ALMA detection of a tentative nearly edge-on rotating disk around the nearby AGB star R~Doradus

Abstract

A spectral scan of the circumstellar environment of the asymptotic giant branch (AGB) star R~Doradus was taken with ALMA in cycle 2 at frequencies between 335 and 362 GHz and with a spatial resolution of $\sim$150 milliarcseconds. Many molecular lines show a spatial offset between the blue and red shifted emission in the innermost regions of the wind. The position-velocity diagrams of this feature, in combination with previous SPHERE data and theoretical work point towards the presence of a compact differentially rotating disk, orientated nearly edge-on. We model the ${}^{28}$SiO ($v=1,J=8\to 7$) emission with a disk model. We estimate the disk mass and angular momentum to be $3\times 10^{-6}$ Solar masses and $5\times 10^{40}{\mathrm{m}}^{2}kg/s$. The latter presents an `angular momentum problem' that may be solved by assuming that the disk is the result of wind-companion interactions with a companion of at least 2.5 earth masses, located at 6 AU, the tentatively determined location of the disk's inner rim. An isolated clump of emission is detected to the south-east with a velocity that is high compared to the previously determined terminal velocity of the wind. Its position and mean velocity suggest that it may be associated with a companion planet, located at the disk's inner rim.

arXiv comment11 pages, 7 Figures

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