O. Chesneau

Publications (127)151.1 Total impact

• Article: The H-band Emitting Region of the Luminous Blue Variable P Cygni: Spectrophotometry and Interferometry of the Wind

  N. D. Richardson, G. H. Schaefer, D. R. Gies, O. Chesneau, J. D. Monnier, F. Baron, X. Che, J. R. Parks, R. A. Matson, Y. Touhami, [......], T. A. ten Brummelaar, H. A. McAlister, S. Kraus, S. T. Ridgway, J. Sturmann, L. Sturmann, B. Taylor, N. H. Turner, C. D. Farrington, P. J. Goldfinger
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  ABSTRACT: We present the first high angular resolution observations in the nearinfrared H-band (1.6 microns) of the Luminous Blue Variable star P Cygni. We obtained six-telescope interferometric observations with the CHARA Array and the MIRC beam combiner. These show that the spatial flux distribution is larger than expected for the stellar photosphere. A two component model for the star (uniform disk) plus a halo (two-dimensional Gaussian) yields an excellent fit of the observations, and we suggest that the halo corresponds to flux emitted from the base of the stellar wind. This wind component contributes about 45% of the H-band flux and has an angular FWHM = 0.96 mas, compared to the predicted stellar diameter of 0.41 mas. We show several images reconstructed from the interferometric visibilities and closure phases, and they indicate a generally spherical geometry for the wind. We also obtained near-infrared spectrophotometry of P Cygni from which we derive the flux excess compared to a purely photospheric spectral energy distribution. The H-band flux excess matches that from the wind flux fraction derived from the two component fits to the interferometry. We find evidence of significant near-infrared flux variability over the period from 2006 to 2010 that appears similar to the variations in the H-alpha emission flux from the wind. Future interferometric observations may be capable of recording the spatial variations associated with temporal changes in the wind structure.
  04/2013;
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  Available from: Carla Susana Gil

  Dataset: aa5408-06

  F. Millour, R. G. Petrov, O. Chesneau, D. Bonneau, L. Dessart, Clémentine Béchet, Isabelle Tallon-Bosc, Michel Tallon, Eric Thiébaut, F. Vakili, [......], J. Behrend, C. Baffa, E. Aristidi, B. Arezki, K. Agabi, B. Acke, M Accardo, M. Kiekebusch, F. Rantakyrö, Markus Schoeller
• Article: PEGASE, an infrared interferometer to study stellar environments and low mass companions around nearby stars

  M. Ollivier, O. Absil, F. Allard, J.-P. Berger, P. Bordé, F. Cassaing, B. Chazelas, A. Chelli, O. Chesneau, V. Coudé du Foresto, [......], D. Mourard, D. Pelat, G. Perrin, Y. Rabbia, D. Rouan, J.-M. Reiss, G. Rousset, F. Selsis, P. Stee, J. Surdej
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  ABSTRACT: PEGASE is a mission dedicated to the exploration of the environment (including habitable zone) of young and solar-type stars (particularly those in the DARWIN catalogue) and the observation of low mass companions around nearby stars. It is a space interferometer project composed of three free flying spacecraft, respectively featuring two 40cm siderostats and a beam combiner working in the visible and near infrared. It has been proposed to ESA as an answer to the first “Cosmic Vision” call for proposals, as an M mission. The concept also enables full-scale demonstration of space nulling interferometry operation for DARWIN.
  Experimental Astronomy 04/2012; 23(1):403-434. · 1.82 Impact Factor
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  Available from: F. X. Schmider

  Article: The diameter of the CoRoT target HD 49933. Combining the 3D limb darkening, asteroseismology, and interferometry

  L. Bigot, D. Mourard, P. Berio, F. Thévenin, R. Ligi, I. Tallon-Bosc, O. Chesneau, O. Delaa, N. Nardetto, K. Perraut, [......], P. Kervella, F. X. Schmider, H. McAlister, T. ten Brummelaar, S. T. Ridgway, J. Sturmann, L. Sturmann, N. Turner, C. Farrington, P. J. Goldfinger
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  ABSTRACT: Context. The interpretation of stellar pulsations in terms of internal structure depends on the knowledge of the fundamental stellar parameters. Long-base interferometers permit us to determine very accurate stellar radii, which are independent constraints for stellar models that help us to locate the star in the HR diagram. Aims: Using a direct interferometric determination of the angular diameter and advanced three-dimensional (3D) modeling, we derive the radius of the CoRoT target HD 49933 and reduce the global stellar parameter space compatible with seismic data. Methods: The VEGA/CHARA spectro-interferometer is used to measure the angular diameter of the star. A 3D radiative hydrodynamical simulation of the surface is performed to compute the limb darkening and derive a reliable diameter from visibility curves. The other fundamental stellar parameters (mass, age, and Teff) are found by fitting the large and small p-mode frequency separations using a stellar evolution model that includes microscopic diffusion. Results: We obtain a limb-darkened angular diameter of {\theta}LD = 0.445 \pm 0.012 mas. With the Hipparcos parallax, we obtain a radius of R = 1.42 \pm 0.04 Rsun. The corresponding stellar evolution model that fits both large and small frequency separations has a mass of 1.20 \pm 0.08 Msun and an age of 2.7 Gy. The atmospheric parameters are Teff = 6640 \pm 100 K, log g = 4.21 \pm 0.14, and [Fe/H] = -0.38.
  10/2011;
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  Available from: Alain Spang

  Article: The 2011 outburst of the recurrent nova T Pyxidis . Evidence for a face-on bipolar ejection

  O Chesneau, A Meilland, D ~P ~K Banerjee, J -B Le Bouquin, H McAlister, F Millour, S ~T Ridgway, A Spang, T Ten Brummelaar, M Wittkowski, [......], T Boyajian, C Farrington, P ~J Goldfinger, A Merand, N Nardetto, R Petrov, T Rivinius, G Schaefer, Y Touhami, G Zins
  åp. 10/2011; 534:L11.
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  Available from: Alain Spang

  Article: Chromosphere of K giant stars Geometrical extent and spatial structure detection

  P. Berio, T. Merle, F. Thevenin, D. Bonneau, D. Mourard, O. Chesneau, O. Delaa, R. Ligi, N. Nardetto, K. Perraut, [......], I. Tallon-Bosc, J. M. Clausse, A. Spang, H. McAlister, T. ten Brummelaar, J. Sturmann, L. Sturmann, N. Turner, C. Farrington, P. J. Goldfinger
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  ABSTRACT: We aim to constrain the geometrical extent of the chromosphere of non-binary K giant stars and detect any spatial structures in the chromosphere. We performed observations with the CHARA interferometer and the VEGA beam combiner at optical wavelengths. We observed seven non-binary K giant stars. We measured the ratio of the radii of the photosphere to the chromosphere using the interferometric measurements in the Halpha and the Ca II infrared triplet line cores. For beta Ceti, spectro-interferometric observations are compared to an non-local thermal equilibrium (NLTE) semi-empirical model atmosphere including a chromosphere. The NLTE computations provide line intensities and contribution functions that indicate the relative locations where the line cores are formed and can constrain the size of the limb-darkened disk of the stars with chromospheres. We measured the angular diameter of seven K giant stars and deduced their fundamental parameters: effective temperatures, radii, luminosities, and masses. We determined the geometrical extent of the chromosphere for four giant stars. The chromosphere extents obtained range between 16% to 47% of the stellar radius. The NLTE computations confirm that the Ca II/849 nm line core is deeper in the chromosphere of ? Cet than either of the Ca II/854 nm and Ca II/866 nm line cores. We present a modified version of a semi-empirical model atmosphere derived by fitting the Ca II triplet line cores of this star. In four of our targets, we also detect the signature of a differential signal showing the presence of asymmetries in the chromospheres. Conclusions. It is the first time that geometrical extents and structure in the chromospheres of non-binary K giant stars are determined by interferometry. These observations provide strong constrains on stellar atmosphere models.
  09/2011;
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  Available from: Eric Lagadec

  Article: Observing Compact Disks Inside Pre-Planetary Nebulae with the Very Large Telescope Interferometer

  S. N. Bright, O. De Marco, O. Chesneau, E. Lagadec, H. Van Winckel, B. J. Hrivnak
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  ABSTRACT: AGB stars appear to lose mass spherically, but many PNe resulting from the AGB mass-loss have non-spherical morphologies. Compact disks have been found in some bipolar PNe, but their role in the shaping process remains unknown. Compact Keplarian disks are found to be common around post-AGB binaries, however, these objects may never develop into PNe. Another group of post-AGB stars, known as pre-PNe, are surrounded by collimated nebulae shining by reflected light or shock ionisation. We are observing the inner circumstellar regions of pre-PNe at high angular resolutions with the VLTI. We seek to compare pre-PNe disks to those around other post-AGB stars and PNe. New observations of the pre-PN, IRAS 16279-4757, show evidence for a disk similar to those seen in young PNe.
  09/2011;
• Conference Proceeding: Interferometric Constraints on Surface Brightness Asymmetries in Long-Period Variable Stars: A Threat to Accurate Gaia Parallaxes

  S Sacuto, A Jorissen, P Cruzalèbes, E Pasquato, A Chiavassa, A Spang, Y Rabbia, O Chesneau
  Why Galaxies Care about AGB Stars II: Shining Examples and Common Inhabitants; 09/2011
• Conference Proceeding: Photocentric and Photometric Variability of Red Supergiant Stars

  A Chiavassa, E Pasquato, A Jorissen, S Sacuto, C Babusiaux, B Freytag, H -G Ludwig, P Cruzalèbes, Y Rabbia, A Spang, O Chesneau
  Why Galaxies Care about AGB Stars II: Shining Examples and Common Inhabitants; 09/2011
• Article: CalVin 3 mdash A New Release of the ESO Calibrator Selection Tool for the VLT Interferometer

  M Wittkowski, P Ballester, D Bonneau, A Chelli, O Chesneau, P Cruzalèbes, G Duvert, C Hummel, S Lafrasse, G Mella, J Melnick, A Mérand, D Mourard, I Percheron, S Sacuto, K Shabun, S Stefl, J Vinther
  The Messenger. 09/2011; 145:7-9.
• Article: Very Large Telescope Interferometer observations of the dust geometry around R Coronae Borealis stars★

  S. N. Bright, O. Chesneau, G. C. Clayton, O. De Marco, I. C. Leão, J. Nordhaus, J. S. Gallagher
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  ABSTRACT: We are investigating the formation and evolution of dust around the hydrogen-deficient supergiants known as R Coronae Borealis (RCB) stars. We aim to determine the connection between the probable merger past of these stars and their current dust-production activities.We carried out high angular resolution interferometric observations of three RCB stars, namely RY Sgr, V CrA and V854 Cen, with the mid-infrared interferometer (MIDI) on the Very Large Telescope Interferometer (VLTI), using two telescope pairs. The baselines ranged from 30 to 60 m, allowing us to probe the dusty environment at very small spatial scales (∼50 mas or 400R★). The observations of the RCB star dust environments were interpreted using both geometrical models and one-dimensional radiative transfer codes.From our analysis, we find that asymmetric circumstellar material is apparent in RY Sgr, may also exist in V CrA and is possible for V854 Cen. Overall, we find that our observations are consistent with dust forming in clumps ejected randomly around the RCB star so that over time they create a spherically symmetric distribution of dust. However, we conclude that the determination of whether there is a preferred plane of dust ejection must wait until a time series of observations are obtained.
  Monthly Notices of the Royal Astronomical Society 05/2011; 414(2):1195 - 1206. · 4.90 Impact Factor
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  Available from: Alain Spang

  Article: Kinematics and geometrical study of the Be stars 48 Per and ψ Per with the VEGA/CHARA interferometer

  O Delaa, Ph Stee, A Meilland, J Zorec, D Mourard, Ph Bério, D Bonneau, O Chesneau, J M Clausse, P Cruzalebes, [......], A Marcotto, A Roussel, A Spang, H Mcalister, T Ten Brummelaar, J Sturmann, L Sturmann, N Turner, C Farrington, P J Goldfinger
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  ABSTRACT: Context. Five different physical processes might be responsible for the formation of decretion disks around Be stars: fast rotation of the star, stellar pulsations, binarity, stellar winds and magnetic fields. Our observations indicate that fast rotation seems to produce a disk in Keplerian rotation, at least in the specific case of the two stars observed. We do not know if this observational result is a generality or not. Aims. We measure the size, orientation, shape, and kinematics of the disks around 2 Be stars, namely 48 Per and ψ Per. Methods. We used the VEGA/CHARA interferometer with a spectral resolution of 5000 to obtain spectrally dispersed visibility modulus and phases within the Hα emission line. Results. We were able to estimate the disk extension in the continuum and in the Hα line, as well as flattening, for both stars. Both stars rotate at nearly a critical rotation, but while the disk of 48 Per seems to be in Keplerian rotation, our preliminary data suggest that the disk of ψ Per is possibly faster than Keplerian, similarly to what has been found for κ CMa with observations carried out in the near-IR. However, more data is needed to confirm the fast rotation of the disk. Conclusions. Assuming a simple uniform disk model for the stellar photosphere in the continuum and a Gaussian brightness distribution in the line emission region, we obtain a ratio of the disk diameter over the photospheric diameter of 8 48 Per and 11 for and ψ Per. We also found that the major axis of 48 Per is parallel to the polarization angle and not perpendicular to it as previously observed for many Be stars, including ψ Per. This might be due to the optical thickness of the disk, which is also responsible for the incoherent scattering of a non negligible part of the Hα line emission. To our knowledge, this is the first time that this effect has been measured in a Be star.
  03/2011;
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  Available from: ArXiv

  Article: VLTI observations of the dust geometry around R Coronae Borealis stars

  S. N. Bright, O. Chesneau, G. C. Clayton, O. De Marco, I. C. Leão, J. Nordhaus, J. S. Gallagher
  [show abstract] [hide abstract]
  ABSTRACT: We are investigating the formation and evolution of dust around the hydrogen-deficient supergiants known as R Coronae Borealis (RCB) stars. We aim to determine the connection between the probable merger past of these stars and their current dust-production activities. We carried out high-angular resolution interferometric observations of three RCB stars, namely RY Sgr, V CrA, and V854 Cen with the mid-IR interferometer, MIDI on the VLTI, using two telescope pairs. The baselines ranged from 30 to 60 m, allowing us to probe the dusty environment at very small spatial scales (~ 50 mas or 400 stellar radii). The observations of the RCB star dust environments were interpreted using both geometrical models and one-dimensional radiative transfer codes. From our analysis we find that asymmetric circumstellar material is apparent in RY Sgr, may also exist in V CrA, and is possible for V854 Cen. Overall, we find that our observations are consistent with dust forming in clumps ejected randomly around the RCB star so that over time they create a spherically symmetric distribution of dust. However, we conclude that the determination of whether there is a preferred plane of dust ejection must wait until a time series of observations are obtained.
  02/2011;
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  Available from: A. Jorissen

  Article: Radiative hydrodynamics simulations of red supergiant stars. III. Spectro-photocentric variability, photometric variability, and consequences on Gaia measurements

  A. Chiavassa, E. Pasquato, A. Jorissen, S. Sacuto, C. Babusiaux, B. Freytag, H. -G. Ludwig, P. Cruzalebes, Y. Rabbia, A. Spang, O. Chesneau
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  ABSTRACT: Context. It has been shown that convection in red supergiant stars gives rise to large granules causing surface inhomogeneities together with shock waves in the photosphere. The resulting motion of the photocenter (on time scales ranging from months to years) could possibly have adverse effects on the parallax determination with Gaia. Aims. We explore the impact of the granulation on the photocentric and photometric variability. We quantify these effects in order to better characterize the error possibly altering the parallax. Methods. We use 3D radiative-hydrodynamics simulations of convection with CO5BOLD and the post-processing radiative transfer code OPTIM3D to compute intensity maps and spectra in the Gaia G band [325-1030 nm]. Results. We provide astrometric and photometric predictions from 3D simulations of RSGs that are used to evaluate the degradation of the astrometric parameters of evolved stars derived by Gaia. We show from RHD simulations that a supergiant like Betelgeuse exhibits a photocentric noise characterised by a standard deviation of the order of 0.1 AU. The number of bright giant and supergiant stars whose Gaia parallaxes will be altered by the photocentric noise ranges from a few tens to several thousandths. The degradation of the astrometric fit due to the presence of this photocentric noise will be noticeable up to about 5 kpc for the brightest supergiants. Moreover, parallaxes of supergiants are affected by a error of the order of a few percents. We show that the photocentric noise, as predicted by the 3D simulation, does account for a substantial part of the supplementary 'cosmic noise' that affects Hipparcos measurements of Betelgeuse and Antares. Comment: 17 pages, accepted Astronomy & Astrophysics
  12/2010;
• Conference Proceeding: Photocentric variability of red supergiant stars and consequences on Gaia measurements

  A Chiavassa, E Pasquato, A Jorissen, S Sacuto, C Babusiaux, B Freytag, H -G Ludwig, P Cruzalèbes, Y Rabbia, A Spang, O Chesneau
  SF2A-2010: Proceedings of the Annual meeting of the French Society of Astronomy and Astrophysics; 12/2010
• Source

  Available from: Alain Spang

  Article: The fundamental parameters of the roAp star $\gamma$ Equulei

  K. Perraut, I. Brandão, D. Mourard, M. Cunha, Ph. Bério, D. Bonneau, O. Chesneau, J. M. Clausse, O. Delaa, A. Marcotto, [......], A. Spang, Ph. Stee, I. Tallon-Bosc, H. McAlister, T. ten Brummelaar, J. Sturmann, L. Sturmann, N. Turner, C. Farrington, P. J. Goldfinger
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  ABSTRACT: Physical processes working in the stellar interiors as well as the evolution of stars depend on some fundamental stellar properties, such as mass, radius, luminosity, and chemical abundances. A classical way to test stellar interior models is to compare the predicted and observed location of a star on theoretical evolutionary tracks in a H-R diagram. This requires the best possible determinations of stellar mass, radius, luminosity and abundances. To derive its fundamental parameters, we observed the well-known rapidly oscillating Ap star, $\gamma$ Equ, using the visible spectro-interferometer VEGA installed on the optical CHARA array. We computed the calibrated squared visibility and derived the limb-darkened diameter. We used the whole energy flux distribution, the parallax and this angular diameter to determine the luminosity and the effective temperature of the star. We obtained a limb-darkened angular diameter of 0.564~$\pm$~0.017~mas and deduced a radius of $R$~=~2.20~$\pm$~0.12~${\rm R_{\odot}}$. Without considering the multiple nature of the system, we derived a bolometric flux of $(3.12\pm 0.21)\times 10^{-7}$ erg~cm$^{-2}$~s$^{-1}$ and an effective temperature of 7364~$\pm$~235~K, which is below the effective temperature that has been previously determined. Under the same conditions we found a luminosity of $L$~=~12.8~$\pm$~1.4~${\rm L_{\odot}}$. When the contribution of the closest companion to the bolometric flux is considered, we found that the effective temperature and luminosity of the primary star can be, respectively, up to $\sim$~100~K and up to $\sim$~0.8~L$_\odot$ smaller than the values mentioned above.These new values of the radius and effective temperature should bring further constraints on the asteroseismic modelling of the star. Comment: Accepted by A&A
  11/2010;
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  Available from: Alain Blazit

  Article: An investigation of the close environment of beta Cep with the VEGA/CHARA interferometer

  N. Nardetto, D. Mourard, I. Tallon-Bosc, M. Tallon, P. Berio, E. Chapellier, D. Bonneau, O. Chesneau, P. Mathias, K. Perraut, [......], F. Millour, A. Roussel, A. Spang, H. McAlister, T. ten Brummelaar, J. Sturmann, L. Sturmann, N. Turner, C. Farrington, P. J. Goldfinger
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  ABSTRACT: High-precision interferometric measurements of pulsating stars help to characterize their close environment. In 1974, a close companion was discovered around the pulsating star beta Cep using the speckle interferometry technique and features at the limit of resolution (20 milli-arcsecond or mas) of the instrument were mentioned that may be due to circumstellar material. Beta Cep has a magnetic field that might be responsible for a spherical shell or ring-like structure around the star as described by the MHD models. Using the visible recombiner VEGA installed on the CHARA long-baseline interferometer at Mt. Wilson, we aim to determine the angular diameter of beta Cep and resolve its close environment with a spatial resolution up to 1 mas level. Medium spectral resolution (R=6000) observations of beta Cep were secured with the VEGA instrument over the years 2008 and 2009. These observations were performed with the S1S2 (30m) and W1W2 (100m) baselines of the array. We investigated several models to reproduce our observations. A large-scale structure of a few mas is clearly detected around the star with a typical flux relative contribution of 0.23 +- 0.02. Our best model is a co-rotational geometrical thin ring around the star as predicted by magnetically-confined wind shock models. The ring inner diameter is 8.2 +- 0.8 mas and the width is 0.6 +- 0.7 mas. The orientation of the rotation axis on the plane of the sky is PA = 60 +- 1 deg, while the best fit of the mean angular diameter of beta Cep gives UD[V] = 0.22 +- 0.05 mas. Our data are compatible with the predicted position of the close companion of beta Cep. These results bring additional constraints on the fundamental parameters and on the future MHD and asteroseismological models of the star. Comment: Paper accepted for publication in A&A (in press)
  10/2010;
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  Available from: E. T. Whelan

  Article: The 2008 outburst in the young stellar system ZCMa: I. Evidence of an enhanced bipolar wind on the AU-scale

  M. Benisty, F. Malbet, C. Dougados, A. Natta, J. -B. Le Bouquin, F. Massi, M. Bonnefoy, J. Bouvier, G. Chauvin, O. Chesneau, P. J. V. Garcia, K. Grankin, A. Isella, T. Ratzka, E. Tatulli, L. Testi, G. Weigelt, E. T. Whelan
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  ABSTRACT: Accretion is a fundamental process in star formation. Although the time evolution of accretion remains a matter of debate, observations and modelling studies suggest that episodic outbursts of strong accretion may dominate the formation of the protostar. Observing young stellar objects during these elevated accretion states is crucial to understanding the origin of unsteady accretion. ZCMa is a pre-main-sequence binary system composed of an embedded Herbig Be star, undergoing photometric outbursts, and a FU Orionis star. The Herbig Be component recently underwent its largest optical photometric outburst detected so far. We aim to constrain the origin of this outburst by studying the emission region of the HI Brackett gamma line, a powerful tracer of accretion/ejection processes on the AU-scale in young stars. Using the AMBER/VLTI instrument at spectral resolutions of 1500 and 12 000, we performed spatially and spectrally resolved interferometric observations of the hot gas emitting across the Brackett gamma emission line, during and after the outburst. From the visibilities and differential phases, we derive characteristic sizes for the Brackett gamma emission and spectro-astrometric measurements across the line, with respect to the continuum. We find that the line profile, the astrometric signal, and the visibilities are inconsistent with the signature of either a Keplerian disk or infall of matter. They are, instead, evidence of a bipolar wind, maybe partly seen through a disk hole inside the dust sublimation radius. The disappearance of the Brackett gamma emission line after the outburst suggests that the outburst is related to a period of strong mass loss rather than a change of the extinction along the line of sight. Based on these conclusions, we speculate that the origin of the outburst is an event of enhanced mass accretion, similar to those occuring in EX Ors and FU Ors. Comment: Accepted for publication in Astronomy and Astrophysics Letters
  07/2010;
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  Available from: Alain Spang

  Article: The H$\alpha$ line forming region of AB Aur spatially resolved at sub-AU with the VEGA/CHARA spectro-interferometer

  K. Perraut, M. Benisty, D. Mourard, S. Rajabi, F. Bacciotti, Ph. Bério, D. Bonneau, O. Chesneau, J. M. Clausse, O. Delaa, [......], A. Spang, Ph. Stee, I. Tallon-Bosc, H. McAlister, T. ten Brummelaar, J. Sturmann, L. Sturmann, N. Turner, C. Farrington, P. J. Goldfinger
  [show abstract] [hide abstract]
  ABSTRACT: A crucial issue in star formation is to understand the physical mechanism by which mass is accreted onto and ejected by a young star. The visible spectrometer VEGA on the CHARA array can be an efficient means of probing the structure and the kinematics of the hot circumstellar gas at sub-AU. For the first time, we observed the Herbig Ae star AB Aur in the H$\alpha$ emission line, using the VEGA low spectral resolution on two baselines of the array. We computed and calibrated the spectral visibilities between 610 nm and 700 nm. To simultaneously reproduce the line profile and the visibility, we used a 1-D radiative transfer code that calculates level populations for hydrogen atoms in a spherical geometry and synthetic spectro-interferometric observables. We clearly resolved AB Aur in the H$\alpha$ line and in a part of the continuum, even at the smallest baseline of 34 m. The small P-Cygni absorption feature is indicative of an outflow but could not be explained by a spherical stellar wind model. Instead, it favors a magneto-centrifugal X-disk or disk-wind geometry. The fit of the spectral visibilities could not be accounted for by a wind alone, so we considered a brightness asymmetry possibly caused by large-scale nebulosity or by the known spiral structures, inducing a visibility modulation around H$\alpha$. Thanks to the unique capabilities of VEGA, we managed to simultaneously record for the first time a spectrum at a resolution of 1700 and spectral visibilities in the visible range on a target as faint as $m_{V}$ = 7.1. It was possible to rule out a spherical geometry for the wind of AB Aur and provide realistic solutions to account for the H$\alpha$ emission compatible with magneto-centrifugal acceleration. The study illustrates the advantages of optical interferometry and motivates observations of other bright young stars to shed light on the accretion/ejection processes.
  05/2010;
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  Available from: archives-ouvertes.fr

  Article: Imaging “Pinwheel” nebulae with optical long-baseline interferometry

  F Millour, T Driebe, J H Groh, O Chesneau, G Weigelt, A Liermann, A Meilland
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  ABSTRACT: Dusty Wolf-Rayet stars are few but remarkable in terms of dust production rates (up to ˙ M = 10 −6 M⊙/yr). Infrared excesses associated to mass-loss are found in the sub-types WC8 and WC9. Few WC9d stars are hosting a "pinwheel" nebula, indirect evidence of a companion star around the primary. While few other WC9d stars have a dust shell which has been barely resolved so far, the available angular resolution offered by single telescopes is insufficient to confirm if they also host "pinwheel" nebulae or not. In this article, we present the possible de-tection of such nebula around the star WR 118. We discuss about the potential of interferometry to image more "pinwheel" nebulae around other WC9d stars.
  01/2010;