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See detailThe Gaia-ESO Survey: The analysis of high-resolution UVES spectra of FGK-type stars
Smiljanic, R.; Korn, A. J.; Bergemann, M. et al

in Astronomy and Astrophysics (2014), 570

Context. The ongoing Gaia-ESO Public Spectroscopic Survey is using FLAMES at the VLT to obtain high-quality medium-resolution Giraffe spectra for about 10[SUP]5[/SUP] stars and high-resolution UVES ... [more ▼]

Context. The ongoing Gaia-ESO Public Spectroscopic Survey is using FLAMES at the VLT to obtain high-quality medium-resolution Giraffe spectra for about 10[SUP]5[/SUP] stars and high-resolution UVES spectra for about 5000 stars. With UVES, the Survey has already observed 1447 FGK-type stars. <BR /> Aims: These UVES spectra are analyzed in parallel by several state-of-the-art methodologies. Our aim is to present how these analyses were implemented, to discuss their results, and to describe how a final recommended parameter scale is defined. We also discuss the precision (method-to-method dispersion) and accuracy (biases with respect to the reference values) of the final parameters. These results are part of the Gaia-ESO second internal release and will be part of its first public release of advanced data products. Methods: The final parameter scale is tied to the scale defined by the Gaia benchmark stars, a set of stars with fundamental atmospheric parameters. In addition, a set of open and globular clusters is used to evaluate the physical soundness of the results. Each of the implemented methodologies is judged against the benchmark stars to define weights in three different regions of the parameter space. The final recommended results are the weighted medians of those from the individual methods. Results: The recommended results successfully reproduce the atmospheric parameters of the benchmark stars and the expected T[SUB]eff[/SUB]-log g relation of the calibrating clusters. Atmospheric parameters and abundances have been determined for 1301 FGK-type stars observed with UVES. The median of the method-to-method dispersion of the atmospheric parameters is 55 K for T[SUB]eff[/SUB], 0.13 dex for log g and 0.07 dex for [Fe/H]. Systematic biases are estimated to be between 50-100 K for T[SUB]eff[/SUB], 0.10-0.25 dex for log g and 0.05-0.10 dex for [Fe/H]. Abundances for 24 elements were derived: C, N, O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Mo, Ba, Nd, and Eu. The typical method-to-method dispersion of the abundances varies between 0.10 and 0.20 dex. Conclusions: The Gaia-ESO sample of high-resolution spectra of FGK-type stars will be among the largest of its kind analyzed in a homogeneous way. The extensive list of elemental abundances derived in these stars will enable significant advances in the areas of stellar evolution and Milky Way formation and evolution. Based on observations made with the ESO/VLT, at Paranal Observatory, under program 188.B-3002 (The Gaia-ESO Public Spectroscopic Survey, PIs Gilmore and Randich). Appendices are available in electronic form at <A href="http://www.aanda.org/10.1051/0004-6361/201423937/olm">http://www.aanda.org</A> [less ▲]

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See detailWASP-104b and WASP-106b: two transiting hot Jupiters in 1.75-day and 9.3-day orbits
Smith, A. M. S.; Anderson, D. R.; Armstrong, D. J. et al

in Astronomy and Astrophysics (2014)

We report the discovery from the WASP survey of two exoplanetary systems, each consisting of a Jupiter-sized planet transiting an 11th magnitude (V) main-sequence star. WASP-104b orbits its star in 1.75 d ... [more ▼]

We report the discovery from the WASP survey of two exoplanetary systems, each consisting of a Jupiter-sized planet transiting an 11th magnitude (V) main-sequence star. WASP-104b orbits its star in 1.75 d, whereas WASP-106b has the fourth-longest orbital period of any planet discovered by means of transits observed from the ground, orbiting every 9.29 d. Each planet is more massive than Jupiter (WASP-104b has a mass of 1.27±0.05 MJup, while WASP-106b has a mass of 1.93±0.08 MJup). Both planets are just slightly larger than Jupiter, with radii of 1.14±0.04 and 1.09±0.04 RJup for WASP-104 and WASP-106 respectively. No significant orbital eccentricity is detected in either system, and while this is not surprising in the case of the short-period WASP-104b, it is interesting in the case of WASP-106b, because many otherwise similar planets are known to have eccentric orbits. [less ▲]

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See detailKepler detection of a new extreme planetary system orbiting the subdwarf-B pulsator KIC 10001893
Silvotti, R.; Charpinet, S.; Green, E.M. et al

in Astronomy and Astrophysics (2014), 570

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See detailPhase resolved X-ray spectroscopy of HDE 228766: Probing the wind of an extreme Of+/WNLha star (Corrigendum)
Rauw, Grégor ULg; Mahy, Laurent; Nazé, Yaël ULg et al

in Astronomy and Astrophysics (2014), 569

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 on data collected at the San Pedro ... [more ▼]

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 on data collected at the San Pedro Mártir observatory (Mexico). Corrigendum [less ▲]

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See detailModulated X-ray emission of the magnetic O8.5V-star Tr16-22
Nazé, Yaël ULg; Wade, Gregg A.; Petit, Véronique

in Astronomy and Astrophysics (2014), 569

Using an extensive X-ray dataset, we analyzed the X-ray emission of the massive O-star Tr16-22, which was recently found to be magnetic. Its bright X-ray emission is found to be modulated with a ~54 d ... [more ▼]

Using an extensive X-ray dataset, we analyzed the X-ray emission of the massive O-star Tr16-22, which was recently found to be magnetic. Its bright X-ray emission is found to be modulated with a ~54 d period. This timescale should represent the rotational timescale of the star, as it does for other magnetic massive stars. In parallel, new spectropolarimetric data confirm the published magnetic detection. Based on observations collected with the ESA science mission XMM-Newton, Chandra, and ESO-FORS2 instrument.Tables 1-3 are available in electronic form at <A href="http://www.aanda.org/10.1051/0004-6361/201424416/olm">http://www.aanda.org</A> [less ▲]

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See detailProper use of Schwarzschild Ledoux criteria in stellar evolution computations
Gabriel, Maurice; Noels-Grötsch, Arlette ULg; Montalbán, J. et al

in Astronomy and Astrophysics (2014), 569

The era of detailed asteroseismic analyses opened by space missions such as CoRoT and Kepler has highlighted the need for stellar models devoid of numerical inaccuracies, in order to be able to diagnose ... [more ▼]

The era of detailed asteroseismic analyses opened by space missions such as CoRoT and Kepler has highlighted the need for stellar models devoid of numerical inaccuracies, in order to be able to diagnose which physical aspects are being ignored or poorly treated in standard stellar modeling. We tackle here the important problem of fixing convective zone boundaries in the frame of the local mixing length theory. First we show that the only correct way to locate a convective zone boundary is to find, at each iteration step, through interpolations or extrapolations from points within the convective zone, the mass where the radiative luminosity is equal to the total luminosity. We then discuss two misuses of the boundary condition and the ways they affect stellar modeling and stellar evolution. The first consists in applying the neutrality condition for convective instability on the radiative side of the convective boundary. The second way of misusing the boundary condition comes from the process of fixing the convective boundary through the search for a change of sign of a possibly discontinuous function. We show that these misuses can lead to completely wrong estimates of convective core sizes with important consequences for the following evolutionary phases. We point out the advantages of using a double mesh point at each convective zone boundary. The specific problem of a convective shell is discussed and some remarks concerning overshooting are given. [less ▲]

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See detailThe puzzling new class of variable stars in NGC 3766 : old friend pulsators?
Salmon, Sébastien ULg; Montalban Iglesias, Josefa ULg; Reese, Daniel et al

in Astronomy and Astrophysics (2014), 569

The recent variability survey of the NGC 3766 cluster revealed a considerable number of periodic variable stars in a region of the H-R diagram where no pulsation is expected. This region lies between the ... [more ▼]

The recent variability survey of the NGC 3766 cluster revealed a considerable number of periodic variable stars in a region of the H-R diagram where no pulsation is expected. This region lies between the instability strips of the delta Scuti and SPB stars. Moreover the periods of the new phenomenon, P~0.1-0.7 d, do not allow to associate it a priori to either of these two types of pulsations. Stars in the NGC 3766 cluster are known as fast rotators with rotational velocities typically larger than half of their critical velocity. Rotation can affect both the geometrical properties and period domain of pulsations. It also alters the apparent stellar luminosity through gravity darkening, effect seldom taken considered in theoretical studies of the rotation-pulsation interaction. We explore if both of these effects are able to deliver a consistent interpretation for the observed properties of the "new variables" in NGC 3766: explaining their presence outside the known instability strips and their variability periods. We carry out an instability analysis of SPB models within the framework of the Traditional Approximation of Rotation and study the visibility of modes according to the angle of view and rotation. We also check how gravity darkening affects the effective temperature and luminosity of stellar models for different angles of view and rotation velocities. At the red (cold) border of the instability strip, prograde sectoral modes are preferentially excited and their visibilities are maximum when seen equator-on. Furthermore low-mass SPB models seen equator-on can appear in the gap between non-rotating SPB and delta Scuti stars due to gravity darkening. In that case, periods of these most visible modes are shifted to the 0.2-0.5 d range due to the effects of the Coriolis force. We hence suggest that the new variable stars observed in NGC 3766 are actually fast rotating SPB pulsators. [less ▲]

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See detailWASP-117b: a 10-day-period Saturn in an eccentric and misaligned orbit
Lendl, Monika ULg; Triaud, A. H. M. J.; Anderson, D. R. et al

in Astronomy and Astrophysics (2014), 568

We report the discovery of WASP-117b, the first planet with a period beyond 10 days found by the WASP survey. The planet has a mass of M_p = 0.2755 (+/-0.0090) M_jup, a radius of R_p = 1.021 (-0.065 +0 ... [more ▼]

We report the discovery of WASP-117b, the first planet with a period beyond 10 days found by the WASP survey. The planet has a mass of M_p = 0.2755 (+/-0.0090) M_jup, a radius of R_p = 1.021 (-0.065 +0.076) R_jup and is in an eccentric (e = 0.302 +/-0.023), 10.02165 +/- 0.00055 d orbit around a main-sequence F9 star. The host star's brightness (V=10.15 mag) makes WASP-117 a good target for follow-up observations, and with a planetary equilibrium temperature of T_eq = 1024 (-26 +30) K and a low planetary density (rho_p = 0.259 (-0.048 +0.054) rho_jup) it is one of the best targets for transmission spectroscopy among planets with periods around 10 days. From a measurement of the Rossiter-McLaughlin effect, we infer a projected angle between the planetary orbit and stellar spin axes of beta = -44 (+/-11) deg, and we further derive an orbital obliquity of psi = 69.5 (+3.6 -3.1) deg. Owing to the large orbital separation, tidal forces causing orbital circularization and realignment of the planetary orbit with the stellar plane are weak, having had little impact on the planetary orbit over the system lifetime. WASP-117b joins a small sample of transiting giant planets with well characterized orbits at periods above ~8 days. [less ▲]

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See detailInvestigation of the stellar content in the western part of the Carina nebula
Kumar, Brajesh; Sharma, Saurabh; Manfroid, Jean ULg et al

in Astronomy and Astrophysics (2014), 567

Context. The low obscuration and proximity of the Carina nebula make it an ideal place to study the ongoing star formation process and impact of massive stars on low-mass stars in their surroundings. <BR ... [more ▼]

Context. The low obscuration and proximity of the Carina nebula make it an ideal place to study the ongoing star formation process and impact of massive stars on low-mass stars in their surroundings. <BR /> Aims: To investigate this process, we generated a new catalog of the pre-main-sequence stars in the Carina west (CrW) region and studied their nature and spatial distribution. We also determined various parameters (reddening, reddening law, age, mass), which are used further to estimate the initial mass function and K-band luminosity function for the region under study. <BR /> Methods: We obtained deep UBVRI Hα photometric data of the field situated to the west of the main Carina nebula and centered on WR 22. Medium-resolution optical spectroscopy of a subsample of X-ray selected objects along with archival data sets from Chandra, XMM-Newton and 2MASS surveys were used for the present study. Different sets of color-color and color-magnitude diagrams are used to determine reddening for the region and to identify young stellar objects (YSOs) and estimate their age and mass. <BR /> Results: Our spectroscopic results indicate that the majority of the X-ray sources are late spectral type stars. The region shows a large amount of differential reddening with minimum and maximum values of E(B - V) as 0.25 and 1.1 mag, respectively. Our analysis reveals that the total-to-selective absorption ratio R[SUB]V[/SUB] is ~3.7 ± 0.1, suggesting an abnormal grain size in the observed region. We identified 467 YSOs and studied their characteristics. The ages and masses of the 241 optically identified YSOs range from ~0.1 to 10 Myr and ~0.3 to 4.8 M[SUB]⊙[/SUB], respectively. However, the majority of them are younger than 1 Myr and have masses below 2 M[SUB]⊙[/SUB]. The high mass star WR 22 does not seem to have contributed to the formation of YSOs in the CrW region. The initial mass function slope, Γ, in this region is found to be -1.13 ± 0.20 in the mass range of 0.5 < M/M[SUB]⊙[/SUB] < 4.8. The K-band luminosity function slope (α) is also estimated as 0.31 ± 0.01. We also performed minimum spanning tree analysis of the YSOs in this region, which reveals that there are at least ten YSO cores associated with the molecular cloud, and that leads to an average core radius of 0.43 pc and a median branch length of 0.28 pc. 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> (ftp://130.79.128.5) or via <A href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/567/A109">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/567/A109</A> [less ▲]

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See detailTransiting exoplanets from the CoRoT space mission. XXVI. CoRoT-24: a transiting multiplanet system
Alonso, R.; Moutou, C.; Endl, M. et al

in Astronomy and Astrophysics (2014), 567

We present the discovery of a candidate multiply transiting system, the first one found in the CoRoT mission. Two transit-like features with periods of 5.11 and 11.76 d are detected in the CoRoT light ... [more ▼]

We present the discovery of a candidate multiply transiting system, the first one found in the CoRoT mission. Two transit-like features with periods of 5.11 and 11.76 d are detected in the CoRoT light curve around a main sequence K1V star of r = 15.1. If the features are due to transiting planets around the same star, these would correspond to objects of 3.7 ± 0.4 and 5.0 ± 0.5 R[SUB]⊕[/SUB] , respectively. Several radial velocities serve to provide an upper limit of 5.7 M[SUB]⊕[/SUB] for the 5.11 d signal and to tentatively measure a mass of 28[SUP]+11[/SUP][SUB]-11[/SUB] M[SUB]⊕[/SUB] for the object transiting with a 11.76 d period. These measurements imply low density objects, with a significant gaseous envelope. The detailed analysis of the photometric and spectroscopic data serves to estimate the probability that the observations are caused by transiting Neptune-sized planets as much as over 26 times higher than a blend scenario involving only one transiting planet and as much as over 900 times higher than a scenario involving two blends and no planets. The radial velocities show a long-term modulation that might be attributed to a 1.5 M[SUB]Jup[/SUB] planet orbiting at 1.8 AU from the host, but more data are required to determine the precise orbital parameters of this companion. The CoRoT space mission, launched on 27 December 2006, has been developed and is operated by the CNES, with the contribution of Austria, Belgium, Brazil, ESA (RSSD and Science Program), Germany, and Spain. Some of the observations were made with the HARPS spectrograph at ESO La Silla Observatory (184.C-0639) and with the HIRES spectrograph at the Keck Telescope (N035Hr, N143Hr 260 and N095Hr). Partly based on observations obtained at ESO Paranal Observatory, Chile (086.C-0235(A) and B).Tables 2-4 and Fig. 12 are available in electronic form at <A href="http://www.aanda.org/10.1051/0004-6361/201118662/olm">http://www.aanda.org</A> [less ▲]

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See detailVery deep images of the innermost regions of the beta Pictoris debris disc at L'
Milli, J.; Lagrange, A.-M.; Mawet, D. et al

in Astronomy and Astrophysics (2014), 566

Context. Very few debris discs have been imaged in scattered light at wavelengths beyond 3 mum because the thermal emission from both the sky and the telescope is generally too strong with respect to the ... [more ▼]

Context. Very few debris discs have been imaged in scattered light at wavelengths beyond 3 mum because the thermal emission from both the sky and the telescope is generally too strong with respect to the faint emission of a debris disc. We present here the first analysis of a high angular resolution image of the disc of beta Pictoris at 3.8 mum. <BR /> Aims: Our primary objective is to probe the innermost parts of the beta Pictoris debris disc and describe its morphology. We performed extensive forward modelling to correct for the biases induced by angular differential imaging on extended objects and derive the physical parameters of the disc. <BR /> Methods: This work relies on a new analysis of seven archival data sets of beta Pictoris observed with the NaCo instrument at the Very Large Telescope in the L' band, including observations made with the Annular Groove Phase Mask vortex coronagraph in 2013. The data analysis consists of angular differential imaging associated with disc forward modelling to correct for the biases induced by that technique. The disc model is subtracted from the data and the reduction performed again in order to minimize the residuals in the final image. <BR /> Results: The disc is detected above a 5sigma level between 0.4'' and 3.8''. The two extensions have a similar brightness within error bars. We confirm an asymmetry previously observed at larger distances from the star and at shorter wavelengths: the isophotes are more widely spaced [less ▲]

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See detailPhase resolved X-ray spectroscopy of HDE 228766: Probing the wind of an extreme Of+/WNLha star
Rauw, Grégor ULg; Mahy, Laurent; Nazé, Yaël ULg et al

in Astronomy and Astrophysics (2014), 566

Context. HDE 228766 is a very massive binary system hosting a secondary component, which is probably in an intermediate evolutionary stage between an Of supergiant and an WN star. The wind of this star ... [more ▼]

Context. HDE 228766 is a very massive binary system hosting a secondary component, which is probably in an intermediate evolutionary stage between an Of supergiant and an WN star. The wind of this star collides with the wind of its O8 II companion, leading to relatively strong X-ray emission. <BR /> Aims: Measuring the orbital variations of the line-of-sight absorption toward the X-ray emission from the wind-wind interaction zone yields information on the wind densities of both stars. <BR /> Methods: X-ray spectra have been collected at three key orbital phases to probe the winds of both stars. Optical photometry has been gathered to set constraints on the orbital inclination of the system. <BR /> Results: The X-ray spectra reveal prominent variations of the intervening column density toward the X-ray emission zone, which are in line with the expectations for a wind-wind collision. We use a toy model to set constraints on the stellar wind parameters by attempting to reproduce the observed variations of the relative fluxes and wind optical depths at 1 keV. <BR /> Conclusions: The lack of strong optical eclipses sets an upper limit of ~ 68° on the orbital inclination. The analysis of the variations of the X-ray spectra suggests an inclination in the range 54-61° and indicates that the secondary wind momentum ratio exceeds that of the primary by at least a factor 5. Our models further suggest that the bulk of the X-ray emission arises from the innermost region of the wind interaction zone, which is from a region whose outer radius, as measured from the secondary star, lies between 0.5 and 1.5 times the orbital separation. 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 on data collected at the San Pedro Mártir observatory (Mexico). [less ▲]

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See detailMicrolensing of the broad-line region in the quadruply imaged quasar HE0435-1223
Braibant, Lorraine ULg; Hutsemekers, Damien ULg; Sluse, Dominique ULg et al

in Astronomy and Astrophysics (2014), 565

Using infrared spectra of the z = 1.693 quadruply lensed quasar HE0435-1223 acquired in 2009 with the spectrograph SINFONI at the ESO Very Large Telescope, we have detected a clear microlensing effect in ... [more ▼]

Using infrared spectra of the z = 1.693 quadruply lensed quasar HE0435-1223 acquired in 2009 with the spectrograph SINFONI at the ESO Very Large Telescope, we have detected a clear microlensing effect in images A and D. While microlensing affects the blue and red wings of the Hα line profile in image D very differently, it de-magnifies the line core in image A. The combination of these different effects sets constraints on the line-emitting region; these constraints suggest that a rotating ring is at the origin of the Hα line. Visible spectra obtained in 2004 and 2012 indicate that the MgII line profile is microlensed in the same way as the Hα line. Our results therefore favour flattened geometries for the low-ionization line-emitting region, for example, a Keplerian disk. Biconical models cannot be ruled out but require more fine-tuning. Flux ratios between the different images are also derived and confirm flux anomalies with respect to estimates from lens models with smooth mass distributions. Based on observations made with the ESO-VLT, Paranal, Chile; Proposal 084.B-0013 (PI: Rix).Tables 2, 3 and Appendix A are available in electronic form at <A href="http://www.aanda.org/10.1051/0004-6361/201423633/olm">http://www.aanda.org</A> [less ▲]

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See detailThe PLATO Simulator: modelling of high-precision high-cadence space-based imaging
Marcos-Arenal, P.; Zima, W.; De Ridder, J. et al

in Astronomy and Astrophysics (2014)

Many aspects of the design trade-off of a space-based instrument and its performance can best be tackled through simulations of the expected observations. The complex interplay of various noise sources in ... [more ▼]

Many aspects of the design trade-off of a space-based instrument and its performance can best be tackled through simulations of the expected observations. The complex interplay of various noise sources in the course of the observations make such simulations an indispensable part of the assessment and design study of any space-based mission. We present a formalism to model and simulate photometric time series of CCD images by including models of the CCD and its electronics, the telescope optics, the stellar field, the jitter movements of the spacecraft, and all important natural noise sources. This formalism has been implemented in a versatile end-to-end simulation software tool, called PLATO Simulator, specifically designed for the PLATO space mission to be operated from L2, but easily adaptable to similar types of missions. We provide a detailed description of several noise sources and discuss their properties, in connection with the optical design, the allowable level of jitter, the quantum efficiency of the detectors, etc. The expected overall noise budget of generated light curves is computed as a function of the stellar magnitude, for different sets of input parameters describing the instrument properties. The simulator is offered to the scientific community for future use. [less ▲]

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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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