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Evolved low- to intermediate-mass stars are known to shed their gaseousenvelope into a large, dusty, molecule-rich circumstellar nebula whichtypically develops a high degree of structural complexity. Most of thelarge-scale, spatially correlated structures in the nebula are thought tooriginate from the interaction of the stellar wind with a companion. As part ofthe Atomium large programme, we observed the M-type asymptotic giant branch(AGB) star R Hydrae with ALMA. The morphology of the inner wind of R Hya, whichhas a known companion at ~3500 au, was determined from maps of CO and SiOobtained at high angular resolution. A map of the CO emission reveals amulti-layered structure consisting of a large elliptical feature at an angularscale of ~10'' that is oriented along the north-south axis. The wind morphologywithin the elliptical feature is dominated by two hollow bubbles. The bubblesare on opposite sides of the AGB star and lie along an axis with a positionangle of ~115 deg. Both bubbles are offset from the central star, and theirappearance in the SiO channel maps indicates that they might be shock wavestravelling through the AGB wind. An estimate of the dynamical age of thebubbles yields an age of the order of 100 yr, which is in agreement with thepreviously proposed elapsed time since the star last underwent a thermal pulse.When the CO and SiO emission is examined on subarcsecond angular scales, thereis evidence for an inclined, differentially rotating equatorial densityenhancement, strongly suggesting the presence of a second nearby companion. Theposition angle of the major axis of this disc is ~70 deg in the plane of thesky. We tentatively estimate that a lower limit on the mass of the nearbycompanion is ~0.65 Msol on the basis of the highest measured speeds in the discand the location of its inner rim at ~6 au from the AGB star.

astronomy and astrophysics

Atomium: The astounding complexity of the near circumstellar environment  of the M-type AGB star R Hydrae. I. Morpho-kinematical interpretation of CO  and SiO emission