Evidence for the Keplerian orbit of a close companion around a giant star

Abstract

Close companions influence stellar evolution through tidal interactions, mass transfer, and mass loss effects. While such companions are detected around young stellar objects, main-sequence stars, red giants, and compact objects, direct observational evidence of close-in companions around asymptotic giant branch (AGB) stars has remained elusive. Here, we present (sub)millimeter time-domain imaging spectroscopy revealing the Keplerian motion of a close-in companion around the AGB star pi1 Gruis. The companion, slightly more massive than the AGB star, is likely a main-sequence star. Unlike more evolved stars with companions at comparable distances, pi1 Gru's companion follows a circular orbit, suggesting an eccentricity-generating mechanism late- or post-AGB. Our analysis suggests that model-predicted circularization rates may be underestimated. Our results highlight the potential of multi-epoch (sub)millimeter interferometry in detecting the Keplerian motion of close companions to giant stars and open avenues for our understanding of tidal interaction physics and binary evolution.

arXiv commentpublished in Nature Astronomy: https://www.nature.com/articles/s41550-025-02697-2

References in corpus (68)

• On the variation of the Initial Mass Function
• Gaia Data Release 3: Summary of the content and survey properties
• Validation of the new Hipparcos reduction
• Binary interaction dominates the evolution of massive stars
• Evolution of binary stars and the effect of tides on binary populations
• Estimating distances from parallaxes. V: Geometric and photogeometric distances to 1.47 billion stars in Gaia Early Data Release 3
• Mind your Ps and Qs: the Interrelation between Period (P) and Mass-ratio (Q) Distributions of Binary Stars
• The All-Sky Automated Survey for Supernovae (ASAS-SN) Light Curve Server v1.0
• The Dawes Review 2: Nucleosynthesis and stellar yields of low and intermediate-mass single stars
• Modules for Experiments in Stellar Astrophysics (MESA): Time-Dependent Convection, Energy Conservation, Automatic Differentiation, and Infrastructure
• Estimating distances from parallaxes
• Tidal dissipation in stars and giant planets
• Phantom: A smoothed particle hydrodynamics and magnetohydrodynamics code for astrophysics
• Slowing the Spins of Stellar Cores
• The massive binary companion star to the progenitor of supernova 1993J
• A Robust Measure of Tidal Circularization in Coeval Binary Populations: The solar-type spectroscopic Binary Population in The Open Cluster M35
• AGB Variables and the Mira Period-Luminosity Relation
• A New Version of Reimers' law of Mass Loss Based on a Physical Approach
• Eccentricity growth and orbit flip in coplanar hierarchical three body systems
• Variability in red supergiant stars: pulsations, long secondary periods and convection noise
• A Neptune-sized transiting planet closely orbiting a 5-10-million-year-old star
• UVMULTIFIT: A versatile tool for fitting astronomical radio interferometric data
• One Relation for All Wavelengths: The Far-Ultraviolet to Mid-Infrared Milky Way Spectroscopic R(V) Dependent Dust Extinction Relationship
• On the Measurement of Fundamental Parameters of White Dwarfs in the Gaia Era
• (Sub)stellar companions shape the winds of evolved stars
• Helium enrichment and Carbon-star Production in Metal-rich Populations
• The Reddening of Red Supergiants: When Smoke Gets In Your Eyes
• The ASAS-SN Catalog of Variable Stars V: Variables in the Southern Hemisphere
• White-Dwarf Kicks and Implications for Barium Stars
• ALMA observations of the nearby AGB star L2 Puppis - I. Mass of the central star and detection of a candidate planet
• Orbital evolution of mass-transferring eccentric binary systems. II. Secular Evolution
• Distance estimates for AGB stars from parallax measurements
• A new interpretation of the period-luminosity sequences of long-period variables
• K2-97b: A (Re-?)Inflated Planet Orbiting a Red Giant Star
• Evolution and Mass Loss of Cool Ageing Stars: a Daedalean Story
• Modelling Long-Period Variables - I. A new grid of O-rich and C-rich pulsation models
• Slowly, slowly in the wind: 3D hydrodynamical simulations of wind mass transfer and angular-momentum loss in AGB binary systems
• The ASAS-SN Catalog of Variable Stars X: Discovery of 116,000 New Variable Stars Using g-band Photometry
• Evolution and Nucleosynthesis of AGB stars in Three Magellanic Cloud Clusters
• SPHERE / ZIMPOL observations of the symbiotic system R Aqr. I. Imaging of the stellar binary and the innermost jet clouds
• ALMA Observations of Anisotropic Dust Mass-loss in the Inner Circumstellar Environment of the Red Supergiant VY Canis Majoris
• Wide Binary Effects on Asymmetries in Asymptotic Giant Branch Circumstellar Envelopes
• Binarity as the Origin of Long Secondary Periods in Red Giant Stars
• ATOMIUM: ALMA tracing the origins of molecules in dust forming oxygen rich M-type stars: Motivation, sample, calibration, and initial results
• 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
• Infrared Spectroscopy of Symbiotic Stars. VII. Binary Orbit and Long Secondary Period Variability of CH Cygni
• Long-term photometry and periods for 261 nearby pulsating M giants
• Toward an internally consistent astronomical distance scale
• The eccentric behaviour of windy binary stars
• SPH modelling of companion-perturbed AGB outflows including a new morphology classification scheme
• 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
• The Orbital Nature of 81 Ellipsoidal Red Giant Binaries in the Large Magellanic Cloud
• Optical spectroscopy of the recurrent nova RS Ophiuchi - from the outburst of 2006 to quiescence
• Binarity and Accretion in AGB Stars: HST/STIS Observations of UV Flickering in Y Gem
• 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
• 3D simulations of AGB stellar winds -- I. Steady winds and dust formation
• Semi-regular red giants as distance indicators I. The period-luminosity relations of semi-regular variables revisited
• Unseen companions of V Hya inferred from periodic ejections
• The VLT/SPHERE view of the ATOMIUM cool evolved star sample. I. Overview: Sample characterization through polarization analysis
• Bridging the Gap between Intermediate and Massive Stars I: Validation of MESA against the State-of-the-Art Monash Stellar Evolution Program for a 2$M_{\odot }$ AGB Star
• Impact of HI cooling and study of accretion disks in AGB wind-companion smoothed particle hydrodynamic simulations
• Chemical tracers of a highly eccentric AGB-main sequence star binary
• 3D simulations of AGB stellar winds -- II. Ray-tracer implementation and impact of radiation on the outflow morphology
• Tidal Dissipation in Evolved Low and Intermediate Mass Stars
• Testing tidal theory using Gaia binaries: the red giant branch
• A dynamic view of V Hydrae. Monitoring of a spectroscopic-binary AGB star with an alkaline jet
• An accreting dwarf star orbiting the S-type giant star pi1 Gru
• Self-Excited Pulsations and the Instability Strip of Long-Period Variables: the Transition from Small-Amplitude Red Giants to Semi-Regular Variables

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