Aperture synthesis imaging of the carbon AGB star R Sculptoris: Detection of a complex structure and a dominating spot on the stellar disk

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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

Wittkowski, M. (författare): European Southern Observatory (ESO),European Southern Observ, Karl Schwarzschild Str 2, D-85748 Garching, Germany.

Hofmann, K. H. (författare): Max Planck Gesellschaft zur Förderung der Wissenschaften e.V. (MPG),Max Planck Society for the Advancement of Science (MPG),Max Planck Inst Radioastron, Hugel 69, D-53121 Bonn, Germany

Höfner, Susanne (författare): Uppsala universitet,Institutionen för fysik och astronomi

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Le Bouquin, J. B. (författare): Université Grenoble Alpes,Grenoble Alpes University,Univ Grenoble Alpes, CNRS, IPAG, F-38000 Grenoble, France.

Nowotny, W. (författare): Universität Wien,University of Vienna,Univ Vienna, Dept Astrophys, Turkenschanzstr 17, A-1180 Vienna, Austria.

Paladini, C. (författare): Université libre de Bruxelles (ULB),Univ Libre Bruxelles, Inst Astron & Astrophys, CP 226,Blvd Triomphe, B-1050 Brussels, Belgium.

Young, J. (författare): University Of Cambridge,Cavendish Lab, Astrophys Grp, JJ Thomson Ave, Cambridge CB3 0HE, England.

Berger, J. P. (författare): Université Grenoble Alpes,Grenoble Alpes University,Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France

Brunner, M. (författare): Universität Wien,University of Vienna,Univ Vienna, Dept Astrophys, Turkenschanzstr 17, A-1180 Vienna, Austria.

de Gregorio-Monsalvo, I. (författare): European Southern Observatory Santiago,Atacama Large Millimeter-submillimeter Array (ALMA),Joint ALMA Off, Alonso de Cordova 3107,Casilla 19001, Santiago 19, Chile.;European Southern Observ, Alonso de Cordova 3107, Santiago, Chile.

Eriksson, K. (författare): Uppsala universitet,Institutionen för fysik och astronomi

Hron, J. (författare): Universität Wien,University of Vienna,Univ Vienna, Dept Astrophys, Turkenschanzstr 17, A-1180 Vienna, Austria.

Humphreys, E. M. (författare): European Southern Observatory (ESO),European Southern Observ, Karl Schwarzschild Str 2, D-85748 Garching, Germany.,Chalmers, Onsala Space Observ, Dept Earth & Space Sci, S-43992 Onsala, Sweden.

Lindqvist, Michael, 1960 (författare): Chalmers tekniska högskola,Chalmers University of Technology,Chalmers, Onsala Space Observ, Dept Earth & Space Sci, S-43992 Onsala, Sweden.

Maercker, Matthias, 1979 (författare): Chalmers tekniska högskola,Chalmers University of Technology

Mohamed, S. (författare): University of Cape Town,South African Astronomical Observatory,National Institute for Theoretical Physics,South African Astron Observ, POB 9, ZA-7935 Observatory, South Africa.;Univ Cape Town, Astron Dept, ZA-7701 Rondebosch, South Africa.;Natl Inst Theoret Phys, Private Bag X1, ZA-7602 Matieland, South Africa.

Olofsson, Hans, 1952 (författare): Chalmers tekniska högskola,Chalmers University of Technology,Chalmers, Onsala Space Observ, Dept Earth & Space Sci, S-43992 Onsala, Sweden.

Ramstedt, S. (författare): Uppsala universitet,Institutionen för fysik och astronomi

Weigelt, G. (författare): Max Planck Gesellschaft zur Förderung der Wissenschaften e.V. (MPG),Max Planck Society for the Advancement of Science (MPG),Max Planck Inst Radioastron, Hugel 69, D-53121 Bonn, Germany.

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European Southern Observatory (ESO) European Southern Observ, Karl Schwarzschild Str 2, D-85748 Garching, Germany (creator_code:org_t)

2017-04-19
2017
Engelska.
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 601

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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?, an effective temperature of 2640 ± 80 K, and a luminosity of log L/L? = 3.74 ± 0.18. These parameters match evolutionary tracks of initial mass 1.5 ± 0.5 M? and current mass 1.3 ± 0.7 M?. 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. © ESO, 2017.

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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

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