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

¹ Institute of Astronomy, KU Leuven, Celestijnenlaan 200D B2401, 3001 Leuven, Belgium
e-mail: ward.homan@ster.kuleuven.be
² Sterrenkundig Instituut “Anton Pannekoek”, Science Park 904, 1098 XH Amsterdam, The Netherlands
³ NASA Goddard Space Flight Center, Code 690, Greenbelt, MD 20771, USA

Received: 6 November 2017
Accepted: 14 March 2018

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 ~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 ²⁸SiO (v = 1,  J = 8 → 7) emission with a disk model. We estimate the disk mass and angular momentum to be 3 × 10⁻⁶ M_⊙ and 5 × 10⁴⁰ m² kg s⁻¹. 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.