J/A+A/707/A315ivo://CDS.VizieR/J/A+A/707/A315CDSWang W.Chen G.Jiang C.Palle E.Murgas F.Parviainen H.2026-04-02T06:28:33Z2026-03-24T11:07:26ZCDS support team

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

cds-question@unistra.frmultiple-starsk-starsexoplanetsspectroscopyTransmission spectroscopy serves as a valuable tool for probing atmospheric absorption features in the terminator regions of exoplanets. Stellar surface heterogeneity can introduce wavelength-dependent contamination that complicates the interpretation of planetary spectra. We aim to investigate the atmosphere of the warm sub-Saturn NGTS-5b through optical transmission spectroscopy. Two transits were observed with the low-resolution Optical System for Imaging and low-Intermediate-Resolution Integrated Spectroscopy (OSIRIS) on the 10.4 m Gran Telescopio Canarias (GTC). Chromatic transit light curves were modeled to derive optical transmission spectra, and multiple Bayesian spectral retrievals were performed to characterize the atmospheric properties. Model comparisons provide strong evidence for contamination from unocculted stellar spots. A joint retrieval of the transmission spectra, assuming equilibrium chemistry, indicates a relatively clear atmosphere with a subsolar C/O ratio of <0.22 (90% upper limit) and a low metallicity of 0.10^+0.34^_-0.05_solar. Retrievals assuming free chemistry yield strong evidence for the presence of H_2_O, with its abundance constrained to X_H2O_=-0.79^+0.14^_-0.17_. However, the abundances of other species remain unconstrained due to limited optical wavelength coverage. The discrepancies between the two NGTS-5b transit spectra can be attributed to varying levels of stellar contamination. NGTS-5b thus appears to host a relatively clear, water-rich atmosphere, pending confi2026A&A...707A.315Whttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/707/A315CatalogResearchIsServedByTAP VizieR generic servicehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/707/A315https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/707/A315http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/707/A315https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/707/A315https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/707/A315http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/707/A315GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapdefaultJ/A+A/707/A315/wlcn1NGTS-5b GTC/OSIRIS white light curve on N1recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintBJDBarycentric Julian Date (TDB standard)dtime.epochdoubleFluxRelative fluxphot.flux;arith.ratiodoublee_FluxUncertainty of relative fluxstat.error;phot.fluxdoubleposXDrift of star on CCD in dispersion directionpixpos.cartesian.x;instr.detdoubleposYDrift of star on CCD in spatial directionpixpos.cartesian.y;instr.detdoubleFWHMXRelative change of full width at half maximum of the stellar absorption line profilepixarith.rate;spect.line.widthdoubleFWHMYFull width at half maximum of the stellar spatial profilepixspect.line.widthdoubleAirmassAirmass during observationobs.airMassdoubleNightStarting nighttime.startintwave-leftWavelength at the left bordernmem.wlfloatwave-rightWavelength at the right bordernmem.wlfloatBandBand sequenceinstr.bandpasscharJ/A+A/707/A315/wlcn2NGTS-5b GTC/OSIRIS white light curve on N2recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintBJDBarycentric Julian Date (TDB standard)dtime.epochdoubleFluxRelative fluxphot.flux;arith.ratiodoublee_FluxUncertainty of relative fluxstat.error;phot.fluxdoubleposXDrift of star on CCD in dispersion directionpixpos.cartesian.x;instr.detdoubleposYDrift of star on CCD in spatial directionpixpos.cartesian.y;instr.detdoubleFWHMXRelative change of full width at half maximum of the stellar absorption line profilepixarith.rate;spect.line.widthdoubleFWHMYFull width at half maximum of the stellar spatial profilepixspect.line.widthdoubleAirmassAirmass during observationobs.airMassdoubleNightStarting nighttime.startintwave-leftWavelength at the left bordernmem.wlfloatwave-rightWavelength at the right bordernmem.wlfloatBandBand sequenceinstr.bandpasscharJ/A+A/707/A315/slcn1NGTS-5b GTC/OSIRIS spectroscopic light curves on N1recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintBJDBarycentric Julian Date (TDB standard)dtime.epochdoubleindexedFluxRelative fluxphot.flux;arith.ratiodoublee_FluxUncertainty of relative fluxstat.error;phot.fluxdoubleposXDrift of star on CCD in dispersion directionpixpos.cartesian.x;instr.detdoubleposYDrift of star on CCD in spatial directionpixpos.cartesian.y;instr.detdoubleFWHMXRelative change of full width at half maximum of the stellar absorption line profilepixarith.rate;spect.line.widthdoubleFWHMYFull width at half maximum of the stellar spatial profilepixspect.line.widthdoubleAirmassAirmass during observationobs.airMassdoubleNightStarting nighttime.startintwave-leftWavelength at the left bordernmem.wlfloatwave-rightWavelength at the right bordernmem.wlfloatBandBand sequenceinstr.bandpasscharJ/A+A/707/A315/slcn2NGTS-5b GTC/OSIRIS spectroscopic light curves on N2posYDrift of star on CCD in spatial directionpixpos.cartesian.y;instr.detdoublerecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintBJDBarycentric Julian Date (TDB standard)dtime.epochdoubleindexedFluxRelative fluxphot.flux;arith.ratiodoublee_FluxUncertainty of relative fluxstat.error;phot.fluxdoubleposXDrift of star on CCD in dispersion directionpixpos.cartesian.x;instr.detdoubleFWHMXRelative change of full width at half maximum of the stellar absorption line profilepixarith.rate;spect.line.widthdoubleFWHMYFull width at half maximum of the stellar spatial profilepixspect.line.widthdoubleAirmassAirmass during observationobs.airMassdoubleNightStarting nighttime.startintwave-leftWavelength at the left bordernmem.wlfloatwave-rightWavelength at the right bordernmem.wlfloatBandBand sequenceinstr.bandpasschar