18 Sco: a solar twin rich in refractory and neutron-capture elements. Implications for chemical tagging

TL;DR

This study provides a highly precise chemical and stellar parameter analysis of the solar twin 18 Sco, revealing its detailed elemental abundance pattern, age, and implications for chemical tagging and nucleosynthesis.

Contribution

It offers the most precise differential abundance measurements of 18 Sco relative to the Sun, including neutron-capture elements, and discusses implications for chemical tagging and r-process universality.

Findings

18 Sco is slightly hotter and more metal-rich than the Sun.

18 Sco is approximately 1.6 billion years younger than the Sun.

Enhanced refractory and neutron-capture element abundances in 18 Sco.

Abstract

We study with unprecedented detail the chemical composition and stellar parameters of the solar twin 18 Sco in a strictly differential sense relative to the Sun. Our study is mainly based on high resolution (R ~ 110 000) high S/N (800-1000) VLT UVES spectra, which allow us to achieve a precision of about 0.005 dex in differential abundances. The effective temperature and surface gravity of 18 Sco are Teff = 5823+/-6 K and log g = 4.45+/-0.02 dex, i.e., 18 Sco is 46+/-6 K hotter than the Sun and log g is 0.01+/-0.02 dex higher. Its metallicity is [Fe/H] = 0.054+/-0.005 dex and its microturbulence velocity is +0.02+/-0.01 km/s higher than solar. Our precise stellar parameters and differential isochrone analysis show that 18 Sco has a mass of 1.04+/-0.02M_Sun and that it is ~1.6 Gyr younger than the Sun. We use precise HARPS radial velocities to search for planets, but none were detected. The chemical abundance pattern of 18 Sco displays a clear trend with condensation temperature, showing thus higher abundances of refractories in 18 Sco than in the Sun. Intriguingly, there are enhancements in the neutron-capture elements relative to the Sun. Despite the small element-to-element abundance differences among nearby n-capture elements (~0.02 dex), we successfully reproduce the r-process pattern in the solar system. This is independent evidence for the universality of the r-process. Our results have important implications for chemical tagging in our Galaxy and nucleosynthesis in general.