A Detailed Investigation of HD 209458 b HST & JWST Transmission Spectra with SANSAR

Abstract

HD 209458 b is the first exoplanet on which an atmosphere was detected. Since then, its atmosphere has been investigated using multiple telescopes and instruments. However, many of its atmospheric constraints remain debatable. While HST observations suggested a highly sub-solar metallicity, recent JWST NIRCam observations by Xue et al. 2024 constrained a super-solar metallicity with highly sub-solar C/O. In this work, we show a detailed investigation of HD 209458 b transmission spectra observations from JWST and HST using SANSAR, a newly developed planetary atmosphere modeling framework, with free, equilibrium chemistry and self-consistent grid retrievals. The overall best-fitting model with free retrievals (${\chi }_{\mathrm{red}}^2$=1.21) constrains its metallicity and C/O to be highly sub-solar, while equilibrium chemistry and grid retrievals (${\chi }_{\mathrm{red}}^2$=1.27 and 1.30, respectively) are consistent with solar values using STIS+WFC3+NIRCam observations. The retrieved abundances of H${}_2$O and CO${}_2$ are almost three orders of magnitude lower (highly sub-solar) with STIS+WFC3+NIRCam compared to just NIRCam, using free retrievals. NIRCam observations alone also result in misleading constraints on metallicity and C/O, with equilibrium chemistry and grid retrieval. We find that the model choice of varying C/H or O/H to vary the C/O in equilibrium chemistry retrievals leads to different metallicity constraints with NIRCam, but similar constraints with STIS+WFC3+NIRCam. We conclude that NIRCam observations alone can lead to overestimation of abundances for exoplanet atmospheres and, therefore, should be used in combination with UV/Optical and near-infrared observations to obtain robust constraints on abundances, C/O, and metallicity. In particular, even though we can detect the CO${}_2$ feature with just NIRCam, we cannot constrain its abundances robustly without the optical baseline.

arXiv commentFinal Published Version

References in corpus (72)

• SciPy 1.0--Fundamental Algorithms for Scientific Computing in Python
• Array Programming with NumPy
• The chemical composition of the Sun
• MultiNest: an efficient and robust Bayesian inference tool for cosmology and particle physics
• X-ray spectral modelling of the AGN obscuring region in the CDFS: Bayesian model selection and catalogue
• Detection of an Extrasolar Planet Atmosphere
• The effects of snowlines on C/O in planetary atmospheres
• A continuum from clear to cloudy hot-Jupiter exoplanets without primordial water depletion
• The orbital motion, absolute mass, and high-altitude winds of exoplanet HD209458b
• Theoretical Transmission Spectra During Extrasolar Giant Planet Transits
• A high accuracy computed water line list
• ExoMol molecular line lists XXX: a complete high-accuracy line list for water
• A Temperature and Abundance Retrieval Method for Exoplanet Atmospheres
• petitRADTRANS: a Python radiative transfer package for exoplanet characterization and retrieval
• On the radiative equilibrium of irradiated planetary atmospheres
• Infrared Transmission Spectroscopy of the Exoplanets HD209458b and XO-1b Using the Wide Field Camera-3 on the Hubble Space Telescope
• Improved parameters for extrasolar transiting planets
• Accurate, Empirical Radii and Masses of Planets and their Host Stars with Gaia Parallaxes
• ExoMol line lists IV: The rotation-vibration spectrum of methane up to 1500 K
• A Systematic Retrieval Analysis of Secondary Eclipse Spectra I: A Comparison of Atmospheric Retrieval Techniques
• A variationally computed line list for hot NH3
• Early Release Science of the exoplanet WASP-39b with JWST NIRSpec PRISM
• HD 209458b in New Light: Evidence of Nitrogen Chemistry, Patchy Clouds and Sub-Solar Water
• Tau-REx I: A next generation retrieval code for exoplanetary atmospheres
• Early Release Science of the Exoplanet WASP-39b with JWST NIRSpec G395H
• An ultrahot gas-giant exoplanet with a stratosphere
• Fingering convection and cloudless models for cool brown dwarf atmospheres
• Improved HCN/HNC linelist, model atmospheres and synthetic spectra for WZ Cas
• Model atmospheres of irradiated exoplanets: The influence of stellar parameters, metallicity, and the C/O ratio
• H${}_2$O abundances and cloud properties in ten hot giant exoplanets
• ExoMol molecular line lists - XIV: The rotation-vibration spectrum of hot SO${}_2$
• A consistent retrieval analysis of 10 Hot Jupiters observed in transmission
• Early Release Science of the exoplanet WASP-39b with JWST NIRCam
• Identification of carbon dioxide in an exoplanet atmosphere
• Accuracy tests of radiation schemes used in hot Jupiter global circulation models
• Five carbon- and nitrogen-bearing species in a hot giant planet's atmosphere
• No Thermal Inversion and a Solar Water Abundance for the Hot Jupiter HD209458b from HST WFC3 Emission Spectroscopy
• The Complete transmission spectrum of WASP-39b with a precise water constraint
• Identification of Absorption Features in an Extrasolar Planet Atmosphere
• The Effects of Consistent Chemical Kinetics Calculations on the Pressure-Temperature Profiles and Emission Spectra of Hot Jupiters
• Eureka!: An End-to-End Pipeline for JWST Time-Series Observations
• Treatment of overlapping gaseous absorption with the correlated-k method in hot Jupiter and brown dwarf atmosphere models
• A library of ATMO forward model transmission spectra for hot Jupiter exoplanets
• Exploring Biases of Atmospheric Retrievals in Simulated JWST Transmission Spectra of Hot Jupiters
• FastChem 2: An improved computer program to determine the gas-phase chemical equilibrium composition for arbitrary element distributions
• A High Internal Heat Flux and Large Core in a Warm Neptune Exoplanet
• Metal enrichment leads to low atmospheric C/O ratios in transiting giant exoplanets
• Water in HD 209458b's atmosphere from 3.6 - 8 microns IRAC photometric observations in primary transit
• PLATON II: New Capabilities And A Comprehensive Retrieval on HD 189733b Transit and Eclipse Data
• On degeneracies in retrievals of exoplanetary transmission spectra
• The ARCiS framework for Exoplanet Atmospheres: Modelling Philosophy and Retrieval
• A warm Neptune's methane reveals core mass and vigorous atmospheric mixing
• POSEIDON: A Multidimensional Atmospheric Retrieval Code for Exoplanet Spectra
• Awesome SOSS: Transmission Spectroscopy of WASP-96b with NIRISS/SOSS
• Water vapor detection in the transmission spectra of HD 209458 b with the CARMENES NIR channel
• TRIDENT: A Rapid 3D Radiative Transfer Model for Exoplanet Transmission Spectra
• Unveiling cloudy exoplanets: the influence of cloud model choices on retrieval solutions
• Aurora: A Generalised Retrieval Framework for Exoplanetary Transmission Spectra
• Exonephology: Transmission spectra from a 3D simulated cloudy atmosphere of HD209458b
• The Pyrat Bay Framework for Exoplanet Atmospheric Modeling: A Population Study of Hubble/WFC3 Transmission Spectra
• A Library of Self-Consistent Simulated Exoplanet Atmospheres
• JWST transmission spectroscopy of HD 209458b: a super-solar metallicity, a very low C/O, and no evidence of CH4, HCN, or C2H2
• Awesome SOSS: Atmospheric Characterisation of WASP-96 b using the JWST Early Release Observations
• Signatures of Nitrogen Chemistry in Hot Jupiter Atmospheres
• Into the UV: The Atmosphere of the Hot Jupiter HAT-P-41b Revealed
• Spectral binning of precomputed correlated-k coefficients
• The carbon-to-oxygen ratio: implications for the spectra of hydrogen-dominated exoplanet atmospheres
• A Catalogue of Exoplanet Atmospheric Retrieval Codes
• Origin and extent of the opacity challenge for atmospheric retrievals of WASP-39 b
• Why is it So Hot in Here? Exploring Population Trends in $\text{Spitzer}$ Thermal Emission Observations of Hot Jupiters using Planet-Specific Self-Consistent Atmospheric Models
• First Comparative Exoplanetology Within a Transiting Multi-planet System: Comparing the atmospheres of V1298 Tau b and c
• Knobs and dials of retrieving JWST transmission spectra. I. The importance of p-T profile complexity