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Carone, L., Molliere, P., Zhou, Y. F., Bouwman, J., Yan, F., Baeyens, R., et al. (2021). Indications for very high metallicity and absence of methane in the eccentric exo-Saturn WASP-117b. Astron. Astrophys., 646, A168.
Abstract: Aims. We investigate the atmospheric composition of the long-period (P-orb = 10 days) eccentric exo-Saturn WASP-117b. WASP-117b could be similar in atmospheric temperature and chemistry to WASP-107b. In mass and radius, WASP-117b is similar to WASP-39b, which allows a comparative study of these planets.Methods. We analyzed a near-infrared transmission spectrum of WASP-117b taken with the Hubble Space Telescope (HST) WFC3 G141, which was reduced with two independent pipelines. High-resolution measurements were taken with VLT/ESPRESSO in the optical.Results. We report the robust (3 sigma) detection of a water spectral feature. In a 1D atmosphere model with isothermal temperature, uniform cloud deck, and equilibrium chemistry, the Bayesian evidence of a retrieval analysis of the transmission spectrum indicates a preference for a high atmospheric metallicity
[Fe/H] = 2.58(-0.37)(+0.26)
[Fe/H]=2.58-0.37+0.26 and clear skies. The data are also consistent with a lower metallicity composition [Fe/H] < 1.75 and a cloud deck between 10(-2.2) and 10(-5.1) bar, but with weaker Bayesian preference. We retrieve a low CH4 abundance of <10(-4) volume fraction within 1 sigma and <2 x 10(-1) volume fraction within 3<sigma>. We cannot constrain the equilibrium temperature between theoretically imposed limits of 700 and 1000 K. Further observations are needed to confirm quenching of CH4 with K-zz >= 10(8) cm(2) s(-1). We report indications of Na and K in the VLT/ESPRESSO high-resolution spectrum with substantial Bayesian evidence in combination with HST data.
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Christie, D. A., E.K.H., Innes, H., Noti, P. A., Charnay, B., Fauchez, T. J., et al. (2022). CAMEMBERT: A Mini-Neptunes General Circulation Model Intercomparison, Protocol Version 1.0.A CUISINES Model Intercomparison Project. Planet. Sci., 3(11), 261.
Abstract: With an increased focus on the observing and modeling of mini-Neptunes, there comes a need to better understand the tools we use to model their atmospheres. In this Paper, we present the protocol for the Comparing Atmospheric Models of Extrasolar Mini-Neptunes Building and Envisioning Retrievals and Transits, CAMEMBERT, project, an intercomparison of general circulation models (GCMs) used by the exoplanetary science community to simulate the atmospheres of mini-Neptunes. We focus on two targets well studied both observationally and theoretically with planned JWST cycle 1 observations: the warm GJ 1214b and the cooler K2-18b. For each target, we consider a temperature-forced case, a clear sky dual-gray radiative transfer case, and a clear sky multiband radiative transfer case, covering a range of complexities and configurations where we know differences exist between GCMs in the literature. This Paper presents all the details necessary to participate in the intercomparison, with the intention of presenting the results in future papers. Currently, there are eight GCMs participating (ExoCAM, Exo-FMS, FMS PCM, Generic PCM, MITgcm, RM-GCM, THOR, and the Unified Model), and membership in the project remains open. Those interested in participating are invited to contact the authors.
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Schlecker, M., Kossakowski, D., Brahm, R., Espinoza, N., Henning, T., Carone, L., et al. (2020). A highly eccentric warm jupiter orbiting TIC 237913194. Astron. J., 160(6), 275.
Abstract: The orbital parameters of warm Jupiters serve as a record of their formation history, providing constraints on formation scenarios for giant planets on close and intermediate orbits. Here, we report the discovery of TIC.237913194b, detected in full-frame images from Sectors 1 and 2 of the Transiting Exoplanet Survey Satellite (TESS), ground-based photometry (Chilean-Hungarian Automated Telescope, Las Cumbres Observatory Global Telescope), and Fiber-fed Extended Range Optical Spectrograph radial velocity time series. We constrain its mass to M-P = 1.942(-0.091)(+0.091) M-J and its radius to R-P = 1.117(-0.047)(+0.054) R-J, implying a bulk density similar to Neptune's. It orbits a G-type star (M-* = 1.026(-0.055)(+0.057) M-circle dot, V = 12.1 mag) with a period of 15.17 days on one of the most eccentric orbits of all known warm giants (e approximate to 0.58). This extreme dynamical state points to a past interaction with an additional, undetected massive companion. A tidal evolution analysis showed a large tidal dissipation timescale, suggesting that the planet is not a progenitor for a hot Jupiter caught during its high-eccentricity migration. TIC.237913194b further represents an attractive opportunity to study the energy deposition and redistribution in the atmosphere of a warm Jupiter with high eccentricity.
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Yan, F., Espinoza, N., Molaverdikhani, K., Henning, T., Mancini, L., Mallonn, M., et al. (2020). LBT transmission spectroscopy of HAT-P-12b: Confirmation of a cloudy atmosphere with no significant alkali features. Astron. Astrophys., 642, 13 pp.
Abstract: The hot sub-Saturn-mass exoplanet HAT-P-12b is an ideal target for transmission spectroscopy because of its inflated radius. We observed one transit of the planet with the multi-object double spectrograph (MODS) on the Large Binocular Telescope (LBT) with the binocular mode and obtained an atmosphere transmission spectrum with a wavelength coverage of similar to 0.4-0.9 μm. The spectrum is relatively flat and does not show any significant sodium or potassium absorption features. Our result is consistent with the revised Hubble Space Telescope (HST) transmission spectrum of a previous work, except that the HST result indicates a tentative detection of potassium. The potassium discrepancy could be the result of statistical fluctuation of the HST dataset. We fit the planetary transmission spectrum with an extensive grid of cloudy models and confirm the presence of high-altitude clouds in the planetary atmosphere. The fit was performed on the combined LBT and HST spectrum, which has an overall wavelength range of 0.4-1.6 μm. The LBT/MODS spectrograph has unique advantages in transmission spectroscopy observations because it can cover a wide wavelength range with a single exposure and acquire two sets of independent spectra simultaneously.
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