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Aperture synthesis imaging of the carbon AGB star R Sculptoris Detection of a complex structure and a dominating spot on the stellar disk
European Southern Observ, Karl Schwarzschild Str 2, D-85748 Garching, Germany..
Max Planck Inst Radioastron, Hugel 69, D-53121 Bonn, Germany.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
Univ Grenoble Alpes, CNRS, IPAG, F-38000 Grenoble, France..
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2017 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 601, article id A3Article in journal (Refereed) Published
Abstract [en]

Aims. We present near-infrared interferometry of the carbon-rich asymptotic giant branch (AGB) star R Sculptoris (R Scl). Methods. We employ medium spectral resolution K-band interferometry obtained with the instrument AMBER at the Very Large Telescope Interferometer (VLTI) and H-band low spectral resolution interferometric imaging observations obtained with the VLTI instrument PIONIER. We compare our data to a recent grid of dynamic atmosphere and wind models. We compare derived fundamental parameters to stellar evolution models. Results. The visibility data indicate a broadly circular resolved stellar disk with a complex substructure. The observed AMBER squared visibility values show drops at the positions of CO and CN bands, indicating that these lines form in extended layers above the photosphere. The AMBER visibility values are best fit by a model without a wind. The PIONIER data are consistent with the same model. We obtain a Rosseland angular diameter of 8.9 +/- 0.3 mas, corresponding to a Rosseland radius of 355 +/- 55 R-Theta, an effective temperature of 2640 +/- 80 K, and a luminosity of log L/L-Theta = 3.74 +/- 0.18. These parameters match evolutionary tracks of initial mass 1.5 +/- 0.5 M-Theta and current mass 1.3 +/- 0.7 M-Theta. The reconstructed PIONIER images exhibit a complex structure within the stellar disk including a dominant bright spot located at the western part of the stellar disk. The spot has an H- band peak intensity of 40% to 60% above the average intensity of the limb-darkening-corrected stellar disk. The contrast between the minimum and maximum intensity on the stellar disk is about 1:2.5. Conclusions. Our observations are broadly consistent with predictions by dynamic atmosphere and wind models, although models with wind appear to have a circumstellar envelope that is too extended compared to our observations. The detected complex structure within the stellar disk is most likely caused by giant convection cells, resulting in large-scale shock fronts, and their effects on clumpy molecule and dust formation seen against the photosphere at distances of 2-3 stellar radii.

Place, publisher, year, edition, pages
EDP Sciences, 2017. Vol. 601, article id A3
Keywords [en]
techniques: interferometric, stars: AGB and post-AGB, stars: atmospheres, stars: fundamental parameters, stars: mass-loss, stars: individual: R Scl
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
URN: urn:nbn:se:uu:diva-327053DOI: 10.1051/0004-6361/201630214ISI: 000402313500003OAI: oai:DiVA.org:uu-327053DiVA, id: diva2:1129458
Available from: 2017-08-03 Created: 2017-08-03 Last updated: 2017-08-03Bibliographically approved

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Höfner, S.Eriksson, K.Ramstedt, S.

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