# Lithium, masses, and kinematics of young Galactic dwarf and giant stars with extreme [α/Fe] ratios

**Authors:** S. Borisov, N. Prantzos, C. Charbonnel  
**arXiv:** [2209.11915](https://arxiv.org/abs/2209.11915)  
**Date:** 2022-09-24  
**Summary page:** https://www.summarizepaper.com/en/paper/2209.11915v1/

## Key points

- Recent spectroscopic studies have found red giants with high [{\alpha}/Fe] ratios despite their young ages.
- The authors of this study revisit the GALAH DR3 survey to identify dwarf and giant stars with extreme [{\alpha}/Fe] ratios in the upper 1% range.
- These outliers are called ex{\alpha}fe stars, and their properties (chemical abundances, masses, ages, and kinematics) are investigated using data from GALAH DR3 and a Value-Added Catalogue.
- The authors explore the effects of secular stellar evolution and magnitude limitations of the GALAH survey on the mass and metallicity distributions of sample stars.
- Both dwarf and giant ex{\alpha}fe stars younger than 3 Gyr are found, which exhibit lithium abundances similar to those of young [{\alpha}/Fe]-normal dwarfs at the same age and [Fe/H].
- Both dwarf and giant y-ex{\alpha}fe stars' [Fe/H] and mass distributions do not differ from those found in thin disk counterparts with normal [{\alpha}/Fe], sharing similar kinematic properties.
- The authors conclude that y-exαfe dwarf and giant stars are indeed young, with no peculiarity in their mass distribution but differing from young [α/Fe]-normal stars only by their extreme α content.
- However, the origin of these y-exαfe stars remains unclear.

## Summary

Recent spectroscopic studies of large Galactic stellar samples have revealed the presence of red giants with high [{\alpha}/Fe] ratios, which is unusual given their relatively young ages. In this study, the authors revisit the GALAH DR3 survey to identify both dwarf and giant stars with extreme [{\alpha}/Fe] ratios in the upper 1% range in the [{\alpha}/Fe]-[Fe/H] plane over a range in [Fe/H] between -1.1 and +0.4 dex. These outliers are referred to as ex{\alpha}fe stars. The authors use data from GALAH DR3 along with their Value-Added Catalogue to investigate the properties (chemical abundances, masses, ages, and kinematics) of these ex{\alpha}fe stars. The authors explore the effects of secular stellar evolution and magnitude limitations of the GALAH survey to understand the mass and metallicity distributions of sample stars while discussing corresponding biases in previous studies of stars with high [{\alpha}/Fe] content but not necessarily extreme values found in other spectroscopic surveys. They find both dwarf and giant ex{\alpha}fe stars younger than 3 Gyr that they call y-ex{\alpha}fe. Dwarf y-ex{\alpha}fe stars exhibit lithium abundances similar to those of young [{\alpha}/Fe]-normal dwarfs at the same age and [Fe/H]. The youngest and most massive stars from both populations exhibit high Li abundances (A(Li){\sim}3.5 dex), while cooler or older ones show similar Li depletion patterns increasing with decreasing mass and increasing age. Moreover, both dwarf and giant y-ex{\alpha}fe stars' [Fe/H] and mass distributions do not differ from those found in thin disk counterparts with normal [{\alpha}/Fe], sharing similar kinematic properties. The authors conclude that y-exαfe dwarf and giant stars are indeed young, with no peculiarity in their mass distribution and differing from young [α/Fe]-normal stars only by their extreme α content. However, the origin of these y-exαfe stars remains unclear. This study provides insights into the properties of exαfe stars and highlights the need for further research to understand their formation mechanisms.