Rotation of the asymptotic giant branch star R Doradus

Author： Vlemmings W. H. T. Khouri T. Beck E. De Olofsson H. García-Segura G. Villaver E. Baudry A. Humphreys E. M. L. Maercker M. Ramstedt S.

Publisher： Edp Sciences

E-ISSN： 1432-0746|613|issue|L4-L4

ISSN： 0004-6361

Source： Astronomy & Astrophysics, Vol.613, Iss.issue, 2018-05, pp. : L4-L4

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Abstract

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 ω_R sin i = (3.5 ± 0.3) × 10⁻⁹ rad s⁻¹, which indicates a rotational velocity of |υ_rot 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.