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

Bouquin, J.-B. Le; Lacour, S.; Renard, Stéphanie; Thiébaut, Éric; Mérand, A.; Verhoelst, Tijl

doi:10.1051/0004-6361/200811579

Cited by 52 publications

(60 citation statements)

References 22 publications

(22 reference statements)

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“…Observations in specific narrow-band filters pointed to CO and H 2 O vapors as potential major contributors to the opacity in K band, with water vapor being the main contributor. Spectrally dispersed observations in the near-infrared confirmed this finding (Eisner et al 2007;Wittkowski et al 2008;Le Bouquin et al 2009). At the lowest opacity (in J and H bands), the impact of the envelope is reduced and the diameter of the object is close to that of the photosphere.…”

Section: Near-infraredsupporting

confidence: 58%

High-resolution IR and radio observations of AGB stars

Perrin

Cotton

Millan-Gabet

et al. 2015

A&A

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Aims. We present the results of observations with interferometers of a sample of pulsating asymptotic giant branch (AGB) stars in the infrared and at radio wavelengths. The goal of these observations is to explore the extended stellar atmospheres and to establish links between the spatial scales of molecular envelopes and of the dust shell. This is the key to better understand the process of dust formation and therefore of mass loss. Methods. We used the ESO VLTI/MIDI interferometer in the N band, the Keck Interferometer in the K band, and NRAO VLBA observations of SiO masers at 7 mm wavelength of a sample of AGB stars: U Ari, W Cnc, RX Tau, RT Tau, RT Aql, S Ser, and V Mon. The various instruments probe different altitudes of the atmosphere of the AGB stars. They are sensitive to regions below the silicate dust condensation distance and provide the opportunity of finding hints about how dust and its precursors form in the extended atmosphere of an AGB star. The K-band observations are sensitive to water and carbon-monoxyde vapors. Unfortunately, we were only able to observe S Ser in this wavelength range. Results. We find a ratio of 2.2 between the molecular envelope radius and the photospheric size, which is consistent with previous results. The N-band observations are mostly sensitive to vapors of SiO and water and to dust (alumina and silicate). The silicate dust shell is fully resolved, and no precise parameters can be deduced from the N-band observations other than a spatial extension of at least 12-16 R for our sample. The sizes found for the SiO region are consistent with the radii of the SiO maser rings provided by the VLBA observations. The sizes of the alumina and water vapor regions are systematically found to be larger. There is clear evidence that SiO is absent from regions farther from the star where silicate dust condenses. Conclusions. These observations support a possible scenario in which SiO is adsorbed by species such as corundum. An alternative explanation could be that SiO has chemically disappeared at this range of distances.

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Section: Near-infraredsupporting

confidence: 58%

High-resolution IR and radio observations of AGB stars

Perrin

Cotton

Millan-Gabet

et al. 2015

A&A

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“…In retrospect, it is interesting to note that the image reconstruction of T Lep (P ∼ 380 d, Le Bouquin et al 2009), made at a phase of 0.8-0.9, shows the clear signature of an extended molecular layer with a brightness ratio of ∼10%, unlike its closest model series o54, which supports our findings. Woodruff et al (2009) found fair agreement between the wavelength dependence of their measured 1.1-3.8 μm UDs and the predictions of the CODEX models, for several Miras at phases 0.5 to 0.8, but needed slightly larger model continuum diameters than predicted.…”

Section: Discussionsupporting

confidence: 87%

The dynamic atmospheres of Mira stars: comparing the CODEX models to PTI time series of TU Andromedae

Hillen

Verhoelst

Degroote

et al. 2012

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Context. Our comprehension of stellar evolution on the AGB still faces many difficulties. To improve on this, a quantified understanding of large-amplitude pulsator atmospheres and interpretation in terms of their fundamental stellar parameters are essential. Aims. We wish to evaluate the effectiveness of the recently released CODEX dynamical model atmospheres in representing M-type Mira variables through a confrontation with the time-resolved spectro-photometric and interferometric PTI data set of TU And. Methods. We calibrated the interferometric K-band time series to high precision. This results in 50 nights of observations, covering 8 subsequent pulsation cycles. At each phase, the flux at 2.2 μm is obtained, along with the spectral shape and visibility points in 5 channels across the K-band. We compared the data set to the relevant dynamical, self-excited CODEX models. Results. Both spectrum and visibilities are consistently reproduced at visual minimum phases. Near maximum, our observations show that the current models predict a photosphere that is too compact and hot, and we find that the extended atmosphere lacks H 2 O opacity. Since coverage in model parameter space is currently poor, more models are needed to make firm conclusions on the cause of the discrepancies. We argue that for TU And, the discrepancy could be lifted by adopting a lower value of the mixing length parameter combined with an increase in the stellar mass and/or a decrease in metallicity, but this requires the release of an extended model grid.

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“…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).…”

Section: Image Reconstructionmentioning

confidence: 99%

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

Chiavassa¹,

Lacour²,

Millour³

et al. 2010

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

Cited by 52 publications

References 22 publications

High-resolution IR and radio observations of AGB stars

High-resolution IR and radio observations of AGB stars

The dynamic atmospheres of Mira stars: comparing the CODEX models to PTI time series of TU Andromedae

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

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