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

• Published in: Astronomy and astrophysics (Berlin) 2018-08, Vol.616, p.L3
• Main Authors: Bujarrabal, V., Alcolea, J., Mikołajewska, J., Castro-Carrizo, A., Ramstedt, S.
• Format: Article
• Language: English
• Subjects: binaries : close; binaries: symbiotic; circumstellar matter; stars: AGB and post-AGB; stars: individual: R Aqr
• ISSN: 0004-6361; 1432-0746; 1432-0746
• DOI: 10.1051/0004-6361/201833633

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 12 CO and 13 CO 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 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.