Impact 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 sub-stellar 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 impact 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.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- November 2021
- DOI:
- 10.3847/1538-4357/ac1e90
- arXiv:
- arXiv:2105.07000
- Bibcode:
- 2021ApJ...922...26T
- Keywords:
-
- Brown dwarfs;
- Y dwarfs;
- Exoplanet atmospheres;
- Planetary atmospheres;
- Exoplanet structure;
- 185;
- 1827;
- 487;
- 1244;
- 495;
- Astrophysics - Earth and Planetary Astrophysics;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- 16 pages, 10 figures, ApJ accepted version, data public available on zenodo