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Ahrer, E. M., Alderson, L., Batalha, N. M., Batalha, N. E., Bean, J. L., Beatty, T. G., et al. (2023). Identification of carbon dioxide in an exoplanet atmosphere. Nature, Early Access.
Abstract: Carbon dioxide (CO2) is a key chemical species that is found in a wide range of planetary atmospheres. In the context of exoplanets, CO2 is an indicator of the metal enrichment (that is, elements heavier than helium, also called 'metallicity')(1-3), and thus the formation processes of the primary atmospheres of hot gas giants(4-6). It is also one of the most promising species to detect in the secondary atmospheres of terrestrial exoplanets(7-9). Previous photometric measurements of transiting planets with the Spitzer Space Telescope have given hints of the presence of CO2, but have not yielded definitive detections owing to the lack of unambiguous spectroscopic identification(10-12). Here we present the detection of CO2 in the atmosphere of the gas giant exoplanet WASP-39b from transmission spectroscopy observations obtained with JWST as part of the Early Release Science programme(13,14). The data used in this study span 3.0-5.5micrometres in wavelength and show a prominent CO2 absorption feature at 4.3micrometres (26-sigma significance). The overall spectrum is well matched by one-dimensional, ten-times solar metallicity models that assume radiative-convective-thermochemical equilibrium and have moderate cloud opacity. These models predict that the atmosphere should have water, carbon monoxide and hydrogen sulfide in addition to CO2, but little methane. Furthermore, we also tentatively detect a small absorption feature near 4.0micrometres that is not reproduced by these models.
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Mancini, L., Sarkis, P., Henning, T., Bakos, G. A., Bayliss, D., Bento, J., et al. (2020). The highly inflated giant planet WASP-174b. Astron. Astrophys., 633, 12 pp.
Abstract: Context. The transiting exoplanetary system WASP-174 was reported to be composed by a main-sequence F star (V = 11.8 mag) and a giant planet, WASP-174b (orbital period P-orb = 4.23 days). However only an upper limit was placed on the planet mass (<1.3 M-Jup), and a highly uncertain planetary radius (0.7-1.7 R-Jup) was determined.Aims. We aim to better characterise both the star and the planet and precisely measure their orbital and physical parameters.Methods. In order to constrain the mass of the planet, we obtained new measurements of the radial velocity of the star and joined them with those from the discovery paper. Photometric data from the HATSouth survey and new multi-band, high-quality (precision reached up to 0.37 mmag) photometric follow-up observations of transit events were acquired and analysed for getting accurate photometric parameters. We fit the model to all the observations, including data from the TESS space telescope, in two different modes: incorporating the stellar isochrones into the fit, and using an empirical method to get the stellar parameters. The two modes resulted to be consistent with each other to within 2<sigma>.Results. We confirm the grazing nature of the WASP-174b transits with a confidence level greater than 5 sigma, which is also corroborated by simultaneously observing the transit through four optical bands and noting how the transit depth changes due to the limb-darkening effect. We estimate that approximate to 76% of the disk of the planet actually eclipses the parent star at mid-transit of its transit events. We find that WASP-174b is a highly-inflated hot giant planet with a mass of M-p = 0.330 +/- 0.091 M-Jup and a radius of R-p = 1.435 +/- 0.050 R-Jup, and is therefore a good target for transmission-spectroscopy observations. With a density of rho (p) = 0.135 +/- 0.042 g cm(-3), it is amongst the lowest-density planets ever discovered with precisely measured mass and radius.
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