The GAPS Programme at TNG

Abstract

Aims. We present a novel method for studying the thermal emission of exoplanets as a function of orbital phase at very high spectral resolution, and use it to investigate the climate of the ultra-hot Jupiter KELT-9b. Methods. We combine three nights of HARPS-N and two nights of CARMENES optical spectra, covering orbital phases between quadratures (0.25 < ϕ < 0.75), when the planet shows its day-side hemisphere with different geometries. We co-add the signal of thousands of Fe i lines through cross-correlation, which we map to a likelihood function. We investigate the phase-dependence of two separate observable quantities, namely (i) the line depths of Fe i and (ii) their Doppler shifts, introducing a new method that exploits the very high spectral resolution of our observations. Results. We confirm a previous detection of Fe i emission, and demonstrate a precision of 0.5 km s −1 on the orbital properties of KELT-9b when combining all nights of observations. By studying the phase-resolved Doppler shift of Fe i lines, we detect an anomaly in the planet's orbital radial velocity well-fitted with a slightly eccentric orbital solution (e = 0.016 ± 0.003, ω = 150 +13 • −11 , 5σ preference). However, we argue that this anomaly is caused by atmospheric circulation patterns, and can be explained if neutral iron gas is advected by day-to-night atmospheric wind flows of the order of a few km s −1 . We additionally show that the Fe i emission line depths are symmetric around the substellar point within 10 • (2σ), possibly indicating the lack of a large hot-spot offset at the altitude probed by neutral iron emission lines. Finally, we do not obtain a significant preference for models with a strong phase-dependence of the Fe i emission line strength. We show that these results are qualitatively compatible with predictions from general circulation models (GCMs) for ultra-hot Jupiter planets. Conclusions. Very high-resolution spectroscopy phase curves are of sufficient sensitivity to reveal a phase dependence in both the line depths and their Doppler shifts throughout the orbit. They constitute an under-exploited treasure trove of information that is highly complementary to space-based phase curves obtained with HST and JWST, and open a new window onto the still poorly understood climate and atmospheric structure of the hottest planets known to date.

High-resolution Emission Spectroscopy of the Ultrahot Jupiter KELT-9b: Little Variation in Day- and Nightside Emission Line Contrasts

“…However, as the evidence for Ca II emission is only at the 3.1σ level, this interpretation should be confirmed with additional observations. We robustly detected neutral iron in emission, confirming the previous detections of Fe I emission at high resolution by Pino et al (2020Pino et al ( , 2022 and Kasper et al (2021).…”

“…We robustly detected neutral iron in emission, confirming the previous detections of Fe I emission at highresolution by Pino et al (2020Pino et al ( , 2022 and Kasper et al (2021).…”

“…For TiO they find an upper limit on the volume mixing ratio of 10 −8.5 , which is inconsistent with the detection reported by Changeat & Edwards (2021). Pino et al (2022) also studied KELT-9b's Fe I emission with phase-resolved high-resolution spectra from HARPS-N and CARMENES. Their analysis of the Fe I emission's Doppler shifts as a function of the orbital phase revealed a radial velocity anomaly that is likely explained by KELT-9b's atmospheric circulation patterns.…”

“…To better understand KELT-9b's atmosphere, we observed partial phase curves using CARMENES 1 and searched for emission from several species, including those previously detected in transmission. Our observations found evidence for emission by Ca II, Mg I, and 1 Some of these data were also used in Pino et al (2022).…”

Magnetic Effects and 3D Structure in Theoretical High-resolution Transmission Spectra of Ultrahot Jupiters: the Case of WASP-76b

“…Due to the level of precision offered by HRS (and the fact that planets are multidimensional objects), three-dimensional (3D) atmospheric models are ideal for interpreting these spectra. Previous work has found that not only do 3D effects show up in high-resolution transmission (Louden & Wheatley 2015;Flowers et al 2019) and emission (Herman et al 2022;Pino et al 2022;van Sluijs et al 2023) spectra, but detection strengths can increase when using spectra generated from a 3D model compared to 1D models (Beltz et al 2021). Typically the 3D structure of exoplanet atmospheres are simulated with general circulation models (GCMs).…”