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 ($30\times42$~mas) observations we have, for the first time, resolved stellar rotation of an AGB star, R~Dor. We measure an angular rotation velocity of $\omega_R\sin{i}=(3.5\pm0.3)\times10^{-9}$~rad~s$^{-1}$ which indicates a rotational velocity of $|\upsilon_{\rm rot}\sin{i}|=1.0\pm0.1$~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 $\Phi=7\pm6^\circ$. 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.
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Contributor : Marie-Paule Pomies <>
Submitted on : Monday, April 16, 2018 - 11:41:57 AM
Last modification on : Friday, April 5, 2019 - 8:24:09 PM

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W. H. T. Vlemmings, T. Khouri, E. de Beck, H. Olofsson, G. Garcia-Segura, et al.. Rotation of the asymptotic giant branch star R Doradus. Astronomy and Astrophysics - A&A, EDP Sciences, 2018, ⟨10.1051/0004-6361/201832929⟩. ⟨hal-01767493⟩



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