A detailed view on the circumstellar environment of the M-type AGB star EP Aquarii I. High-resolution ALMA and SPHERE observations

Abstract

Cool evolved stars are known to be significant contributors to the enrichment of the interstellar medium through their dense and dusty stellar winds. High resolution observations of these outflows have shown them to possess high degrees of morphological complexity. We observed the asymptotic giant branch (AGB) star EP Aquarii with ALMA in band 6 and VLT/SPHERE/ZIMPOL in four filters the visible. Both instruments had an angular resolution of 0.025''. These are follow-up observations to the lower-resolution 2016 ALMA analysis of EP Aquarii, which revealed that its wind possesses a nearly face-on, spiral-harbouring equatorial density enhancement, with a nearly pole-on bi-conical outflow. At the base of the spiral, the SiO emission revealed a distinct emission void approximately 0.4'' to the west of the continuum brightness peak, which was proposed to be linked to the presence of a companion. The new ALMA data better resolve the inner wind and reveal that its morphology as observed in CO is consistent with hydrodynamical companion-induced perturbations. Assuming that photodissociation by the UV-field of the companion is responsible for the emission void in SiO, we deduced the spectral properties of the tentative companion from the size of the hole. We conclude that the most probable companion candidate is a white dwarf with a mass between 0.65 and 0.8 Msol , though a solar-like companion could not be definitively excluded. The radial SiO emission shows periodic, low-amplitude perturbations. We tentatively propose that they could be the consequence of the interaction of the AGB wind with another much closer low-mass companion. The polarised SPHERE/ZIMPOL data show a circular signal surrounding the AGB star with a radius of 0.1''...

24 pages, 25 Figures

References in corpus (24)

• Unexpectedly large mass loss during the thermal pulse cycle of the red giant R Sculptoris!
• (Sub)stellar companions shape the winds of evolved stars
• Testing the white dwarf mass-radius relationship with eclipsing binaries
• 2D Models for Dust-driven AGB Star Winds
• The enigmatic nature of the circumstellar envelope and bow shock surrounding Betelgeuse as revealed by Herschel. I. Evidence of clumps, multiple arcs, and a linear bar-like structure
• ALMA data suggest the presence of a spiral structure in the inner wind of CW Leo
• ALMA observations of the nearby AGB star L2 Puppis - I. Mass of the central star and detection of a candidate planet
• The wonderful complexity of the Mira AB system
• Exploring wind-driving dust species in cool luminous giants III. Wind models for M-type AGB stars: dynamic and photometric properties
• The Gaia DR1 Mass-Radius Relation for White Dwarfs
• Three-dimensional hydrodynamical simulations of mass transfer in binary systems by a free wind
• Low-temperature MIR to submillimeter mass absorption coefficient of interstellar dust analogues II: Mg and Fe-rich amorphous silicates
• A Catalog of GALEX Ultraviolet Emission from Asymptotic Giant Branch Stars
• Detection of Keplerian dynamics in a disk around the post-AGB star AC Her
• ALMA Observations of Anisotropic Dust Mass-loss in the Inner Circumstellar Environment of the Red Supergiant VY Canis Majoris
• Chemical content of the circumstellar envelope of the oxygen-rich AGB star R Dor: Non-LTE abundance analysis of CO, SiO, and HCN
• Wind morphology around cool evolved stars in binaries: the case of slowly accelerating oxygen-rich outflows
• Reduction of the maximum mass-loss rate of OH/IR stars due to unnoticed binary interaction
• Resolving the extended stellar atmospheres of Asymptotic Giant Branch stars at (sub-)millimetre wavelengths
• The extended molecular envelope of the asymptotic giant branch star ${\pi }^1$ Gruis as seen by ALMA I. Large-scale kinematic structure and CO excitation properties
• Simplified models of stellar wind anatomy for interpreting high-resolution data: Analytical approach to embedded spiral geometries
• The morpho-kinematics of the circumstellar envelope around the AGB star EP Aqr
• Eyes in the sky: Interactions between AGB winds and the interstellar magnetic field
• Observation of narrow polar jets in the nascent wind of oxygen-rich AGB star EP Aqr

Cited by in corpus (5)

• SPH modelling of wind-companion interactions in eccentric AGB binary systems
• 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
• Morpho-kinematics of the wind of AGB star L${}_2$ Pup
• Impact of a binary companion in AGB outflows on CO spectral lines
• 3D models of the circumstellar environments of evolved stars: Formation of multiple spiral structures