Physically-motivated basis functions for temperature maps of exoplanets

Abstract

Thermal phase curves of exoplanet atmospheres have revealed temperature maps as a function of planetary longitude, often by sinusoidal decomposition of the phase curve. We construct a framework for describing two-dimensional temperature maps of exoplanets with mathematical basis functions derived for a fluid layer on a rotating, heated sphere with drag/friction, which are generalizations of spherical harmonics. These basis functions naturally produce physically-motivated temperature maps for exoplanets with few free parameters. We investigate best practices for applying this framework to temperature maps of hot Jupiters by splitting the problem into two parts: (1) we constrain the temperature map as a function of latitude by tuning the basis functions to reproduce general circulation model (GCM) outputs, since disk-integrated phase curve observations do not constrain this dimension; and (2) we infer the temperature maps of real hot Jupiters using original reductions of several Spitzer phase curves, which directly constrain the temperature variations with longitude. The resulting phase curves can be described with only three free parameters per bandpass -- an efficiency improvement over the usual five or so used to describe sinusoidal decompositions of phase curves. Upon obtaining the hemispherically averaged dayside and nightside temperatures, the standard approach would be to use zero-dimensional box models to infer the Bond albedo and redistribution efficiency. We elucidate the limitation of these box models by demonstrating that negative Bond albedos may be obtained due to a choice of boundary condition on the nightside temperature. We propose generalized definitions for the Bond albedo and heat redistribution efficiency for use with two-dimensional (2D) temperature maps. Open-source software called kelp is provided to efficiently compute these phase curves.

arXiv commentAccepted in A&A

References in corpus (62)

• SciPy 1.0--Fundamental Algorithms for Scientific Computing in Python
• Array Programming with NumPy
• Astropy: A Community Python Package for Astronomy
• emcee: The MCMC Hammer
• Binary companions of evolved stars in APOGEE DR14: Search method and catalog of ~5,000 companions
• Analytic Lightcurves for Planetary Transit Searches
• A new extensive library of PHOENIX stellar atmospheres and synthetic spectra
• batman: BAsic Transit Model cAlculatioN in Python
• A map of the day-night contrast of the extrasolar planet HD 189733b
• On the radiative equilibrium of irradiated planetary atmospheres
• Equatorial superrotation on tidally locked exoplanets
• The Statistics of Albedo and Heat Recirculation on Hot Exoplanets
• Thermal structure of an exoplanet atmosphere from phase-resolved emission spectroscopy
• Exoplanetary Atmospheres: Key Insights, Challenges and Prospects
• 3.6 and 4.5 Micron Phase Curves and Evidence for Non-Equilibrium Chemistry in the Atmosphere of Extrasolar Planet HD 189733b
• STARRY: Analytic Occultation Light Curves
• Reflected Spectra and Albedos of Extrasolar Giant Planets I: Clear and Cloudy Atmospheres
• A map of the large day-night temperature gradient of a super-Earth exoplanet
• Aerosol Composition of Hot Giant Exoplanets Dominated by Silicates and Hydrocarbon Hazes
• Global Climate and Atmospheric Composition of the Ultra-Hot Jupiter WASP-103b from HST and Spitzer Phase Curve Observations
• exoplanet: Gradient-based probabilistic inference for exoplanet data & other astronomical time series
• Inverting Phase Functions to Map Exoplanets
• A Two-Dimensional Infrared Map of the Extrasolar Planet HD 189733b
• Atmospheric Dynamics of Hot Exoplanets
• Increased Heat Transport in Ultra-Hot Jupiter Atmospheres Through H${}_2$ Dissociation/Recombination
• Transit and Eclipse Analyses of Exoplanet HD 149026b Using BLISS Mapping
• Understanding Trends Associated with Clouds in Irradiated Exoplanets
• Variability in the super-Earth 55 Cnc e
• Balancing the Energy Budget of Short-Period Giant Planets: Evidence for Reflective Clouds and Optical Absorbers
• The Effects of Irradiation on Hot Jovian Atmospheres: Heat Redistribution and Energy Dissipation
• On the Absorption and Redistribution of Energy in Irradiated Planets
• Towards consistent mapping of distant worlds: secondary-eclipse scanning of the exoplanet HD189733b
• Spitzer 3.6 micron and 4.5 micron full-orbit lightcurves of WASP-18
• 3.6 and 4.5 $\mu$m $Spitzer$ Phase Curves of the Highly-Irradiated Hot Jupiters WASP-19b and HAT-P-7b
• A Model for Thermal Phase Variations of Circular and Eccentric Exoplanets
• A global analysis of Spitzer and new HARPS data confirms the loneliness and metal-richness of GJ 436 b
• Improved precision on the radius of the nearby super-Earth 55 Cnc e
• 3.6 and 4.5 $\mu$m Phase Curves of the Highly-Irradiated Eccentric Hot Jupiter WASP-14b
• 3D Structures of equatorial waves and the resulting superrotation in the atmosphere of a tidally locked hot Jupiter
• Spitzer Phase Curves of KELT-1b and the Signatures of Nightside Clouds in Thermal Phase Observations
• A Semi-Analytical Model of Visible-Wavelength Phase Curves of Exoplanets and Applications to Kepler-7 b and Kepler-10 b
• Helios-r2 -- A new Bayesian, open-source retrieval model for brown dwarfs and exoplanet atmospheres
• Thermal Emission from Transiting Very-Hot Jupiters: Prospects for Ground-based Detection at Optical Wavelengths
• Repeatability and Accuracy of Exoplanet Eclipse Depths Measured with Post-Cryogenic Spitzer
• Revisiting the Phase Curves of WASP-43b: Confronting Reanalyzed Spitzer Data with Cloudy Atmospheres
• Uniformly hot nightside temperatures on short-period gas giants
• Evidence for H${}_2$ Dissociation and Recombination Heat Transport in the Atmosphere of KELT-9b
• Lightcurves of Stars & Exoplanets: Estimating Inclination, Obliquity, and Albedo
• Exploring the atmospheric dynamics of the extreme ultra-hot Jupiter KELT-9b using TESS photometry
• Magnetohydrodynamic Shallow Water Waves: Linear Analysis
• Mass Loss from the Exoplanet WASP-12b Inferred from $\text{Spitzer}$ Phase Curves
• A Comprehensive Reanalysis of $\text{Spitzer}$'s 4.5 $\mu$m Phase Curves, and the Phase Variations of the Ultra-hot Jupiters MASCARA-1b and KELT-16b
• Visible-light Phase Curves from the Second Year of the TESS Primary Mission
• Phase Offsets and the Energy Budgets of Hot Jupiters
• Revisiting the Energy Budget of WASP-43b: Enhanced day-night heat transport
• Exoplanet phase curves: observations and theory
• A More Informative Map: Inverting Thermal Orbital Phase and Eclipse Lightcurves of Exoplanets
• Analytical Models of Exoplanetary Atmospheres. I. Atmospheric Dynamics via the Shallow Water System
• Closed-formed ab initio solutions of geometric albedos and reflected light phase curves of exoplanets
• Pseudo-2D Modelling of Heat Redistribution Through H${}_2$ Thermal Dissociation/Recombination: Consequences for Ultra-Hot Jupiters
• Mapping Exoplanets
• The Spitzer search for the transits of HARPS low-mass planets - II. Null results for 19 planets

Cited by in corpus (8)

• The atmosphere and architecture of WASP-189 b probed by its CHEOPS phase curve
• Spi-OPS: Spitzer and CHEOPS confirm the near-polar orbit of MASCARA-1 b and reveal a hint of dayside reflection
• The stable climate of KELT-9b
• Temperature Structures Associated with Different Components of the Atmospheric Circulation on Tidally Locked Exoplanets
• Observations of scattered light from exoplanet atmospheres
• Is binning always sinning? The impact of time-averaging for exoplanet phase curves
• TESS phase curve of ultra-hot Jupiter WASP-189 b
• TOI-4552 b: A new ultra-short period rocky world revealed by NIRPS and TESS