Atomium: A high-resolution view on the highly asymmetric wind of the AGB star Pi1 Gruis. I. First detection of a new companion and its effect on the inner wind

Abstract

The nebular circumstellar environments of cool evolved stars are known to harbour a rich morphological complexity of gaseous structures on different length scales. A large part of these density structures are thought to be brought about by the interaction of the stellar wind with a close companion. The S-type asymptotic giant branch star Pi1 Gruis, which has a known companion at ~440 au and is thought to harbour a second, closer-by (<10 au) companion, was observed with the Atacama Large Millimeter/submillimeter Array as part of the ATOMIUM Large programme. In this work, the brightest CO, SiO, and HCN molecular line transitions are analysed. The continuum map shows two maxima, separated by 0.04'' (6 au). The CO data unambiguously reveal that Pi1 Gru's circumstellar environment harbours an inclined, radially outflowing, equatorial density enhancement. It contains a spiral structure at an angle of 38+/-3 deg with the line-of-sight. The HCN emission in the inner wind reveals a clockwise spiral, with a dynamical crossing time of the spiral arms consistent with a companion at a distance of 0.04'' from the asymptotic giant branch star, which is in agreement with the position of the secondary continuum peak. The inner wind dynamics imply a large acceleration region, consistent with a beta-law power of ~6. The CO emission suggests that the spiral is approximately Archimedean within 5'', beyond which this trend breaks down as the succession of the spiral arms becomes less periodic. The SiO emission at scales smaller than 0.5'' exhibits signatures of gas in rotation, which is found to fit the expected behaviour of gas in the wind-companion interaction zone. An investigation of SiO maser emission reveals what could be a stream of gas accelerating from the surface of the AGB star to the companion. Using these dynamics, we have tentatively derived an upper limit on the companion mass to be ~1.1 Msol.

arXiv comment19 pages, 20 figures

References in corpus (46)

• SciPy 1.0--Fundamental Algorithms for Scientific Computing in Python
• Astropy: A Community Python Package for Astronomy
• The NumPy array: a structure for efficient numerical computation
• Validation of the new Hipparcos reduction
• A Survey of Stellar Families: Multiplicity of Solar-Type Stars
• One or more bound planets per Milky Way star from microlensing observations
• Probing the mass-loss history of AGB and red supergiant stars from CO rotational line profiles - II. CO line survey of evolved stars: derivation of mass-loss rate formulae
• Dust formation in the oxygen-rich AGB star IK Tau
• Too little radiation pressure on dust in the winds of oxygen-rich AGB stars
• A far-infrared survey of bow shocks and detached shells around AGB stars and red supergiants
• Unexpectedly large mass loss during the thermal pulse cycle of the red giant R Sculptoris!
• On the reliability of mass-loss-rate estimates for AGB stars
• Imaging the circumstellar envelopes of AGB stars
• Probing the mass-loss history of AGB and red supergiant stars from CO rotational line profiles I. Theoretical model -- Mass-loss history unravelled in VY CMa
• (Sub)stellar companions shape the winds of evolved stars
• An Improved Model of SiO Maser Emission in Miras
• 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
• New observations and models of circumstellar CO line emission of AGB stars in the Herschel SUCCESS programme
• Study of the inner dust envelope and stellar photosphere of the AGB star R Doradus using SPHERE/ZIMPOL
• Jets and Tori in Proto-Planetary Nebulae
• 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
• Clumpy dust clouds and extended atmosphere of the AGB star W Hya revealed with VLT/SPHERE-ZIMPOL and VLTI/AMBER
• ALMA spectral line and imaging survey of a low and a high mass-loss rate AGB star between 335 and 362 GHz
• The wind of W Hya as seen by Herschel - I. The CO envelope
• Slowly, slowly in the wind: 3D hydrodynamical simulations of wind mass transfer and angular-momentum loss in AGB binary systems
• Three-dimensional hydrodynamical simulations of mass transfer in binary systems by a free wind
• An extensive grid of DARWIN models for M-type AGB stars I. Mass-loss rates and other properties of dust-driven winds
• The evolution of DARWIN: current status of wind models for AGB stars
• Minkowski's Footprint revisited. Planetary Nebula formation from a single sudden event?
• Herschel's view into Mira's head
• Wind morphology around cool evolved stars in binaries: the case of slowly accelerating oxygen-rich outflows
• Observational evidence for the shrinking of bright maser spots
• The onset of the AGB wind tied to a transition between sequences in the period-luminosity diagram
• 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
• A New Method of Determining the Characteristics of Evolved Binary Systems Revealed in the Observed Circumstellar Patterns: Application to AFGL 3068
• Substellar multiplicity in the Hyades cluster
• An unusual face-on spiral in the wind of the M-type AGB star EP Aquarii
• ALMA detection of a tentative nearly edge-on rotating disk around the nearby AGB star R~Doradus
• Evidence of a Binary-Induced Spiral from an Incomplete Ring Pattern of CIT 6
• High-resolution observations of the symbiotic system R Aqr. Direct imaging of the gravitational effects of the secondary on the stellar wind
• Gravitationally Induced Density Wake of a Circularly Orbiting Object As an Interpretative Framework of Ubiquitous Spirals and Arcs
• The extended molecular envelope of the asymptotic giant branch star ${\pi }^1$ Gruis as seen by ALMA II. The spiral-outflow observed at high-angular resolution
• HD101584: Circumstellar characteristics and evolutionary status
• Polarization morphology of SiO masers in the circumstellar envelope of the AGB star R Cassiopeiae
• Simplified models of circumstellar morphologies for interpreting high-resolution data. Analytical approach to the equatorial density enhancement

Cited by in corpus (20)

• ATOMIUM: ALMA tracing the origins of molecules in dust forming oxygen rich M-type stars: Motivation, sample, calibration, and initial results
• SPH modelling of companion-perturbed AGB outflows including a new morphology classification scheme
• ATOMIUM: Probing the inner wind of evolved O-rich stars with new, highly excited H${}_2$O and OH lines
• ATOMIUM: Molecular inventory of 17 oxygen-rich evolved stars observed with ALMA
• SPH modelling of wind-companion interactions in eccentric AGB binary systems
• ATOMIUM: Halide molecules around the S-type AGB star W Aquilae
• 3D simulations of AGB stellar winds -- I. Steady winds and dust formation
• Investigating Anomalous Photochemistry in the Inner Wind of IRC+10216 Through Interferometric Observations of HC${}_3$N
• Salt-bearing disk candidates around high-mass young stellar objects
• The VLT/SPHERE view of the ATOMIUM cool evolved star sample. I. Overview: Sample characterization through polarization analysis
• 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
• Impact of HI cooling and study of accretion disks in AGB wind-companion smoothed particle hydrodynamic simulations
• The Rapidly Evolving AGB Star, V Hya: ALMA finds a Multi-Ring Circus with High-Velocity Outflows
• Chemical tracers of a highly eccentric AGB-main sequence star binary
• An accreting dwarf star orbiting the S-type giant star pi1 Gru
• Two-wind interactions in binaries with two orbiting giant stars
• ATOMIUM: Continuum emission and evidence of dust enhancement from binary motion
• Molecules, shocks, and disk in the axi-symmetric wind of the MS-type AGB star RS Cancri
• Disentangling physics and chemistry in AGB outflows: revealing degeneracies when adding complexity
• Evidence for the Keplerian orbit of a close companion around a giant star