Issue |
A&A
Volume 613, May 2018
|
|
---|---|---|
Article Number | L4 | |
Number of page(s) | 11 | |
Section | Letters to the Editor | |
DOI | https://doi.org/10.1051/0004-6361/201832929 | |
Published online | 23 May 2018 |
Letter to the Editor
Rotation of the asymptotic giant branch star R Doradus
1
Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory,
439 92
Onsala,
Sweden
e-mail: wouter.vlemmings@chalmers.se
2
Instituto de Astronomía, Universidad Nacional Autónoma de México,
Km. 107 Carr. Tijuana-Ensenada,
22860
Ensenada
B. C.,
Mexico
3
Departamento de Física Teórica, Universidad Autónoma de Madrid, Cantoblanco,
28049
Madrid,
Spain
4
Laboratoire d’astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N,
Allée Geoffroy Saint-Hilaire,
33615
Pessac,
France
5
European Southern Observatory,
Karl-Schwarzschild-Str. 2,
85748
Garching,
Germany
6
Department of Physics and Astronomy, Uppsala University,
Box 516,
751 20
Uppsala,
Sweden
Received:
1
March
2018
Accepted:
12
April
2018
High-resolution observations of the extended atmospheres of asymptotic giant branch (AGB) stars can now directly be compared to the theories that describe stellar mass loss. Using Atacama Large Millimeter/submillimeter Array (ALMA) high angular resolution (30 × 42 mas) observations, we have for the first time resolved stellar rotation of an AGB star, R Dor. We measure an angular rotation velocity of ωR sin i = (3.5 ± 0.3) × 10−9 rad s−1, which indicates a rotational velocity of |υrot sin i| = 1.0 ± 0.1 km s−1 at the stellar surface (R* = 31.2 mas at 214 GHz). The rotation axis projected on the plane of the sky has a position angle Φ = 7 ± 6°. We find that the rotation of R Dor is two orders of magnitude faster than expected for a solitary AGB star that will have lost most of its angular momentum. Its rotational velocity is consistent with angular momentum transfer from a close companion. As a companion has not been directly detected, we suggest R Dor has a low-mass, close-in companion. The rotational velocity approaches the critical velocity, set by the local sound speed in the extended envelope, and is thus expected to affect the mass-loss characteristics of R Dor.
Key words: stars: AGB and post-AGB / stars: rotation
© ESO 2018
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