Aperture synthesis imaging of the carbon AGB star R Sculptoris: Detection of a complex structure and a dominating spot on the stellar disk
Artikel i vetenskaplig tidskrift, 2017
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.
stars: mass-loss
techniques: interferometric
stars: AGB and post-AGB
stars: fundamental parameters
stars: individual: R Scl
stars: atmospheres
Författare
M. Wittkowski
European Southern Observatory (ESO)
K. H. Hofmann
Max-Planck-Gesellschaft
S. Höfner
Uppsala universitet
J. B. Le Bouquin
Université Grenoble Alpes
W. Nowotny
Universität Wien
C. Paladini
Université libre de Bruxelles (ULB)
J. Young
University of Cambridge
J. P. Berger
Université Grenoble Alpes
M. Brunner
Universität Wien
I. de Gregorio-Monsalvo
European Southern Observatory Santiago
Atacama Large Millimeter-submillimeter Array (ALMA)
K. Eriksson
Uppsala universitet
J. Hron
Universität Wien
E. M. Humphreys
European Southern Observatory (ESO)
Michael Lindqvist
Chalmers, Rymd- och geovetenskap, Onsala rymdobservatorium
Matthias Maercker
Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik
Chalmers, Rymd- och geovetenskap, Onsala rymdobservatorium
S. Mohamed
University of Cape Town
South African Astronomical Observatory
National Institute for Theoretical Physics
Hans Olofsson
Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik
Chalmers, Rymd- och geovetenskap, Onsala rymdobservatorium
S. Ramstedt
Uppsala universitet
G. Weigelt
Max-Planck-Gesellschaft
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 601 -Article number A3 A3Ämneskategorier
Astronomi, astrofysik och kosmologi
Fundament
Grundläggande vetenskaper
Infrastruktur
Onsala rymdobservatorium
DOI
10.1051/0004-6361/201630214