Volume 658, February 2022
|Number of page(s)||15|
|Published online||21 February 2022|
The extended atmosphere and circumstellar environment of the cool evolved star VX Sagittarii as seen by MATISSE★
Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS,
Lagrange, CS 34229,
2 European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
3 Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Straße 1, 85741 Garching, Germany
4 Max Planck Institute for extraterrestrial Physics, Giessenbachstraße 1, 85748 Garching, Germany
5 LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de Paris, 5 place Jules Janssen, 92195 Meudon, France
6 Theoretical Astrophysics, Department of Physics and Astronomy at Uppsala University, Regementsvägen 1, Box 516, 75120 Uppsala, Sweden
7 Nicolaus Copernicus Astronomical Centre, Polish Academy of Sciences, Bartycka 18, 00-716 Warszawa, Poland
8 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
9 Leiden Observatory, Leiden University, Niels Bohrweg 2, 2333 CA Leiden, The Netherlands
10 Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
11 I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937, Köln, Germany
12 Univ. Grenoble Alpes, CNRS, IPAG, 38000, Grenoble, France
13 Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Eötvös Loránd Research Network (ELKH), Konkoly-Thege Miklós út 15-17, 1121 Budapest, Hungary
14 NASA Goddard Space Flight Center, Astrophysics Division, Greenbelt, MD 20771, USA
15 Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, 1090 GE Amsterdam, The Netherlands
16 Department of Astrophysics, University of Vienna, 1180 Vienna, Türkenschanzstrasse 17, Austria
17 Zselic Park of Stars, 064/2 hrsz., 7477 Zselickisfalud, Hungary
18 European Southern Observatory, Alonso de Cordova 3107, Casilla 19, Santiago 19001, Chile
19 AIM, CEA, CNRS, Université Paris-Saclay, Université Paris Diderot, Sorbonne Paris Cité, 91191 Gif-sur-Yvette, France
20 CSFK Lendület Near-Field Cosmology Research Group, Budapest, Hungary
21 Institute for Mathematics, Astrophysics and Particle Physics, Radboud University, PO Box 9010, MC 62, 6500 GL Nijmegen, the Netherlands
22 SRON Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
23 Institute of Theoretical Physics and Astrophysics, Kiel University, Leibnizstr. 15, 24118 Kiel, Germany
Accepted: 6 December 2021
Context. VX Sgr is a cool, evolved, and luminous red star whose stellar parameters are difficult to determine, which affects its classification.
Aims. We aim to spatially resolve the photospheric extent as well as the circumstellar environment.
Methods. We used interferometric observations obtained with the MATISSE instrument in the L (3–4 μm), M (4.5–5 μm), and N (8–13 μm) bands. We reconstructed monochromatic images using the MIRA software. We used 3D radiation-hydrodynamics simulations carried out with CO5BOLD and a uniform disc model to estimate the apparent diameter and interpret the stellar surface structures. Moreover, we employed the radiative transfer codes OPTIM3D and RADMC3D to compute the spectral energy distribution for the L, M, and N bands, respectively.
Results. MATISSE observations unveil, for the first time, the morphology of VX Sgr across the L, M, and N bands. The reconstructed images show a complex morphology with brighter areas whose characteristics depend on the wavelength probed. We measured the angular diameter as a function of the wavelength and showed that the photospheric extent in the L and M bands depends on the opacity through the atmosphere. In addition to this, we also concluded that the observed photospheric inhomogeneities can be interpreted as convection-related surface structures. The comparison in the N band yielded a qualitative agreement between the N-band spectrum and simple dust radiative transfer simulations. However, it is not possible to firmly conclude on the interpretation of the current data because of the difficulty in constraing the model parameters using the limited accuracy of our absolute flux calibration.
Conclusions. MATISSE observations and the derived reconstructed images unveil the appearance of VX Sgr’s stellar surface and circumstellar environment across a very large spectral domain for the first time.
Key words: stars: atmospheres / stars: late-type / stars: individual: VX Sgr / techniques: interferometric / infrared: stars / stars: imaging
Based on the observations made with VLTI-ESO Paranal, Chile under the programme IDs 0103.D-0153(D, E, G). The data are available at oidb.jmmc.fr
© A. Chiavassa et al. 2022
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.