IGRINS Observations of WASP-127 b: H<sub>2</sub>O, CO, and Super-solar Atmospheric Metallicity in the Inflated Sub-Saturn
Krishna Kanumalla, Michael R. Line, Megan Mansfield, Luis Welbanks, Peter Smith, Jacob L. Bean, Lorenzo Pino, Matteo Brogi, Vatsal Panwar
Abstract
Abstract High-resolution spectroscopy of exoplanet atmospheres provides insights into their composition and dynamics from the resolved line shape and depth of thousands of spectral lines. WASP-127 b is an extremely inflated sub-Saturn ( R p = 1.311 R Jup , M p = 0.16 M Jup ) with previously reported detections of H 2 O and CO 2 . However, the seeming absence of the primary carbon reservoir expected at WASP-127 b temperatures ( T eq ∼1400 K) from chemical equilibrium, CO, posed a mystery. In this manuscript, we present the analysis of high-resolution observations of WASP-127 b with the Immersion Grating Infrared Spectrometer on Gemini South. We confirm the presence of H 2 O (8.67 σ ) and report the detection of CO (4.34 σ ). Additionally, we conduct a suite of Bayesian retrieval analyses covering a hierarchy of model complexity and self-consistency. When freely fitting for the molecular gas volume mixing ratios, we obtain super-solar metal enrichment for H 2 O abundance of log 10 X <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow/> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">H</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> <mml:mi mathvariant="normal">O</mml:mi> </mml:mrow> </mml:msub> </mml:math> = −1.23 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow/> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.49</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.29</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> and a lower limit on the CO abundance of log 10 X CO ≥–2.20 at 2 σ confidence. We also report tentative evidence of photochemistry in WASP-127 b based upon the indicative depletion of H 2 S. This is also supported by the data preferring models with photochemistry over free-chemistry and thermochemistry. The overall analysis implies a super-solar (∼39× Solar; [M/H] = <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>1.59</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.30</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.30</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> ) metallicity for the atmosphere of WASP-127 b and an upper limit on its atmospheric C/O ratio as < 0.68.