J/AJ/170/292ivo://CDS.VizieR/J/AJ/170/292CDSGressier A.Batalha N.E.Wogan N.Alderson L.Doud D.Espinoza N.,MacDonald R.J.Wakeford H.R.Valenti J.A.Lewis N.K.Seager S.,Stevenson K.B.Allen N.H.Canas C.I.Challener R.C.Glidden A.,Huang J.Lin Z.Louie D.R.Maguire C.Mullens E.Sotzen K.,Valentine D.Clampin M.Pueyo L.van der Marel R.P.Mountain C.M.2026-08-18T14:13:27Z2026-08-18T15:03:31ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frexoplanetsinfrared-photometryspectroscopyWe present the James Webb Space Telescope (JWST) transmission spectrum of the exoplanet HAT-P-26 b (18.6M_{Earth}_, 6.33R_{Earth}_), based on a single transit observed with the JWST NIRSpec G395H grating. We detect water vapor (ln(B)=4.1), carbon dioxide (ln(B)=85.6), and sulfur dioxide (ln(B)=13.5) with high confidence, along with marginal indications for hydrogen sulfide and carbon monoxide (ln(B)<0.5). The detection of SO_2_ in a warm super-Neptune-sized exoplanet (R_P_~6R_{Earth}_) bridges the gap between previous detections in hot Jupiters and sub-Neptunes, highlighting the role of disequilibrium photochemistry across a broad range of exoplanet atmospheres, including those cooler than 1000 K. Our precise measurements of carbon, oxygen, and sulfur indicate an atmospheric metallicity of ~10x solar and a subsolar C/O ratio. Retrieved molecular abundances are consistent within 2{sigma} with predictions from self-consistent models including photochemistry. The elevated CO2 abundance and possible H2S signal may also reflect sensitivities to the thermal structure, cloud properties, or additional disequilibrium processes such as vertical mixing. We compare the SO_2_ abundance in HAT-P-26 b with that of 10 other JWST-observed giant exoplanets, and find a correlation with atmospheric metallicity. The trend is consistent with the prediction from I. J. M. Crossfield, showing a steep rise in SO_2_ abundance at low metallicities, and a more gradual increase beyond 30x solar. This work is part of a series of studies by our JWST Telescope Scientist Team (JWST-TST), in which we use Guaranteed Time Observations to perform Deep Reconnaissance of Exoplanet Atmospheres through Multi-instrument Spectroscopy (DREAMS).2025AJ....170..292Ghttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/AJ/170/292CatalogResearchIsServedByTAP VizieR generic servicerelated-toVI/133 : A variationally computed hot NH3 line list - BYTe (Yurchenko+, 2011)J/ApJ/728/138 : Follow-up photometry of HAT-P-26 (Hartman+, 2011)J/MNRAS/437/1828 : ExoMol line list for HCN and HNC (Barber+, 2014)J/A+A/564/A125 : AGN Torus model comparison of AGN in the CDFS (Buchner+, 2014)J/A+A/573/A90 : STAGGER-grid of 3D stellar models. IV. (Magic+, 2015)J/MNRAS/460/4063 : ExoMol line list for H2S AYT2 (Yurchenko+, 2016)J/MNRAS/459/3890 : ExoMol line lists for SO2 (Underwood+, 2016)J/AJ/154/109 : California-Kepler Surv. (CKS). III. Planet radii (Fulton+, 2017)J/A+A/605/A95 : CH4 & hot methane continuum hybrid line list (Yurchenko+, 2017)J/AJ/156/264 : California-Kepler Survey. VII. Planet radius gap (Fulton+, 2018)J/MNRAS/478/3220 : ExoMol. XXVII: spectra of C2H4 (Mant+, 2018)J/A+A/628/A116 : HAT-P-26 differential transit photometry (von Essen+, 2019)J/AJ/164/87 : Elemental abund. of JWST target. I. FGK stars (Kolecki+, 2022)J/A+A/664/A162 : LC and RV for HAT-P-15, 17, 21, 26 and 29 (Mancini+, 2022)J/AJ/166/223 : SPEARNET normalized photometry of HAT-P-26 (A-thano+, 2023)J/AJ/168/297 : JWST transmission spectrum of HIP 67522b (Thao+, 2024)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/AJ/170/292https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/AJ/170/292http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/AJ/170/292https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/AJ/170/292https://vizier.iucaa.in/viz-bin/votable?-source=J/AJ/170/292http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/AJ/170/292GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapInfrareddefaultJ/AJ/170/292/fig1aJWST NRS1 (NIRSpec/G395H) de-trended broadband light curves of HAT-P-26b transit observations (Data behind Figure 1)recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintBJD[2460110/2460111] Barcentric Julian date in TDBdtime.epochdoubleRFlux[0.99/1.001] Relative observed flux; normalized to out-of-transit fluxphot.flux;arith.ratiodoublee_RFlux[9.1e-5/9.2e-5] 1{sigma} uncertainty in RFluxstat.error;phot.flux;arith.ratiodoubleJ/AJ/170/292/fig1bJWST NRS2 (NIRSpec/G395H) de-trended broadband light curves of HAT-P-26b transit observations (Data behind Figure 1)recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintBJD[2460110/2460111] Barcentric Julian date in TDBdtime.epochdoubleRFlux[0.99/1.01] Relative observed flux; normalized to out-of-transit fluxphot.flux;arith.ratiodoublee_RFlux[1.2e-4/1.21e-4] 1{sigma} uncertainty in RFluxstat.error;phot.flux;arith.ratiodoubleJ/AJ/170/292/fig2aTransmission spectrum of HAT-P-26b observations from ExoTiC-JEDI pipeline (Data behind Figure 2)recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintWavelength[2.87/5.13] Central wavelengthumem.wl.centraldoubleDepth[4.6e-3/6e-3] Transit depth; parts per million(10-6)phys.absorption.opticalDepthdoublee_Depth[6.6e-5/2.6e-4] Uncertainty in Depth(10-6)stat.error;phys.absorption.opticalDepthdoubleJ/AJ/170/292/fig2bTransmission spectrum of HAT-P-26b observations from transitspectroscopy pipeline (Data behind Figure 2)recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintWavelength[2.77/5.15] Central wavelengthumem.wl.centraldoubleDepth[4.6e-3/6e-3] Transit depth; parts per million(10-6)phys.absorption.opticalDepthdoublee_Depth[8.8e-5/3e-4] Uncertainty in Depth(10-6)stat.error;phys.absorption.opticalDepthdouble