Hydride ion continuum hides absorption signatures in the NIRPS near-infrared transmission spectrum of the ultra-hot gas giant WASP-189b

Abstract

Ultra-hot Jupiters showcase extreme atmospheric conditions, including molecular dissociation, ionisation, and significant day-to-night temperature contrasts. Their close proximity to host stars subjects them to intense stellar irradiation, driving high temperatures where hydride ions (H${}^{-}$) significantly contribute to opacity, potentially obscuring metal features in near-infrared transmission spectra. We investigate the atmosphere of WASP-189b, targeting atomic, ionic, and molecular species (H, He, Fe, Ti, V, Mn, Na, Mg, Ca, Cr, Ni, Y, Ba, Sc, Fe${}^{+}$, Ti${}^{+}$, TiO, H${}_2$O, CO, and OH), focusing on (i) the role of H${}^{-}$ as a source of continuum opacity, and (ii) the relative hydride-to-Fe abundance using joint optical and near-infrared data. We present two transits of WASP-189b gathered simultaneously in the optical with HARPS and near-infrared with NIRPS, supported by photometric light curves from EulerCam and ExTrA. Transmission spectra were analysed via cross-correlation to detect absorption features and enhance the signal-to-noise ratio. Atmospheric retrievals quantified relative abundances by fitting overall metallicity and proxies for TiO, H${}^{-}$, and e${}^{-}$. Only atomic iron is detected in HARPS data (S/N ~5.5), but not in NIRPS, likely due to H${}^{-}$ continuum dampening. Retrievals on HARPS-only and HARPS+NIRPS suggest the hydride-to-Fe ratio exceeds equilibrium predictions by about 0.5 dex, hinting at strong hydrogen ionisation. Including NIRPS data helps constrain H${}^{-}$ abundance and set an upper limit on free electron density, unconstrained in HARPS-only data. These results emphasise H${}^{-}$ as a significant continuum opacity source impeding detection of planetary absorption features in WASP-189b's near-infrared transmission spectrum.

arXiv comment32 pages, 12 main figures, 3 main tables; accepted for publication in A&A on March 3rd 2025

References in corpus (87)

• emcee: The MCMC Hammer
• The chemical composition of the Sun
• A new extensive library of PHOENIX stellar atmospheres and synthetic spectra
• 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
• Molecfit: A general tool for telluric absorption correction. I. Method and application to ESO instruments
• ExoMol molecular line lists XXX: a complete high-accuracy line list for water
• ESPRESSO@VLT -- On-sky performance and first results
• Molecfit: A general tool for telluric absorption correction II. Quantitative evaluation on ESO-VLT X-Shooter spectra
• Atmospheric Retrieval for Super-Earths: Uniquely Constraining the Atmospheric Composition with Transmission Spectroscopy
• The signature of orbital motion from the dayside of the planet tau Bootis b
• Transmission Spectra as Diagnostics of Extrasolar Giant Planet Atmospheres
• Helium in the eroding atmosphere of an exoplanet
• From thermal dissociation to condensation in the atmospheres of ultra hot Jupiters: WASP-121b in context
• How to Distinguish between Cloudy Mini-Neptunes and Water/Volatile-Dominated Super-Earths
• Spectrally resolved detection of sodium in the atmosphere of HD189733b with the HARPS spectrograph
• Nightside condensation of iron in an ultra-hot giant exoplanet
• Line-profile tomography of exoplanet transits -- II. A gas-giant planet transiting a rapidly-rotating A5 star
• H- Opacity and Water Dissociation in the Dayside Atmosphere of the Very Hot Gas Giant WASP-18 b
• The CHEOPS mission
• ExoMol Molecular linelists -- XXXIII. The spectrum of Titanium Oxide
• Ground-based detection of an extended helium atmosphere in the Saturn-mass exoplanet WASP-69b
• Retrieving Temperatures and Abundances of Exoplanet Atmospheres with High-Resolution Cross-Correlation Spectroscopy
• An ultrahot gas-giant exoplanet with a stratosphere
• A giant planet undergoing extreme ultraviolet irradiation by its hot massive-star host
• Limb darkening and exoplanets: testing stellar model atmospheres and identifying biases in transit parameters
• Extremely Irradiated Hot Jupiters: Non-Oxide Inversions, H- Opacity, and Thermal Dissociation of Molecules
• Atomic iron and titanium in the atmosphere of the exoplanet KELT-9b
• Spectrally resolved helium absorption from the extended atmosphere of a warm Neptune-mass exoplanet
• A Sub-Neptune Exoplanet with a Low-Metallicity Methane-Depleted Atmosphere and Mie-Scattering Clouds
• A New Window into Escaping Exoplanet Atmospheres: 10830 Å Line of Helium
• A spectral survey of an ultra-hot Jupiter: Detection of metals in the transmission spectrum of KELT-9 b
• WASP-121 b: a hot Jupiter in a polar orbit and close to tidal disruption
• Detection of Fe I in the atmosphere of the ultra-hot Jupiter WASP-121b, and a new likelihood-based approach for Doppler-resolved spectroscopy
• HELIOS-K: An Ultrafast, Open-source Opacity Calculator for Radiative Transfer
• An extended hydrogen envelope of the extremely hot giant exoplanet KELT-9b
• Increased Heat Transport in Ultra-Hot Jupiter Atmospheres Through H${}_2$ Dissociation/Recombination
• Hot Exoplanet Atmospheres Resolved with Transit Spectroscopy (HEARTS) IV. A spectral inventory of atoms and molecules in the high-resolution transmission spectrum of WASP-121 b
• Detection of He I $\lambda 10830$ Å absorption on HD 189733 b with CARMENES high-resolution transmission spectroscopy
• HELIOS-K 2.0 Opacity Calculator and Open-source Opacity Database for Exoplanetary Atmospheres
• Atmospheric Rossiter-McLaughlin effect and transmission spectroscopy of WASP-121b with ESPRESSO
• WASP-42 b and WASP-49 b: two new transiting sub-Jupiters
• The Peculiar Atmospheric Chemistry of KELT-9b
• Extrasolar planets and brown dwarfs around A-F type stars. I. Performances of radial velocity measurements, first analyses of variations
• Three irradiated and bloated hot Jupiters: WASP-76b, WASP-82b & WASP-90b
• Hot Exoplanet Atmospheres Resolved with Transit Spectroscopy (HEARTS) - II. A broadened sodium feature on the ultra-hot giant WASP-76b
• Climate of an Ultra hot Jupiter: Spectroscopic phase curve of WASP-18b with HST/WFC3
• Where is the Water? Jupiter-like C/H ratio but strong H${}_2$O depletion found on $\tau$ Boötis b using SPIRou
• Titanium oxide and chemical inhomogeneity in the atmosphere of the exoplanet WASP-189b
• FastChem 2: An improved computer program to determine the gas-phase chemical equilibrium composition for arbitrary element distributions
• The hot dayside and asymmetric transit of WASP-189b seen by CHEOPS
• KELT-20b: A giant planet with a period of P~ 3.5 days transiting the V~ 7.6 early A star HD 185603
• Decomposing the Iron Cross-Correlation Signal of the Ultra-Hot Jupiter WASP-76b in Transmission using 3D Monte-Carlo Radiative Transfer
• Mass loss rate and local thermodynamic state of KELT-9 b thermosphere from the hydrogen Balmer series
• An Atomic Spectral Survey of WASP-76b: Resolving Chemical Gradients and Asymmetries
• APERO: A PipelinE to Reduce Observations -- Demonstration with SPIRou
• Search for water vapor in the high-resolution transmission spectrum of HD189733b in the visible
• Vanadium oxide and a sharp onset of cold-trapping on a giant exoplanet
• Non-detection of TiO and VO in the atmosphere of WASP-121b using high-resolution spectroscopy
• Relative abundance constraints from high-resolution optical transmission spectroscopy of WASP-121b, and a fast model-filtering technique for accelerating retrievals
• A temperature inversion with atomic iron in the ultra-hot dayside atmosphere of WASP-189b
• Retrieval survey of metals in six ultra-hot Jupiters: Trends in chemistry, rain-out, ionisation and atmospheric dynamics
• MASCARA-2 b: A hot Jupiter transiting the $m_V=7.6$ A-star HD185603
• Into the Storm: Diving into the winds of the ultra hot Jupiter WASP-76 b with HARPS and ESPRESSO
• The atmosphere and architecture of WASP-189 b probed by its CHEOPS phase curve
• Cloud property trends in hot and ultra-hot giant gas planets (WASP-43b, WASP-103b, WASP-121b, HAT-P-7b, and WASP-18b)
• Signs of strong Na and K absorption in the transmission spectrum of WASP-103b
• ARES III: Unveiling the Two Faces of KELT-7 b with HST WFC3
• High-resolution transmission spectroscopy study of ultra-hot Jupiters HAT-P-57b, KELT-17b, KELT-21b, KELT-7b, MASCARA-1b, and WASP-189b
• TOI-2109b: An Ultrahot Gas Giant on a 16 hr Orbit
• Time-resolved transmission spectroscopy of the ultra-hot Jupiter WASP-189 b
• High-resolution atmospheric retrievals of WASP-121b transmission spectroscopy with ESPRESSO: Consistent relative abundance constraints across multiple epochs and instruments
• CRIRES+ and ESPRESSO reveal an atmosphere enriched in volatiles relative to refractories on the ultra-hot Jupiter WASP-121b
• Detection of a high-velocity sodium feature on the ultra-hot Jupiter WASP-121 b
• Detection of CO emission lines in the dayside atmospheres of WASP-33b and WASP-189b with GIANO
• Homogeneous search for helium in the atmosphere of 11 gas giant exoplanets with SPIRou
• Automatic model-based telluric correction for the ESPRESSO data reduction software. Model description and application to radial velocity computation
• Hot Exoplanet Atmospheres Resolved with Transit Spectroscopy (HEARTS) V. Detection of sodium on the bloated super-Neptune WASP-166b
• Transmission spectroscopy of MASCARA-1b with ESPRESSO: Challenges of overlapping orbital and Doppler tracks
• Hot Exoplanet Atmospheres Resolved with Transit Spectroscopy (HEARTS) VII. Detection of sodium on the long-transiting inflated sub-Saturn KELT-11 b
• The Colorado Ultraviolet Transit Experiment (CUTE) Mission Overview
• Chemical analysis of early-type stars with planets
• An atlas of resolved spectral features in the transmission spectrum of WASP-189 b with MAROON-X
• A sub-solar metallicity on the ultra-short period planet HIP 65Ab
• Detection of Paschen $\beta$ absorption in the atmosphere of KELT-9 b: A new window into the atmospheres of ultra-hot Jupiters
• Are Am stars and hot-Jupiter planets related?

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