The symbiotic stellar system R Aqr: mm-waveimaging of the WD – AGB wind interaction
February 25, 2021
We have observed the symbiotic stellar system R Aqr. We obtained
high-resolution ALMA maps of the 0.9 mm continuum distribution, the 12CO J=3-2 line, and some other molecular lines in R Aqr. The maps, which have resolutions ranging between 150 milliarcsecond (mas) and less than 20 mas, probe the circumstellar regions down to suborbital scales and directly image the gravitational interaction between the white dwarf (WD) and the wind from the Mira star. The AGB star was identified in our maps from the continuum and molecular line data, and we estimated the probable position of the secondary from a new estimation of the orbital parameters. Our radiocontinuum maps show
the very inner regions of the nascent bipolar jets, down to scales of some AU. Continuum maps obtained with the highest resolution identify the AGB photospheric emission, a clump that very probably corresponds to the emission of the ionized surroundings of the WD, and a bridge of dusty material joining both stars, which is likely material flowing from the AGB primary to the WD secondary. Our maps of the CO J=3-2 line show a strong focusing in the equatorial plane of the wind beyond the orbit, which is composed of two extended plumes and a central strong condensation. We also present unpublished compact-array maps that identify some weak clumps and show that this source shows no significant extended emission of CO. The structure and kinematics of the different components very probably correspond to the expected spiral-like structure due to the interaction. We have developed a very simple heuristic model, based on general ideas from models of the hydrodynamics and chemistry in these objects, whose predictions are surprisingly comparable to the observations and serve to describe the main properties of the circumstellar shells at a scale of a few orbital diameters.
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