J/AJ/168/297 JWST transmission spectrum of HIP 67522b (Thao+, 2024)
The featherweight giant: unraveling the atmosphere of a 17 Myr planet with JWST.
Thao Pa C., Mann A.W., Feinstein A.D., Gao P., Thorngren D., Rotman Y.,
Welbanks L., Brown A., Duvvuri G.M., France K., Longo I., Sandoval A.,
Schneider P.C., Wilson D.J., Youngblood A., Vanderburg A., Barber M.G.,
Wood M.L., Batalha N.E., Kraus A.L., Murray C.A., Newton E.R., Rizzuto A.,
Tofflemire B.M., Tsai S.-M., Bean J.L., Berta-Thompson Z.K.,
Evans-Soma T.M., Froning C.S., Kempton E.M.-R., Miguel Y., Pineda J.S.
<Astron. J., 168, 297 (2024)>
=2024AJ....168..297T 2024AJ....168..297T
ADC_Keywords: Exoplanets; Spectra, infrared
Keywords: Exoplanet atmospheric composition ; Exoplanet evolution ;
James Webb Space Telescope ; Starspots ; Transmission spectroscopy
Abstract:
The characterization of young planets (<300Myr) is pivotal for
understanding planet formation and evolution. We present the 3-5um
transmission spectrum of the 17Myr, Jupiter-size (R∼10R⊕)
planet, HIP 67522b, observed with JWST NIRSpec/G395H. To check for
spot contamination, we obtain a simultaneous g-band transit with the
Southern Astrophysical Research Telescope. The spectrum exhibits
absorption features 30%-50% deeper than the overall depth, far larger
than expected from an equivalent mature planet, and suggests that HIP
67522b's mass is <20M⊕ irrespective of cloud cover and stellar
contamination. A Bayesian retrieval analysis returns a mass constraint
of 13.8±1.0M⊕. This challenges the previous classification
of HIP 67522b as a hot Jupiter and instead, positions it as a
precursor to the more common sub-Neptunes. With a density of
<0.10g/cm3, HIP 67522 b is one of the lowest-density planets known.
We find strong absorption from H2O and CO2 (≥7σ), a modest
detection of CO (3.5σ), and weak detections of H2S and SO2
(∼2σ). Comparisons with radiative-convective equilibrium models
suggest supersolar atmospheric metallicities and solar-to-subsolar C/O
ratios, with photochemistry further constraining the inferred
atmospheric metallicity to 3x10 solar due to the amplitude of the
SO2 feature. These results point to the formation of HIP 67522b
beyond the water snowline, where its envelope was polluted by icy
pebbles and planetesimals. The planet is likely experiencing
substantial mass loss (0.01-0.03M⊕/Myr), sufficient for
envelope destruction within a gigayear. This highlights the dramatic
evolution occurring within the first 100Myr of its existence.
Description:
We obtained a single transit observation of HIP 67522 b on
2023 February 26 UTC using the Near Infrared Spectrograph (NIRSpec) in
the Bright Object Time Series mode on the James Webb Space Telescope
(JWST). The observations were taken with the G395H grating, F290LP
filter (2.87-5.10um), and recorded with a 1.6"x1.6" fixed slit
aperture with the spectra dispersed across both the NRS1 and NRS2
detectors. The observation lasted approximately 8.9hr. We acquired a
total of 2703 integrations, with nine groups per integration,
resulting in an effective integration time of ∼21943s.
Objects:
-----------------------------------------------------
RA (2000) DE Designation(s)
-----------------------------------------------------
13 50 06.27 -40 50 08.8 HIP 67522b = HD 120411b
-----------------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
fig7.dat 34 717 The James Webb Space Telescope transmission
spectrum of HIP 67522 b
--------------------------------------------------------------------------------
See also:
I/239 : The Hipparcos and Tycho Catalogues (ESA 1997)
I/311 : Hipparcos, the New Reduction (van Leeuwen, 2007)
II/135 : Henry Draper Cat. & Extension (Cannon+ 1918-1924; ADC 1989)
J/A+A/397/147 : Activity-rotation relationship in stars (Pizzolato+ 2003)
J/A+A/564/A125 : AGN Torus model comparison of AGN in the CDFS (Buchner+, 2014)
J/A+A/589/A21 : K-H2 line shapes for cool brown dwarfs spectra (Allard+, 2016)
J/MNRAS/460/4063 : ExoMol line list for H2S AYT2 (Yurchenko+, 2016)
J/MNRAS/459/3890 : ExoMol line lists for SO2 (Underwood+, 2016)
J/MNRAS/490/4638 : ExoMol molecular line lists. XXXV. NH3 (Coles+, 2019)
J/ApJ/874/L31 : Giant planet bulk & atmos. metallicities (Thorngren+, 2019)
J/AJ/160/239 : Cluster difference imaging photometric surv. II. (Bouma+, 2020)
J/AJ/159/239 : Transmission Spectroscopy Metric of exoplanets (Guo+, 2020)
J/AJ/159/239 : Transmission Spectroscopy Metric of exoplanets (Guo+, 2020)
J/AJ/159/57 : HST spectroscopic LCs of Kepler 51b & 51d (Libby-Roberts+, 2020)
J/MNRAS/498/5972 : Variables & dippers in young associations (Nardiello, 2020)
J/AJ/164/215 : Candidate members of Cep-Her, RSG-5 and CH-2 (Bouma+, 2022)
J/AJ/164/59 : GJ1132b planet/stellar rad. at 0.7-4.5um (Libby-Roberts+, 2022)
J/AJ/166/62 : New HIRES radial velocity data for V1298 Tau (Blunt+, 2023)
J/AJ/166/196 : V1298 Tau high energy spectrum (Duvvuri+, 2023)
J/AJ/165/85 : THYME. IX. MELANGE-4 association members (Wood+, 2023)
J/AJ/167/210 : <200Myr planet's hosts TESS parameters (Vach+, 2024)
Byte-by-byte Description of file: fig7.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1 I1 --- Pip Pipeline (1)
3- 8 F6.4 um lambda [2.7/5.2] Wavelength
10- 21 F12.10 % Depth [0.02/0.7] Transit depth
23- 34 F12.10 % e_Depth [7e-3/0.12] Error in Depth
--------------------------------------------------------------------------------
Note (1): Pipelines as follows:
1 = JWST Science Calibration Pipeline + ExoTiC-JEDI (Section 5.2);
230 occurrences
2 = ExoTiC + Chromatic (Section 5.3); 141 occurrences
3 = ExoTiC+ custom (Section 5.4); 346 occurrences
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Prepared by [AAS], Robin Leichtnam [CDS] 19-Sep-2025