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Title: Keck Planet Imager and Characterizer Emission Spectroscopy of WASP-33b

We present Keck Planet Imager and Characterizer (KPIC) high-resolution (R∼35,000)K-band thermal emission spectroscopy of the ultrahot Jupiter WASP-33b. The use of KPIC’s single-mode fibers greatly improves both blaze and line-spread stabilities relative to slit spectrographs, enhancing the cross-correlation detection strength. We retrieve the dayside emission spectrum with a nested-sampling pipeline, which fits for orbital parameters, the atmospheric pressure–temperature profile, and the molecular abundances. We strongly detect the thermally inverted dayside and measure mass-mixing ratios for CO (logCOMMR=1.10.6+0.4), H2O (logH2OMMR=4.10.9+0.7), and OH (logOHMMR=2.11.1+0.5), suggesting near-complete dayside photodissociation of H2O. The retrieved abundances suggest a carbon- and possibly metal-enriched atmosphere, with a gas-phase C/O ratio of0.80.2+0.1, consistent with the accretion of high-metallicity gas near the CO2snow line and post-disk migration or with accretion between the soot and H2O snow lines. We also find tentative evidence for12CO/13CO ∼ 50, consistent with values expected in protoplanetary disks, as well as tentative evidence for a metal-enriched atmosphere (2–15 × solar). These observations demonstrate KPIC’s ability to characterize close-in planets and the utility of KPIC’s improved instrumental stability for cross-correlation techniques.

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AAS Journals
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Journal Name:
The Astronomical Journal
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Medium: X
Sponsoring Org:
National Science Foundation
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