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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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See detailWater production in comet 81P/Wild 2 as determined by Herschel/HIFI
de Val-Borro, M.; Hartogh, P.; Crovisier, J. et al

in Astronomy and Astrophysics (2010), 521(Letters), 501-5

The high spectral resolution and sensitivity of Herschel/HIFI allows for the detection of multiple rotational water lines and accurate determinations of water production rates in comets. In this Letter we ... [more ▼]

The high spectral resolution and sensitivity of Herschel/HIFI allows for the detection of multiple rotational water lines and accurate determinations of water production rates in comets. In this Letter we present HIFI observations of the fundamental 1[SUB]10[/SUB]-1[SUB]01[/SUB] (557 GHz) ortho and 1[SUB]11[/SUB]-[SUB]00[/SUB] (1113 GHz) para rotational transitions of water in comet 81P/Wild 2 acquired in February 2010. We mapped the extent of the water line emission with five point scans. Line profiles are computed using excitation models which include excitation by collisions with electrons and neutrals and solar infrared radiation. We derive a mean water production rate of 1.0 × 10[SUP]28[/SUP] molecules s[SUP]-1[/SUP] at a heliocentric distance of 1.61 AU about 20 days before perihelion, in agreement with production rates measured from the ground using observations of the 18-cm OH lines. Furthermore, we constrain the electron density profile and gas kinetic temperature, and estimate the coma expansion velocity by fitting the water line shapes. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Figure 5 (page 5) is only available in electronic form at <A href="http://www.aanda.org">http://www.aanda.org</A> [less ▲]

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See detailHerschel/HIFI observations of Mars: First detection of O2 at submillimetre wavelengths and upper limits on HCl and H2O2
Hartogh, P.; Jarchow, C.; Lellouch, E. et al

in Astronomy and Astrophysics (2010), 521

We report on an initial analysis of Herschel/HIFI observations of hydrogen chloride (HCl), hydrogen peroxide (H[SUB]2[/SUB]O[SUB]2[/SUB]), and molecular oxygen (O[SUB]2[/SUB]) in the Martian atmosphere ... [more ▼]

We report on an initial analysis of Herschel/HIFI observations of hydrogen chloride (HCl), hydrogen peroxide (H[SUB]2[/SUB]O[SUB]2[/SUB]), and molecular oxygen (O[SUB]2[/SUB]) in the Martian atmosphere performed on 13 and 16 April 2010 (L[SUB]s[/SUB] ~ 77°). We derived a constant volume mixing ratio of 1400 ± 120 ppm for O[SUB]2[/SUB] and determined upper limits of 200 ppt for HCl and 2 ppb for H[SUB]2[/SUB]O[SUB]2[/SUB]. Radiative transfer model calculations indicate that the vertical profile of O[SUB]2[/SUB] may not be constant. Photochemical models determine the lowest values of H[SUB]2[/SUB]O[SUB]2[/SUB] to be around L[SUB]s[/SUB] ~ 75° but overestimate the volume mixing ratio compared to our measurements. 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 detailDeep near-infrared interferometric search for low-mass companions around β Pictoris
Absil, Olivier ULg; Le Bouquin, Jean-Baptiste; Lebreton, Jérémy et al

in Astronomy and Astrophysics (2010), 520

Aims. We search for low-mass companions in the innermost region (<300 mas, i.e., 6 AU) of the β Pic planetary system. Methods. We obtained interferometric closure phase measurements in the K-band with the ... [more ▼]

Aims. We search for low-mass companions in the innermost region (<300 mas, i.e., 6 AU) of the β Pic planetary system. Methods. We obtained interferometric closure phase measurements in the K-band with the VLTI/AMBER instrument used in its medium spectral resolution mode. Fringe stabilization was provided by the FINITO fringe tracker. Results. In a search region of between 2 and 60 mas in radius, our observations exclude at 3σ significance the presence of companions with K-band contrasts greater than 5×10^-3 for 90% of the possible positions in the search zone (i.e., 90% completeness). The median 1σ error bar in the contrast of potential companions within our search region is 1.2×10^-3. The best fit to our data set using a binary model is found for a faint companion located at about 14.4 mas from β Pic, which has a contrast of 1.8×10^-3 ± 1.1×10^-3 (a result consistent with the absence of companions). For angular separations larger than 60 mas, both time smearing and field-of-view limitations reduce the sensitivity. Conclusions. We can exclude the presence of brown dwarfs with masses higher than 29 MJup (resp. 47 MJup) at a 50% (resp. 90%) completeness level within the first few AUs around β Pic. Interferometric closure phases offer a promising way to directly image low-mass companions in the close environment of nearby young stars. [less ▲]

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See detailNew findings on the prototypical Of?p stars
Nazé, Yaël ULg; Ud-Doula, Asif; Spano, Maxime et al

in Astronomy and Astrophysics (2010), 520

<BR /> Aims: In recent years several in-depth investigations of the three prototypical Of?p stars were undertaken. These multiwavelength studies revealed the peculiar properties of these objects (in the X ... [more ▼]

<BR /> Aims: In recent years several in-depth investigations of the three prototypical Of?p stars were undertaken. These multiwavelength studies revealed the peculiar properties of these objects (in the X-rays as well as in the optical): magnetic fields, periodic line profile variations, recurrent photometric changes. However, many questions remain unsolved. <BR /> Methods: To clarify some of the properties of the Of?p stars, we have continued their monitoring. A new xmm-Newton observation and two new optical datasets were obtained. <BR /> Results: Additional information about the prototypical Of?p trio has been found. HD 108 has now reached its quiescent, minimum-emission state for the first time in 50-60 yr. The échelle spectra of HD 148937 confirm the presence of the 7d variations in the Balmer lines and reveal similar periodic variations (though of lower amplitudes) in the He i λ 5876 and He ii λ 4686 lines, underlining its similarities with the other two prototypical Of?p stars. The new xmm-Newton observation of HD 191612 was taken at the same phase in the line modulation cycle, but at a different orbital phase from previous data. It clearly shows that the X-ray emission of HD 191612 is modulated by the 538d period and not by the orbital period of 1542d - it is thus not of colliding-wind origin. The phenomenon responsible for the optical changes appears also at work in the high-energy domain. There are problems however: our MHD simulations of the wind magnetic confinement predict both a harder X-ray flux of a much larger strength than what is observed (the modelled differential emission measure peaks at 30-40 MK, whereas the observed one peaks at 2 MK) and narrow lines (hot gas moving with velocities of 100-200 km s[SUP]-1[/SUP], whereas the observed full width at half maximum is ~2000 km s[SUP]-1[/SUP]). Based on observations collected at the Haute-Provence Observatory, at the La Silla and San Pedro Mártir Observatories, and 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 detailTransiting exoplanets from the CoRoT space mission. XII. CoRoT-12b: a short-period low-density planet transiting a solar analog star
Gillon, Michaël ULg; Hatzes, A.; Csizmadia, Szilard et al

in Astronomy and Astrophysics (2010), 520

We report the discovery by the CoRoT satellite of a new transiting giant planet in a 2.83 days orbit about a V = 15.5 solar analog star (M_* = 1.08 ± 0.08 M_ȯ, R_* = 1.1 ± 0.1 R_ȯ, T[SUB]eff[/SUB] = 5675 ... [more ▼]

We report the discovery by the CoRoT satellite of a new transiting giant planet in a 2.83 days orbit about a V = 15.5 solar analog star (M_* = 1.08 ± 0.08 M_ȯ, R_* = 1.1 ± 0.1 R_ȯ, T[SUB]eff[/SUB] = 5675 ± 80 K). This new planet, CoRoT-12b, has a mass of 0.92 ± 0.07 M[SUB]Jup[/SUB] and a radius of 1.44 ± 0.13 R[SUB]Jup[/SUB]. Its low density can be explained by standard models for irradiated planets. The CoRoT space mission, launched on December 27, 2006, has been developed and is operated by CNES, with the contribution of Austria, Belgium, Brazil, ESA (RSSD and Science Program), Germany and Spain. [less ▲]

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See detailTransiting exoplanets from the CoRoT space mission. XI. CoRoT-8b: a hot and dense sub-Saturn around a K1 dwarf
Bordé, P.; Bouchy, F.; Deleuil, M. et al

in Astronomy and Astrophysics (2010), 520

<BR /> Aims: We report the discovery of CoRoT-8b, a dense small Saturn-class exoplanet that orbits a K1 dwarf in 6.2 days, and we derive its orbital parameters, mass, and radius. <BR /> Methods: We ... [more ▼]

<BR /> Aims: We report the discovery of CoRoT-8b, a dense small Saturn-class exoplanet that orbits a K1 dwarf in 6.2 days, and we derive its orbital parameters, mass, and radius. <BR /> Methods: We analyzed two complementary data sets: the photometric transit curve of CoRoT-8b as measured by CoRoT and the radial velocity curve of CoRoT-8 as measured by the HARPS spectrometer. <BR /> Results: We find that CoRoT-8b is on a circular orbit with a semi-major axis of 0.063 ± 0.001 AU. It has a radius of 0.57 ± 0.02 R[SUB]J[/SUB], a mass of 0.22 ± 0.03 M[SUB]J[/SUB], and therefore a mean density of 1.6 ± 0.1 g cm[SUP]-3[/SUP]. <BR /> Conclusions: With 67% of the size of Saturn and 72% of its mass, CoRoT-8b has a density comparable to that of Neptune (1.76 g cm[SUP]-3[/SUP]). We estimate its content in heavy elements to be 47-63 {M}_⊕, and the mass of its hydrogen-helium envelope to be 7-23 {M}_⊕. At 0.063 AU, the thermal loss of hydrogen of CoRoT-8b should be no more than 0.1% over an assumed integrated lifetime of 3 Ga. Observations made with SOPHIE spectrograph at Observatoire de Haute Provence, France (PNP.07B.MOUT), and the HARPS spectrograph at ESO La Silla Observatory (081.C-0388 and 083.C-0186). The CoRoT space mission, launched on December 27, 2006, has been developed and is operated by the CNES with the contribution of Austria, Belgium, Brasil, ESA, Germany, and Spain.Both data sets are 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/520/A66">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/520/A66</A> [less ▲]

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See detailTransiting exoplanets from the CoRoT space mission. X. CoRoT-10b: a giant planet in a 13.24 day eccentric orbit
Bonomo, A. S.; Santerne, A.; Alonso, R. et al

in Astronomy and Astrophysics (2010), 520

Context. The space telescope CoRoT searches for transiting extrasolar planets by continuously monitoring the optical flux of thousands of stars in several fields of view. <BR /> Aims: We report the ... [more ▼]

Context. The space telescope CoRoT searches for transiting extrasolar planets by continuously monitoring the optical flux of thousands of stars in several fields of view. <BR /> Aims: We report the discovery of CoRoT-10b, a giant planet on a highly eccentric orbit (e = 0.53 ± 0.04) revolving in 13.24 days around a faint (V = 15.22) metal-rich K1V star. <BR /> Methods: We used CoRoT photometry, radial velocity observations taken with the HARPS spectrograph, and UVES spectra of the parent star to derive the orbital, stellar, and planetary parameters. <BR /> Results: We derive a radius of the planet of 0.97 ± 0.07 R[SUB]Jup[/SUB] and a mass of 2.75 ± 0.16 M[SUB]Jup[/SUB]. The bulk density, ρ[SUB]p[/SUB] = 3.70 ± 0.83 g cm[SUP]-3[/SUP], is ~2.8 that of Jupiter. The core of CoRoT-10b could contain up to 240 M_⊕ of heavy elements. Moving along its eccentric orbit, the planet experiences a 10.6-fold variation in insolation. Owing to the long circularisation time, τ[SUB]circ[/SUB] > 7 Gyr, a resonant perturber is not required to excite and maintain the high eccentricity of CoRoT-10b. 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. [less ▲]

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See detailMicrolensing in H1413+117: disentangling line profile emission and absorption in a broad absorption line quasar
Hutsemekers, Damien ULg; Borguet, Benoît ULg; Sluse, D. et al

in Astronomy and Astrophysics (2010), 519

On the basis of 16 years of spectroscopic observations of the four components of the gravitationally lensed broad absorption line (BAL) quasar H1413+117, covering the ultraviolet to visible rest-frame ... [more ▼]

On the basis of 16 years of spectroscopic observations of the four components of the gravitationally lensed broad absorption line (BAL) quasar H1413+117, covering the ultraviolet to visible rest-frame spectral range, we analyze the spectral differences observed in the P Cygni-type line profiles and have used the microlensing effect to derive new clues to the BAL profile formation. We first find that the absorption gradually decreases with time in all components and that this intrinsic variation is accompanied by a decrease in the intensity of the emission. We confirm that the spectral differences observed in component D can be attributed to a microlensing effect lasting at least a decade. We show that microlensing magnifies the continuum source in image D, leaving the emission line region essentially unaffected. We interpret the differences seen in the absorption profiles of component D as the result of an emission line superimposed onto a nearly black absorption profile. We also find that the continuum source and a part of the broad emission line region are likely de-magnified in component C, while components A and B are not affected by microlensing. Differential dust extinction is measured between the A and B lines of sight. We show that microlensing of the continuum source in component D has a chromatic dependence compatible with the thermal continuum emission of a standard Shakura-Sunyaev accretion disk. Using a simple decomposition method to separate the part of the line profiles affected by microlensing and coming from a compact region from the part unaffected by this effect and coming from a larger region, we disentangle the true absorption line profiles from the true emission line profiles. The extracted emission line profiles appear double-peaked, suggesting that the emission is occulted by a strong absorber, narrower in velocity than the full absorption profile, and emitting little by itself. We propose that the outflow around H1413+117 is constituted by a high-velocity polar flow and a denser, lower velocity disk seen nearly edge-on. Finally, we report on the first ground-based polarimetric measurements of the four components of H1413+117. Based on observations made with the Canada-France-Hawaii Telescope (Hawaii), with ESO Telescopes at the Paranal Observatory (Chile) and with the NASA/ESA Hubble Space Telescope, and obtained from the data archive at the Space Telescope Institute. ESO program ID: 074.A-0152, 075.B-0675, 081.A-0023. [less ▲]

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See detailTransiting exoplanets from the CoRoT space mission XIV. CoRoT-11b: a transiting massive "hot-Jupiter" in a prograde orbit around a rapidly rotating F-type star
Gandolfi, D.; Hébrard, G.; Alonso, R. et al

in Astronomy and Astrophysics (2010), 524

The CoRoT exoplanet science team announces the discovery of CoRoT-11b, a fairly massive hot-Jupiter transiting a V=12.9 mag F6 dwarf star (M*=1.27 +/- 0.05 Msun, R*=1.37 +/- 0.03 Rsun, Teff=6440 +/- 120 K ... [more ▼]

The CoRoT exoplanet science team announces the discovery of CoRoT-11b, a fairly massive hot-Jupiter transiting a V=12.9 mag F6 dwarf star (M*=1.27 +/- 0.05 Msun, R*=1.37 +/- 0.03 Rsun, Teff=6440 +/- 120 K), with an orbital period of P=2.994329 +/- 0.000011 days and semi-major axis a=0.0436 +/- 0.005 AU. The detection of part of the radial velocity anomaly caused by the Rossiter-McLaughlin effect shows that the transit-like events detected by CoRoT are caused by a planet-sized transiting object in a prograde orbit. The relatively high projected rotational velocity of the star (vsini=40+/-5 km/s) places CoRoT-11 among the most rapidly rotating planet host stars discovered so far. With a planetary mass of mp=2.33+/-0.34 Mjup and radius rp=1.43+/-0.03 Rjup, the resulting mean density of CoRoT-11b (rho=0.99+/-0.15 g/cm^3) can be explained with a model for an inflated hydrogen-planet with a solar composition and a high level of energy dissipation in its interior. [less ▲]

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See detailDetection of frequency spacings in the young O-type binary HD 46149 from CoRoT photometry
Degroote, P.; Briquet, Maryline ULg; Auvergne, M. et al

in Astronomy and Astrophysics (2010), 519

<BR /> Aims: Using the CoRoT space based photometry of the O-type binary HD 46149, stellar atmospheric effects related to rotation can be separated from pulsations, because they leave distinct signatures ... [more ▼]

<BR /> Aims: Using the CoRoT space based photometry of the O-type binary HD 46149, stellar atmospheric effects related to rotation can be separated from pulsations, because they leave distinct signatures in the light curve. This offers the possibility of characterising and exploiting any pulsations seismologically. <BR /> Methods: Combining high-quality space based photometry, multi-wavelength photometry, spectroscopy and constraints imposed by binarity and cluster membership, the detected pulsations in HD 46149 are analyzed and compared with those for a grid of stellar evolutionary models in a proof-of-concept approach. <BR /> Results: We present evidence of solar-like oscillations in a massive O-type star, and show that the observed frequency range and spacings are compatible with theoretical predictions. Thus, we unlock and confirm the strong potential of this seismically unexplored region in the HR diagram. 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. [less ▲]

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See detailEvidence for a sharp structure variation inside a red-giant star
Miglio, Andrea ULg; Montalban Iglesias, Josefa ULg; Carrier, F. et al

in Astronomy and Astrophysics (2010), 520

Context. The availability of precisely determined frequencies of radial and non-radial oscillation modes in red giants is finally paving the way for detailed studies of the internal structure of these ... [more ▼]

Context. The availability of precisely determined frequencies of radial and non-radial oscillation modes in red giants is finally paving the way for detailed studies of the internal structure of these stars. <BR /> Aims: We look for the seismic signature of regions of sharp structure variation in the internal structure of the CoRoT target HR 7349. <BR /> Methods: We analyse the frequency dependence of the large frequency separation and second frequency differences, as well as the behaviour of the large frequency separation obtained with the envelope auto-correlation function. <BR /> Results: We find evidence for a periodic component in the oscillation frequencies, i.e. the seismic signature of a sharp structure variation in HR 7349. In a comparison with stellar models we interpret this feature as caused by a local depression of the sound speed that occurs in the helium second-ionization region. Using solely seismic constraints this allows us to estimate the mass (M = 1.2[SUB]-0.4[/SUB][SUP]+0.6[/SUP] M_&sun;) and radius (R = 12.2[SUB]-1.8[/SUB][SUP]+2.1[/SUP] R_&sun;) of HR 7349, which agrees with the location of the star in an HR diagram. [less ▲]

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See detailEffects of rotational mixing on the asteroseismic properties of solar-type stars
Eggenberger, P.; Meynet, G.; Maeder, A. et al

in Astronomy and Astrophysics (2010), 519

Context. Observations of solar-like oscillations obtained either from the ground or from space stimulated the study of the effects of various physical processes on the modelling of solar-type stars. <BR ... [more ▼]

Context. Observations of solar-like oscillations obtained either from the ground or from space stimulated the study of the effects of various physical processes on the modelling of solar-type stars. <BR /> Aims: The influence of rotational mixing on the evolution and asteroseismic properties of solar-type stars is studied. <BR /> Methods: Global and asteroseismic properties of models of solar-type stars computed with and without a comprehensive treatment of shellular rotation are compared. The effects of internal magnetic fields are also discussed in the framework of the Tayler-Spruit dynamo. <BR /> Results: Rotational mixing changes the global properties of a solar-type star with a significant increase of the effective temperature resulting in a shift of the evolutionary track to the blue part of the HR diagram. These differences observed in the HR diagram are related to changes of the chemical composition, because rotational mixing counteracts the effects of atomic diffusion leading to larger helium surface abundances for rotating models than for non-rotating ones. Higher values of the large frequency separation are then found for rotating models than for non-rotating ones at the same evolutionary stage, because the increase of the effective temperature leads to a smaller radius and hence to an increase of the stellar mean density. In addition to changing the global properties of solar-type stars, rotational mixing also has a considerable impact on the structure and chemical composition of the central stellar layers by bringing fresh hydrogen fuel to the central stellar core, thereby enhancing the main-sequence lifetime. The increase of the central hydrogen abundance together with the change of the chemical profiles in the central layers result in a significant increase of the values of the small frequency separations and of the ratio of the small to large separations for models including shellular rotation. This increase is clearly seen for models with the same age sharing the same initial parameters except for the inclusion of rotation as well as for models with the same global stellar parameters and in particular the same location in the HR diagram. By computing rotating models of solar-type stars including the effects of a dynamo that possibly occurs in the radiative zone, we find that the efficiency of rotational mixing is strongly reduced when the effects of magnetic fields are taken into account, in contrast to what happens in massive stars. [less ▲]

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See detailOptical circular polarization in quasars
Hutsemekers, Damien ULg; Borguet, Benoît ULg; Sluse, D. et al

in Astronomy and Astrophysics (2010), 520(Letters), 71-5

We present new optical circular polarization measurements with typical uncertainties <0.1% for a sample of 21 quasars. All but two objects have null circular polarization. We use this result to constrain ... [more ▼]

We present new optical circular polarization measurements with typical uncertainties <0.1% for a sample of 21 quasars. All but two objects have null circular polarization. We use this result to constrain the polarization due to photon-pseudoscalar mixing along the line of sight. We detect significant (> 3σ) circular polarization in two blazars with high linear polarization and discuss the implications of this result for quasar physics. In particular, the recorded polarization degrees may be indicative of magnetic fields as strong as 1 kG or a significant contribution of inverse Compton scattering to the optical continuum. Based on observations made with ESO Telescopes at the La Silla Observatory (Chile). ESO program ID: 79.A-0625(B).Appendices are only available in electronic form at <A href="http://www.aanda.org">http://www.aanda.org</A> [less ▲]

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See detailNon-thermal radio emission from O-type stars. IV. Cygnus OB2 No. 8A
Blomme, R.; De Becker, Michaël ULg; Volpi, D. et al

in Astronomy and Astrophysics (2010), 519

Context. Several early-type colliding-wind binaries are known to emit synchrotron radiation due to relativistic electrons, which are most probably accelerated by the Fermi mechanism. By studying such ... [more ▼]

Context. Several early-type colliding-wind binaries are known to emit synchrotron radiation due to relativistic electrons, which are most probably accelerated by the Fermi mechanism. By studying such systems we can learn more about this mechanism, which is also relevant in other astrophysical contexts. Colliding-wind binaries are furthermore important for binary frequency determination in clusters and for understanding clumping and porosity in stellar winds. Aims: We study the non-thermal radio emission of the binary Cyg OB2 No. 8A, to see if it is variable and if that variability is locked to the orbital phase. We investigate if the synchrotron emission generated in the colliding-wind region of this binary can explain the observations and we verify that our proposed model is compatible with the X-ray data. Methods: We use both new and archive radio data from the Very Large Array (VLA) to construct a light curve as a function of orbital phase. We also present new X-ray data that allow us to improve the X-ray light curve. We develop a numerical model for the colliding-wind region and the synchrotron emission it generates. The model also includes free-free absorption and emission due to the stellar winds of both stars. In this way we construct artificial radio light curves and compare them with the observed one. Results: The observed radio fluxes show phase-locked variability. Our model can explain this variability because the synchrotron emitting region is not completely hidden by the free-free absorption. In order to obtain a better agreement for the phases of minimum and maximum flux we need to use stellar wind parameters for the binary components which are somewhat different from typical values for single stars. We verify that the change in stellar parameters does not influence the interpretation of the X-ray light curve. Our model has trouble explaining the observed radio spectral index. This could indicate the presence of clumping or porosity in the stellar wind, which - through its influence on both the Razin effect and the free-free absorption - can considerably influence the spectral index. Non-thermal radio emitters could therefore open a valuable pathway to investigate the difficult issue of clumping in stellar winds. [less ▲]

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See detailCold DUst around NEarby Stars (DUNES). First results. A resolved exo-Kuiper belt around the solar-like star ζ2 Ret
Eiroa, C.; Fedele, D.; Maldonado, J. et al

in Astronomy and Astrophysics (2010), 518

We present the first far-IR observations of the solar-type stars δ Pav, HR 8501, 51 Peg and ζ2 Ret, taken within the context of the DUNES Herschel open time key programme (OTKP). This project uses the ... [more ▼]

We present the first far-IR observations of the solar-type stars δ Pav, HR 8501, 51 Peg and ζ2 Ret, taken within the context of the DUNES Herschel open time key programme (OTKP). This project uses the PACS and SPIRE instruments with the objective of studying infrared excesses due to exo-Kuiper belts around nearby solar-type stars. The observed 100 μm fluxes from δ Pav, HR 8501, and 51 Peg agree with the predicted photospheric fluxes, excluding debris disks brighter than Ldust/ ~ 5 × 10-7 (1σ level) around those stars. A flattened, disk-like structure with a semi-major axis of ~100 AU in size is detected around ζ2 Ret. The resolved structure suggests the presence of an eccentric dust ring, which we interpret as an exo-Kuiper belt with Ldust/ ≈ 10-5. [less ▲]

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See detailResolving the cold debris disc around a planet-hosting star. PACS photometric imaging observations of q1 Eridani (HD 10647, HR 506)
Liseau, R.; Eiroa, C.; Fedele, D. et al

in Astronomy and Astrophysics (2010), 518

Context. About two dozen exo-solar debris systems have been spatially resolved. These debris discs commonly display a variety of structural features such as clumps, rings, belts, excentric distributions ... [more ▼]

Context. About two dozen exo-solar debris systems have been spatially resolved. These debris discs commonly display a variety of structural features such as clumps, rings, belts, excentric distributions and spiral patterns. In most cases, these features are believed to be formed, shaped and maintained by the dynamical influence of planets orbiting the host stars. In very few cases has the presence of the dynamically important planet(s) been inferred from direct observation. Aims. The solar-type star q1 Eri is known to be surrounded by debris, extended on scales of 30”. The star is also known to host at least one planet, albeit on an orbit far too small to make it responsible for structures at distances of tens to hundreds of AU. The aim of the present investigation is twofold: to determine the optical and material properties of the debris and to infer the spatial distribution of the dust, which may hint at the presence of additional planets. Methods. The Photodetector Array Camera and Spectrometer (PACS) aboard the Herschel Space Observatory allows imaging observations in the far infrared at unprecedented resolution, i.e. at better than 6” to 12” over the wavelength range of 60 μm to 210 μm. Together with the results from ground-based observations, these spatially resolved data can be modelled to determine the nature of the debris and its evolution more reliably than what would be possible from unresolved data alone. Results. For the first time has the q1 Eri disc been resolved at far infrared wavelengths. The PACS observations at 70 μm, 100 μm and 160 μm reveal an oval image showing a disc-like structure in all bands, the size of which increases with wavelength. Assuming a circular shape yields the inclination of its equatorial plane with respect to that of the sky, i > 53°. The results of image de-convolution indicate that i likely is larger than 63°, where 90° corresponds to an edge-on disc. Conclusions. The observed emission is thermal and optically thin. The resolved data are consistent with debris at temperatures below 30 K at radii larger than 120 AU. From image de-convolution, we find that q1 Eri is surrounded by an about 40 AU wide ring at the radial distance of ~85 AU. This is the first real Edgeworth-Kuiper Belt analogue ever observed. [less ▲]

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