On Lithium-Rich Red Giants. I. Engulfment of Sub-Stellar Companions

Abstract

A small fraction of red giants are known to be lithium (Li) rich, in contradiction with expectations from stellar evolutionary theory. A possible explanation for these atypical giants is the engulfment of a Li-rich planet or brown dwarf by the star. In this work, we model the evolution of Li abundance in canonical red giants including the accretion of a sub-stellar mass companion. We consider a wide range of stellar and companion masses, Li abundances, stellar metallicities, and planetary orbital periods. Based on our calculations, companions with masses lower than 15 M_J dissolve in the convective envelope and can induce Li enrichment in regimes where extra mixing does not operate. Our models indicate that the accretion of a substellar companion can explain abundances up to A(Li)~2.2, setting an upper limit for Li-rich giants formed by this mechanism. Giants with higher abundances need another mechanism to be explained. For reasonable planetary distributions, we predict the Li abundance distribution of low-mass giants undergoing planet engulfment, finding that between 1% to 3% of them should have A(Li)>1.5. We show that depending on the stellar mass range, this traditional definition of Li-rich giants is misleading, as isolated massive stars would be considered anomalous while giants engulfing a companion would be set aside, flagged as normal. We explore the detectability of companion engulfment, finding that planets with masses higher than ~7 M_J produce a distinct signature, and that descendants of stars originating in the Li-dip and low luminosity red giants are ideal tests of this channel.

arXiv commentAccepted for publication, ApJ. 25 pages, 13 figures

References in corpus (67)

• The chemical composition of the Sun
• Evolutionary models for cool brown dwarfs and extrasolar giant planets. The case of HD 20945
• Low Temperature Opacities
• Planet Occurrence within 0.25 AU of Solar-type Stars from Kepler
• Planetary Radii across Five Orders of Magnitude in Mass and Stellar Insolation: Application to Transits
• The Keck Planet Search: Detectability and the Minimum Mass and Orbital Period Distribution of Extrasolar Planets
• Solar fusion cross sections II: the pp chain and CNO cycles
• The Occurrence and Mass Distribution of Close-in Super-Earths, Neptunes, and Jupiters
• First stars VI - Abundances of C, N, O, Li, and mixing in extremely metal-poor giants. Galactic evolution of the light elements
• Influence of gravity waves on the internal rotation and Li abundance of solar-type stars
• Excitation of Activity in Galaxies by Minor Mergers
• Departures from LTE for neutral Li in late-type stars
• Thermohaline mixing: A physical mechanism governing the photospheric composition of low-mass giants
• The Orbital Evolution of Gas Giant Planets around Giant Stars
• Primordial Nucleosynthesis in Light of WMAP
• Time scales of Li evolution: a homogeneous analysis of open clusters from ZAMS to late-MS
• The accretion of planets and brown dwarfs by giant stars -- II. solar mass stars on the red giant branch
• A Detailed Model Grid for Solid Planets from 0.1 through 100 Earth Masses
• Deep Mixing of He-3: Reconciling Big Bang and Stellar Nucleosynthesis
• YREC: The Yale Rotating Stellar Evolution Code
• Lithium abundances in nearby FGK dwarf and subgiant stars: internal destruction, Galactic chemical evolution, and exoplanets
• Hot Jupiters and Cool Stars
• Jupiter models with improved ab initio hydrogen EOS (H-REOS.2)
• Rotational mixing in low-mass stars II. Self-consistent models of Pop II RGB stars
• The Accretion of Brown Dwarfs and Planets by Giant Stars -- I. AGB Stars
• Can Extra Mixing in RGB and AGB Stars Be Attributed to Magnetic Mechanisms?
• Li abundances in F stars: planets, rotation and galactic evolution
• Stellar Models with Microscopic Diffusion and Rotational Mixing II: Application to Open Clusters
• Planet Engulfment by ~1.5-3 Solar-Mass Red Giants
• Lithium Abundances of the Local Thin Disk Stars
• Origin of lithium enrichment in K giants
• Rapidly-rotating lithium-rich K giants: The new case of the giant PDS365
• Observable Signatures of Planet Accretion in Red Giant Stars I: Rapid Rotation and Light Element Replenishment
• Numerical Simulations of Thermohaline Convection: Implications for Extra-Mixing in Low-Mass RGB Stars
• Magnetic Mixing in Red Giant and Asymptotic Giant Branch Stars
• Thermohaline mixing in evolved low-mass stars
• Planet Consumption and Stellar Metallicity Enhancements
• Magneto-Thermohaline Mixing in Red Giants
• Metal-Poor Lithium-Rich Giants in the Radial Velocity Experiment Survey
• The Role of Planet Accretion in Creating the Next Generation of Red Giant Rapid Rotators
• Lithium-Rich Giants in Globular Clusters
• Lithium-Rich Field Giants in the Sloan Digital Sky Survey
• Rapid Rotation of Low-Mass Red Giants Using APOKASC: A Measure of Interaction Rates on the Post-main-sequence
• Old puzzle, new insights: a lithium rich giant quietly burning helium in its core
• The Sensitivity of Convection Zone Depth to Stellar Abundances: An Absolute Stellar Abundance Scale from Asteroseismology
• Abundance Anomalies and Rotational Evolution of Low Mass Red Giants: A Maximal Mixing Approach
• Lithium-rich giants in the Galactic thick disk
• Abundances of lithium, oxygen, and sodium in the turn-off stars of Galactic globular cluster 47 Tuc
• Deep Mixing in Evolved Stars. II. Interpreting Li Abundances in RGB and AGB Stars
• The Role of Thermohaline Mixing in Intermediate- and Low-Metallicity Globular Clusters
• BD+48 740 - Li overabundant giant star with a planet. A case of recent engulfment?
• Three Li-rich K giants: IRAS 12327-6523, IRAS 13539-4153, and IRAS 17596-3952
• Li-rich RGB stars in the Galactic Bulge
• The Penn State - Torun Centre for Astronomy Planet Search stars. II. Lithium abundance analysis of the Red Giant Clump sample
• OPserver: interactive online-computations of opacities and radiative accelerations
• Lithium abundances along the RGB: FLAMES-GIRAFFE spectra of a large sample of low-mass Bulge stars
• Discovery of Super-Li Rich Red Giants in Dwarf Spheroidal Galaxies
• Searching for Li-rich giants in a sample of 12 open clusters: Li enhancement in two stars with substellar companions
• On the nature of Lithium-rich giant stars: constraints from Beryllium abundances
• A New Twist In the Evolution of Low-Mass Stars
• 2D or not 2D: the effect of dimensionality on the dynamics of fingering convection at low Prandtl number
• The Puzzling Li-rich Red Giant Associated with NGC 6819
• Fingering Convection in Red Giants Revisited
• KIC 9821622: An interesting lithium-rich giant in the Kepler field
• Extra-Mixing in Luminous Cool Red Giants. Hints from Evolved Stars with and without Li
• On the serendipitous discovery of a Li-rich giant in the globular cluster NGC 362
• Lithium in Open Cluster Red Giants Hosting Substellar Companions

Cited by in corpus (65)

• A giant planet undergoing extreme ultraviolet irradiation by its hot massive-star host
• VLT/FLAMES high-resolution chemical abundances in Sculptor: a textbook dwarf spheroidal galaxy
• Seeing double with K2: Testing re-inflation with two remarkably similar planets around red giant branch stars
• Discovery of ubiquitous lithium production in low-mass stars
• HD 1397b: a transiting warm giant planet orbiting a V = 7.8 mag sub-giant star discovered by TESS
• The Li-age correlation: the Sun is unusually Li deficient for its age
• A-type Stars, the Destroyers of Worlds: The lives and deaths of Jupiters in evolving stellar binaries
• Lithium in red giant stars: Constraining non-standard mixing with large surveys in the Gaia era
• Survey of Li-rich giants among Kepler and LAMOST fields: Determination of Li-rich giants Evolutionary Phase
• Alkali metals in white dwarf atmospheres as tracers of ancient planetary crusts
• Lithium Enrichment Signatures of Planetary Engulfment Events in Evolved Stars
• Eating Planets for Lunch and Dinner: Signatures of Planet Consumption by Evolving Stars
• Planetary Engulfment in the Hertzsprung--Russell Diagram
• The Gaia -ESO Survey: Lithium enrichment histories of the Galactic thick and thin disc
• The Gaia-ESO Survey: properties of newly discovered Li-rich giants
• Li Evolution and the Open Cluster NGC 6819: A Correlation Between Li Depletion and Spindown in Dwarfs More Massive Than the F-Dwarf Li-Dip
• Giant planet engulfment by evolved giant stars: light curves, asteroseismology, and survivability
• Two new Super Li-rich core He-burning giants: A new twist to the long tale of Li enhancement in K giants
• On Lithium-Rich Red Giants. II. Engulfment on the Giant Branch of Trumpler 20
• Search for lithium-rich giants in 32 open clusters with high-resolution spectroscopy
• WIYN Open Cluster Study: The Old Open Cluster, NGC 188, and a Re-evaluation of Lithium-Richness Among Red Giants
• A comprehensive study of NGC 2345, a young open cluster with a low metallicity
• Accounting for planet-shaped planetary nebulae
• Tracking Advanced Planetary Systems (TAPAS) with HARPS-N. VI. HD 238914 and TYC 3318-01333-1 - two more Li-rich giants with planets
• High-resolution spectroscopic analysis of a large sample of Li-rich giants found by LAMOST
• Many Roads Lead to Lithium: Formation Pathways For Lithium-Rich Red Giants
• The Active Chromospheres of Lithium-Rich Red Giant Stars
• Kepler-1656b's Extreme Eccentricity: Signature of a Gentle Giant
• Evidences of extragalactic origin and planet engulfment in the metal-poor twin pair HD 134439/HD 134440
• Mass Matters: No Evidence for Ubiquitous Lithium Production in Low-Mass Clump Giants
• Hydrodynamics and survivability during post-main-sequence planetary engulfment
• Evidence of extra-mixing in field giants as traced by lithium and carbon isotope ratio
• Spinning up the Surface: Evidence for Planetary Engulfment or Unexpected Angular Momentum Transport?
• The Gaia-ESO Survey: Preparing the ground for 4MOST & WEAVE galactic surveys. Chemical evolution of lithium with machine learning
• The Gaia-ESO Survey: Spectroscopic-asteroseismic analysis of K2 stars in Gaia-ESO
• Characterization of Kepler targets based on medium-resolution LAMOST spectra analyzed with ROTFIT
• Li-rich Giants in LAMOST Survey. III. The statistical analysis of Li-rich giants
• Super lithium-rich K giant with low ${}^{12}\mathrm{C}$ to ${}^{13}\mathrm{C}$ ratio
• On the role of reduced wind mass-loss rate in enabling exoplanets to shape planetary nebulae
• Light chemical elements in stars: mysteries and unsolved problems
• The Class of Jsolated Stars and Luminous Planetary Nebulae in old stellar populations
• Disentangling the origin of chemical differences using GHOST
• Probing infrared excess connection with Li enhancement among red clump giants
• Are Lithium-Rich Giants Binaries? A Radial Velocity Variability Analysis of 1,400 Giants
• The future influence of six exoplanets on the envelope properties of their parent stars on the giant branches
• Quantum effects on plasma screening for thermonuclear reactions in laser-generated plasmas
• Lithium in the lower red giant branch of 5 Galactic globular clusters
• Lithium in Kepler Red Giants: Defining Normal and Anomalous
• Li-rich Giants Identified from LAMOST DR8 Low-Resolution Survey
• Li-rich giant stars under scrutiny: Binarity, magnetic activity and the evolutionary status after Gaia DR2
• Hot Jupiter engulfment by a red giant in 3D hydrodynamics
• Anomalously low-mass core-He-burning star in NGC 6819 as a post-common-envelope phase product
• Sub-stellar engulfment by a main sequence star: where is the lithium?
• The enigma of Li-rich giants and its relation with temporal variations observed in radial velocity and stellar activity signals
• LAMOST/HRS Spectroscopic Analysis of Two New Li-rich Giants
• On Lithium-6 as diagnostic of the lithium-enrichment mechanism in red giants
• Gemini-GRACES high-quality spectra of Kepler evolved stars with transiting planets I. Detailed characterization of multi-planet systems Kepler-278 and Kepler-391
• Discovery of a Metal-Poor Red Giant Star with the Highest Ultra-Lithium Enhancement
• The bi-modal ${}^7$Li distribution of the Milky Way's thin-disk dwarf stars: The role of Galactic-scale events and stellar evolution
• Accretion of Planetary Material onto Host Stars
• Analysis of the non-LTE lithium abundance for a large sample of F-, G-, and K-giants and supergiants
• A Sequoia stellar candidate with very high 7Li and 9Be
• Faint intermediate luminosity optical transients (ILOTs) from engulfing exoplanets on the Hertzsprung gap
• Eccentricity Evolution in Gaseous Dynamical Friction
• Evolution of the ZTF SLRN-2020 star-planet merger