JWST-TST DREAMS: A Supersolar Metallicity in WASP-17 b’s Dayside Atmosphere from NIRISS SOSS Eclipse Spectroscopy
Published in The Astronomical Journal, 2025
We present the first emission spectrum of the hot Jupiter WASP-17 b using one eclipse observation from the JWST Near Infrared Imager and Slitless Spectrograph (NIRISS) Single Object Slitless Spectroscopy (SOSS) mode. Covering a wavelength range of 0.6-2.8 \(\mu\)m, our retrieval analysis reveals a strong detection of H2O in WASP-17 b’s dayside atmosphere (\(6.4\sigma\)). Our retrievals consistently favor a supersolar dayside H2O abundance and a noninverted temperature-pressure profile over a large pressure range. Additionally, our examination of the brightness temperature reveals excess emission below 1 \(\mu\)m, suggesting the possibility of a high internal temperature (600-700 K) and/or contributions from reflected light. We highlight that JWST emission spectroscopy retrieval results can be sensitive to whether negative eclipse depths are allowed at optical wavelengths during light-curve fitting. Our findings deepen our understanding of WASP-17 b’s atmospheric composition while also highlighting the sensitivity of our results to pressure-temperature profile parameterizations. This work is part of a series of studies by our JWST Telescope Scientist Team (TST), in which we will use Guaranteed Time Observations to perform Deep Reconnaissance of Exoplanet Atmospheres through Multi-instrument Spectroscopy (DREAMS).
Recommended citation: Gressier, Amélie et al. (2025). 'JWST-TST DREAMS: A Supersolar Metallicity in WASP-17 b's Dayside Atmosphere from NIRISS SOSS Eclipse Spectroscopy.' The Astronomical Journal.
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