O. Chesneau

French National Centre for Scientific Research, Lutetia Parisorum, Île-de-France, France

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Publications (280)563.6 Total impact

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    [Show abstract] [Hide abstract] ABSTRACT: The diameter of a star is a major observable that serves to test the validity of stellar structure theories. It is also a difficult observable that is mostly obtained with indirect methods since the stars are so remote. Today only ~600 apparent star diameters have been measured by direct methods: optical interferometry and lunar occultations. Accurate star diameters are now required in the new field of exoplanet studies, since they condition the planets' sizes in transit observations, and recent publications illustrate a visible renewal of interest in this topic. Our analysis is based on the modeling of the relationship between measured angular diameters and photometries. It makes use of two new reddening-free concepts: a distance indicator called pseudomagnitude, and a quasi-experimental observable that is independent of distance and specific to each star, called the differential surface brightness (DSB). The use of all the published measurements of apparent diameters that have been collected so far, and a careful modeling of the DSB allow us to estimate star diameters with a median statistical error of 1%, knowing their spectral type and, in the present case, the VJHKs photometries. We introduce two catalogs, the JMMC Measured Diameters Catalog (JMDC), containing measured star diameters, and the second version of the JMMC Stellar Diameter Catalog (JSDC), augmented to about 453000 star diameters. Finally, we provide simple formulas and a table of coefficients to quickly estimate stellar angular diameters and associated errors from (V, Ks) magnitudes and spectral types.
    Preview · Article · Mar 2016 · Astronomy and Astrophysics
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    [Show abstract] [Hide abstract] ABSTRACT: We present new near-infrared photometric measurements of the core of the young massive cluster NGC 3603 obtained with extreme adaptive optics. The data were obtained with the SPHERE instrument mounted on ESO's Very Large Telescope, and cover three fields in the core of this cluster. We applied a correction for the effect of extinction to our data obtained in the J and K broadband filters and estimated the mass of detected sources inside the field of view of SPHERE/IRDIS, which is 13.5″×13.5″. We derived the mass function (MF) slope for each spectral band and field. The MF slope in the core is unusual compared to previous results based on HST and VLT observations. The average slope in the core is estimated as -1.06 ± 0.26 for the main sequence stars with 3.5 MO < M < 120MO. Thanks to the SPHERE extreme adaptive optics, 814 low-mass stars were detected to estimate the MF slope for the pre-main sequence stars with 0.6 MO < M < 3.5MO, Γ = -0.54 ± 0.11 in the K-band images in two fields in the core of the cluster. For the first time, we derive the MF of the very core of the NGC 3603 young cluster for masses in the range 0.6-120 MO. Previous studies were either limited by crowding, lack of dynamic range, or a combination of both.
    Full-text · Article · Mar 2016 · Astronomy and Astrophysics
  • No preview · Book · Sep 2015
  • [Show abstract] [Hide abstract] ABSTRACT: The research of stars with the B[e] phenomenon is still in its infancy, with several unanswered questions. Physically realistic models that treat the formation and evolution of their complex circumstellar environments are rare. The code HDUST (developed by A. C. Carciofi and J. Bjorkman) is one of the few existing codes that provides a self-consistent treatment of the radiative transfer in a gaseous and dusty circumstellar environment seen around B[e] supergiant stars. In this work we used the HDUST code to study the circumstellar medium of the binary system GG Car, where the primary component is probably an evolved B[e] supergiant. This system also presents a disk (probably circumbinary), which is responsible for the molecular and dusty signatures seen in GG Car spectra. We obtained VLTI/MIDI data on GG~Car at eight baselines, which allowed to spatially resolve the gaseous and dusty circumstellar environment. From the interferometric visibilities and SED modeling with HDUST, we confirm the presence of a compact ring, where the hot dust lies. We also show that large grains can reproduce the lack of structure in the SED and visibilities across the silicate band. We conclude the dust condensation site is much closer to the star than previously thought. This result provides stringent constraints on future theories of grain formation and growth around hot stars.
    No preview · Article · Jun 2015 · Proceedings of the International Astronomical Union
  • Z. Khorrami · F. Vakili · O. Chesneau · T. Lanz
    No preview · Article · Jan 2015 · EAS Publications Series
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    I.C. Leão · S.N. Bright · O. Chesneau
    Full-text · Article · Jan 2015 · EAS Publications Series
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    [Show abstract] [Hide abstract] ABSTRACT: A classical nova occurs when material accreting onto the surface of a white dwarf in a close binary system ignites in a thermonuclear runaway. Complex structures observed in the ejecta at late stages could result from interactions with the companion during the common-envelope phase. Alternatively, the explosion could be intrinsically bipolar, resulting from a localized ignition on the surface of the white dwarf or as a consequence of rotational distortion. Studying the structure of novae during the earliest phases is challenging because of the high spatial resolution needed to measure their small sizes. Here we report near-infrared interferometric measurements of the angular size of Nova Delphini 2013, starting one day after the explosion and continuing with extensive time coverage during the first 43 days. Changes in the apparent expansion rate can be explained by an explosion model consisting of an optically thick core surrounded by a diffuse envelope. The optical depth of the ejected material changes as it expands. We detect an ellipticity in the light distribution, suggesting a prolate or bipolar structure that develops as early as the second day. Combining the angular expansion rate with radial velocity measurements, we derive a geometric distance to the nova of 4.54 ± 0.59 kiloparsecs from the Sun.
    Preview · Article · Oct 2014 · Nature
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    Eric Lagadec · Olivier Chesneau
    [Show abstract] [Hide abstract] ABSTRACT: During the last years, many observational studies have revealed that binaries play an active role in the shaping of non spherical planetary nebulae. We review the different works that lead to the direct or indirect evidence for the presence of binary companions during the Asymptotic Giant Branch, proto-Planetary Nebula and Planetary Nebula phases. We also discuss how these binaries can influence the stellar evolution and possible future directions in the field.
    Preview · Article · Oct 2014
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    [Show abstract] [Hide abstract] ABSTRACT: The aim of this work is to improve the SBC relation for early-type stars in the $-1 \leq V-K \leq 0$ color domain, using optical interferometry. Observations of eight B- and A-type stars were secured with the VEGA/CHARA instrument in the visible. The derived uniform disc angular diameters were converted into limb darkened angular diameters and included in a larger sample of twenty four stars, already observed by interferometry, in order to derive a revised empirical relation for O, B, A spectral type stars with a V-K color index ranging from -1 to 0. We also take the opportunity to check the consistency of the SBC relation up to $V-K \simeq 4$ using 100 additional measurements. We determined the uniform disc angular diameter for the eight following stars: $\gamma$ Ori, $\zeta$ Per, $8$ Cyg, $\iota$ Her, $\lambda$ Aql, $\zeta$ Peg, $\gamma$ Lyr and $\delta$ Cyg with V-K color ranging from -0.70 to 0.02 and typical precision of about $1.5\%$. Using our total sample of 132 stars with $V-K$ colors index ranging from about $-1$ to $4$, we provide a revised SBC relation. For late-type stars ($0 \leq V-K \leq 4$), the results are consistent with previous studies. For early-type stars ($-1 \leq V-K \leq 0$), our new VEGA/CHARA measurements combined with a careful selection of the stars (rejecting stars with environment or stars with a strong variability), allows us to reach an unprecedented precision of about 0.16 magnitude or $\simeq 7\%$ in term of angular diameter.
    Full-text · Article · Sep 2014 · Astronomy and Astrophysics
  • [Show abstract] [Hide abstract] ABSTRACT: We report on the testing of the centrosymmetry parameter (CSP), an indicator of deviation from centrosymmetry of a source brightness distribution. This indicator is derived from the spectral distribution of the triple product measured over three baselines of an optical interferometer. Numerical simulations using parametric toy-models (separated or transiting binary, one-spot model), generated with the spidast software, are applied to the VLTI /AMBER facility in the K band (2.2 μm). The simulations show that, in case of centrosymmetry, the CSP parameter is in agreement with the usual phase of the spectral mean of the triple product (called GCP, global closure phase). To justify the preferential use of CSP rather than GCP, we show situations with asymmetric geometries for which GCP diagnoses centrosymmetry, while CSP does not. Using realistic Roche lobe-filling binary and hydrodynamic convective models, we show that CSP can also be used as an indicator for geometric similarity between physical and toy-models. Thus, dealing with real data, the toy-model parameters can be fitted on the measured CSP values, in order to assess the input-parameter values of the most suitable complex physical model that will be used to interpret the data.
    No preview · Article · Aug 2014 · Monthly Notices of the Royal Astronomical Society
  • [Show abstract] [Hide abstract] ABSTRACT: Observing reference stars with a known diameter is almost the only possibility to calibrate optical interferometry observations. The JMMC Calibrator Workgroup develops methods to ascertain the angular diameter of stars since 2000 and provides this expertise in the SearchCal software and associated databases. We provide on a regularly basis the JSDC, a catalogue of such stars, and an open access to our server that dynamically finds calibrators near science objects by querying CDS hosted catalogs. Here we propose a novel approach in the estimation of angular stellar diameters based on observational quantities only. It bypasses the knowledge of the visual extinction and intrinsic colors, thanks to the use of absorption free pseudo-colors (AFC) and the spectral type number on the x-axis. This new methodology allows to compute the angular diameter of 443 703 stars with a relative precision of about 1%. This calibrator set will become after filtering the next JSDC release.
    No preview · Conference Paper · Jul 2014
  • [Show abstract] [Hide abstract] ABSTRACT: We report on a database service that allows users to query calibrated optical interferometry data (OIFITS format) as well as regularly-updated observation logs obtained with a wide range of interferometric instruments. It widely uses Virtual Observatory tools to increase diffusion and operability. In this contribution, we present the characteristics and functionalities of the first global optical interferometry archive service.
    No preview · Conference Paper · Jul 2014
  • B. Lopez · S. Lagarde · W. Jaffe · R. Petrov · M. Schöller · P. Antonelli · U. Beckman · Ph. Bério · F. Bettonvil · U. Graser · [...] · G. Rupprecht · D. Schertl · J. Stegmeier · L. Thiam · N. Tromp · M. Vannier · F. Vakili · G. van Belle · K. Wagner · J. Woillez ·
    No preview · Conference Paper · Jul 2014
  • M. Tallon · I. Tallon-Bosc · O. Chesneau · L. Dessart
    [Show abstract] [Hide abstract] ABSTRACT: Current interferometers often collect data simultaneously in many spectral channels by using dispersed fringes. Such polychromatic data provide powerful insights in various physical properties, where the observed objects show particular spectral features. Furthermore, one can measure spectral differential visibilities that do not directly depend on any calibration by a reference star. But such observations may be sensitive to instrumental artifacts that must be taken into account in order to fully exploit the polychromatic information of interferometric data. As a specimen, we consider here an observation of P Cygni with the VEGA visible combiner on CHARA interferometer. Indeed, although P Cygni is particularly well modeled by the radiative transfer code CMFGEN, we observe questionable discrepancies between expected and actual interferometric data. The problem is to determine their origin and disentangle possible instrumental effects from the astrophysical information. By using an expanded model fitting, which includes several instrumental features, we show that the differential visibilities are well explained by instrumental effects that could be otherwise attributed to the object. Although this approach leads to more reliable results, it assumes a fit specific to a particular instrument, and makes it more difficult to develop a generic model fitting independent of any instrument.
    No preview · Conference Paper · Jul 2014
  • [Show abstract] [Hide abstract] ABSTRACT: In the next 2 or 3 years, the two major interferometric arrays, VLTI and CHARA, will equip their telescopes of 1.8m and 1m respectively with Adaptive Optics (AO hereafter) systems. This improvement will permit to apply with a reasonable e_ciency in the visible domain, the principle of spatial filtering with single mode fibers demonstrated in the near-infrared. It will clearly open new astrophysical fields by taking benefit of an improved sensitivity and state-of-the-art precision and accuracy on interferometric observables. To prepare this future possibility, we started the development of a demonstrator called FRIEND (Fibered and spectrally Resolved Interferometric Experiment - New Design). FRIEND combines the beams coming from 3 telescopes after injection in single mode optical fibers and provides some spectral capabilities for characterization purposes as well as photometric channels. It operates in the R spectral band (from 600nm to 750nm) and uses the world's fastest and more sensitive analogic detector OCAM2. Tests on sky at the focus of the CHARA interferometer are scheduled for December 2014. In this paper, we present the first interferometric tests of the OCAM2 detector performed on CHARA in November 2012 and the concept, the expected performance and the opto-mechanical design of FRIEND.
    No preview · Conference Paper · Jul 2014
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    [Show abstract] [Hide abstract] ABSTRACT: Aims. The hydrogen-deficient supergiants known as R Coronae Borealis Stars might be the result of a double degenerate merger of two white dwarfs (WDs), or a final helium shell flash in a PN central star. In this context, any information on the geometry of their circumstellar environment and, in particular, the potential detection of elongated structures is of great importance. Methods. We obtained near-IR observations of \object{V854\,Cen} with the {{\sc AMBER}} recombiner located at the Very Large Telescope Interferometer ({{\sc VLTI}}) array with the compact array (B$\leq$35m) in 2013 and the long array (B$\leq$140m) in 2014. At each time, \object{V854\,Cen} was at maximum light. The H- and K-band continua were investigated by means of spectrally-dependant geometric models. These data are supplemented with mid-IR {{\sc VISIR}}/VLT images. Results. A dusty slightly elongated over-density is discovered both in the H and K-band images. With the compact array, the central star is unresolved ($\Theta\leq2.5$\,mas), but a flattened dusty environment of $8 \times 11$ mas is discovered whose flux raises from about $\sim$20\% in the H band to reach about $\sim$50\% at 2.3\micron, indicative of the presence of hot (T$\sim$1500\,K) dust in the close vicinity of the star. The major axis is oriented at a position angle (P.A.) of 126$\pm$29\deg. Adding the long array configuration dataset provides tighter constraints on the star diameter ($\Theta\leq1.0$\,mas), a slight increase of the over-density representing $12 \times 15$ mas and a consistent P.A. of 133$\pm$49\deg. The closure phases, sensitive to asymmetries, are null and compatible with a centro-symmetric, unperturbed environment excluding point sources at the level of 3\% of the total flux in 2013 and 2014. The VISIR images exhibit at larger distances ($\sim$1\arcsec) a flattened aspect ratio at the 15-20\% level with a position angle of 92$\pm$19\deg, marginally consistent with the interferometric observations. Conclusions. This is the first time that a moderately elongated structure has been observed around an RCB star. These observations confirm the numerous suggestions for this star for a bipolar structure proposed in the literature, mainly based on polarimetric and spectroscopic observations.
    Full-text · Article · Jul 2014 · Astronomy and Astrophysics
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    [Show abstract] [Hide abstract] ABSTRACT: Aims. V838 Monocerotis erupted in 2002, brightened in a series of outbursts, and eventually developed a spectacular light echo. A very red star emerged a few months after the outburst. The whole event has been interpreted as the result of a merger. Methods. We obtained near-IR and mid-IR interferometric observations of V838 Mon with the AMBER and MIDI recombiners located at the Very Large Telescope Interferometer (VLTI) array. The MIDI two-beam observations were obtained with the 8m Unit Telescopes between October 2011 and February 2012. The AMBER three-beam observations were obtained with the compact array (B≤35m) in April 2013 and the long array (B≤140m) in May 2014, using the 1.8m Auxiliary Telescopes. Results. A significant new result is the detection of a compact structure around V838 Mon, as seen from MIDI data. The extension of the structure increases from a FWHM of 25 mas at 8 {\mu}m to 70 mas at 13 {\mu}m. At the adopted distance of D = 6.1 $\pm$ 0.6 kpc, the dust is distributed from about 150 to 400 AU around V838 Mon. The MIDI visibilities reveal a flattened structure whose aspect ratio increases with wavelength. The major axis is roughly oriented around a position angle of −10◦, which aligns with previous polarimetric studies reported in the literature. This flattening can be interpreted as a relic of the 2002 eruption or by the influence of the currently embedded B3V companion. The AMBER data provide a new diameter for the pseudo-photosphere, which shows that its diameter has decreased by about 40% in 10yrs, reaching a radius R∗ = 750 $\pm$ 200 R⊙ (3.5 $\pm$ 1.0 AU). Conclusions. After the 2002 eruption, interpreted as the merging of two stars, it seems that the resulting source is relaxing to a normal state. The nearby environment exhibits an equatorial over-density of dust up to several hundreds of AU.
    Full-text · Article · Jul 2014 · Astronomy and Astrophysics
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    [Show abstract] [Hide abstract] ABSTRACT: Bright optical transients (i.e. transients typically visible with the naked eye) are populated mainly by novae eruptions plus a few supernovae (among which the SN1987a event). One bright nova happen every two years, either in the North ot in the South hemisphere. It occurs that current interferometers have matching sensitivities, with typically visible or infrared limiting magnitude in the range 5--7. The temporal development of the fireball, followed by a dust formation phase or the appearance of many coronal lines can be sudied with the Very Large Telescope Interferometer. The detailed geometry of the first phases of novae in outburst remains virtually unexplored. This paper summarizes the work which has been done to date using the VLTI.
    Full-text · Article · Jul 2014
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    [Show abstract] [Hide abstract] ABSTRACT: We present a spatially resolved, high-spectral resolution (R=12000) K-band temporal monitoring of Rigel using AMBER at the VLTI. Rigel was observed in the Bracket Gamma line and its nearby continuum in 2006-2007, and 2009-2010. These unprecedented observations were complemented by contemporaneous optical high-resolution spectroscopy. We analyse the near-IR spectra and visibilities with the 1D non-LTE radiative-transfer code CMFGEN. The differential and closure phase signal exhibit asymmetries that are interpreted as perturbations of the wind. A systematic visibility decrease is observed across the Bracket Gamma. During the 2006-2007 period the Bracket Gamma and likely the continuum forming regions were larger than in the 2009-2010 epoch. Using CMFGEN, we infer a mass-loss rate change of about 20% between the two epochs. We further find time variations in the differential visibilities and phases. The 2006-2007 period is characterized by noticeable variations of the differential visibilities in Doppler position and width and by weak variations in differential and closure phase. The 2009-2010 period is much more quiet with virtually no detectable variations in the dispersed visibilities but a strong S-shape signal is observed in differential phase coinciding with a strong ejection event discernible in the optical spectra. The differential phase signal that is sometimes detected is reminiscent of the signal computed from hydrodynamical models of corotating interaction regions. For some epochs the temporal evolution of the signal suggests the rotation of the circumstellar structures.
    Full-text · Article · May 2014 · Astronomy and Astrophysics
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    Full-text · Article · Apr 2014

Publication Stats

3k Citations
563.60 Total Impact Points

Institutions

  • 2000-2015
    • French National Centre for Scientific Research
      • Observatoire de la Côte d'Azur (OCA)
      Lutetia Parisorum, Île-de-France, France
  • 2008-2014
    • University of Nice-Sophia Antipolis
      • • Laboratoire Lagrange
      • • Laboratoire Fizeau
      Nice, Provence-Alpes-Côte d'Azur, France
  • 1999-2014
    • Observatoire de la Côte d'Azur
      • Laboratoire J.L. Lagrange
      Grasse, Provence-Alpes-Côte d'Azur, France
  • 2007
    • Ruhr-Universität Bochum
      Bochum, North Rhine-Westphalia, Germany
    • LG Electronics
      Sŏul, Seoul, South Korea
    • Collège de France
      Lutetia Parisorum, Île-de-France, France
  • 2003-2005
    • Max Planck Institute for Astronomy
      Heidelburg, Baden-Württemberg, Germany