[Paper Review] Planet Signatures In The Chemical Composition Of Sun-Like Stars

J. Meléndez, I. Ramírez|arXiv (Cornell University)|Nov 13, 2016

Stellar, planetary, and galactic studies4 references5 citations

TL;DR

This paper investigates chemical signatures of planet formation in Sun-like stars, identifying refractory element depletion and lithium enrichment as indicators of planetary accretion and core formation. Using high-precision spectroscopy of solar twins and binaries, it demonstrates that the Sun's refractory deficiency—evident at ~0.01 dex—strongly correlates with condensation temperature, providing robust evidence for planet formation imprinting stellar composition.

ABSTRACT

There are two possible mechanisms to imprint planet signatures in the chemical composition of Sun-like stars: i) dust condensation at the early stages of planet formation, causing a depletion of refractory elements in the gas accreted by the star in the late stages of its formation; ii) planet engulfment, enriching the host star in lithium and refractory elements. We discuss both planet signatures, the influence of galactic chemical evolution, and the importance of binaries composed of stellar twins as laboratories to verify abundance anomalies imprinted by planets.

Motivation & Objective

• To identify chemical imprints of planet formation in the atmospheres of Sun-like stars.
• To disentangle the effects of galactic chemical evolution (GCE) from planetary signatures in stellar abundance trends.
• To use solar twins and planet-hosting binaries as high-precision laboratories to isolate planetary signatures.
• To test whether observed abundance anomalies in stars like the Sun and Kepler-10 are due to planet formation or stellar age and population effects.
• To evaluate the role of planet engulfment and dust condensation in altering stellar surface composition.

Proposed method

• Employing line-by-line differential abundance analysis on high-resolution, high-S/N spectra of solar twins and stellar twins in binaries to minimize systematic errors.
• Comparing stellar abundances to condensation temperature (Tcond) to detect correlations indicative of refractory element sequestration during planet formation.
• Correcting for galactic chemical evolution (GCE) effects using age and metallicity trends from stellar populations like the thick disk.
• Analyzing abundance ratios such as [Mg/Fe], [Y/Mg], and [Y/Al] as tracers of GCE and their impact on Tcond trends.
• Using lithium abundance as a tracer of recent planet engulfment, given lithium's rapid destruction in evolved stars.
• Applying stellar evolution models with episodic accretion to resolve the timescale mismatch between disk dispersal and convection zone contraction.

Experimental results

Research questions

• RQ1 Can refractory element depletion in Sun-like stars be attributed to planet formation rather than stellar evolution or galactic chemical evolution?
• RQ2 To what extent does galactic chemical evolution influence the observed Tcond trend in stellar abundances?
• RQ3 Can lithium enrichment in solar twins be linked to the accretion of rocky planets or planetary cores?
• RQ4 How do planet-hosting binaries composed of stellar twins help isolate planetary signatures from other stellar effects?
• RQ5 What role do dynamical processes like planet migration and engulfment play in altering the chemical composition of host stars?

Key findings

• The Sun exhibits a refractory element deficiency of approximately 0.01 dex relative to solar twins, strongly correlated with condensation temperature (p < 10−9 by chance).
• High-precision differential abundance analysis of solar twins confirms the Sun is one of the most refractory-poor stars, supporting a connection to planet formation.
• Planet engulfment can explain lithium and refractory element enhancements in stars like HIP 68468, with up to 6 Earth masses of rocky material potentially accreted.
• The Tcond trend in solar twins is not fully explained by stellar age or galactocentric distance, though GCE introduces scatter that must be corrected for.
• Stars like 16 Cyg A, with enhanced lithium and refractories, may have already engulfed a planet, suggesting a history of planetary accretion.
• Episodic accretion models reduce the time for convection zone contraction to ~5 Myr, resolving the timescale conflict between disk dispersal and convection zone evolution.