References of "Astronomy and Astrophysics"
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See detailSpectral analysis of Kepler SPB and β Cephei candidate stars
Lehmann, H.; Tkachenko, A.; Semaan, T. et al

in Astronomy and Astrophysics (2011), 526

Context. For asteroseismic modelling, analysis of the high-accuracy light curves delivered by the Kepler satellite mission needs support by ground-based, multi-colour and spectroscopic observations. <BR ... [more ▼]

Context. For asteroseismic modelling, analysis of the high-accuracy light curves delivered by the Kepler satellite mission needs support by ground-based, multi-colour and spectroscopic observations. <BR /> Aims: We determine the fundamental parameters of SPB and β Cep candidate stars observed by the Kepler satellite mission and estimate the expected types of non-radial pulsators. <BR /> Methods: We compared newly obtained high-resolution spectra with synthetic spectra computed on a grid of stellar parameters assuming LTE, and checked for NLTE effects for the hottest stars. For comparison, we determined T[SUB]eff[/SUB] independently from fitting the spectral energy distribution of the stars obtained from the available photometry. <BR /> Results: We determine T[SUB]eff[/SUB], log g, microturbulent velocity, v sin i, metallicity, and elemental abundance for 14 of the 16 candidate stars. Two stars are spectroscopic binaries. No significant influence of NLTE effects on the results could be found. For hot stars, we find systematic deviations in the determined effective temperatures from those given in the Kepler Input Catalogue. The deviations are confirmed by the results obtained from ground-based photometry. Five stars show reduced metallicity, two stars are He-strong, one is He-weak, and one is Si-strong. Two of the stars could be β Cep/SPB hybrid pulsators, four SPB pulsators, and five more stars are located close to the borders of the SPB instability region. Based on observations with the 2-m Alfred Jensch telescope at the Thüringer Landessternwarte (TLS) Tautenburg. [less ▲]

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See detailThe radius and mass of the close solar twin 18 Scorpii derived from asteroseismology and interferometry
Bazot, Michaël; Ireland, M. J.; Huber, D. et al

in Astronomy and Astrophysics (2011), 526

The growing interest in solar twins is motivated by the possibility of comparing them directly to the Sun. To carry on this kind of analysis, we need to know their physical characteristics with precision ... [more ▼]

The growing interest in solar twins is motivated by the possibility of comparing them directly to the Sun. To carry on this kind of analysis, we need to know their physical characteristics with precision. Our first objective is to use asteroseismology and interferometry on the brightest of them: 18 Sco. We observed the star during 12 nights with HARPS for seismology and used the PAVO beam-combiner at CHARA for interferometry. An average large frequency separation 134.4 ± 0.3 μHz and angular and linear radiuses of 0.6759 ± 0.0062 mas and 1.010 ± 0.009 Rsun were estimated. We used these values to derive the mass of the star, 1.02 ± 0.03 Msun. [less ▲]

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See detailA search for X-ray sources around WR 22 in the Carina region
Claeskens, Jean-François ULg; Gosset, Eric ULg; Nazé, Yaël ULg et al

in Astronomy and Astrophysics (2011), 525

We present the results of a deep search for X-ray sources in a circular field of 30' in diameter situated around WR 22 in the Carina region and observed with the XMM-Newton observatory. This field is ... [more ▼]

We present the results of a deep search for X-ray sources in a circular field of 30' in diameter situated around WR 22 in the Carina region and observed with the XMM-Newton observatory. This field is broadly located to the west of the main part of the Carina nebula. On the basis of six pointings (nominal exposure time: 10 ks each) centred on the WR+O binary star WR 22, we perform a survey with an effective exposure time of 68.8 ks. We introduce a catalogue of 43 bona-fide X-ray point sources, most of which were unknown before the XMM-Newton observations, and perform the first steps towards their identifications by cross-correlating the positions with optical/infrared catalogues. We investigated the possible variability of these sources in the X-ray domain and we extracted a few X-ray spectra for the brightest ones. A short description of the diffuse X-ray emission present in the region is also given. Based on observations with XMM-Newton, an ESA Science Mission with instruments and contributions directly funded by ESA Member States and the USA (NASA). [less ▲]

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See detailPlaskett's star: analysis of the CoRoT photometric data
Mahy, Laurent ULg; Gosset, Eric ULg; Baudin, F. et al

in Astronomy and Astrophysics (2011), 525

Context. The second short run (SRa02) of the CoRoT space mission for asteroseismology was partly devoted to stars belonging to the Mon OB2 association. An intense monitoring has been performed on Plaskett ... [more ▼]

Context. The second short run (SRa02) of the CoRoT space mission for asteroseismology was partly devoted to stars belonging to the Mon OB2 association. An intense monitoring has been performed on Plaskett's star (HD 47129) and the unprecedented quality of the light curve allows us to shed new light on this very massive, non-eclipsing binary system. <BR /> Aims: We particularly aimed at detecting periodic variability that might be associated with pulsations or interactions between both components. We also searched for variations related to the orbital cycle that could help to constrain the inclination and the morphology of the binary system. <BR /> Methods: We applied an iterative Fourier-based prewhitening and a multiperiodic fitting procedure to analyse the time series and extract the frequencies of variations from the CoRoT light curve. We describe the noise properties to tentatively define an appropriate significance criterion and, in consequence, to only point out the peaks at a certain significance level. We also detect the variations related to the orbital motion and study them with the NIGHTFALL programme. <BR /> Results: The periodogram computed from Plaskett's star CoRoT light curve mainly exhibits a majority of peaks at low frequencies. Among these peaks, we highlight a list of 43 values, notably including two different sets of harmonic frequencies whose fundamental peaks are located at about 0.07 and 0.82 d[SUP]-1[/SUP]. The former represents the orbital frequency of the binary system, whilst the latter could probably be associated with non-radial pulsations. The study of the 0.07 d[SUP]-1[/SUP] variations reveals a hot spot most probably situated on the primary star and facing the secondary. <BR /> Conclusions: The investigation of this unique dataset constitutes a further step in the understanding of Plaskett's star. These results provide a first basis for future seismic modelling and put forward the probable existence of non-radial pulsations in Plaskett's star. Moreover, the fit of the orbital variations confirms the problem of the distance of this system which was already mentioned in previous works. A hot region between both components renders the determination of the inclination ambiguous. 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.Table 2 is only available in electronic form at <A href="http://www.aanda.org">http://www.aanda.org</A> [less ▲]

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See detailTransiting exoplanets from the CoRoT space mission. XV. CoRoT-15b: a brown-dwarf transiting companion
Bouchy, F.; Deleuil, M.; Guillot, T. et al

in Astronomy and Astrophysics (2011), 525

We report the discovery by the CoRoT space mission of a transiting brown dwarf orbiting a F7V star with an orbital period of 3.06 days. CoRoT-15b has a radius of 1.12[SUP]+0.30[/SUP][SUB]-0.15[/SUB] {R ... [more ▼]

We report the discovery by the CoRoT space mission of a transiting brown dwarf orbiting a F7V star with an orbital period of 3.06 days. CoRoT-15b has a radius of 1.12[SUP]+0.30[/SUP][SUB]-0.15[/SUB] {R}_Jup and a mass of 63.3 ± 4.1 {M}_Jup, and is thus the second transiting companion lying in the theoretical mass domain of brown dwarfs. CoRoT-15b is either very young or inflated compared to standard evolution models, a situation similar to that of M-dwarf stars orbiting close to solar-type stars. Spectroscopic constraints and an analysis of the lightcurve imply a spin period in the range 2.9-3.1 days for the central star, which is compatible with a double-synchronisation of the system. The CoRoT space mission, launched on December 27th 2006, has been developed and is operated by CNES, with the contribution of Austria, Belgium, Brazil, ESA (RSSD and Science Programme), Germany, and Spain. Observations made with HARPS spectrograph at ESO La Silla Observatory (184.C-0639). [less ▲]

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See detailAtomic decay data for modeling the Al K-lines
Palmeri, P; Quinet, Pascal ULg; Mendoza, C et al

in Astronomy and Astrophysics (2011), 525

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See detailAmplitudes and lifetimes of solar-like oscillations observed by CoRoT. Red-giant versus main-sequence stars
Baudin, F.; Barban, C.; Belkacem, K. et al

in Astronomy and Astrophysics (2011), 529

Context. The advent of space-borne missions such as CoRoT or Kepler providing photometric data has brought new possibilities for asteroseismology across the H-R diagram. Solar-like oscillations are now ... [more ▼]

Context. The advent of space-borne missions such as CoRoT or Kepler providing photometric data has brought new possibilities for asteroseismology across the H-R diagram. Solar-like oscillations are now observed in many stars, including red giants and main-sequence stars. Aims: Based on several hundred identified pulsating red giants, we aim to characterize their oscillation amplitudes and widths. These observables are compared with those of main-sequence stars in order to test trends and scaling laws for these parameters for main-sequence stars and red giants. Methods: An automated fitting procedure is used to analyze several hundred Fourier spectra. For each star, a modeled spectrum is fitted to the observed oscillation spectrum, and mode parameters are derived. Results: Amplitudes and widths of red-giant solar-like oscillations are estimated for several hundred modes of oscillation. Amplitudes are relatively high (several hundred ppm) and widths relatively small (very few tenths of a μHz). Conclusions: Widths measured in main-sequence stars show a different variation with the effective temperature from red giants. A single scaling law is derived for mode amplitudes of red giants and main-sequence stars versus their luminosity to mass ratio. However, our results suggest that two regimes may also be compatible with the observations. [less ▲]

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See detailAn educated search for transiting habitable planets: (Research Note) Targetting M dwarfs with known transiting planets
Gillon, Michaël ULg; Bonfils, X.; Demory, B-O et al

in Astronomy and Astrophysics (2011), 525

Because the planets of a system form in a flattened disk, they are expected to share similar orbital inclinations at the end of their formation. The high-precision photometric monitoring of stars known to ... [more ▼]

Because the planets of a system form in a flattened disk, they are expected to share similar orbital inclinations at the end of their formation. The high-precision photometric monitoring of stars known to host a transiting planet could thus reveal the transits of one or more other planets. We investigate here the potential of this approach for the M dwarf GJ 1214 that hosts a transiting super-Earth. For this system, we infer the transit probabilities as a function of orbital periods. Using Monte-Carlo simulations we address both the cases for fully coplanar and for non-coplanar orbits, with three different choices of inclinations distribution for the non-coplanar case. GJ 1214 reveals to be a very promising target for the considered approach. Because of its small size, a ground-based photometric monitoring of this star could detect the transit of a habitable planet as small as the Earth, while a space-based monitoring could detect any transiting habitable planet down to the size of Mars. The mass measurement of such a small planet would be out of reach for current facilities, but we emphasize that a planet mass would not be needed to confirm the planetary nature of the transiting object. Furthermore, the radius measurement combined with theoretical arguments would help us to constrain the structure of the planet [less ▲]

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See detailA much lower density for the transiting extrasolar planet WASP-7 (Research Note)
Southworth, J.; Dominik, M.; Jorgensen, U~G et al

in Astronomy and Astrophysics (2011), 527

We present the first high-precision photometry of the transiting extrasolar planetary system WASP-7, obtained using telescope defocussing techniques and reaching a scatter of 0.68 mmag per point. We find ... [more ▼]

We present the first high-precision photometry of the transiting extrasolar planetary system WASP-7, obtained using telescope defocussing techniques and reaching a scatter of 0.68 mmag per point. We find that the transit depth is greater and that the host star is more evolved than previously thought. The planet has a significantly larger radius (1.330 +/- 0.093 Rjup versus 0.915 +0.046 -0.040 Rjup) and much lower density (0.41 +/- 0.10 rhojup versus 1.26 +0.25 -0.21 rhojup) and surface gravity (13.4 +/- 2.6 m/s2 versus 26.4 +4.4 -4.0 m/s2) than previous measurements showed. Based on the revised properties it is no longer an outlier in planetary mass--radius and period--gravity diagrams. We also obtain a more precise transit ephemeris for the WASP-7 system. [less ▲]

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See detailFlux and color variations of the quadruply imaged quasar HE 0435--1223
Ricci, Davide ULg; Poels, Joël ULg; Elyiv, Andrii ULg et al

in Astronomy and Astrophysics (2011), 528

We present VRi photometric observations of the quadruply imaged quasar HE 0435-1223, carried out with the Danish 1.54m telescope at the La Silla Observatory. Our aim was to monitor and study the ... [more ▼]

We present VRi photometric observations of the quadruply imaged quasar HE 0435-1223, carried out with the Danish 1.54m telescope at the La Silla Observatory. Our aim was to monitor and study the magnitudes and colors of each lensed component as a function of time. methods: We monitored the object during two seasons (2008 and 2009) in the VRi spectral bands, and reduced the data with two independent techniques: difference imaging and PSF (Point Spread Function) fitting.results: Between these two seasons, our results show an evident decrease in flux by ~0.2-0.4 magnitudes of the four lensed components in the three filters. We also found a significant increase (~0.05-0.015) in their V-R and R-i color indices. conclusions: These flux and color variations are very likely caused by intrinsic variations of the quasar between the observed epochs. Microlensing effects probably also affect the brightest "A" lensed component. [less ▲]

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See detailHard X-ray identification of η Carinae and steadiness close to periastron
Leyder, Jean-Christophe ULg; Walter, R.; Rauw, Grégor ULg

in Astronomy and Astrophysics (2010), 524

Context. The colliding-wind binary η Carinae exhibits soft X-ray thermal emission that varies strongly around the periastron passage. It has been found to have non-thermal emission, thanks to its ... [more ▼]

Context. The colliding-wind binary η Carinae exhibits soft X-ray thermal emission that varies strongly around the periastron passage. It has been found to have non-thermal emission, thanks to its detection in hard X-rays using INTEGRAL and Suzaku, and also in γ-rays with AGILE and Fermi. <BR /> Aims: This paper attempts to definitively identify η Carinae as the source of the hard X-ray emission, to examine how changes in the 2-10 keV band influence changes in the hard X-ray band, and to understand more clearly the mechanisms producing the non-thermal emission using new INTEGRAL observations obtained close to periastron passage. <BR /> Methods: To strengthen the identification of η Carinae with the hard X-ray source, a long Chandra observation encompassing the INTEGRAL/ISGRI error circle was analysed, and all other soft X-ray sources (including the outer shell of η Carinae itself) were discarded as likely counter-parts. To expand the knowledge of the physical processes governing the X-ray lightcurve, new hard X-ray images of η Carinae were studied close to periastron, and compared to previous observations far from periastron. <BR /> Results: The INTEGRAL component, when represented by a power law (with a photon index Γ of 1.8), would produce more emission in the Chandra band than observed from any point source in the ISGRI error circle apart from η Carinae, as long as the hydrogen column density to the ISGRI source is lower than N[SUB]H[/SUB] ≲ 10[SUP]24[/SUP] cm[SUP]-2[/SUP]. Sources with such a high absorption are very rare, thus the hard X-ray emission is very likely to be associated with η Carinae. The eventual contribution of the outer shell to the non-thermal component also remains fairly limited. Close to periastron passage, a 3-σ detection is achieved for the hard X-ray emission of η Carinae, with a flux similar to the average value far from periastron. <BR /> Conclusions: Assuming a single absorption component for both the thermal and non-thermal sources, this 3-σ detection can be explained with a hydrogen column density that does not exceed N[SUB]H[/SUB] ≲ 6 × 10[SUP]23[/SUP] cm[SUP]-2[/SUP] without resorting to an intrinsic increase in the hard X-ray emission. The energy injected in hard X-rays (averaged over a month timescale) appears to be rather constant at least as close as a few stellar radii, well within the acceleration region of the wind. [less ▲]

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See detailSpin-orbit angle measurements for six southern transiting planets. New insights into the dynamical origins of hot Jupiters
Triaud, A H M J; Collier Cameron, A.; Queloz, D. et al

in Astronomy and Astrophysics (2010), 524

Context. Several competing scenarios for planetary-system formation and evolution seek to explain how hot Jupiters came to be so close to their parent stars. Most planetary parameters evolve with time ... [more ▼]

Context. Several competing scenarios for planetary-system formation and evolution seek to explain how hot Jupiters came to be so close to their parent stars. Most planetary parameters evolve with time, making it hard to distinguish between models. The obliquity of an orbit with respect to the stellar rotation axis is thought to be more stable than other parameters such as eccentricity. Most planets, to date, appear aligned with the stellar rotation axis; the few misaligned planets so far detected are massive (> 2 M[SUB]J[/SUB]). <BR /> Aims: Our goal is to measure the degree of alignment between planetary orbits and stellar spin axes, to search for potential correlations with eccentricity or other planetary parameters and to measure long term radial velocity variability indicating the presence of other bodies in the system. <BR /> Methods: For transiting planets, the Rossiter-McLaughlin effect allows the measurement of the sky-projected angle β between the stellar rotation axis and a planet's orbital axis. Using the HARPS spectrograph, we observed the Rossiter-McLaughlin effect for six transiting hot Jupiters found by the WASP consortium. We combine these with long term radial velocity measurements obtained with CORALIE. We used a combined analysis of photometry and radial velocities, fitting model parameters with the Markov Chain Monte Carlo method. After obtaining β we attempt to statistically determine the distribution of the real spin-orbit angle ψ. <BR /> Results: We found that three of our targets have β above 90°: WASP-2b: β = 153°[SUP]+11[/SUP][SUB]-15[/SUB], WASP-15b: β = 139.6°[SUP]+5.2[/SUP][SUB]-4.3[/SUB] and WASP-17b: β = 148.5°[SUP]+5.1[/SUP][SUB]-4.2[/SUB]; the other three (WASP-4b, WASP-5b and WASP-18b) have angles compatible with 0°. We find no dependence between the misaligned angle and planet mass nor with any other planetary parameter. All six orbits are close to circular, with only one firm detection of eccentricity e = 0.00848[SUP]+0.00085[/SUP][SUB]-0.00095[/SUB] in WASP-18b. No long-term radial acceleration was detected for any of the targets. Combining all previous 20 measurements of β and our six and transforming them into a distribution of ψ we find that between about 45 and 85% of hot Jupiters have ψ > 30°. <BR /> Conclusions: Most hot Jupiters are misaligned, with a large variety of spin-orbit angles. We find observations and predictions using the Kozai mechanism match well. If these observational facts are confirmed in the future, we may then conclude that most hot Jupiters are formed from a dynamical and tidal origin without the necessity to use type I or II migration. At present, standard disc migration cannot explain the observations without invoking at least another additional process. Using observations with the high resolution échelle spectrograph HARPS mounted on the ESO 3.6 m (under proposals 072.C-0488, 082.C-0040 & 283.C-5017), and with the high resolution échelle spectrograph CORALIE on the 1.2 m Euler Swiss Telescope, both installed at the ESO La Silla Observatory in Chile.RV data is only available 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/524/A25">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/524/A25</A> [less ▲]

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See detailStructural and core parameters of the hot B subdwarf KPD 0629-0016 from CoRoT g-mode asteroseismology
Van Grootel, Valérie ULg; Charpinet, Stéphane; Fontaine, Gilles et al

in Astronomy and Astrophysics (2010), 524

Context. The asteroseismic exploitation of long period, g-mode hot B subdwarf pulsators (sdBVs), undermined so far by limitations associated with ground-based observations, has now become possible, thanks ... [more ▼]

Context. The asteroseismic exploitation of long period, g-mode hot B subdwarf pulsators (sdBVs), undermined so far by limitations associated with ground-based observations, has now become possible, thanks to high quality data obtained from space such as those recently gathered with the CoRoT (COnvection, ROtation, and planetary Transits) satellite. Aims. We propose a detailed seismic analysis of the sdBVs star KPD 0629-0016, the first compact pulsator monitored with CoRoT, using the g-mode pulsations recently uncovered by that space-borne observatory during short run SRa03. Methods. We use a forward modeling approach on the basis of our latest sdB models, which are now suitable for the accurate com- putation of the g-mode pulsation properties. The simultaneous match of the independent periods observed in KPD 0629-0016 with those of the models leads objectively to the identification of the pulsation modes and, more importantly, to the determination of the structural and core parameters of the star. Results. The optimal model we found closely reproduces the 18 observed periods retained in our analysis at a 0.23% level on av- erage. These are identified as low-degree (l = 1 and 2), intermediate-order (k = −9 through −74) g-modes. The structural and core parameters for KPD 0629-0016 are the following (formal fitting errors only): Teff = 26 290 ± 530 K, log g = 5.450 ± 0.034, M∗ = 0.471 ± 0.002 M⊙, log (Menv/M∗) = −2.42 ± 0.07, log (1 − Mcore/M∗) = −0.27 ± 0.01, and Xcore(C+O) = 0.41 ± 0.01. We addition- ally derive an age of 42.6 ± 1.0 Myr after the zero-age extreme horizontal branch, the radius R = 0.214 ± 0.009 R⊙, the luminosity L = 19.7 ± 3.2 L⊙, the absolute magnitude MV = 4.23 ± 0.13, the reddening index E(B − V) = 0.128 ± 0.023, and the distance d = 1190 ± 115 pc. Conclusions. The advent of high-precision time-series photometry from space with instruments like CoRoT now allows as demon- strated with KPD 0629-0016 the full exploitation of g-modes as deep probes of the internal structure of these stars, in particular for determining the mass of the convective core and its chemical composition. [less ▲]

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See detailTransiting exoplanets from the CoRoT space mission . XIII. CoRoT-13b: a dense hot Jupiter in transit around a star with solar metallicity and super-solar lithium content
Cabrera, J.; Bruntt, H.; Ollivier, M. et al

in Astronomy and Astrophysics (2010), 522

We announce the discovery of the transiting planet CoRoT-13b. Ground-based follow-up in CFHT and IAC80 confirmed CoRoT's observations. The mass of the planet was measured with the HARPS spectrograph and ... [more ▼]

We announce the discovery of the transiting planet CoRoT-13b. Ground-based follow-up in CFHT and IAC80 confirmed CoRoT's observations. The mass of the planet was measured with the HARPS spectrograph and the properties of the host star were obtained analyzing HIRES spectra from the Keck telescope. It is a hot Jupiter-like planet with an orbital period of 4.04 days, 1.3 Jupiter masses, 0.9 Jupiter radii, and a density of 2.34 g cm[SUP]-3[/SUP]. It orbits a G0V star with T_eff = 5 945 K, M[SUB]*[/SUB] = 1.09 M[SUB]ȯ[/SUB], R_* = 1.01 R[SUB]ȯ[/SUB], solar metallicity, a lithium content of + 1.45 dex, and an estimated age of between 0.12 and 3.15 Gyr. The lithium abundance of the star is consistent with its effective temperature, activity level, and age range derived from the stellar analysis. The density of the planet is extreme for its mass, implies that heavy elements are present with a mass of between about 140 and 300 {M}[SUB]⊕[/SUB]. The CoRoT space mission, launched on December 27th 2006, has been developed and is operated by CNES, with the contribution of Austria, Belgium, Brazil, ESA (RSSD and Science Programme), Germany and Spain. Part of the observations were obtained at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii. Based on observations made with HARPS spectrograph on the 3.6-m European Organisation for Astronomical Research in the Southern Hemisphere telescope at La Silla Observatory, Chile (ESO program 184.C-0639). Based on observations made with the IAC80 telescope operated on the island of Tenerife by the Instituto de Astrofísica de Canarias in the Spanish Observatorio del Teide. Part of the data presented herein were obtained at 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. [less ▲]

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See detailA spectroscopic survey of faint, high-Galactic-latitude red clump stars. I. The high resolution sample
Valentini, Marica ULg; Munari, U.

in Astronomy and Astrophysics (2010), 522

Context. Their high intrinsic brightness and small dispersion in absolute magnitude make red clump (RC) stars a prime tracer of Galactic structure and kinematics. <BR /> Aims: We aim to derive accurate ... [more ▼]

Context. Their high intrinsic brightness and small dispersion in absolute magnitude make red clump (RC) stars a prime tracer of Galactic structure and kinematics. <BR /> Aims: We aim to derive accurate, multi-epoch radial velocities and atmospheric parameters (T[SUB]eff[/SUB], log g, [M/H], V[SUB]rot[/SUB] sin i) of a large sample of carefully selected RC stars, fainter than those present in other spectroscopic surveys and located over a great circle at high Galactic latitudes. <BR /> Methods: We acquired data of the program stars of high signal-to-noise ratio (S/N) and high resolution with the Asiago Echelle spectrograph. Radial velocities were obtained by applying cross-correlation and atmospheric parameters via χ^2 fit to a synthetic spectral library. Extensive tests were carried out by re-observing with the same instrument a large number of standard stars taken from a variety of sources in the literature. During these tests, we found that the absolute Tycho V[SUB]T[/SUB] magnitude of local red clump stars is not dependent on metallicity <BR /> Results: A total of 277 red clump stars (101 of them with a second epoch observation) of the extended solar neighborhood and 55 calibration stars were observed and included in an output catalog that contains (in addition to relevant support astrometric and photometric data taken from literature) the main output of our survey: accurate multi-epoch radial velocities (σ(RV)_&sun; ≤ 0.4 km s[SUP]-1[/SUP]), accurate atmospheric parameters (σ(T[SUB]eff[/SUB]) = 68 K, σ(log g) = 0.11 dex, σ([M/H]) = 0.10 dex, σ(V[SUB]rot[/SUB] sin i) = 1.1 km s[SUP]-1[/SUP]), distances, and space velocities (U, V, W). [less ▲]

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See detailCore properties of α Centauri A using asteroseismology
de Meulenaer, P.; Carrier, F.; Miglio, A. et al

in Astronomy and Astrophysics (2010), 523

Context. A set of long and nearly continuous observations of α Centauri A should allow us to derive an accurate set of asteroseismic constraints to compare to models, and make inferences on the internal ... [more ▼]

Context. A set of long and nearly continuous observations of α Centauri A should allow us to derive an accurate set of asteroseismic constraints to compare to models, and make inferences on the internal structure of our closest stellar neighbour. <BR /> Aims: We intend to improve the knowledge of the interior of α Centauri A by determining the nature of its core. <BR /> Methods: We combined the radial velocity time series obtained in May 2001 with three spectrographs in Chile and Australia: CORALIE, UVES, and UCLES. The resulting combined time series has a length of 12.45 days and contains over 10 000 data points and allows to greatly reduce the daily alias peaks in the power spectral window. <BR /> Results: We detected 44 frequencies that are in good overall agreement with previous studies, and found that 14 of these show possible rotational splittings. New values for the large (Δν) and small separations (δν[SUB]02[/SUB], δν[SUB]13[/SUB]) have been derived. <BR /> Conclusions: A comparison with stellar models indicates that the asteroseismic constraints determined in this study (namely r[SUB]10[/SUB] and δν[SUB]13[/SUB]) allows us to set an upper limit to the amount of convective-core overshooting needed to model stars of mass and metallicity similar to those of α Cen A. [less ▲]

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See detailCOSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses VIII. Deconvolution of high resolution near-IR images and simple mass models for 7 gravitationally lensed quasars
Chantry, Virginie ULg; Sluse, Dominique; Magain, Pierre ULg

in Astronomy and Astrophysics (2010), 522

Aims: We attempt to place very accurate positional constraints on seven gravitationally lensed quasars currently being monitored by the COSMOGRAIL collaboration, and shape parameters for the light ... [more ▼]

Aims: We attempt to place very accurate positional constraints on seven gravitationally lensed quasars currently being monitored by the COSMOGRAIL collaboration, and shape parameters for the light distribution of the lensing galaxy. We attempt to determine simple mass models that reproduce the observed configuration and predict time delays. We finally test, for the quads, whether there is evidence of astrometric perturbations produced by substructures in the lensing galaxy, which may preclude a good fit with the simple models. Methods: We apply the iterative MCS deconvolution method to near-IR HST archival data of seven gravitationally lensed quasars. This deconvolution method allows us to differentiate the contributions of the point sources from those of extended structures such as Einstein rings. This method leads to an accuracy of 1-2 mas in the relative positions of the sources and lens. The limiting factor of the method is the uncertainty in the instrumental geometric distortions. We then compute mass models of the lensing galaxy using state-of-the-art modeling techniques. Results: We determine the relative positions of the lensed images and lens shape parameters of seven lensed quasars: HE 0047-1756, RX J1131-1231, SDSS J1138+0314, SDSS J1155+6346, SDSS J1226-0006, WFI J2026-4536, and HS 2209+1914. The lensed image positions are derived with 1-2 mas accuracy. Isothermal and de Vaucouleurs mass models are calculated for the whole sample. The effect of the lens environment on the lens mass models is taken into account with a shear term. Doubly imaged quasars are equally well fitted by each of these models. A large amount of shear is necessary to reproduce SDSS J1155+6346 and SDSS J1226-006. In the latter case, we identify a nearby galaxy as the dominant source of shear. The quadruply imaged quasar SDSS J1138+0314 is reproduced well by simple lens models, which is not the case for the two other quads, RX J1131-1231 and WFI J2026-4536. This might be the signature of astrometric perturbations caused by massive substructures in the galaxy, which are unaccounted for by the models. Other possible explanations are also presented. Based on observations made with the NASA/ESA HST Hubble Space Telescope, obtained from the data archive at the Space Science Institute, which is operated by AURA, the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS-5-26555. [less ▲]

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See detailThe rapid rotation and complex magnetic field geometry of Vega
Petit, Pascal; Lignières, F.; Wade, G. A. et al

in Astronomy and Astrophysics (2010), 523

Context. The recent discovery of a weak surface magnetic field on the normal intermediate-mass star Vega raises the question of the origin of this magnetism in a class of stars that was not previously ... [more ▼]

Context. The recent discovery of a weak surface magnetic field on the normal intermediate-mass star Vega raises the question of the origin of this magnetism in a class of stars that was not previously known to host detectable magnetic fields. <br />Aims: We aim to confirm the field detection reported by Lignières et al. (2009, A&A, 500, L41) and provide additional observational constraints about the field characteristics, by modelling the large-scale magnetic geometry of the star and by investigating a possible seasonal variability of the reconstructed field topology. <br />Methods: We analyse a total of 799 high-resolution circularly-polarized spectra collected with the NARVAL and ESPaDOnS spectropolarimeters during 2008 and 2009. Using about 1100 spectral lines, we employ a cross-correlation procedure to compute, from each spectrum, a mean polarized line profile with a signal-to-noise ratio of about 20 000. The technique of Zeeman-Doppler Imaging is then used to determine the rotation period of the star and reconstruct the large-scale magnetic geometry of Vega at two different epochs. <br />Results: We confirm the detection of circularly polarized signatures in the mean line profiles. The signal shows up in four independent data sets acquired with both NARVAL and ESPaDOnS. The amplitude of the polarized signatures is larger when spectral lines of higher magnetic sensitivity are selected for the analysis, as expected for a signal of magnetic origin. The short-term evolution of polarized signatures is consistent with a rotational period of 0.732 ± 0.008 d. The reconstruction of the magnetic topology unveils a magnetic region of radial field orientation, closely concentrated around the rotation pole. This polar feature is accompanied by a small number of magnetic patches at lower latitudes. No significant variability in the field structure is observed over a time span of one year. <br />Conclusions: The repeated observational evidence that Vega possesses a weak photospheric magnetic field strongly suggests that a previously unknown type of magnetic stars exists in the intermediate-mass domain. Vega may well be the first confirmed member of a much larger, as yet unexplored, class of weakly-magnetic stars now investigatable with the current generation of stellar spectropolarimeters. [less ▲]

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See detailMode identification from monochromatic amplitude and phase variations for the rapidly pulsating subdwarf B star EC 20338-1925
Randall, S. K.; Fontaine, G.; Brassard, P. et al

in Astronomy and Astrophysics (2010), 522

We obtain time-series spectrophotometry observations at the VLT with the aim of partially identifying the dominant oscillation modes in the rapidly pulsating subdwarf B star EC 20338-1925 on the basis of ... [more ▼]

We obtain time-series spectrophotometry observations at the VLT with the aim of partially identifying the dominant oscillation modes in the rapidly pulsating subdwarf B star EC 20338-1925 on the basis of monochromatic amplitude and phase variations. From the data gathered, we detect four previously known pulsations with periods near 147, 168, 126 and 140 s and amplitudes between 0.2 and 2.3 % of the star's mean brightness. We also determine the atmospheric parameters of EC 20338-1925 by fitting our non-LTE model atmospheres to an averaged combined spectrum. The inferred parameters are Teff = 34 153±94 K, log g = 5.966±0.017 and log N(He)/N(H) = -1.642±0.022, where the uncertainty estimates quoted refer to the formal fitting errors. Finally, we calculate the observed monochromatic amplitudes and phases for the periodicities extracted using least-squares fitting to the light curves obtained for each wavelength bin. These observed quantities are then compared to the corresponding theoretical values computed on the basis of dedicated model atmosphere codes and also taking into account non-adiabatic effects. We find that the quality of the data is sufficient to identify the dominant pulsation at 146.9 s as a radial mode, while two of the lower amplitude periodicities must be low-degree modes with ell = 0-2. This is the first time that monochromatic amplitudes and phases have been used for mode identification in a subdwarf B star, and the results are highly encouraging. [less ▲]

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See detailFirst results on Martian carbon monoxide from Herschel/HIFI observations
Hartogh, P.; Błecka, M. I.; Jarchow, C. et al

in Astronomy and Astrophysics (2010), 521

We report on the initial analysis of Herschel/HIFI carbon monoxide (CO) observations of the Martian atmosphere performed between 11 and 16 April 2010. We selected the (7-6) rotational transitions of the ... [more ▼]

We report on the initial analysis of Herschel/HIFI carbon monoxide (CO) observations of the Martian atmosphere performed between 11 and 16 April 2010. We selected the (7-6) rotational transitions of the isotopes [SUP]13[/SUP]CO at 771 GHz and C[SUP]18[/SUP]O and 768 GHz in order to retrieve the mean vertical profile of temperature and the mean volume mixing ratio of carbon monoxide. The derived temperature profile agrees within less than 5 K with general circulation model (GCM) predictions up to an altitude of 45 km, however, show about 12-15 K lower values at 60 km. The CO mixing ratio was determined as 980 ± 150 ppm, in agreement with the 900 ppm derived from Herschel/SPIRE observations in November 2009. 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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