[Paper Review] The age-mass relation for chromospherically active binaries: III. Lithium depletion in giant components

D. Barrado, E. de Castro+3 more|arXiv (Cornell University)|May 19, 1999

Stellar, planetary, and galactic studies3 citations

TL;DR

This study investigates lithium abundances in evolved components of chromospherically active binary systems (CABS), finding significant lithium excesses independent of mass or age. The authors attribute these overabundances to enhanced stellar rotation driven by angular momentum transfer from the orbit, suggesting Li depletion is not age-dependent in giant CABS components, unlike in isolated stars.

ABSTRACT

We present a study of the lithium abundances of a sample of evolved components of Chromospherically Active Binary Systems. We show that a significant part of them have lithium excesses, independently of their mass and evolutionary stage. Therefore, it can be concluded that Li abundance does not depend on age for giant components of CABS. These overabundances appear to be closely related to the stellar rotation, and we interpret them as a consequence of the transfer of angular momentum from the orbit to the rotation as the stars evolve in and off the Main Sequence, in a similar way as it happens in the dwarf components of the same systems and in the Tidally Locked Binaries belonging to the Hyades and M67.

Motivation & Objective

• To investigate lithium abundance variations in evolved components of chromospherically active binary systems (CABS).
• To determine whether lithium depletion in giant stars correlates with age or mass in CABS.
• To explore the role of stellar rotation and angular momentum transfer in driving lithium overabundances.
• To compare lithium behavior in giant CABS components with that in main-sequence dwarfs and tidally locked binaries in open clusters.
• To establish the age-mass relation for CABS using lithium as a diagnostic tool, despite evolutionary complexities.

Proposed method

• Analyzed high-resolution spectroscopic data to measure lithium (Li) equivalent widths in evolved components of CABS.
• Compiled a sample of evolved stars in chromospherically active binary systems with known orbital and rotational parameters.
• Correlated lithium abundances with stellar mass, evolutionary stage, and rotation rates to identify trends.
• Used angular momentum transfer models to explain observed lithium excesses via orbital-to-rotational coupling.
• Compared results with lithium behavior in field stars and in tidally locked systems (e.g., Hyades, M67) to contextualize findings.
• Applied standard stellar atmosphere models to derive lithium abundances from observed spectral lines.

Experimental results

Research questions

• RQ1 Does lithium abundance in evolved components of CABS depend on age or mass?
• RQ2 What physical mechanism explains lithium overabundance in giant stars of CABS?
• RQ3 How is stellar rotation related to lithium abundance in evolved CABS components?
• RQ4 To what extent does angular momentum transfer from the orbit to the star influence lithium depletion?
• RQ5 How do lithium abundances in CABS giants compare to those in isolated giants or tidally locked binaries?

Key findings

• A significant fraction of evolved CABS components exhibit lithium excesses, regardless of their mass or evolutionary stage.
• Lithium overabundance is strongly correlated with high stellar rotation rates, indicating rotational mixing or inhibition of depletion.
• The observed lithium excesses are interpreted as a result of angular momentum transfer from the orbit to the star during evolution.
• Lithium abundance does not correlate with age in giant CABS components, challenging standard models of Li depletion in evolved stars.
• The mechanism is analogous to that observed in tidally locked binaries in the Hyades and M67 clusters, suggesting a common physical origin.
• These findings imply that Li abundance cannot be used as a reliable age indicator for giant stars in active binary systems.