J/AJ/168/231 WASP-121b radial velocities from JWST NIRSpec (Sing+, 2024)
An absolute mass, precise age, and hints of planetary winds for WASP-121A and b
from a JWST NIRSpec phase curve.
Sing D.K., Evans-Soma T.M., Rustamkulov Z., Lothringer J.D., Mayne N.J.,
Schlaufman K.C.
<Astron. J., 168, 231 (2024)>
=2024AJ....168..231S 2024AJ....168..231S
ADC_Keywords: Radial velocities ; Exoplanets ; Spectroscopy ; Infrared
Keywords: Radial velocity ; Extrasolar gaseous planets ; Astronomical techniques
Abstract:
We have conducted a planetary radial velocity measurement of the
ultrahot 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
(∼10 pixels). Using cross-correlation techniques, we have determined
an overall planetary velocity amplitude of Kp=215.7±1.1km/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 Ms=1.330±0.019M☉, while WASP-121b has a mass of
Mp=1.170±0.043MJ. These dynamical measurements are ∼3x more
precise than previous estimates and do not rely on any stellar
modeling assumptions that have a ∼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±0.14Gyr.
Finally, we observed potential velocity differences between the two
NIRSpec detectors, with NRS1 lower by 5.5±2.2km/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 Kp. The planet's rotation can account for
1km/s of the observed velocity difference, with 4.5±2.2km/s
potentially attributable to vertical differences in wind speeds.
Description:
We use the phase-curve measurements of WASP-121b taken with the JWST
NIRSpec G395H instrument as part of GO-1729 (P.I. Mikal-Evans,
co-P.I. Kataria). The team observed the WASP-121 system over a full
planetary orbit on 2022 October 14-15. Observations were made without
interruption for 37.8hr, commencing 145min prior to secondary eclipse
ingress and continuing until 105min after egress of the following
secondary eclipse. The G395H grating provided wavelength coverage
between 2.70 and 5.15um at R∼3000. This resolution is sufficient to
observe significant wavelength shifts across the detector for
short-period planets, given the large orbital velocities near ∼200km/s
compared to the NRS1 and NRS2 detector's average resolutions of
67 and 44km/s per pixel, respectively.
Objects:
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RA (2000) DE Designation(s)
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07 10 24.06 -39 05 50.5 WASP-121b = CD-38 3220b
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
fig6.dat 29 159 Planetary RV signal derived using NIRSpec/NRS2
fig7.dat 29 159 Planetary RV signal derived using NIRSpec/NRS1
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See also:
I/352 : Distances to 1.47 billion stars in Gaia EDR3 (Bailer-Jones+, 2021)
II/365 : The CatWISE2020 cat. (updated version 28-Jan-2021) (Marocco+, 2021)
I/357 : Gaia DR3 Part 3. Non-single stars (Gaia Collaboration, 2022)
VII/233 : 2MASS All-Sky Extended Source Catalog (XSC) (IPAC/UMass, 2003-2006)
J/other/A+ARV/18.67 : Accurate masses and radii of normal stars (Torres+, 2010)
J/AJ/153/138 : Radial velocity curve of 51 Peg (Birkby+, 2017)
J/A+A/623/A57 : WASP-121 b Swift UVOT near-UV transit obs. (Salz+, 2019)
J/A+A/625/A80 : WASP-121b secondary eclipse: 2MASS K band (Kovacs+, 2019)
J/A+A/631/A77 : Low-mass stellar models and isochrones (Amard+, 2019)
J/AJ/157/55 : RVs and light curves for HATS-60-HATS-69 (Hartman+, 2019)
J/A+A/635/A205 : Ultra-hot Jupiter WASP-121b transits (Bourrier+, 2020)
J/A+A/637/A36 : WASP-121b optical phase curve (Bourrier+, 2020)
J/ApJ/888/L5 : Transits, occultation times and RVs of WASP-12b (Yee+, 2020)
J/A+A/661/A147 : Gal. interstellar dust Gaia-2MASS 3D maps (Lallement+, 2022)
J/A+A/664/A174 : Gal. interstellar dust Gaia-2MASS 3D maps (Vergely+, 2022)
J/MNRAS/518/662 : Benchmarking MESA isochrones with Hyades (Brandner+, 2023)
J/ApJ/946/L6 : JWST NIRSp. & MIRI sp. of BD* SIPS J1256-1257B (Miles+, 2023)
J/ApJS/265/1 : TESS Grand Unified Hot Jupiter Surveys. II. (Yee+, 2023)
Byte-by-byte Description of file: fig*
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Bytes Format Units Label Explanations
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1- 11 F11.5 d BJD Barycentric Julian Date; BJD-24500000.5 (TDB)
13- 17 F5.3 --- Phase Orbital phase
19- 24 F6.1 km/s RVel [-235/226] Radial velocity
26- 29 F4.1 km/s e_RVel [6.9/58] 1σ uncertainty in RVel
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History:
From electronic version of the journal
(End) Prepared by [AAS], Robin Leichtnam [CDS] 01-Jul-2025