Impacts of Water Latent Heat on the Thermal Structure of Ultra-Cool Objects: Brown Dwarfs and Free-Floating Planets

Abstract

Brown dwarfs are essential targets for understanding planetary and sub-stellar atmospheres across a wide range of thermal and chemical conditions. As surveys continue to probe ever deeper, and as observing capabilities continue to improve, the number of known Y dwarfs -the coldest class of substellar objects, with effective temperatures below about 600 K -is rapidly growing. Critically, this class of ultra-cool objects has atmospheric conditions that overlap with Solar System worlds and, as a result, tools and ideas developed from studying Earth, Jupiter, Saturn and other nearby worlds are well-suited for application to sub-stellar atmospheres. To that end, we developed a one-dimensional (vertical) atmospheric structure model for ultra-cool objects that includes moist adiabatic convection, as this is an important process for many Solar System planets. Application of this model across a range of effective temperatures (350, 300, 250, 200 K), metallicities ([M/H] of 0.0, 0.5, 0.7, 1.5), and gravities (log g of 4.0, 4.5, 4.7, 5.0) demonstrates strong impacts of water latent heat release on simulated temperature-pressure profiles. At the highest metallicities, water vapor mixing ratios reach an Earth-like 3%, with associated major alterations to the thermal structure in the atmospheric regions where water condenses. Spectroscopic and photometric signatures of metallicity and moist convection should be readily detectable at near-and mid-infrared wavelengths, especially with James Webb Space Telescope observations, and can help indicate the formation history of an object.

Cloudy and Cloud-free Thermal Phase Curves with PICASO: Applications to WASP-43b

“…We expand this tool by adding a pipeline to map 3D GCM output onto a radiative transfer scheme that enables the computation of thermal phase curves, with the capability of including scattering by a diversity of cloud species. While PICASO has been previously used for 1D (Fraine et al 2021) and 3D reflected light (Adams et al 2021), and thermal emission spectroscopy in 1D (Tang et al 2021), the work presented here represents the first test of the 3D thermal component of the code. Here we focus on thermal phase curves, but our methodology can also be easily applied to phase-resolved observations in reflected light.…”