CO or no CO? Narrowing the CO abundance constraint and recovering the H2O detection in the atmosphere of WASP-127 b using SPIRou

Abstract

Precise measurements of chemical abundances in planetary atmospheres are necessary to constrain the formation histories of exoplanets. A recent study of WASP-127 b, 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 μm. 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 μm) transit observations of WASP-127 b using the high-resolution SPIRou spectrograph, with the goal to disentangle CO from CO2 through the 2.3 μm CO band. With SPIRou, we detect H2O at a t-test significance of 5.3 σ and observe a tentative (3 σ) 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 4.5 μm. 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.

A Combined Ground-based and JWST Atmospheric Retrieval Analysis: Both IGRINS and NIRSpec Agree that the Atmosphere of WASP-77A b Is Metal-poor

“…Brogi & Line (2019) predicted that such combinations would enable more precise estimates of atmospheric properties than either data set could provide alone. Using real data, this has indeed been the case in the literature, but there are only a handful of studies that have done such analysis (Gandhi et al 2019;Boucher et al 2023;Kasper et al 2023). Line et al (2021) recently demonstrated the HRCCS capabilities of the Immersion GRating INfrared Spectrometer (IGRINS; R ∼ 45,000, 1.45-2.6 μm) on Gemini South by applying the HRCCS retrieval framework to pre-secondaryeclipse (0.325 < j < 0.47, j = 0.5 being secondary eclipse) data of the hot Jupiter WASP-77A b (T eq = 1700 K, R P = 1.21 R J , P = 1.36 days; Maxted et al 2013).…”

“…While previous combined high-and low-resolution retrievals have only used HST and Spitzer data (Gandhi et al 2019;Boucher et al 2023;Kasper et al 2023), no such analysis has been attempted with data taken with JWST. Both IGRINS and NIRSpec have been shown to provide stringent estimates on atmospheric composition and thermal structure, and combining the unique strengths of both instruments could provide powerful probes into transiting giant atmospheres.…”

Evidence for Nightside Water Emission Found in Transit of Ultra-hot Jupiter WASP-33 b

“…where R eff is the effective planetary radius as a function of wavelength, R s is the stellar radius, and ψ m is the planetary rotational broadening profile for the transmission spectrum. We computed the rotational broadening kernel of the transmission spectrum according to the method of Boucher et al (2023) and modified the code developed by Carvalho & Johns-Krull (2023) to implement fast rotational broadening over a wide range of wavelengths. We initially set the thickness of the atmosphere to z = 5H, where H is the atmospheric scale height and tidal locking is assumed.…”

High-resolution Transmission Spectroscopy of Ultrahot Jupiter WASP–33b with NEID

“…The purple and cyan lines in the fifth row of Figure 1 show the hydrostatic models of Hα with 2710 K (i.e., the equilibrium temperature of WASP-33b) and 10,000 K, respectively. The planetary rotation broadening is considered assuming tidal locking using the method of Boucher et al (2023). Each hydrostatic model is calculated by petitRADTRANS assuming an isothermal temperature structure, chemical equilibrium, and other settings consistent with Section 4.2.1.…”