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-institutet

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-institutet

Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 601 -Article number A3 A3

Ämneskategorier

Astronomi, astrofysik och kosmologi

Fundament

Grundläggande vetenskaper

Infrastruktur

Onsala rymdobservatorium

DOI

10.1051/0004-6361/201630214