TY - JOUR
T1 - Near-infrared transmission spectroscopy of HAT-P-18 b with NIRISS
T2 - disentangling planetary and stellar features in the era of JWST
AU - Fournier-Tondreau, Marylou
AU - MacDonald, Ryan J.
AU - Radica, Michael
AU - Lafrenière, David
AU - Welbanks, Luis
AU - Piaulet, Caroline
AU - Coulombe, Louis-Philippe
AU - Allart, Romain
AU - Morel, Kim
AU - Artigau, Étienne
AU - Albert, Loïc
AU - Lim, Olivia
AU - Doyon, René
AU - Benneke, Björn
AU - Rowe, Jason F.
AU - Darveau-Bernier, Antoine
AU - Cowan, Nicolas B.
AU - Lewis, Nikole K.
AU - Cook, Neil J.
AU - Flagg, Laura
AU - Genest, Frédéric
AU - Pelletier, Stefan
AU - Johnstone, Doug
AU - Dang, Lisa
AU - Kaltenegger, Lisa
AU - Taylor, Jake
AU - Turner, Jake D.
N1 - Funding: This project is undertaken with the financial support of the Canadian Space Agency. MFT acknowledges financial support from the Fonds de Recherche du Québec – Nature et technologies (FRQNT) and funding from the Trottier Family Foundation in their support of iREx. RJM acknowledges support for this work provided by NASA through the NASA Hubble Fellowship grant number HST-HF2-51513.001, awarded by the Space Telescope Science Institute (STScI), which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555. MR acknowledges financial support from the Natural Sciences and Engineering Research Council of Canada (NSERC) as well as from FRQNT and iREx. CP acknowledges support from FRQNT and TEPS Ph.D. scholarships and the NSERC Vanier scholarship. KM acknowledges financial support from the FRQNT. OL acknowledges financial support from FRQNT and iREx. DJ is supported by NRC Canada and by an NSERC Discovery Grant. JDT was supported for this work by NASA through the NASA Hubble Fellowship grant number HST-HF2-51495.001-A awarded by the STScI, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract number NAS5-26555.
PY - 2024/2/1
Y1 - 2024/2/1
N2 - The JWST Early Release Observations (ERO) included a NIRISS/SOSS (0.6–2.8 μm) transit of the ∼ 850 K Saturn-mass exoplanet HAT-P-18 b. Initial analysis of these data reported detections of water, escaping helium and haze. However, active K dwarfs like HAT-P-18 possess surface heterogeneities – star-spots and faculae – that can complicate the interpretation of transmission spectra, and indeed, a spot-crossing event is present in HAT-P-18 b’s NIRISS/SOSS light curves. Here, we present an extensive reanalysis and interpretation of the JWST ERO transmission spectrum of HAT-P-18 b, as well as HST/WFC3 and Spitzer/IRAC transit observations. We detect H2O (12.5σ), CO2 (7.3σ), a cloud deck (7.4σ), and unocculted star-spots (5.8σ), alongside hints of Na (2.7σ). We do not detect the previously reported CH4 (log CH4 < −6 to 2σ). We obtain excellent agreement between three independent retrieval codes, which find a sub-solar H2O abundance (log H2O ≈ −4.4 ± 0.3). However, the inferred CO2 abundance (log CO2 ≈ −4.8 ± 0.4) is significantly super-solar and requires further investigation into its origin. We also introduce new stellar heterogeneity considerations by fitting for the active regions’ surface gravities – a proxy for the effects of magnetic pressure. Finally, we compare our JWST inferences to those from HST/WFC3 and Spitzer/IRAC. Our results highlight the exceptional promise of simultaneous planetary atmosphere and stellar heterogeneity constraints in the era of JWST and demonstrate that JWST transmission spectra may warrant more complex treatments of the transit light source effect.
AB - The JWST Early Release Observations (ERO) included a NIRISS/SOSS (0.6–2.8 μm) transit of the ∼ 850 K Saturn-mass exoplanet HAT-P-18 b. Initial analysis of these data reported detections of water, escaping helium and haze. However, active K dwarfs like HAT-P-18 possess surface heterogeneities – star-spots and faculae – that can complicate the interpretation of transmission spectra, and indeed, a spot-crossing event is present in HAT-P-18 b’s NIRISS/SOSS light curves. Here, we present an extensive reanalysis and interpretation of the JWST ERO transmission spectrum of HAT-P-18 b, as well as HST/WFC3 and Spitzer/IRAC transit observations. We detect H2O (12.5σ), CO2 (7.3σ), a cloud deck (7.4σ), and unocculted star-spots (5.8σ), alongside hints of Na (2.7σ). We do not detect the previously reported CH4 (log CH4 < −6 to 2σ). We obtain excellent agreement between three independent retrieval codes, which find a sub-solar H2O abundance (log H2O ≈ −4.4 ± 0.3). However, the inferred CO2 abundance (log CO2 ≈ −4.8 ± 0.4) is significantly super-solar and requires further investigation into its origin. We also introduce new stellar heterogeneity considerations by fitting for the active regions’ surface gravities – a proxy for the effects of magnetic pressure. Finally, we compare our JWST inferences to those from HST/WFC3 and Spitzer/IRAC. Our results highlight the exceptional promise of simultaneous planetary atmosphere and stellar heterogeneity constraints in the era of JWST and demonstrate that JWST transmission spectra may warrant more complex treatments of the transit light source effect.
KW - Planets and satellites: atmospheres
KW - Planets and satellites: gaseous planets
KW - Planets and satellites: individual: HAT-P-18 b
KW - Starspots
KW - Methods: data analysis
KW - Techniques: spectroscopic
UR - https://www.scopus.com/pages/publications/85184854522
U2 - 10.1093/mnras/stad3813
DO - 10.1093/mnras/stad3813
M3 - Article
SN - 0035-8711
VL - 528
SP - 3354
EP - 3377
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
IS - 2
ER -