CO or no CO? Narrowing the CO Abundance Constraint and Recovering the H2O Detection in the Atmosphere of WASP-127 b using SPIRou

By Keith Cowing
Status Report
March 7, 2023
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CO or no CO? Narrowing the CO Abundance Constraint and Recovering the H2O Detection in the Atmosphere of WASP-127 b using SPIRou
Best ln L (dark) and 100 randomly generated from MCMC sample models (light) of the transmission spectrum of WASP-127 b (with đť‘… = 1000) using the HRR (blue), the LRR (green) and the JR parameters (orange), compared to the HST and Spitzer data from S21 (black). The best-fit model with OH is shown in magenta for comparison. The red shaded region shows the wavelength range of SPIRou. The position of the absorption bands of the major molecules considered are shown. — astro-ph.EP

Precise measurements of chemical abundances in planetary atmospheres are necessary to constrain the formation histories of exoplanets. A recent study of WASP-127b, a close-in puffy sub-Saturn orbiting its solar-type host star in 4.2 d, using HST and Spitzer revealed a feature-rich transmission spectrum with strong excess absorption at 4.5 um.

However, the limited spectral resolution and coverage of these instruments could not distinguish between CO and/or CO2 absorption causing this signal, with both low and high C/O ratio scenarios being possible. Here we present near-infrared (0.9–2.5 um) transit observations of WASP-127 b using the high-resolution SPIRou spectrograph, with the goal to disentangle CO from CO2 through the 2.3 um CO band.

With SPIRou, we detect H2O at a t-test significance of 5.3 sigma and observe a tentative (3 sigma) signal consistent with OH absorption. From a joint SPIRou + HST + Spitzer retrieval analysis, we rule out a CO-rich scenario by placing an upper limit on the CO abundance of log10[CO]<-4.0, and estimate a log10[CO2] of -3.7^(+0.8)_(-0.6), which is the level needed to match the excess absorption seen at 4.5um.

We also set abundance constraints on other major C-, O-, and N-bearing molecules, with our results favoring low C/O (0.10^(+0.10)_(-0.06)), disequilibrium chemistry scenarios. We further discuss the implications of our results in the context of planet formation. Additional observations at high and low-resolution will be needed to confirm these results and better our understanding of this unusual world.

Anne Boucher, David Lafrenière, Stefan Pelletier, Antoine Darveau-Bernier, Michael Radica, Romain Allart, Étienne Artigau, Neil J. Cook, Florian Debras, René Doyon, Eric Gaidos, Björn Benneke, Charles Cadieux, Andres Carmona, Ryan Cloutier, Pía Cortés-Zuleta, Nicolas B. Cowan, Xavier Delfosse, Jean-François Donati, Pascal Fouqué, Thierry Forveille, Konstantin Grankin, Guillaume Hébrard, Jorge H. C. Martins, Eder Martioli, Adrien Masson, Sandrine Vinatier

Comments: 23 pages, 13 figures, Submitted for publication in the Monthly Notice of the Royal Astronomical Society
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2303.03232 [astro-ph.EP] (or arXiv:2303.03232v1 [astro-ph.EP] for this version)
Submission history
From: Anne Boucher
[v1] Mon, 6 Mar 2023 15:49:37 UTC (7,351 KB)
Astrobiology, Astrochemistry

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