as the mixing of the chemical elements. <BR /> Aims: By analysing the potential of combining information from multiple seismic inversions, our aim is to help disentangle the origins of the solar modelling problem. <BR /> Methods: We combined inversions of the adiabatic sound speed, an entropy proxy and the Ledoux discriminant with other constraints such as the position of the base of the convective zone and the photospheric helium abundance. First, we tested various combinations of standard ingredients available for solar modelling such as abundance tables, equation of state, formalism for convection and diffusion and opacity tables. Second, we studied the diagnostic potential of the inversions on models including ad hoc modifications of the opacity profile and additional mixing below the convective envelope. <BR /> Results: We show that combining inversions provides stringent constraints on the required modifications to the solar ingredients, far beyond what can be achieved from sound speed inversions alone. We constrain the form and amplitude of the opacity increase required in solar models and show that a 15% increase at log T = 6.35 provides a significant improvement, but is insufficient on its own. A more global increase in the opacity, within the uncertainties of the current tables, coupled with a localized additional mixing at the bottom of the convective zone provides the best agreement for low-metallicity models. We show that high-metallicity models do not satisfy all the inversion results. We conclude that the solar modelling problem likely occurs from multiple small contributors, as other ingredients such as the equation of state or the formalism of convection can induce small but significant changes in the models and that using phase shift analyses combined with our approach is the next step for a better understanding of the inaccuracies of solar models just below the convective envelope. [less ▲]

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See detailBRITE photometry of the massive post-RLOF system HD149 404
Rauw, Grégor ULiege; Pigulski, A.; Nazé, Yaël ULiege et al

in Astronomy and Astrophysics (2019), 621

Context. HD 149 404 is an evolved non-eclipsing O-star binary that has previously undergone a Roche lobe overflow interaction. <BR /> Aims: Understanding some key properties of the system requires a ... [more ▼]

Context. HD 149 404 is an evolved non-eclipsing O-star binary that has previously undergone a Roche lobe overflow interaction. <BR /> Aims: Understanding some key properties of the system requires a determination of the orbital inclination and of the dimensions of the components. <BR /> Methods: The BRITE-Heweliusz satellite was used to collect photometric data of HD 149 404. Additional photometry was retrieved from the SMEI archive. These data were analysed using a suite of period search tools. The orbital part of the lightcurve was modelled with the nightfall binary star code. The Gaia-DR2 parallax of HD 149 404 was used to provide additional constraints. <BR /> Results: The periodograms reveal a clear orbital modulation of the lightcurve with a peak-to-peak amplitude near 0.04 mag. The remaining non-orbital part of the variability is consistent with red noise. The lightcurve folded with the orbital period reveals ellipsoidal variations, but no eclipses. The minimum when the secondary star is in inferior conjunction is deeper than the other minimum due to mutual reflection effects between the stars. Combined with the Gaia-DR2 parallaxes, the photometric data indicate an orbital inclination in the range of 23°-31° and a Roche lobe filling factor of the secondary larger than or equal to 0.96. <BR /> Conclusions: The luminosity of the primary star is consistent with its present-day mass, whereas the more evolved secondary appears overluminous for its mass. We confirm that the primary's rotation period is about half the orbital period. Both features most probably stem from the past Roche lobe overflow episode. Based on data collected by the BRITE-Constellation satellite mission, designed, built, launched, operated and supported by the Austrian Research Promotion Agency (FFG), the University of Vienna, the Technical University of Graz, the University of Innsbruck, the Canadian Space Agency (CSA), the University of Toronto Institute for Aerospace Studies (UTIAS), the Foundation for Polish Science & Technology (FNiTP MNiSW), and the National Science Centre (NCN). [less ▲]

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See detailAsteroseismology of evolved stars to constrain the internal transport of angular momentum. I. Efficiency of transport during the subgiant phase
Eggenberger, P.; Deheuvels, S.; Miglio, A. et al

in Astronomy and Astrophysics (2019), 621

Context. The observations of solar-like oscillations in evolved stars have brought important constraints on their internal rotation rates. To correctly reproduce these data, an efficient transport ... [more ▼]

Context. The observations of solar-like oscillations in evolved stars have brought important constraints on their internal rotation rates. To correctly reproduce these data, an efficient transport mechanism is needed in addition to the transport of angular momentum by meridional circulation and shear instability. The efficiency of this undetermined process is found to increase both with the mass and the evolutionary stage during the red giant phase. <BR /> Aims: We study the efficiency of the transport of angular momentum during the subgiant phase. <BR /> Methods: The efficiency of the unknown transport mechanism is determined during the subgiant phase by comparing rotating models computed with an additional corresponding viscosity to the asteroseismic measurements of both core and surface-rotation rates for six subgiants observed by the Kepler spacecraft. We then investigate the change in the efficiency of this transport of angular momentum with stellar mass and evolution during the subgiant phase. <BR /> Results: The precise asteroseismic measurements of both core and surface-rotation rates available for the six Kepler targets enable a precise determination of the efficiency of the transport of angular momentum needed for each of these subgiants. These results are found to be insensitive to all the uncertainties related to the modelling of rotational effects before the post-main sequence (poMS) phase. An interesting exception in this context is the case of young subgiants (typical values of log(g) close to 4), because their rotational properties are sensitive to the degree of radial differential rotation on the main sequence (MS). These young subgiants constitute therefore perfect targets to constrain the transport of angular momentum on the MS from asteroseismic observations of evolved stars. As for red giants, we find that the efficiency of the additional transport process increases with the mass of the star during the subgiant phase. However, the efficiency of this undetermined mechanism decreases with evolution during the subgiant phase, contrary to what is found for red giants. Consequently, a transport process with an efficiency that increases with the degree of radial differential rotation cannot account for the core-rotation rates of subgiants, while it correctly reproduces the rotation rates of red giant stars. This suggests that the physical nature of the additional mechanism needed for the internal transport of angular momentum may be different in subgiant and red giant stars. [less ▲]

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See detailComprehensive stellar seismic analysis : New method exploiting the glitches information in solar-like pulsators
Farnir, Martin ULiege; Dupret, Marc-Antoine ULiege; Salmon, Sébastien ULiege et al

in Astronomy and Astrophysics (2019)

Aims. We develop a method that provides a comprehensive analysis of the oscillation spectra of solar-like pulsators. We define new seismic indicators that should be as uncorrelated and as precise as ... [more ▼]

Aims. We develop a method that provides a comprehensive analysis of the oscillation spectra of solar-like pulsators. We define new seismic indicators that should be as uncorrelated and as precise as possible and should hold detailed information about stellar interiors. This is essential to improve the quality of the results obtained from asteroseismology as it will provide better stellar models which in turn can be used to refine inferences made in exoplanetology and galactic archaeology. Methods. The presented method – WhoSGlAd – relies on Gram-Schmidt’s orthogonalisation process. A Euclidean vector sub-space of functions is defined and the oscillation frequencies are projected over an orthonormal basis in a specific order. This allowed us to obtain independent coefficients that we combined to define independent seismic indicators. Results. The developed method has been shown to be stable and to converge efficiently for solar-like pulsators. Thus, detailed and precise inferences can be obtained on the mass, the age, the chemical composition and the undershooting in the interior of the studied stars. However, attention has to be paid when studying the helium glitch as there seems to be a degeneracy between the influence of the helium abundance and that of the heavy elements on the glitch amplitude. As an example, we analyse the 16CygA (HD 186408) oscillation spectrum to provide an illustration of the capabilities of the method. [less ▲]

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See detailARGOS at the LBT. Binocular laser guided ground layer adaptive optics
Rabien, S.; Angel, R.; Barl, L. et al

in Astronomy and Astrophysics (2018), 621

Having completed its commissioning phase, the Advanced Rayleigh guided Ground-layer adaptive Optics System (ARGOS) facility is coming online for scientific observations at the Large Binocular Telescope ... [more ▼]

Having completed its commissioning phase, the Advanced Rayleigh guided Ground-layer adaptive Optics System (ARGOS) facility is coming online for scientific observations at the Large Binocular Telescope (LBT). With six Rayleigh laser guide stars in two constellations and the corresponding wavefront sensing, ARGOS corrects the ground-layer distortions for both LBT 8.4 m eyes with their adaptive secondary mirrors. Under regular observing conditions, this set-up delivers a point spread function (PSF) size reduction by a factor of 2–3 compared to a seeing-limited operation. With the two LUCI infrared imaging and multi-object spectroscopy instruments receiving the corrected images, observations in the near-infrared can be performed at high spatial and spectral resolution. We discuss the final ARGOS technical set-up and the adaptive optics performance. We show that imaging cases with ground-layer adaptive optics (GLAO) are enhancing several scientific programmes, from cluster colour magnitude diagrams and Milky Way embedded star formation, to nuclei of nearby galaxies or extragalactic lensing fields. In the unique combination of ARGOS with the multi-object near-infrared spectroscopy available in LUCI over a 4 × 4 arcmin field of view, the first scientific observations have been performed on local and high-z objects. Those high spatial and spectral resolution observations demonstrate the capabilities now at hand with ARGOS at the LBT. [less ▲]

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See detailDetermination of physical parameters of particle-accelerating colliding-wind binaries based on generalized partition considerations
De Becker, Michaël ULiege

in Astronomy and Astrophysics (2018), 620

The sub-set of massive binaries known to accelerate particles, the so-called category of particle-accelerating colliding-wind binaries (PACWBs), constitutes a valuable laboratory for investigating the non ... [more ▼]

The sub-set of massive binaries known to accelerate particles, the so-called category of particle-accelerating colliding-wind binaries (PACWBs), constitutes a valuable laboratory for investigating the non-thermal physics in stellar environments. In particular, their synchrotron emitter status allows us to derive some basic properties of their population of relativistic electrons. In this paper, considerations about energy partitions (not restricted to equipartition or minimum energy) are developed to derive relevant physical parameters of PACWBs in an appropriate assumption context. This approach was applied to three PACWBs with known stellar wind and orbital parameters, along with rather well-known radio properties. For long-period systems, a local magnetic field of the order of 0.1-10 mG was determined for a wide range of assumptions on partition parameters, while values of a few G are obtained for the shorter period system we investigated. Normalization parameters of the relativistic electron populations were also determined. Synchrotron self-absorption appears to be an unlikely turn-over process for long-period systems, while it may compete with free-free absorption for a shorter period object. Our results are discussed in the context of the energy budget of non-thermal processes in PACWBs, and prospects for high energy emission are also addressed. The sensitivity of this approach, applied for the first time to PACWBs, was also investigated through a critical discussion of the dependence of determined physical quantities on adopted and assumed parameters. Even though this method is certainly not adequate to reproduce the physics of PACWBs in detail, it offers the advantage of allowing for the determination of valuable average quantities provided a few fundamental parameters and measurements are known, without the need of any detailed hydrodynamic and radiative modelling. In the absence of any relevant measurement of non-thermal radiation in the high-energy domain, the method presented here constitutes the most straightforward and accessible approach to date to discuss physical parameters that are relevant for the non-thermal physics of PACWBs. [less ▲]

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See detailAsteroseismic potential of CHEOPS
Moya, A.; Barceló Forteza, S.; Bonfanti, Andrea ULiege et al

in Astronomy and Astrophysics (2018), 620

Context. Asteroseismology has been impressively boosted during the last decade mainly thanks to space missions such as Kepler/K2 and CoRoT. This has a large impact, in particular, in exoplanetary sciences ... [more ▼]

Context. Asteroseismology has been impressively boosted during the last decade mainly thanks to space missions such as Kepler/K2 and CoRoT. This has a large impact, in particular, in exoplanetary sciences since the accurate characterization of the exoplanets is convoluted in most cases with the characterization of their hosting star. In the decade before the expected launch of the ESA mission PLATO 2.0, only two important missions will provide short-cadence high-precision photometric time-series: NASA–TESS and ESA–CHEOPS missions, both having high capabilities for exoplanetary sciences. Aims. In this work we want to explore the asteroseismic potential of CHEOPS time-series. Methods. Following the works estimating the asteroseismic potential of Kepler and TESS, we have analysed the probability of detecting solar-like pulsations using CHEOPS light-curves. Since CHEOPS will collect runs with observational times from hours up to a few days, we have analysed the accuracy and precision we can obtain for the estimation of νmax. This is the only asteroseismic observable we can recover using CHEOPS observations. Finally, we have analysed the impact of knowing νmax in the characterization of exoplanet host stars. Results. Using CHEOPS light-curves with the expected observational times we can determine νmax for massive G and F-type stars from late main sequence (MS) on, and for F, G, and K-type stars from post-main sequence on with an uncertainty lower than a 5%. For magnitudes V <  12 and observational times from eight hours up to two days, the HR zone of potential detectability changes. The determination of νmax leads to an internal age uncertainty reduction in the characterization of exoplContext. Asteroseismology has been impressively boosted during the last decade mainly thanks to space missions such as Kepler/K2 and CoRoT. This has a large impact, in particular, in exoplanetary sciences since the accurate characterization of the exoplanets is convoluted in most cases with the characterization of their hosting star. In the decade before the expected launch of the ESA mission PLATO 2.0, only two important missions will provide short-cadence high-precision photometric time-series: NASA–TESS and ESA–CHEOPS missions, both having high capabilities for exoplanetary sciences. Aims. In this work we want to explore the asteroseismic potential of CHEOPS time-series. Methods. Following the works estimating the asteroseismic potential of Kepler and TESS, we have analysed the probability of detecting solar-like pulsations using CHEOPS light-curves. Since CHEOPS will collect runs with observational times from hours up to a few days, we have analysed the accuracy and precision we can obtain for the estimation of νmax. This is the only asteroseismic observable we can recover using CHEOPS observations. Finally, we have analysed the impact of knowing νmax in the characterization of exoplanet host stars. Results. Using CHEOPS light-curves with the expected observational times we can determine νmax for massive G and F-type stars from late main sequence (MS) on, and for F, G, and K-type stars from post-main sequence on with an uncertainty lower than a 5%. For magnitudes V <  12 and observational times from eight hours up to two days, the HR zone of potential detectability changes. The determination of νmax leads to an internal age uncertainty reduction in the characterization of exoplanet host stars from 52% to 38%; mass uncertainty reduction from 2.1% to 1.8%; radius uncertainty reduction from 1.8% to 1.6%; density uncertainty reduction from 5.6% to 4.7%, in our best scenarios.anet host stars from 52% to 38%; mass uncertainty reduction from 2.1% to 1.8%; radius uncertainty reduction from 1.8% to 1.6%; density uncertainty reduction from 5.6% to 4.7%, in our best scenarios. [less ▲]

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See detailXXL Survey XXI. The environment and clustering of X-ray AGN in the XXL-South field
Melnyk, O.; Elyiv, A.; Smolcic, V. et al

in Astronomy and Astrophysics (2018), 620(A6),

This work is part of a series of studies focusing on the environment and the properties of the X-ray selected active galactic nuclei (AGN) population from the XXL survey. The present survey, given its ... [more ▼]

This work is part of a series of studies focusing on the environment and the properties of the X-ray selected active galactic nuclei (AGN) population from the XXL survey. The present survey, given its large area, continuity, extensive multiwavelength coverage, and large-scale structure information, is ideal for this kind of study. Here, we focus on the XXL-South (XXL-S) field. Our main aim is to study the environment of the various types of X-ray selected AGN and investigate its possible role in AGN triggering and evolution. We studied the large-scale (>1 Mpc) environment up to redshift z=1 using the nearest neighbour distance method to compare various pairs of AGN types. We also investigated the small-scale environment (<0.4 Mpc) by calculating the local overdensities of optical galaxies. In addition, we built a catalogue of AGN concentrations with two or more members using the hierarchical clustering method and we correlated them with the X-ray galaxy clusters detected in the XXL survey. It is found that radio detected X-ray sources are more obscured than non-radio ones, though not all radio sources are obscured AGN. We did not find any significant differences in the large-scale clustering between luminous and faint X-ray AGN, or between obscured and unobscured ones, or between radio and non-radio sources. At local scales (<0.4 Mpc), AGN typically reside in overdense regions, compared to non-AGN; however, no differences were found between the various types of AGN. A majority of AGN concentrations with two or more members are found in the neighbourhood of X-ray galaxy clusters within <25-45 Mpc. Our results suggest that X-ray AGN are typically located in supercluster filaments, but they are also found in over- and underdense regions. [less ▲]

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See detailActivity induced variation in spin-orbit angles as derived from Rossiter-McLaughlin measurements
Oshagh, M.; Triaud, A. H. M. J.; Burdanov, Artem ULiege et al

in Astronomy and Astrophysics (2018), 619(150),

One of the most powerful methods used to estimate sky-projected spin-orbit angles of exoplanetary systems is through a spectroscopic transit observation known as the Rossiter-McLaughlin (RM) effect. So ... [more ▼]

One of the most powerful methods used to estimate sky-projected spin-orbit angles of exoplanetary systems is through a spectroscopic transit observation known as the Rossiter-McLaughlin (RM) effect. So far mostly single RM observations have been used to estimate the spin-orbit angle, and thus there have been no studies regarding the variation of estimated spin-orbit angle from transit to transit. Stellar activity can alter the shape of photometric transit light curves and in a similar way they can deform the RM signal. In this paper we discuss several RM observations, obtained using the HARPS spectrograph, of known transiting planets that all transit extremely active stars, and by analyzing them individually we assess the variation in the estimated spin-orbit angle. Our results reveal that the estimated spin-orbit angle can vary significantly (up to 42 degrees) from transit to transit, due to variation in the configuration of stellar active regions over different nights. This finding is almost two times larger than the expected variation predicted from simulations. We could not identify any meaningful correlation between the variation of estimated spin-orbit angles and the stellar magnetic activity indicators. We also investigated two possible approaches to mitigate the stellar activity influence on RM observations. The first strategy was based on obtaining several RM observations and folding them to reduce the stellar activity noise. Our results demonstrated that this is a feasible and robust way to overcome this issue. The second approach is based on acquiring simultaneous high-precision short-cadence photometric transit light curves using TRAPPIST/SPECULOOS telescopes, which provide more information about the stellar active region's properties and allow a better RM modeling. [less ▲]

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See detail(16) Psyche: A mesosiderite-like asteroid?
Viikinkoski, M.; Vernazza, P.; Hanuš, J. et al

in Astronomy and Astrophysics (2018), 619

Context. Asteroid (16) Psyche is the target of the NASA Psyche mission. It is considered one of the few main-belt bodies that could be an exposed proto-planetary metallic core and that would thus be ... [more ▼]

Context. Asteroid (16) Psyche is the target of the NASA Psyche mission. It is considered one of the few main-belt bodies that could be an exposed proto-planetary metallic core and that would thus be related to iron meteorites. Such an association is however challenged by both its near- and mid-infrared spectral properties and the reported estimates of its density. <BR /> Aims: Here, we aim to refine the density of (16) Psyche to set further constraints on its bulk composition and determine its potential meteoritic analog. <BR /> Methods: We observed (16) Psyche with ESO VLT/SPHERE/ZIMPOL as part of our large program (ID 199.C-0074). We used the high angular resolution of these observations to refine Psyche's three-dimensional (3D) shape model and subsequently its density when combined with the most recent mass estimates. In addition, we searched for potential companions around the asteroid. <BR /> Results: We derived a bulk density of 3.99 ± 0.26 g cm[SUP]-3[/SUP] for Psyche. While such density is incompatible at the 3-sigma level with any iron meteorites (˜7.8 g cm[SUP]-3[/SUP]), it appears fully consistent with that of stony-iron meteorites such as mesosiderites (density ˜4.25 g cm[SUP]-3[/SUP]). In addition, we found no satellite in our images and set an upper limit on the diameter of any non-detected satellite of 1460 ± 200 m at 150 km from Psyche (0.2% × R[SUB]Hill[/SUB], the Hill radius) and 800 ± 200 m at 2000 km (3% × R[SUB]Hill[/SUB]). <BR /> Conclusions: Considering that the visible and near-infrared spectral properties of mesosiderites are similar to those of Psyche, there is merit to a long-published initial hypothesis that Psyche could be a plausible candidate parent body for mesosiderites. Based on observations made with 1) ESO Telescopes at the La Silla Paranal Observatory under programs 086.C-0785 (PI Carry) and 199.C-0074 (PI Vernazza); and 2) the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.Tables A1 and A2 and reduced images 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://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/619/L3">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/619/L3</A> [less ▲]

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See detailMonitoring of the activity and composition of comets 41P/Tuttle-Giacobini-Kresak and 45P/Honda-Mrkos-Pajdusakova
Moulane, Y.; Jehin, Emmanuel ULiege; Opitom, C. et al

in Astronomy and Astrophysics (2018), 619

We report on photometry and imaging of the Jupiter Family Comets 41P/Tuttle-Giacobini-Kresak and 45P/Honda-Mrkos-Pajdusakova with the TRAPPIST-North telescope. We observed 41P on 34 nights from February ... [more ▼]

We report on photometry and imaging of the Jupiter Family Comets 41P/Tuttle-Giacobini-Kresak and 45P/Honda-Mrkos-Pajdusakova with the TRAPPIST-North telescope. We observed 41P on 34 nights from February 16, 2017 to July 27, 2017 pre- and post-perihelion (r$_h$=1.04 au), while we collected data for comet 45P from February 10 to March 30 after perihelion (r$_h$=0.53 au). We computed the production rates of the daughter species OH, NH, CN, C$_3$ and C$_2$ and we measured the dust proxy, Af$\rho$, for both comets. The peak of water production rate of 41P was (3.46$\pm$0.20)$\times$10$^{27}$ molecules/s on April 3, 2017 when the comet was at 1.05 au from the Sun. We have shown that the activity of 41P is decreasing by about 30% to 40% from one apparition to the next. We measured a mean water production rate for 45P of (1.43$\pm$0.62)$\times$10$^{27}$ molecules/s during a month after perihelion. Our results show that these Jupiter Family Comets had low gas and dust activity and no outburst was detected. Relative abundances, expressed as ratios of production rates and Af$\rho$ parameter with respect to OH and to CN, were compared to those measured in other comets. We found that 41P and 45P have a typical composition in term of carbon bearing species. The study of coma features exhibited by the CN gas species allowed the measurement of the rotation period of 41P, showing a surprisingly large increase of the rotation period from (30$\pm$5) hrs at the end of March to (50$\pm$10) hrs at the end of April, 2017 in agreement with recent observations by other teams. [less ▲]

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See detailOptical linear polarization measurements of quasars obtained with the Very Large Telescope at Paranal Observatory⋆
Hutsemekers, Damien ULiege; Borguet, B.; Sluse, Dominique ULiege et al

in Astronomy and Astrophysics (2018), 620

We report 87 previously unpublished optical linear polarization measurements of 86 quasars obtained in May and October 2008, and from April to July 2015 with the FOcal Reducer and low-dispersion ... [more ▼]

We report 87 previously unpublished optical linear polarization measurements of 86 quasars obtained in May and October 2008, and from April to July 2015 with the FOcal Reducer and low-dispersion Spectrographs FORS1 and FORS2 attached to the Very Large Telescope at the Paranal Observatory. Of the 86 quasars, 37 have p ≥ 0.6%, 9 have p ≥ 2%, and 1 has p ≥ 10%. Based on observations made with the ESO VLT at the Paranal Observatory under programme ID 081.A-0023, 082.B-0029, 095.A-0600.Full Table 3 is only available at the CDS via anonymous ftp to <A href="http://cdsarc.u-strasbg.fr/">http://cdsarc.u-strasbg.fr</A> (<A href="http://ftp://130.79.128.5">http://130.79.128.5</A>) or via <A href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/620/A68">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/620/A68</A> [less ▲]

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See detailHot stars observed by XMM-Newton. II. A survey of Oe and Be stars
Nazé, Yaël ULiege; Motch, Christian

in Astronomy and Astrophysics (2018), 619

We perform a survey of Oe and Be stars in the X-ray range. To this aim, we cross-correlated XMM-Newton and Chandra catalogs of X-ray sources with a list of Be stars, finding 84 matches in total. Of these ... [more ▼]

We perform a survey of Oe and Be stars in the X-ray range. To this aim, we cross-correlated XMM-Newton and Chandra catalogs of X-ray sources with a list of Be stars, finding 84 matches in total. Of these, 51 objects had enough counts for a spectral analysis. This paper provides the derived X-ray properties (X-ray luminosities, and whenever possible, hardness ratios, plasma temperatures, and variability assessment) of this largest ever sample of Oe and Be stars. The targets display a wide range in luminosity and hardness. In particular, the significant presence of very bright and hard sources is atypical for X-ray surveys of OB stars. Several types of sources are identified. A subset of stars display the typical characteristics of O-stars, magnetic OB stars, or pre-main-sequence (PMS) objects: their Be nature does not seem to play an important role. However, another subset comprises γ Cas analogs, which are responsible for the luminous and hard detections. Our sample contains seven known γ Cas analogs, but we also identify eight new γ Cas analogs and one γ Cas candidate. This nearly doubles the sample of such stars. Based on observations collected with NASA missions Chandra and Swift as well as the ESA observatory XMM-Newton, an ESA Science Mission with instruments and contributions directly funded by ESA Member States and the USA (NASA).All tables 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/619/A148">http://cdsarc. u-strasbg.fr/viz-bin/qcat?J/A+A/619/A148</A> [less ▲]

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