The Deuterium-Burning Mass Limit for Brown Dwarfs and Giant Planets

TL;DR

This paper examines the deuterium-burning mass limit to distinguish brown dwarfs from planets, revealing it depends on composition and burning criteria, with a typical threshold around 13 Jupiter masses but with significant variability.

Contribution

It provides a detailed analysis of how the deuterium-burning mass limit varies with composition and burning fraction, refining the commonly used 13 M_J criterion.

Findings

Deuterium-burning mass depends on helium, deuterium abundance, and metallicity.

Typical deuterium burning occurs around 13 M_J, but varies from 11 to 16.3 M_J.

The deuterium burning threshold is not universal but model-dependent.

Abstract

There is no universally acknowledged criterion to distinguish brown dwarfs from planets. Numerous studies have used or suggested a definition based on an object's mass, taking the ~13-Jupiter mass (M_J) limit for the ignition of deuterium. Here, we investigate various deuterium-burning masses for a range of models. We find that, while 13 M_J is generally a reasonable rule of thumb, the deuterium fusion mass depends on the helium abundance, the initial deuterium abundance, the metallicity of the model, and on what fraction of an object's initial deuterium abundance must combust in order for the object to qualify as having burned deuterium. Even though, for most proto-brown dwarf conditions, 50% of the initial deuterium will burn if the object's mass is ~(13.0 +/- 0.8)M_J, the full range of possibilities is significantly broader. For models ranging from zero-metallicity to more than three times solar metallicity, the deuterium burning mass ranges from ~11.0 M_J (for 3-times solar metallicity, 10% of initial deuterium burned) to ~16.3 M_J (for zero metallicity, 90% of initial deuterium burned).