Kavli Affiliate: Sara Seager
| First 5 Authors: Dana R. Louie, Elijah Mullens, Lili Alderson, Ana Glidden, Nikole K. Lewis
| Summary:
Water has proven to be ubiquitously detected in near-infrared (NIR)
transmission spectroscopy observations of hot Jupiter atmospheres, including
WASP-17b. However, previous analyses of WASP-17b’s atmosphere based upon Hubble
Space Telescope (HST) and Spitzer data could not constrain the water abundance,
finding that sub-solar, super-solar and bimodal posterior distributions were
all statistically valid. In this work, we observe one transit of the hot
Jupiter WASP-17b using JWST’s Near Infrared Imager and Slitless Spectrograph
Single Object Slitless Spectroscopy (NIRISS SOSS) mode. We analyze our data
using three independent data analysis pipelines, finding excellent agreement
between results. Our transmission spectrum shows multiple H$_2$O absorption
features and a flatter slope towards the optical than seen in previous HST
observations. We analyze our spectrum using both PICASO+Virga forward models
and free retrievals. POSEIDON retrievals provide a well-constrained super-solar
$log$(H$_2$O) abundance (-2.96$^{+0.31}_{-0.24}$), breaking the degeneracy
from the previous HST/Spitzer analysis. We verify our POSEIDON results with
petitRADTRANS retrievals. Additionally, we constrain the abundance of
$log$(H$^-$), -10.19$^{+0.30}_{-0.23}$, finding that our model including H$^-$
is preferred over our model without H$^-$ to 5.1 $sigma$. Furthermore, we
constrain the $log$(K) abundance (-8.07$^{+0.58}_{-0.52}$) in WASP-17b’s
atmosphere for the first time using space-based observations. Our abundance
constraints demonstrate the power of NIRISS SOSS’s increased resolution,
precision, and wavelength range to improve upon previous NIR space-based
results. 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).
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