C/O vs Mg/Si ratios in solar type stars: The HARPS sample

TL;DR

This study analyzes the Mg/Si and C/O elemental ratios in 499 solar-like stars from the HARPS sample to understand how these ratios influence planetary mineralogy and composition, revealing diverse planetary system types.

Contribution

It provides a detailed analysis of Mg/Si and C/O ratios in a large stellar sample, linking these ratios to planetary mass and composition, highlighting diversity beyond our solar system.

Findings

All planetary hosts have C/O < 0.8.

High-mass planet hosts mostly have 0.4 < C/O < 0.8.

Low-mass planet hosts have Mg/Si ratios similar to the Sun.

Abstract

Aims. We present a detailed study of the Mg/Si and C/O ratios and their importance in determining the mineralogy of planetary companions. Methods. Using 499 solar-like stars from the HARPS sample, we determine C/O and Mg/Si elemental abundance ratios to study the nature of the possible planets formed. We separated the planetary population in low-mass planets ( < 30 $\rm M_{\odot}$) and high-mass planets ( > 30 $\rm M_{\odot}$) to test for possible relation with the mass. Results. We find a diversity of mineralogical ratios that reveal the different kinds of planetary systems that can be formed, most of them dissimilar to our solar system. The different values of the Mg/Si and C/O ratios can determine different composition of planets formed. We found that 100\% of our planetary sample present C/O < 0.8. 86\% of stars with high-mass companions present 0.8 > C/O > 0.4, while 14\% present C/O values lower than 0.4. Regarding Mg/Si, all stars with low-mass planetary companion showed values between 1 and 2, while 85% of the high-mass companion sample does. The other 15\% showed Mg/Si values below 1. No stars with planets were found with Mg/Si > 2. Planet hosts with low-mass companions present C/O and Mg/Si ratios similar to those found in the Sun, whereas stars with high-mass companions have lower C/O.