Rotation of the asymptotic giant branch star R Doradus

Abstract

High resolution observations of the extended atmospheres of asymptotic giant branch (AGB) stars can now directly confront the theories that describe stellar mass loss. Using Atacama Large Millimeter/submillimeter Array (ALMA) high angular resolution ($30\times 42$~mas) observations we have, for the first time, resolved stellar rotation of an AGB star, R~Dor. We measure an angular rotation velocity of ${\omega }_R\sin i=(3.5\pm 0.3)\times 10^{-9}$~rad~s${}^{-1}$ which indicates a rotational velocity of $|{\upsilon }_{\mathrm{rot}}\sin i|=1.0\pm 0.1$~km~s${}^{-1}$ at the stellar surface ($R_{\ast }=31.2$~mas at $214$~GHz). The rotation axis projected on the plane of the sky has a position angle $\Phi =7\pm 6^{\circ }$. 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 thus 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.

arXiv comment12 pages, 15 figures, Accepted for publication in Astronomy & Astrophysics

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• Is Betelgeuse Really Rotating? Synthetic ALMA Observations of Large-scale Convection in 3D Simulations of Red Supergiants
• Infrared interferometric three-dimensional diagnosis of the atmospheric dynamics of the AGB star R Dor with VLTI/AMBER
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• ALMA observations of the "fresh" carbon-rich AGB star TX Piscium. The discovery of an elliptical detached shell
• Morpho-kinematics of the circumstellar envelope of the AGB star R Dor: a global view
• DEATHSTAR: Nearby AGB stars with the Atacama Compact Array II. CO envelope sizes and asymmetries: The S-type stars
• Tidal Dissipation in Evolved Low and Intermediate Mass Stars
• VLTI-PIONIER imaging of the red supergiant V602 Carinae
• One month convection timescale on the surface of a giant evolved star
• Gas infall and possible circumstellar rotation in R Leo
• Constraining stellar parameters and atmospheric dynamics of the carbon AGB star V Oph
• A large bubble around the AGB star R Dor detected in the UV
• Mira Ceti, atypical archetype
• Molecules, shocks, and disk in the axi-symmetric wind of the MS-type AGB star RS Cancri
• The nascent wind of AGB star R Doradus: evidence for a recent episode of enhanced mass loss
• Probing the Extended Atmospheres of AGB Stars: I. Synthetic imaging of 1D hydrodynamical models at radio and (sub-)millimeter wavelengths
• Extended far-UV emission surrounding asymptotic giant branch stars as seen by GALEX
• Contributions of rotation, expansion and line broadening to the morpho-kinematics of the inner CSE of oxygen-rich AGB star R Hya
• Millimetre observations of the S-type AGB star $\chi$ Cygni: variability of the emission of the inner envelope