Advanced Imaging Methods for Long-Baseline Optical Interferometry

Besnerais, Guy Le; Lacour, S.; Mugnier, Laurent M.; Thiébaut, Éric; Perrin, G.; Meimon, Serge

doi:10.1109/jstsp.2008.2005353

Cited by 32 publications

(55 citation statements)

References 48 publications

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“…In this paper we used two of them: MIRA and WISARD. Both are presented and compared in Le Besnerais (2008) and in Lacour et al (2008). The major advantage of such methods is that they can reveal structures by reconstructing an image which fits the data and which is also close to an a priori image of the object.…”

Section: Image Reconstruction and Asymmetriesmentioning

confidence: 99%

Imaging the spotty surface of Betelgeuse in theHband

Haubois¹,

Perrin²,

Lacour³

et al. 2009

A&A

160

171

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Aims. This paper reports on H-band interferometric observations of Betelgeuse made at the three-telescope interferometer IOTA. We image Betelgeuse and its asymmetries to understand the spatial variation of the photosphere, including its diameter, limb darkening, effective temperature, surrounding brightness, and bright (or dark) star spots. Methods. We used different theoretical simulations of the photosphere and dusty environment to model the visibility data. We made images with parametric modeling and two image reconstruction algorithms: MIRA and WISARD. Results. We measure an average limb-darkened diameter of 44.28 ± 0.15 mas with linear and quadratic models and a Rosseland diameter of 45.03 ± 0.12 mas with a MARCS model. These measurements lead us to derive an updated effective temperature of 3600 ± 66 K. We detect a fully-resolved environment to which the silicate dust shell is likely to contribute. By using two imaging reconstruction algorithms, we unveiled two bright spots on the surface of Betelgeuse. One spot has a diameter of about 11 mas and accounts for about 8.5% of the total flux. The second one is unresolved (diameter < 9 mas) with 4.5% of the total flux. Conclusions. Resolved images of Betelgeuse in the H band are asymmetric at the level of a few percent. The MOLsphere is not detected in this wavelength range. The amount of measured limb-darkening is in good agreement with model predictions. The two spots imaged at the surface of the star are potential signatures of convective cells.

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Section: Image Reconstruction and Asymmetriesmentioning

confidence: 99%

Imaging the spotty surface of Betelgeuse in theHband

Haubois¹,

Perrin²,

Lacour³

et al. 2009

A&A

160

171

View full text Add to dashboard Cite

show abstract

“…The image reconstruction process is similar to the one performed for T Lep in Le Bouquin et al (2009). For the reconstruction, we used the MIRA software package (Thiébaut 2008;Cotton et al 2008;Le Besnerais et al 2008). The image was sought by minimizing a so-called cost function which is the sum of a regularization term plus data-related terms.…”

Section: Image Reconstructionmentioning

confidence: 99%

VLTI/AMBER spectro-interferometric imaging of VX Sagittarii's inhomogenous outer atmosphere

Chiavassa¹,

Lacour²,

Millour³

et al. 2010

A&A

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Aims. We aim to explore the photosphere of the very cool late-type star VX Sgr and in particular the characterization of molecular layers above the continuum forming photosphere. Methods. We obtained interferometric observations with the VLTI/AMBER interferometer using the fringe tracker FINITO in the spectral domain 1.45−2.50 μm with a spectral resolution of ≈35 and baselines ranging from 15 to 88 m. We performed independent image reconstruction for different wavelength bins and fit the interferometric data with a geometrical toy model. We also compared the data to 1D dynamical models of Miras atmosphere and to 3D hydrodynamical simulations of red supergiant (RSG) and asymptotic giant branch (AGB) stars. Results. Reconstructed images and visibilities show a strong wavelength dependence. The H-band images display two bright spots whose positions are confirmed by the geometrical toy model. The inhomogeneities are qualitatively predicted by 3D simulations. At ≈2.00 μm and in the region 2.35−2.50 μm, the photosphere appears extended and the radius is larger than in the H band. In this spectral region, the geometrical toy model locates a third bright spot outside the photosphere that can be a feature of the molecular layers. The wavelength dependence of the visibility can be qualitatively explained by 1D dynamical models of Mira atmospheres. The best-fitting photospheric models show a good match with the observed visibilities and give a photospheric diameter of Θ = 8.82 ± 0.50 mas. The H 2 O molecule seems to be the dominant absorber in the molecular layers. Conclusions. We show that the atmosphere of VX Sgr seems to resemble Mira/AGB star model atmospheres more closely than do RSG model atmospheres. In particular, we see molecular (water) layers that are typical of Mira stars.

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“…We then used MIRA with a strong smoothness regularization to reconstruct the first stage images. The second step uses these brightness distributions as a support for a quadratic regularization of a 2D brightness map (Le Besnerais et al 2008). Each of the spectral channels was processed separately.…”

Section: Image Reconstructionmentioning

confidence: 99%

Pre-maximum spectro-imaging of the Mira star T Leporis with AMBER/VLTI

Bouquin¹,

Lacour

Renard

et al. 2009

A&A

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Context. Diffuse envelopes around Mira variables are among the most important sources influencing the chemical evolution of galaxies. However they represent an observational challenge because of their complex spectral features and their rapid temporal variability. Aims. We aimed at constraining the exact brightness distribution of the Mira star T Lep with a model-independent analysis. Methods. We obtained single-epoch interferometric observations with a dataset continuous in the spectral domain (λ = 1.5−2.4 μm) and in the spatial domain (interferometric baselines ranging from 11 to 96 m). We performed a model independent image reconstruction for each spectral bin using the MIRA software. We completed the analysis by modeling the data with a simple star+layer model inspired from the images. Results. Reconstructed images confirm the general picture of a central star partially obscured by the surrounding molecular shell of changing opacity. At 1.7 μm, the shell becomes optically thin, with corresponding emission appearing as a ring circling the star. This is the first direct evidence of the spherical morphology of the molecular shell. Model fitting confirmed a spherical layer of constant size and changing opacity over the wavelengths. Rough modeling points to a continuum opacity within the shell, in addition to the CO and H 2 O features. Accordingly, it appeared impossible to model the data by a photosphere alone in any of the spectral bins.

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Advanced Imaging Methods for Long-Baseline Optical Interferometry

Cited by 32 publications

References 48 publications

Imaging the spotty surface of Betelgeuse in theHband

Imaging the spotty surface of Betelgeuse in theHband

VLTI/AMBER spectro-interferometric imaging of VX Sagittarii's inhomogenous outer atmosphere

Pre-maximum spectro-imaging of the Mira star T Leporis with AMBER/VLTI

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