The Sonora Brown Dwarf Atmosphere and Evolution Models. I. Model Description and Application to Cloudless Atmospheres in Rainout Chemical Equilibrium

Abstract

We present a new generation of substellar atmosphere and evolution models, appropriate for application to studies of L, T, and Y-type brown dwarfs and self-luminous extrasolar planets. The atmosphere models describe the expected temperature-pressure profiles and emergent spectra of atmospheres in radiative-convective equilibrium with effective temperatures and gravities within the ranges 200 ≤ T eff ≤ 2400 K and 2.5 ≤ log g ≤ 5.5. These ranges encompass masses from about 0.5 to 85 Jupiter masses for a set of metallicities ([M/H] = −0.5 to +0.5), C/O ratios (from 0.5 to 1.5 times that of solar), and ages. The evolution tables describe the cooling of these substellar objects through time. These models expand the diversity of model atmospheres currently available, notably to cooler effective temperatures and greater ranges in C/O. Notable improvements from past such models include updated opacities and atmospheric chemistry. Here we describe our modeling approach and present our initial tranche of models for cloudless, chemical equilibrium atmospheres. We compare the modeled spectra, photometry, and evolution to various datasets.

TOI-2119: A transiting brown dwarf orbiting an active M-dwarf from NASA's TESS mission

“…Here we will examine what this latest addition to the transiting BD population contributes to our understanding of substellar evolutionary models from Phillips et al (2020) (ATMO 2020) and Marley et al (2021) (S21 for 'Sonora 2021'). However, before discussing the significance of TOI-2119b to the transiting BD population, let us first recapitulate our understanding of the nature of the host star.…”

“…In order to derive the BD effective temperature 𝑇 𝑏,eff , we simplify Equation 4by assuming a blackbody profile for both the star and BD. This is a reasonable assumption given we are using the TESS bandpass at optical wavelengths where BDs with 𝑇 eff 1800K are approximately blackbody-like (Marley et al 2021). Given the mass and age of the BD, this is a reasonable assumption.…”

“…Though transit detections typically restrict us to exploring a parameter space for short-period BDs (usually 𝑃 orb < 30 days to efficiently detect and characterise multiple transits), they play a critical role in filling out the population of BDs with measured masses and surface gravity (log 𝑔) estimates. The mass and radius are key parameters involved in the construction of BD evolutionary models (Chabrier & Baraffe 1997; Baraffe et al 2003;Saumon & Marley 2008;Phillips et al 2020;Marley et al 2021), to which we compare the observed population of transiting BDs. This improves our understanding of the evolution of these objects and with a large enough sample size of BDs with known masses, radii, and ages (from age dating techniques of the host stars), we stand to learn more about how the dominant formation mechanism changes for objects from giant planets to low-mass stars as a function of mass.…”

“…One way to do this testing is in mass-radius space for BDs and principally involves testing how well theoretical and simulation-driven works (e.g. Baraffe et al 2003;Saumon & Marley 2008;Phillips et al 2020;Marley et al 2021) predict the rate at which the radius of BDs decreases with age. We generally expect BDs to contract with age as they cool over time as they lack a mechanism to initiate any increase in radius like stars do.…”

Jet Streams and Tracer Mixing in the Atmospheres of Brown Dwarfs and Isolated Young Giant Planets

“…The Rosseland-mean gas opacity as a function of temperature and pressure from Freedman et al (2014) is coupled to the RT calculation. Our radiative-convective equilibrium RT calculations generate temperature-pressure (T-P) profiles with reasonable radiative-convective boundaries (RCBs) compared to the more sophisticated one-dimensional (1D) atmospheric models (e.g., Allard et al 2001;Tsuji 2002;Burrows et al 2006;Marley et al 2021).…”