Paper

The GAPS Programme at TNG LV. Multiple molecular species in the atmosphere of HAT-P-11 b and review of the HAT-P-11 planetary system

Brogi, M, Pedani, M, Molinaro, M, Southworth, J, Ghedina, A, Damasso, M, Molinari, E, Mainella, G, Micela, G, Giacobbe, P, Borsa, F, Maggio, A, A Di Paola, Desidera, S, Cabona, L, Poretti, E, Stangret, M, Turrini, D, Scandariato, G, Pino, L, Guilluy, G, Lanza, A F, Mancini, L, Singh, V, Sozzetti, A, Bignamini, A, Bonomo, A S, Biazzo, K, Cubillos, P E, Basilicata, M, Nardiello, D, Carleo, I

2024

Overview

The atmospheric characterisation of hot and warm Neptune-size exoplanets is challenging due to their small radius and atmospheric scale height. The warm-Neptune HAT-P-11b is a remarkable target for such characterisation due to the large brightness of its host star (V=9.46 mag; H=7.13 mag). The aims of this work are to review the main physical and architectural properties of the HAT-P-11 planetary system, and to probe the presence of 8 molecular species in the atmosphere of HAT-P-11b at high spectral resolution in the near-infrared. The planetary system was reviewed by analysing transits and occultations of HAT-P-11b from the Kepler data set as well as HIRES at Keck archival radial-velocity (RV) data. We modelled the latter with Gaussian-process regression and a combined quasi-periodic and squared-exponential kernel to account for stellar variations on both (short-term) rotation and (long-term) activity-cycle timescales. In order to probe the atmospheric composition of HAT-P-11b, we observed 4 transits of this target with GIANO-B at TNG. We find that the long-period (\\(P\\sim9.3\\) years) RV signal previously attributed to planet HAT-P-11c is more likely due to the stellar magnetic activity cycle. Nonetheless, the Hipparcos-Gaia difference in the proper-motion anomaly suggests that an outer-bound companion might still exist. For HAT-P-11b, we measure a radius \\(R_{\\rm p}=0.4466\\pm0.0059\\,R_{\\rm J}\\), a mass \\(M_{\\rm p}=0.0787\\pm0.0048\\,M_{\\rm J}\\), and an eccentricity \\(e=0.2577^{+0.0033}_{-0.0025}\\), in accordance with values in the literature. Probing its atmosphere, we detect \\(NH_3\\) (S/N\\(=5.3\\), significance\\(=5.0\\sigma\\)) and confirm the presence of \\(H_2O\\) (S/N\\(=5.1\\), significance\\(=3.4\\sigma\\)). We also tentatively detect the signal of \\(CO_2\\) (S/N\\(=3.0\\), significance\\(=3.2\\sigma\\)) and \\(CH_4\\) (S/N\\(=4.8\\), significance\\(=2.6\\sigma\\)), whose presence need to be confirmed by further observations.

• Publisher: Cornell University Library, arXiv.org
• Subject: Atmosphere / Atmospheric composition / Extrasolar planets / Gas giant planets / Gaussian process / Infrared analysis / Planetary systems / Scale height / Spectral resolution