Spatially resolving the inhomogeneous structure of the dynamical atmosphere 
of Betelgeuse with VLTI/AMBER

Ohnaka, K.; Hofmann, K.-H.; Benisty, M.; Chelli, A.; Driebe, T.; Millour, F.; Petrov, R.; Schertl, D.; Stee, Philippe; Vakili, F.; Weigelt, G.

doi:10.1051/0004-6361/200912247

Cited by 79 publications

(94 citation statements)

References 66 publications

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“…Beyond that limit, the data show a great complexity which is not reproduced by the simpler models. Contrary to AMBER K-band observations made in January 2008 and recently published in Ohnaka et al (2009) where the data points are scattered around a limb darkening model, the present observations reveal significant departure from symmetry. All limb darkening models that we used (linear, quadratic and MARCS model) hint at the presence of additional asymmetric structures suggested by the excess of contrast at high frequency and are beyond the scope of the limb-darkening models.…”

Section: Discussioncontrasting

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: Discussioncontrasting

confidence: 99%

Imaging the spotty surface of Betelgeuse in theHband

Haubois¹,

Perrin²,

Lacour³

et al. 2009

A&A

160

171

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“…Details of the reduction are described in Ohnaka et al (2009Ohnaka et al ( , 2011Ohnaka et al ( , and 2013. The wavelength calibration and the spectroscopic calibration of the W Hya data were carried out with the method described in Ohnaka et al (2013).…”

Section: Long-baseline Spectro-interferometric Observations With Vltimentioning

confidence: 99%

Clumpy dust clouds and extended atmosphere of the AGB star W Hydrae revealed with VLT/SPHERE-ZIMPOL and VLTI/AMBER

Ohnaka

Weigelt

Hofmann

2016

A&A

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Aims. Our recent visible polarimetric images of the well-studied AGB star W Hya taken at pre-maximum light (phase 0.92) with VLT/SPHERE-ZIMPOL have revealed clumpy dust clouds close to the star at ∼2 R . We present second-epoch SPHERE-ZIMPOL observations of W Hya at minimum light (phase 0.54) as well as high-spectral resolution long-baseline interferometric observations with the AMBER instrument at the Very Large Telescope Interferometer (VLTI). Methods. We observed W Hya with VLT/SPHERE-ZIMPOL at three wavelengths in the continuum (645, 748, and 820 nm), in the Hα line at 656.3 nm, and in the TiO band at 717 nm. The VLTI/AMBER observations were carried out in the wavelength region of the CO first overtone lines near 2.3 µm with a spectral resolution of 12 000. Results. The high-spatial resolution polarimetric images obtained with SPHERE-ZIMPOL have allowed us to detect clear time variations in the clumpy dust clouds as close as 34-50 mas (1.4-2.0 R ) to the star. We detected the formation of a new dust cloud as well as the disappearance of one of the dust clouds detected at the first epoch. The Hα and TiO emission extends to ∼150 mas (∼6 R ), and the Hα images obtained at two epochs reveal time variations. The degree of linear polarization measured at minimum light, which ranges from 13 to 18%, is higher than that observed at pre-maximum light. The power-law-type limb-darkened disk fit to the AMBER data in the continuum results in a limb-darkened disk diameter of 49.1 ± 1.5 mas and a limb-darkening parameter of 1.16±0.49, indicating that the atmosphere is more extended with weaker limb-darkening compared to pre-maximum light. Our Monte Carlo radiative transfer modeling shows that the second-epoch SPHERE-ZIMPOL data can be explained by a shell of 0.1 µm grains of Al 2 O 3 , Mg 2 SiO 4 , and MgSiO 3 with a 550 nm optical depth of 0.6±0.2 and an inner and outer radii of 1.3 R and 10±2 R , respectively. Our modeling suggests the predominance of small (0.1 µm) grains at minimum light, in marked contrast to the predominance of large (0.5 µm) grains at pre-maximum light. Conclusions. The variability phase dependence of the characteristic grain size implies that small grains might just have started to form at minimum light in the wake of a shock, while the pre-maximum light phase might have corresponded to the phase of efficient grain growth.

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“…We binned the raw data in the spectral direction with a box car filter with a width of three pixels to increase the signal-to-noise ratio. The details of the reduction are described in Ohnaka et al (2009). We excluded the data sets #2, #6-9, #13, and #15.…”

Section: Observationsmentioning

confidence: 99%

AMBER-NACO aperture-synthesis imaging of the half-obscured central star and the edge-on disk of the red giant L₂Puppis

Ohnaka

Schertl

Hofmann

et al. 2015

A&A

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Aims. The red giant L 2 Pup started a dimming event in 1994, which is considered to be caused by the ejection of dust clouds. We present near-IR aperture-synthesis imaging of L 2 Pup achieved by combining data from VLT/NACO and the AMBER instrument of the Very Large Telescope Interferometer (VLTI). Our aim is to spatially resolve the innermost region of the circumstellar environment. Methods. We carried out speckle interferometric observations at 2.27 µm with VLT/NACO and long-baseline interferometric observations with VLTI/AMBER at 2.2-2.35 µm with baselines of 15-81 m. We also extracted an 8.7 µm image from the mid-IR VLTI instrument MIDI.Results. The diffraction-limited image obtained by bispectrum speckle interferometry with NACO with a spatial resolution of 57 mas shows an elongated component. The aperture-synthesis imaging combining the NACO speckle data and AMBER data with a spatial resolution of 5.6 × 7.3 mas further resolves not only this elongated component, but also the central star. The reconstructed image reveals that the elongated component is a nearly edge-on disk with a size of ∼180 × 50 mas lying in the E-W direction, and furthermore, that the southern hemisphere of the central star is severely obscured by the equatorial dust lane of the disk. The angular size of the disk is consistent with the distance that the dust clouds that were ejected at the onset of the dimming event should have traveled by the time of our observations, if we assume that the dust clouds moved radially. This implies that the formation of the disk may be responsible for the dimming event. The 8.7 µm image with a spatial resolution of 220 mas extracted from the MIDI data taken in 2004 (seven years before the AMBER and NACO observations) shows an approximately spherical envelope without a signature of the disk. This suggests that the mass loss before the dimming event may have been spherical.

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Spatially resolving the inhomogeneous structure of the dynamical atmosphere of Betelgeuse with VLTI/AMBER

Cited by 79 publications

References 66 publications

Imaging the spotty surface of Betelgeuse in theHband

Imaging the spotty surface of Betelgeuse in theHband

Clumpy dust clouds and extended atmosphere of the AGB star W Hydrae revealed with VLT/SPHERE-ZIMPOL and VLTI/AMBER

AMBER-NACO aperture-synthesis imaging of the half-obscured central star and the edge-on disk of the red giant L₂Puppis

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Spatially resolving the inhomogeneous structure of the dynamical atmosphere of Betelgeuse with VLTI/AMBER

Cited by 79 publications

References 66 publications

Imaging the spotty surface of Betelgeuse in theHband

Imaging the spotty surface of Betelgeuse in theHband

Clumpy dust clouds and extended atmosphere of the AGB star W Hydrae revealed with VLT/SPHERE-ZIMPOL and VLTI/AMBER

AMBER-NACO aperture-synthesis imaging of the half-obscured central star and the edge-on disk of the red giant L2Puppis

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About

AMBER-NACO aperture-synthesis imaging of the half-obscured central star and the edge-on disk of the red giant L₂Puppis