Atmosphere Models of Brown Dwarfs Irradiated by White Dwarfs: Analogues for Hot and Ultra-Hot Jupiters

Abstract

Irradiated brown dwarfs (BDs) provide natural laboratories to test our understanding of substellar and irradiated atmospheres. A handful of short-period BDs around white dwarfs (WDs) have been observed, but the uniquely intense UV-dominated irradiation presents a modeling challenge. Here, we present the first fully self-consistent 1D atmosphere models that take into account the UV irradiation's effect on the object's temperature structure. We explore two BD-WD systems, namely WD-0137-349 and EPIC-212235321. WD-0137-349B has an equilibrium temperature that would place it in the transition between hot and ultra-hot Jupiters, while EPIC-212235321B has an equilibrium temperature higher than all ultra-hot Jupiters except KELT-9b. We explore some peculiar aspects of irradiated BD atmospheres and show that existing photometry can be well-fit with our models. Additionally, the detections of atomic emission lines from these BDs can be explained by a strong irradiation-induced temperature inversion, similar to inversions recently explored in ultra-hot Jupiters. Our models of WD-0137-349B can reproduce the observed equivalent width of many but not all of these atomic lines. We use the observed photometry of these objects to retrieve the temperature structure using the PHOENIX ExoplaneT Retrieval Algorithm (PETRA) and demonstrate that the structures are consistent with our models, albeit somewhat cooler at low pressures. We then discuss the similarities and differences between this class of irradiated brown dwarf and the lower-mass ultra-hot Jupiters. Lastly, we describe the behavior of irradiated BDs in color-magnitude space to show the difficulty in classifying irradiated BDs using otherwise well-tested methods for isolated objects.

15 pages, 12 figures. Accepted for publication in ApJ

References in corpus (21)

• An ultrahot gas-giant exoplanet with a stratosphere
• A giant planet undergoing extreme ultraviolet irradiation by its hot massive-star host
• A spectral survey of an ultra-hot Jupiter: Detection of metals in the transmission spectrum of KELT-9 b
• Simultaneous Detection of Water, Methane and Carbon Monoxide in the Atmosphere of Exoplanet HR8799b
• A Giant Planet Candidate Transiting a White Dwarf
• Survival of a brown dwarf after engulfment by a red giant star
• A New 24 micron Phase Curve for upsilon Andromedae b
• An emission spectrum for WASP-121b measured across the 0.8-1.1 micron wavelength range using the Hubble Space Telescope
• A temperature inversion with atomic iron in the ultra-hot dayside atmosphere of WASP-189b
• The Influence of Host Star Spectral Type on Ultra-Hot Jupiter Atmospheres
• A near-infrared spectroscopic detection of the brown dwarf in the post common envelope binary WD0137-349
• Multiwaveband photometry of the irradiated brown dwarf WD0137-349B
• The White Dwarf Opportunity: Robust Detections of Molecules in Earth-like Exoplanet Atmospheres with the James Webb Space Telescope
• UV Exoplanet Transmission Spectral Features as Probes of Metals and Rainout
• Simplified 3D GCM modelling of the irradiated brown dwarf WD0137-349B
• Emission lines in the atmosphere of the irradiated brown dwarf WD0137-349B
• Colour-magnitude diagrams of transiting Exoplanets - II. A larger sample from photometric distances
• The PHOENIX Exoplanet Retrieval Algorithm and Using H${}^{-}$ Opacity as a Probe in Ultra-hot Jupiters
• High-resolution Spectra and Biosignatures of Earth-like Planets Transiting White Dwarfs
• Colour-magnitude diagrams of transiting Exoplanets -- III. A public code, nine strange planets, and the role of Phosphine
• Colour-colour and colour-magnitude diagrams for Hot Jupiters

Cited by in corpus (11)

• Grid of Pseudo-2D Chemistry Models for Tidally-Locked Exoplanets. I. The Role of Vertical and Horizontal Mixing
• Methane Emission From a Cool Brown Dwarf
• The Mantis Network II: Examining the 3D high-resolution observable properties of the UHJs WASP-121b and WASP-189b through GCM modelling
• HST/WFC3 Complete Phase-resolved Spectroscopy of White Dwarf-Brown Dwarf Binaries WD 0137 and EPIC 2122
• Mapping the pressure-dependent day-night temperature contrast of a strongly irradiated atmosphere with HST spectroscopic phase curve
• Exploring deep and hot adiabats as a potential solution to the radius inflation problem in brown dwarfs: Long-timescale models of the deep atmospheres of KELT-1b, Kepler-13Ab, and SDSS1411B
• Hotter Than Expected: HST/WFC3 Phase-resolved Spectroscopy of a Rare Irradiated Brown Dwarf with Strong Internal Heat Flux
• The Impact of Irradiation on the Radius and Thermal Evolution of Transiting Brown Dwarfs
• An irradiated-Jupiter analogue hotter than the Sun
• Near-infrared spectra of the inflated post-common envelope brown dwarf NLTT 5306B
• EPIC 206197016: A very hot white dwarf orbited by a strongly irradiated red dwarf