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See detailFirst evidence of pulsations in Vega?. Results of today's most extensive spectroscopic search
Böhm, T.; Lignières, F.; Wade, G. et al

in Astronomy and Astrophysics (2012), 537

Context. The impact of rapid rotation on stellar evolution theory remains poorly understood as of today. Vega is a special object in this context as spectroscopic and interferometric studies have shown ... [more ▼]

Context. The impact of rapid rotation on stellar evolution theory remains poorly understood as of today. Vega is a special object in this context as spectroscopic and interferometric studies have shown that it is a rapid rotator seen nearly pole one, a rare orientation particularly interesting for seismic studies. In this paper, we present a first systematic search for pulsations in Vega. <BR /> Aims: The goal of the present work is to detect for the first time pulsations in a rapidly rotating star seen nearly pole-on. <BR /> Methods: Vega was monitored in quasi-continuous high-resolution echelle spectroscopy. A total of 4478 spectra were obtained. More precisely in 2008 we obtained 1213 spectra during 19.9 h on 3 nights (26th, 27th and 29th of July 2008) with NARVAL/TBL (at R = 65 000 and R = 75 000), in 2009 we obtained 1293 spectra during 13.7 h on 3 nights (9th-11th of September 2009) with ESPaDOnS/CFHT (at R = 68 000) and in 2010 we gathered again 1972 with NARVAL/TBL during 28.8 h on five nights (July 15th-19th). This data set should represent the most extensive high S/N, high resolution quasi-continuous survey obtained on Vega as of today. Least square deconvolved (LSD) profiles were obtained for each spectrum representing the photospheric absorption profile potentially deformed by the presence of pulsations. In addition, we calculated for each spectrum a telluric line LSD profile subsequently used as radial velocity reference. LSD profile centroids were adjusted and velocity differences (stellar-telluric) determined. These residual velocities were analysed and periodic low amplitude variations, potentially indicative of stellar pulsations, detected. In a subsequent step, the temporal line profile variations during the longest (2010) data set was calculated for each individual velocity bin of 1.8 km s[SUP]-1[/SUP] by computing a 2D (velocity-frequency) Lomb-Scargle periodogram. <BR /> Results: Based on high resolution echelle spectroscopy, we have obtained indications of periodic variations of very small amplitudes within the residual radial velocity curves of Vega. All three data sets revealed the presence of residual periodic variations: 5.32 and 9.19 d[SUP]-1[/SUP] (A ≈ 6 m s[SUP]-1[/SUP]) in 2008, 12.71 and 13.25 d[SUP]-1[/SUP] (A ≈ 8 m s[SUP]-1[/SUP]) in 2009 and 5.42 and 10.82 d[SUP]-1[/SUP] (A ≈ 3-4 m s[SUP]-1[/SUP]) in 2010. However, it is too early to conclude that the variations are due to stellar pulsations, and a confirmation of the detection with a highly stable spectrograph is a necessary next step. <BR /> Conclusions: If pulsations are confirmed, their very small amplitudes show that the star would belong to a category of very "quiet" pulsators. Based on observations obtained at the Bernard Lyot Telescope (TBL, Pic du Midi, France) of the Midi-Pyrénées Observatory, which is operated by the Institut National des Sciences de l'Univers (INSU) of the Centre National de la Recherche Scientifique of France (CNRS), and at the Canada-France-Hawaii Telescope (CFHT), which is operated by the National Research Council of Canada, INSU/CNRS and the University of Hawaii. [less ▲]

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See detailAngular correlation functions of X-ray point-like sources in the full exposure XMM-LSS field
Elyiv, Andrii ULg; Clerc, N.; Plionis, M. et al

in Astronomy and Astrophysics (2012), 537

<BR /> Aims: Our aim is to study the large-scale structure of different types of AGN using the medium-deep XMM-LSS survey. <BR /> Methods: We measure the two-point angular correlation function of 5700 and ... [more ▼]

<BR /> Aims: Our aim is to study the large-scale structure of different types of AGN using the medium-deep XMM-LSS survey. <BR /> Methods: We measure the two-point angular correlation function of 5700 and 2500 X-ray point-like sources over the 11 sq. deg. XMM-LSS field in the soft (0.5-2 keV) and hard (2-10 keV) bands. For the conversion from the angular to the spatial correlation function we used the Limber integral equation and the luminosity-dependent density evolution model of the AGN X-ray luminosity function. <BR /> Results: We have found significant angular correlations with the power-law parameters γ = 1.81 ± 0.02, θ[SUB]0[/SUB] = 1.3'' ± 0.2'' for the soft, and γ = 2.00 ± 0.04, θ[SUB]0[/SUB] = 7.3'' ± 1.0'' for the hard bands. The amplitude of the correlation function w(θ) is higher in the hard than in the soft band for f[SUB]x[/SUB] ≲ 10[SUP]-14[/SUP] erg s[SUP]-1[/SUP] cm[SUP]-2[/SUP] and lower above this flux limit. We confirm that the clustering strength θ[SUB]0[/SUB] grows with the flux limit of the sample, a trend which is also present in the amplitude of the spatial correlation function, but only for the soft band. In the hard band, it remains almost constant with r[SUB]0[/SUB] ≃ 10h[SUP]-1[/SUP] Mpc, irrespective of the flux limit. Our analysis of AGN subsamples with different hardness ratios shows that the sources with a hard-spectrum are more clustered than soft-spectrum ones. This result may be a hint that the two main types of AGN populate different environments. Finally, we find that our clustering results correspond to an X-ray selected AGN bias factor of 2.5 for the soft band sources (at a median <inline-formula>bar{z} ≃ 1.1) and 3.3 for the hard band sources (at a median <inline-formula>bar{z} ≃ 1), which translates into a host dark matter halo mass of 10[SUP]13[/SUP]h[SUP]-1[/SUP]M[SUB]&sun;[/SUB] and 10[SUP]13.7[/SUP]h[SUP]-1[/SUP]M[SUB]&sun;[/SUB] for the soft and hard bands, respectively. This paper is dedicated to the memory of Olivier Garcet who has initiated the present work just before his sudden death. [less ▲]

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See detailModelling the huge, Herschel-resolved debris ring around HD 207129
Löhne, T.; Augereau, J.-C.; Ertel, S. et al

in Astronomy and Astrophysics (2012), 537

Debris disks, which are inferred from the observed infrared excess to be ensembles of dust, rocks, and probably planetesimals, are common features of stellar systems. As the mechanisms of their formation ... [more ▼]

Debris disks, which are inferred from the observed infrared excess to be ensembles of dust, rocks, and probably planetesimals, are common features of stellar systems. As the mechanisms of their formation and evolution are linked to those of planetary bodies, they provide valuable information. The few well-resolved debris disks are even more valuable because they can serve as modelling benchmarks and help resolve degeneracies in modelling aspects such as typical grain sizes and distances. Here, we present an analysis of the HD 207129 debris disk, based on its well-covered spectral energy distribution and Herschel/PACS images obtained in the framework of the DUNES (DUst around NEarby Stars) programme. We use an empirical power-law approach to the distribution of dust and we then model the production and removal of dust by means of collisions, direct radiation pressure, and drag forces. The resulting best-fit model contains a total of nearly 10[SUP]-2[/SUP] Earth masses in dust, with typical grain sizes in the planetesimal belt ranging from 4 to 7 μm. We constrain the dynamical excitation to be low, which results in very long collisional lifetimes and a drag that notably fills the inner gap, especially at 70 μm. The radial distribution stretches from well within 100 AU in an unusual, outward-rising slope towards a rather sharp outer edge at about 170-190 AU. The inner edge is therefore smoother than that reported for Fomalhaut, but the contribution from the extended halo of barely bound grains is similarly small. Both slowly self-stirring and planetary perturbations could potentially have formed and shaped this disk. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. [less ▲]

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See detailSpectral modelling of circular massive binary systems. Towards an understanding of the Struve-Sahade effect?
Palate, Matthieu ULg; Rauw, Grégor ULg

in Astronomy and Astrophysics (2012), 537

Context. Some secondary effects are known to introduce variations in spectra of massive binaries. These phenomena, such as the Struve-Sahade effect and the difficulties in determining properly the ... [more ▼]

Context. Some secondary effects are known to introduce variations in spectra of massive binaries. These phenomena, such as the Struve-Sahade effect and the difficulties in determining properly the spectral type have been reported and documented in the literature. <BR /> Aims: We simulate the spectra of circular massive binaries at different phases of the orbital cycle and account for the gravitational influence of the companion star on the shape and physical properties of the stellar surface. <BR /> Methods: We use the Roche potential to compute the stellar surface, von Zeipel theorem, and reflection effects to compute the surface temperature. We then interpolate in a grid of non-local thermodynamic equilibrium (NLTE) plan-parallel atmosphere model spectra to obtain the local spectrum at each surface point. We finally sum all the contributions, accounting for the reflection, Doppler shift, and limb-darkening to obtain the total spectrum. The computation is done for different orbital phases and for different sets of physical and orbital parameters. <BR /> Results: Our models reproduce the Struve-Sahade effect for several lines. Another effect on the surface temperature distribution is visible but the distribution predicted by our current model is not yet consistent with observations. <BR /> Conclusions: In some cases, the Struve-Sahade effect as well as more complex line intensity variations could be linked to blends of intrinsically asymmetric line profiles that are not appropriately treated by the deblending routine. Systematic variations in the lines of (nearly) contact systems are also predicted by the model. [less ▲]

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See detailDetecting and modelling the magnetic field of the β Cephei star V 2052 Ophiuchi
Neiner, C.; Alecian, E.; Briquet, Maryline ULg et al

in Astronomy and Astrophysics (2012), 537

<BR /> Aims: Following the indirect detection of a magnetic field in the β Cephei star <ASTROBJ>V 2052 Oph</ASTROBJ> by Neiner and collaborators in 2003 with the Musicos spectropolarimeter, we remeasured ... [more ▼]

<BR /> Aims: Following the indirect detection of a magnetic field in the β Cephei star <ASTROBJ>V 2052 Oph</ASTROBJ> by Neiner and collaborators in 2003 with the Musicos spectropolarimeter, we remeasured the magnetic field of this star to attempt to directly confirm the detection of a magnetic field and study its configuration in greater detail. <BR /> Methods: We used the Narval spectropolarimeter installed at TBL (Pic du Midi, France), which is about 20 times more efficient than the Musicos spectropolarimeter. We applied the least-squares deconvolution (LSD) technique to various groups of lines to measure the circular polarisation of the light coming from <ASTROBJ>V 2052 Oph</ASTROBJ>. We synthesized the measured Stokes V profiles with a centred and off-centred dipole model. <BR /> Results: For the first time, we clearly detect the Zeeman signature in the Stokes V profiles of <ASTROBJ>V 2052 Oph</ASTROBJ> and thus directly prove the presence of a magnetic field in this star. The modulation with the rotation period is also confirmed and reflects an oblique dipole field. Thanks to the small error bars on the measurements, we are able to study the behaviour of different groups of lines and the centring of the dipole in the star. We find that the dipole is most likely off-centred along the magnetic axis and that He spots are present at the surface next to the magnetic axis. <BR /> Conclusions: We conclude that <ASTROBJ>V 2052 Oph</ASTROBJ> is a magnetic He-strong β Cep star, with a dipole field, probably off-centred, with B[SUB]pol[/SUB] ~ 400 G and He patches close to the magnetic poles. Based on observations obtained with the Narval spectropolarimeter at the Télescope Bernard Lyot, Observatoire du Pic du Midi, France. [less ▲]

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See detailAtomic decay data for modeling K lines of iron peak and light odd-Z elements
Palmeri, P; Quinet, Pascal ULg; Mendoza, C et al

in Astronomy and Astrophysics (2012), 543

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See detailStellar laboratories : new Ge V and Ge VI oscillator strengths and their validation in the hot white dwarf RE 0503-289
Rauch, T; Werner, K; Biémont, Emile ULg et al

in Astronomy and Astrophysics (2012), 546

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See detailOscillator strengths for lines of astrophysical interest in Rh II
Quinet, Pascal ULg; Biémont, Emile ULg; Palmeri, P et al

in Astronomy and Astrophysics (2012), 537

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See detailA brown dwarf orbiting an M-dwarf: MOA 2009-BLG-411L
Bachelet, E.; Fouqué, P.; Han, C. et al

in Astronomy and Astrophysics (2012), 547

Context. Caustic crossing is the clearest signature of binary lenses in microlensing. In the present context, this signature is diluted by the large source star but a detailed analysis has allowed the ... [more ▼]

Context. Caustic crossing is the clearest signature of binary lenses in microlensing. In the present context, this signature is diluted by the large source star but a detailed analysis has allowed the companion signal to be extracted. <BR /> Aims: MOA 2009-BLG-411 was detected on August 5, 2009 by the MOA-Collaboration. Alerted as a high-magnification event, it was sensitive to planets. Suspected anomalies in the light curve were not confirmed by a real-time model, but further analysis revealed small deviations from a single lens extended source fit. <BR /> Methods: Thanks to observations by all the collaborations, this event was well monitored. We first decided to characterize the source star properties by using a more refined method than the classical one: we measure the interstellar absorption along the line of sight in five different passbands (VIJHK). Secondly, we model the lightcurve by using the standard technique: make (s,q,α) grids to look for local minima and refine the results by using a downhill method (Markov chain Monte Carlo). Finally, we use a Galactic model to estimate the physical properties of the lens components. <BR /> Results: We find that the source star is a giant G star with radius 9 R[SUB]&sun;[/SUB]. The grid search gives two local minima, which correspond to the theoretical degeneracy s ≡ s[SUP]-1[/SUP]. We find that the lens is composed of a brown dwarf secondary of mass M[SUB]S[/SUB] = 0.05 M[SUB]&sun;[/SUB] orbiting a primary M-star of mass M[SUB]P[/SUB] = 0.18 M[SUB]&sun;[/SUB]. We also reveal a new mass-ratio degeneracy for the central caustics of close binaries. <BR /> Conclusions: As far as we are aware, this is the first detection using the microlensing technique of a binary system in our Galaxy composed of an M-star and a brown dwarf. Appendix is available in electronic form at <A href="http://www.aanda.org">http://www.aanda.org</A> [less ▲]

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See detailTowards a systematic spectroscopic characterization of pre-main sequence instability strip. Search for pulsations in three Herbig stars: V1247 Ori, HD35929 and HD 190073
Fumel, Aurélie ULg; Böhm, T; David, J

in Astronomy and Astrophysics (2012)

The origin of the strong activity and winds exhibited by Herbig Ae/Be stars is a still open question with regard to current young stellar evolutionary theory. On the supposition that this origin could be ... [more ▼]

The origin of the strong activity and winds exhibited by Herbig Ae/Be stars is a still open question with regard to current young stellar evolutionary theory. On the supposition that this origin could be internal, as growing evidences tend to indicate, probing Herbig stars interiors by means of the asteroseisomoly tool is therefore of great importance. The early-stage evolutionary tracks of the Herbig Ae stars cross the theoretical pre-main sequence (PMS) instability strip, that has to be spectroscopically characterized and whose boundaries and location, roughly in the same area of the HR diagram as the δ Scuti variables, should continue to be constrained by observations. In this context, it is necessary to extend the sample of studied pulsating Herbig Ae stars observed in high-resolution spectroscopy. The aim of this paper is to contribute to the systematic spectroscopic investigation of the PMS instability strip. We choose as targets the three Herbig stars V1247 Ori, HD35929 and HD190073. Our data were collected during three nights from 10 to 12 November 2008 with the HARPS spectrograph. V1247 Ori and HD35929 are known pulsating herbig stars, both having one photometrically detected frequency with timescale typical of δ Scuti pulsations. Till now, no search for stellar pulsations in HD190073 has been published. In this article, we search for stellar pulsations, and especially very faint signatures of non-radial pulsations, in the equivalent photospheric (LSD) profile time-series of our targets. Temporal variations of the LSD-profile central depth, if present, was studied with the time-series analysis tools Period04 and SigSpec. In case of oscillation detection, we then performed a 2D Fourier analysis of the entire profile in order to identify the modes corresponding to the dominant frequencies. The pulsating nature of V1247 Ori and HD35929 was confirmed by our results. V1247 Ori: frequencies of 18.99±1d−1 and 11.26±1d−1 were detected, corresponding to modes of degree ℓ = 3 to 5 and ℓ = 0 or 1, respectively. HD35929: a frequency of 5.75±1.28d−1 was detected, corresponding to a mode of degre ℓ = 6 or 7. No pulsation signatures were found in the LSD-profile time-series of HD190073. [less ▲]

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See detailSpectroscopic monitoring of the Herbig Ae star HD 104237 - II. Non-radial pulsations, mode analysis and fundamental stellar parameters
Fumel, Aurélie ULg; Böhm, Torsten

in Astronomy and Astrophysics (2012)

Context. Herbig Ae/Be stars are intermediate-mass pre-main sequence (PMS) stars showing signs of intense activity and strong stellar winds, whose origin is not yet understood in the frame of current ... [more ▼]

Context. Herbig Ae/Be stars are intermediate-mass pre-main sequence (PMS) stars showing signs of intense activity and strong stellar winds, whose origin is not yet understood in the frame of current theoretical models of stellar evolution for young stars. In addition, the evolutionary tracks of the earlier Herbig Ae stars cross the theoretical PMS instability strip located roughly in the same area of the HR diagram as the δ Scuti variables. Many of these stars exhibit pulsations of δ Scuti type. Aims. Understanding the internal structure of pulsating Herbig Ae stars based on asteroseismic studies will help constraining the origin of their tremendous activity, winds, and variability. It is therefore necessary to investigate the location of the PMS instability strip and of its boundaries, and to extend the sample of observed and studied pulsating Herbig Ae stars. The aim of this work was to carry out a thorough analysis of the line profile variations of the prototype Herbig Ae star HD104237 based on high-resolution spectroscopy and to redetermine precisely its fundamental parameters, which are the basic ingredients of a forthcoming asteroseismic modeling. Methods. HD104237 is a pulsating Herbig Ae star with eight detected frequencies based on the analysis of radial velocity variations. In this article, we reinvestigated an extensive high-resolution quasi-continuous spectroscopic data set in order to search for very faint indications of non-radial pulsations in the line profile by working on dynamical spectra of equivalent photospheric (LSD) profiles of HD104237. A 2D Fourier analysis (F2D) was performed of the entire profile and the temporal variation of the central depth of the line was studied with the time-series analysis tools Period04 and SigSpec. We present the results of these analysis including the mode identification corresponding to the detected dominant frequency, as well as a new determination of its fundamental stellar parameters. Results. The analysis of spectroscopic data set of April 22 - 25 obtained at SAAO in 1999 has confirmed the presence of multiple oscillation modes of low-degree ℓ in HD104237 and led to the first direct detection of a non-radial pulsation mode in this star: the dominant mode F1 was identified by the Fourier 2D method having a degree ℓ value comprised between 1 and 2, the symmetry of the pattern variation indicating an azimuthal order of ± 1. The detailed study of the fundamental stellar parameters has provided a Teff, log g, and iron abundance of 8550 ± 150 K, 3.9 ± 0.3, and −4.38 ± 0.19 (i.e. [Fe/H]= +0.16 ± 0.19 ), respectively. [less ▲]

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See detailTime delays for eleven gravitationally lensed quasars revisited
Eulaers, Eva ULg; Magain, Pierre ULg

in Astronomy and Astrophysics (2011), 536

Aims. We test the robustness of published time delays for 11 lensed quasars by using two techniques to measure time shifts in their light curves. Methods. We chose to use two fundamentally different ... [more ▼]

Aims. We test the robustness of published time delays for 11 lensed quasars by using two techniques to measure time shifts in their light curves. Methods. We chose to use two fundamentally different techniques to determine time delays in gravitationally lensed quasars: a method based on fitting a numerical model and another one derived from the minimum dispersion method introduced by Pelt and collaborators. To analyse our sample in a homogeneous way and avoid bias caused by the choice of the method used, we apply both methods to 11 different lensed systems for which delays have been published: JVAS B0218+357, SBS 0909+523, RX J0911+0551, FBQS J0951+2635, HE 1104-1805, PG 1115+080, JVAS B1422+231, SBS 1520+530, CLASS B1600+434, CLASS B1608+656, and HE 2149-2745 Results. Time delays for three double lenses, JVAS B0218+357, HE 1104-1805, and CLASS B1600+434, as well as the quadruply lensed quasar CLASS B1608+656 are confirmed within the error bars. We correct the delay for SBS 1520+530. For PG 1115+080 and RX J0911+0551, the existence of a second solution on top of the published delay is revealed. The time delays in four systems, SBS 0909+523, FBQS J0951+2635, JVAS B1422+231, and HE 2149-2745 prove to be less reliable than previously claimed. Conclusions. If we wish to derive an estimate of H0 based on time delays in gravitationally lensed quasars, we need to obtain more robust light curves for most of these systems in order to achieve a higher accuracy and robustness on the time delays. [less ▲]

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See detailTransiting exoplanets from the CoRoT space mission - XIX. CoRoT-23b: a dense hot Jupiter on an eccentric orbit
Rouan, D.; Parviainen, H.; Moutou, C. et al

in Astronomy and Astrophysics (2011), 537

We report the detection of CoRoT-23b, a hot Jupiter transiting in front of its host star with a period of 3.6314 \pm 0.0001 days. This planet was discovered thanks to photometric data secured with the ... [more ▼]

We report the detection of CoRoT-23b, a hot Jupiter transiting in front of its host star with a period of 3.6314 \pm 0.0001 days. This planet was discovered thanks to photometric data secured with the CoRoT satellite, combined with spectroscopic radial velocity (RV) measurements. A photometric search for possible background eclipsing binaries conducted at CFHT and OGS concluded with a very low risk of false positives. The usual techniques of combining RV and transit data simultaneously were used to derive stellar and planetary parameters. The planet has a mass of Mp = 2.8 \pm 0.3 MJup, a radius of Rpl = 1.05 \pm 0.13 RJup, a density of \approx 3 g cm-3. RV data also clearly reveal a non zero eccentricity of e = 0.16 \pm 0.02. The planet orbits a mature G0 main sequence star of V =15.5 mag, with a mass M\star = 1.14 \pm 0.08 M\odot, a radius R\star = 1. 61 \pm 0.18 R\odot and quasi-solar abundances. The age of the system is evaluated to be 7 Gyr, not far from the transition to subgiant, in agreement with the rather large stellar radius. The two features of a significant eccentricity of the orbit and of a fairly high density are fairly uncommon for a hot Jupiter. The high density is, however, consistent with a model of contraction of a planet at this mass, given the age of the system. On the other hand, at such an age, circularization is expected to be completed. In fact, we show that for this planetary mass and orbital distance, any initial eccentricity should not totally vanish after 7 Gyr, as long as the tidal quality factor Qp is more than a few 105, a value that is the lower bound of the usually expected range. Even if Corot-23b features a density and an eccentricity that are atypical of a hot Jupiter, it is thus not an enigmatic object. [less ▲]

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See detailHerschel discovery of a new class of cold, faint debris discs
Eiroa, C.; Marshall, J. P.; Mora, A. et al

in Astronomy and Astrophysics (2011), 536

We present Herschel PACS 100 and 160 μm observations of the solar-type stars α Men, HD 88230 and HD 210277, which form part of the FGK stars sample of the Herschel open time key programme (OTKP) DUNES ... [more ▼]

We present Herschel PACS 100 and 160 μm observations of the solar-type stars α Men, HD 88230 and HD 210277, which form part of the FGK stars sample of the Herschel open time key programme (OTKP) DUNES (DUst around NEarby Stars). Our observations show small infrared excesses at 160 μm for all three stars. HD 210277 also shows a small excess at 100 μm, while the 100 μm fluxes of α Men and HD 88230 agree with the stellar photospheric predictions. We attribute these infrared excesses to a new class of cold, faint debris discs. Both α Men and HD 88230 are spatially resolved in the PACS 160 μm images, while HD 210277 is point-like at that wavelength. The projected linear sizes of the extended emission lie in the range from ~115 to ≤ 250 AU. The estimated black body temperatures from the 100 and 160 μm fluxes are ≲22 K, and the fractional luminosity of the cold dust is L[SUB]dust[/SUB]/L[SUB] ⋆ [/SUB] ~ 10[SUP]-6[/SUP], close to the luminosity of the solar-system's Kuiper belt. These debris discs are the coldest and faintest discs discovered so far around mature stars, so they cannot be explained easily invoking "classical" debris disc models. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. [less ▲]

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See detailA multi-epoch XMM-Newton campaign on the core of the massive Cygnus OB2 association
Rauw, Grégor ULg

in Astronomy and Astrophysics (2011), 536

Context. Cyg OB2 is one of the most massive associations of O-type stars in our Galaxy. Despite the large interstellar reddening towards Cyg OB2, many studies, spanning a wide range of wavelengths, have ... [more ▼]

Context. Cyg OB2 is one of the most massive associations of O-type stars in our Galaxy. Despite the large interstellar reddening towards Cyg OB2, many studies, spanning a wide range of wavelengths, have been conducted to more clearly understand this association. X-ray observations provide a powerful tool to overcome the effect of interstellar absorption and study the most energetic processes associated with the stars in Cyg OB2. <BR /> Aims: We analyse XMM-Newton data to investigate the X-ray and UV properties of massive O-type stars as well as low-mass pre-main sequence stars in Cyg OB2. <BR /> Methods: We obtained six XMM-Newton observations of the core of Cyg OB2. In our analysis, we pay particular attention to the variability of the X-ray bright OB stars, especially the luminous blue variable candidate Cyg OB2 #12. <BR /> Results: We find that X-ray variability is quite common among the stars in Cyg OB2. Whilst short-term variations are restricted mostly to low-mass pre-main sequence stars, one third of the OB stars display long-term variations. The X-ray flux of Cyg OB2 #12 varies by 37%, over timescales from days to years, whilst its mean log L[SUB]X[/SUB]/L[SUB]bol[/SUB] amounts to - 6.10. <BR /> Conclusions: These properties suggest that Cyg OB2 #12 is either an interacting-wind system or displays a magnetically confined wind. Two other X-ray bright O-type stars (MT91 516 and CPR2002 A11) display variations that suggest they are interacting wind binary systems. 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).Full Table 2 and Table 4 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via <A href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/536/A31">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/536/A31</A> [less ▲]

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See detailCOSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses. IX. Time delays, lens dynamics and baryonic fraction in HE 0435-1223
Courbin, F.; Chantry, Virginie ULg; Revaz, Y. et al

in Astronomy and Astrophysics (2011), 536

We present accurate time delays for the quadruply imaged quasar HE 0435-1223. The delays were measured from 575 independent photometric points obtained in the R-band between January 2004 and March 2010 ... [more ▼]

We present accurate time delays for the quadruply imaged quasar HE 0435-1223. The delays were measured from 575 independent photometric points obtained in the R-band between January 2004 and March 2010. With seven years of data, we clearly show that quasar image A is affected by strong microlensing variations and that the time delays are best expressed relative to quasar image B. We measured ΔtBC = 7.8 ± 0.8 days, ΔtBD = -6.5 ± 0.7 days and ΔtCD = -14.3 ± 0.8 days. We spacially deconvolved HST NICMOS2 F160W images to derive accurate astrometry of the quasar images and to infer the light profile of the lensing galaxy. We combined these images with a stellar population fitting of a deep VLT spectrum of the lensing galaxy to estimate the baryonic fraction, fb, in the Einstein radius. We measured fb = 0.65-0.10+0.13 if the lensing galaxy has a Salpeter IMF and fb = 0.45-0.07+0.04 if it has a Kroupa IMF. The spectrum also allowed us to estimate the velocity dispersion of the lensing galaxy, σap = 222 ± 34 km s-1. We used fb and σap to constrain an analytical model of the lensing galaxy composed of an Hernquist plus generalized NFW profile. We solved the Jeans equations numerically for the model and explored the parameter space under the additional requirement that the model must predict the correct astrometry for the quasar images. Given the current error bars on fb and σap, we did not constrain H0 yet with high accuracy, i.e., we found a broad range of models with χ2 < 1. However, narrowing this range is possible, provided a better velocity dispersion measurement becomes available. In addition, increasing the depth of the current HST imaging data of HE 0435-1223 will allow us to combine ourconstraints with lens reconstruction techniques that make use of the full Einstein ring that is visible in this object. Based on observations made with the 1.2 m Euler Swiss Telescope, the 1.5 m telescope of Maidanak Observatory in Uzbekistan, and with the 1.2 m Mercator Telescope, operated on the island of La Palma by the Flemish Community, at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias. The NASA/ESA Hubble Space Telescope data was obtained from the data archive at the Space Telescope Science Institute, which is operated by AURA, the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS-5-26555.Light curves are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/536/A53 [less ▲]

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See detailFirst HARPSpol discoveries of magnetic fields in massive stars
Alecian, E.; Kochukhov, O.; Neiner, C. et al

in Astronomy and Astrophysics (2011), 536

In the framework of the Magnetism in Massive Stars (MiMeS) project, a HARPSpol Large Program at the 3.6m-ESO telescope has recently started to collect high-resolution spectropolarimetric data of a large ... [more ▼]

In the framework of the Magnetism in Massive Stars (MiMeS) project, a HARPSpol Large Program at the 3.6m-ESO telescope has recently started to collect high-resolution spectropolarimetric data of a large number of Southern massive OB stars in the field of the Galaxy and in many young clusters and associations. We report on the first discoveries of magnetic fields in two massive stars with HARPSpol - HD 130807 and HD 122451, and confirm the presence of a magnetic field at the surface of HD 105382 that was previously observed with a low spectral resolution device. The longitudinal magnetic field measurements strongly vary for HD 130807 from ~-100 G to ~700 G. Those of HD 122451 and HD 105382 are less variable with values ranging from ~-40 to -80 G, and from ~-300 to -600 G, respectively. The discovery and confirmation of three new magnetic massive stars, including at least two He-weak stars, is an important contribution to one of MiMeS objectives: the understanding of the origin of magnetic fields in massive stars and their impact on stellar structure and evolution. Based on observations collected at the European Southern Observatory, Chile (Program ID 187.D-0917). [less ▲]

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See detailCoRoT's view on variable B8/9 stars: spots versus pulsations. Evidence for differential rotation in HD 174648
Degroote, P.; Acke, B.; Samadi, R. et al

in Astronomy and Astrophysics (2011), 536

Context. There exist few variability studies of stars in the region in the Hertzsprung-Russell diagram between the A and B-star pulsational instability strips. With the aid of the high precision ... [more ▼]

Context. There exist few variability studies of stars in the region in the Hertzsprung-Russell diagram between the A and B-star pulsational instability strips. With the aid of the high precision continuous measurements of the CoRoT space satellite, low amplitudes are more easily detected, making a study of this neglected region worthwhile. <BR /> Aims: We collected a small sample of B stars observed by CoRoT to determine the origin of the different types of variability observed. <BR /> Methods: We combine literature photometry and spectroscopy to measure the fundamental parameters of the stars in the sample, and compare asteroseismic modelling of the light curves with (differentially rotating) spotted star models. <BR /> Results: We found strong evidence for the existence of spots and differential rotation in HD 174648, and formulated hypotheses for their origin. We show that the distinction between pulsations and rotational modulation is difficult to make solely based on the light curve, especially in slowly rotating stars. The CoRoT space mission was developed and is operated by the French space agency CNES, with participation of ESA's RSSD and Science Programmes, Austria, Belgium, Brazil, Germany, and Spain.Based on observations made with the ESO telescopes at La Silla Observatory under the ESO Large Programme LP182.D-0356.Based on observations made with the Mercator Telescope, operated on the island of La Palma by the Flemish Community, at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias.Appendix A is available in electronic form at <A href="http://www.aanda.org">http://www.aanda.org</A> [less ▲]

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See detailWASP-43b: The closest-orbiting hot Jupiter
Hellier, Coel; Anderson, D. R.; Collier Cameron, A. et al

in Astronomy and Astrophysics (2011), 535

We report the discovery of WASP-43b, a hot Jupiter transiting a K7V star every 0.81 d. At 0.6-Msun the host star has the lowest mass of any star hosting a hot Jupiter. It also shows a 15.6-d rotation ... [more ▼]

We report the discovery of WASP-43b, a hot Jupiter transiting a K7V star every 0.81 d. At 0.6-Msun the host star has the lowest mass of any star hosting a hot Jupiter. It also shows a 15.6-d rotation period. The planet has a mass of 1.8 Mjup, a radius of 0.9 Rjup, and with a semi-major axis of only 0.014 AU has the smallest orbital distance of any known hot Jupiter. The discovery of such a planet around a K7V star shows that planets with apparently short remaining lifetimes owing to tidal decay of the orbit are also found around stars with deep convection zones. [less ▲]

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See detailPIONIER: a 4-telescope visitor instrument at VLTI
Le Bouquin, J.-B.; Berger, J.-P.; Lazareff, B. et al

in Astronomy and Astrophysics (2011), 535

Context. PIONIER stands for Precision Integrated-Optics Near-infrared Imaging ExpeRiment. It combines four 1.8m Auxilliary Telescopes or four 8m Unit Telescopes of the Very Large Telescope Interferometer ... [more ▼]

Context. PIONIER stands for Precision Integrated-Optics Near-infrared Imaging ExpeRiment. It combines four 1.8m Auxilliary Telescopes or four 8m Unit Telescopes of the Very Large Telescope Interferometer (ESO, Chile) using an integrated optics combiner. The instrument was integrated at IPAG in December 2009 and commissioned at the Paranal Observatory in October 2010. It has provided scientific observations since November 2010. <BR /> Aims: In this paper, we explain the instrumental concept and describe the standard operational modes and the data reduction strategy. We present the typical performance and discuss how to improve them. <BR /> Methods: This paper is based on laboratory data obtained during the integrations at IPAG, as well as on-sky data gathered during the commissioning at VLTI. We illustrate the imaging capability of PIONIER on the binaries δ Sco and HIP11231. <BR /> Results: PIONIER provides six visibilities and three independent closure phases in the H band, either in a broadband mode or with a low spectral dispersion (R = 40), using natural light (i.e. unpolarized). The limiting magnitude is Hmag = 7 in dispersed mode under median atmospheric conditions (seeing < 1, τ[SUB]0[/SUB] > 3ms) with the 1.8m Auxiliary Telescopes. We demonstrate a precision of 0.5deg on the closure phases. The precision on the calibrated visibilities ranges from 3% to 15% depending on the atmospheric conditions. <BR /> Conclusions: PIONIER was installed and successfully tested as a visitor instrument for the VLTI. It permits high angular resolution imaging studies at an unprecedented level of sensitivity. The successful combination of the four 8m Unit Telescopes in March 2011 demonstrates that VLTI is ready for four-telescope operation. Based on observations collected at the European Southern Observatory, Paranal, Chile (commissioning data and 087.C-0709). [less ▲]

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