An absolute mass, precise age, and hints of planetary winds for WASP-121 A and b from a JWST NIRSpec phase curve

Abstract

We have conducted a planetary radial velocity measurement of the ultra-hot Jupiter WASP-121b using JWST NIRSpec phase curve data. Our analysis reveals the Doppler shift of the planetary spectral lines across the full orbit, which shifts considerably across the detector ($\sim$ 10 pixels). Using cross-correlation techniques, we have determined an overall planetary velocity amplitude of $K_{\mathrm{p}}=215.7\pm 1.1$ km/s, which is in good agreement with the expected value. We have also calculated the dynamical mass for both components of the system by treating it as an eclipsing double-line spectroscopic binary, with WASP-121A having a mass of M${}_{\star }$=1.330 $\pm$ 0.019 M${}_{\odot }$, while WASP-121b has a mass of M${}_{\mathrm{p}}$= 1.170 $\pm$ 0.043 M${}_{\mathrm{Jup}}$. These dynamical measurements are $\sim 3\times$ more precise than previous estimates and do not rely on any stellar modeling assumptions which have a $\sim$5\% systematic floor mass uncertainty. Additionally, we used stellar evolution modeling constrained with a stellar density and parallax measurement to determine a precise age for the system, found to be 1.11 $\pm$ 0.14 Gyr. Finally, we observed potential velocity differences between the two NIRSpec detectors, with NRS1 lower by 5.5$\pm$2.2 km/s. We suggest that differences can arise from day/night asymmetries in the thermal emission, which can lead to a sensitivity bias favoring the illuminated side of the planet, with planetary rotation and winds both acting to lower a measured $K_{\mathrm{P}}$. The planet's rotation can account for 1 km/s of the observed velocity difference, with 4.5$\pm$2.2 km/s potentially attributable to vertical differences in wind speeds.

13 pages, 11 Figures, 2 Tables. Submitted 22 July 2024, Accepted in AJ on 22 Sept 2024. Data available on Zenodo at https://doi.org/10.5281/zenodo.11992282

References in corpus (40)

• The Gaia mission
• Modules for Experiments in Stellar Astrophysics (MESA)
• Gaia Data Release 3: Summary of the content and survey properties
• Estimating distances from parallaxes. V: Geometric and photogeometric distances to 1.47 billion stars in Gaia Early Data Release 3
• Modules for Experiments in Stellar Astrophysics (MESA): Pulsating Variable Stars, Rotation, Convective Boundaries, and Energy Conservation
• Modules for Experiments in Stellar Astrophysics (MESA): Time-Dependent Convection, Energy Conservation, Automatic Differentiation, and Infrastructure
• A million binaries from Gaia eDR3: sample selection and validation of Gaia parallax uncertainties
• The Science Performance of JWST as Characterized in Commissioning
• Early Release Science of the exoplanet WASP-39b with JWST NIRSpec PRISM
• The CatWISE2020 Catalog
• Early Release Science of the Exoplanet WASP-39b with JWST NIRSpec G395H
• Ground-based detection of sodium in the transmission spectrum of exoplanet HD209458b
• An ultrahot gas-giant exoplanet with a stratosphere
• Detection of Fe I in the atmosphere of the ultra-hot Jupiter WASP-121b, and a new likelihood-based approach for Doppler-resolved spectroscopy
• Updated Gaia-2MASS 3D maps of Galactic interstellar dust
• Identification of carbon dioxide in an exoplanet atmosphere
• In-orbit Performance of the Near-Infrared Spectrograph NIRSpec on the James Webb Space Telescope
• The JWST Early Release Science Program for Direct Observations of Exoplanetary Systems II: A 1 to 20 Micron Spectrum of the Planetary-Mass Companion VHS 1256-1257 b
• The Orbit of WASP-12b is Decaying
• A broadband thermal emission spectrum of the ultra-hot Jupiter WASP-18b
• Discovery of water at high spectral resolution in the atmosphere of 51 Peg b
• Atmospheric Rossiter-McLaughlin effect and transmission spectroscopy of WASP-121b with ESPRESSO
• A JWST transmission spectrum of a nearby Earth-sized exoplanet
• Three-dimensional extinction maps: Inverting inter-calibrated extinction catalogues
• An emission spectrum for WASP-121b measured across the 0.8-1.1 micron wavelength range using the Hubble Space Telescope
• Analysis of a JWST NIRSpec Lab Time Series: Characterizing Systematics, Recovering Exoplanet Transit Spectroscopy, and Constraining a Noise Floor
• An inventory of atomic species in the atmosphere of WASP-121b using UVES high-resolution spectroscopy
• Carbon monoxide emission lines reveal an inverted atmosphere in the ultra hot Jupiter WASP-33 b consistent with an eastward hot spot
• High atmospheric metal enrichment for a Saturn-mass planet
• Detection of barium in the atmospheres of the ultra-hot gas giants WASP-76b and WASP-121b
• Neutral Cr and V in the atmosphere of ultra hot jupiter WASP-121 b
• Spectroscopic Time-series Performance of JWST/NIRSpec from Commissioning Observations
• High-resolution atmospheric retrievals of WASP-121b transmission spectroscopy with ESPRESSO: Consistent relative abundance constraints across multiple epochs and instruments
• A JWST NIRSpec Phase Curve for WASP-121b: Dayside Emission Strongest Eastward of the Substellar Point and Nightside Conditions Conducive to Cloud Formation
• Detection of a high-velocity sodium feature on the ultra-hot Jupiter WASP-121 b
• The TESS Grand Unified Hot Jupiter Survey. II. Twenty New Giant Planets
• The Mantis Network II: Examining the 3D high-resolution observable properties of the UHJs WASP-121b and WASP-189b through GCM modelling
• Benchmarking MESA isochrones against the Hyades single star sequence
• Detection of carbon monoxide's 4.6 micron fundamental band structure in WASP-39b's atmosphere with JWST NIRSpec G395H
• High-resolution Emission Spectroscopy of the Ultrahot Jupiter KELT-9b: Little Variation in Day- and Nightside Emission Line Contrasts

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