A Concise Treatise on Converting Stellar Mass Fractions to Abundances to Molar Ratios

TL;DR

This paper provides a clear mathematical framework for converting stellar mass fractions into elemental abundances and molar ratios, aiding interdisciplinary understanding of stellar and planetary compositions.

Contribution

It introduces a formalism and clarifies assumptions for converting stellar mass fractions to abundances, including error propagation, with an illustrative case study.

Findings

Provides explicit equations for conversion processes.

Clarifies assumptions and normalizations in stellar composition data.

Includes an example case study of HIP 544.

Abstract

Understanding stellar composition is fundamental not only to our comprehension of the galaxy, especially chemical evolution, but it can also shed light on the interior structure and mineralogy of exoplanets, which are formed from the same material as their host stars. Unfortunately, the underlying mathematics describing stellar mass fractions and stellar elemental abundances is difficult to parse, fragmented across the literature, and contains vexing omissions that makes any calculation far from trivial, especially for non-experts. In this treatise, we present clear mathematical formalism and clarification of inherent assumptions and normalizations within stellar composition measurements, which facilitates the conversion from stellar mass fractions to elemental abundances to molar ratios, including error propagation. We also provide an example case study of HIP 544 to further illustrate the provided equations. Given the important chemical association between stars, as well as the interdisciplinary relationship between stars and their planets, it is vital that stellar mass fractions and abundance data be more transparent and accessible to people within different sub-fields and scientific disciplines.