Rotation of the asymptotic giant branch star R Doradus

• Published in: Astronomy and astrophysics (Berlin) Vol. 613; no. 613; p. L4
• Main Authors: Vlemmings, W. H. T., Khouri, T., De Beck, E., Olofsson, H., García-Segura, G., Villaver, E., Baudry, A., Humphreys, E. M. L., Maercker, M., Ramstedt, S.
• Format: Journal Article
• Language: English
• Published: Heidelberg EDP Sciences 2018
• Subjects: Angular momentum; Angular resolution; Angular velocity; Astrophysics; Asymptotic giant branch stars; Critical velocity; Momentum transfer; Physics; Radio telescopes; Sky; Solar and Stellar Astrophysics; stars: AGB and post-AGB; stars: rotation; Stellar atmospheres; Stellar mass; Stellar rotation; Velocity
• ISSN: 0004-6361; 1432-0746; 1432-0746; 1432-0756
• DOI: 10.1051/0004-6361/201832929

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.