Predicting Cloud Conditions in Substellar Mass Objects Using Ultracool Dwarf Companions

Abstract

We present results from conducting a theoretical chemical analysis of a sample of benchmark companion brown dwarfs whose primary star is of type F, G, or K. We summarize the entire known sample of these types of companion systems, termed “compositional benchmarks,” that are present in the literature or recently published as key systems of study in order to best understand brown dwarf chemistry and condensate formation. Via mass balance and stoichiometric calculations, we predict a median brown dwarf atmospheric oxygen sink of ${17.8}_{-2.3}^{+1.7} \% $ by utilizing published stellar abundances in the local solar neighborhood. Additionally, we predict a silicate condensation sequence such that atmospheres with bulk Mg/Si ≲0.9 will form enstatite (MgSiO _3 ) and quartz (SiO _2 ) clouds, and atmospheres with bulk Mg/Si ≳0.9 will form enstatite and forsterite (Mg _2 SiO _4 ) clouds. The implications of these results on C/O ratio trends in substellar-mass objects and the utility of these predictions in future modeling work are discussed.

Keywords

• Brown dwarfs
• Main sequence stars
• Wide binary stars
• Exoplanet atmospheres
• Atmospheric clouds
• Astrochemistry