High-resolution observations of the symbiotic system R Aqr. Direct imaging of the gravitational effects of the secondary on the stellar wind

TL;DR

This study uses high-resolution ALMA observations to directly image the gravitational effects of a secondary star on the stellar wind in the R Aqr symbiotic system, revealing detailed wind structures and interactions.

Contribution

First direct imaging of gravitational effects of a secondary star on stellar wind in R Aqr using sub-20 mas resolution ALMA maps, matching theoretical predictions.

Findings

Detection of wind focusing and double spiral structures.

Identification of a clump likely from ionized surroundings of the white dwarf.

Observation of a material bridge between the stars.

Abstract

We have observed the symbiotic stellar system R Aqr, aiming to describe the gravitational interaction between the white dwarf (WD) and the wind from the Mira star, the key phenomenon driving the symbiotic activity and the formation of nebulae in such systems. We present high-resolution ALMA maps of the 12CO and 13CO J=3-2 lines, the 0.9 mm continuum distribution, and some high-excitation molecular lines in R Aqr. The maps, which have resolutions ranging between 40 milliarcsecond (mas) and less than 20 mas, probe the circumstellar regions at suborbital scales as the distance between the stars is ~ 40 mas. Our observations show the gravitational effects of the secondary on the stellar wind. 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. The (preliminary) comparison of our maps with theoretical predictions is surprisingly satisfactory and the main expected gravitational effects are directly mapped for the first time. We find a strong focusing in the equatorial plane of the resulting wind, which shows two plumes in opposite directions that have different velocities and very probably correspond to the expected double spiral due to the interaction. Our continuum maps show the very inner regions of the nascent bipolar jets, at scales of some AU. Continuum maps obtained with the highest resolution show the presence of a clump that very probably corresponds to the emission of the ionized surroundings of the WD and of a bridge of material joining both stars, which is likely material flowing from the AGB primary to the accretion disk around the WD secondary.