Exoplanet atmospheres with GIANO

Abstract

Context. The study of exoplanetary atmospheres is key to understanding the differences between their physical, chemical, and dynamical processes. Until now, the bulk of atmospheric characterization analyses have been conducted on transiting planets. On a number of sufficiently bright targets, high-resolution spectroscopy (HRS) has also been successfully tested for nontransiting planets mainly by using spectrographs mounted on 8 and 10 m class ground-based telescopes. Aims. The aim of this analysis is to study the dayside of the nontransiting planet HD 102195b using the GIANO spectrograph mounted at the Telescopio Nazionale Galileo (TNG), and thereby demonstrate the feasibility of atmospheric characterization measurements. In particular, we wish to demonstrate the possibility of molecular detection with the HRS technique for nontransiting planets using 4 m class telescopes. Methods. Our data-analysis technique exploits the fact that the Doppler-shifted planetary signal changes on the order of many kilometers per second during the observations, in contrast with the telluric absorption which is stationary in wavelength. This allows us to effectively remove the contamination from telluric lines in the GIANO spectra while preserving the features of the planetary spectrum. The emission signal from the atmosphere of HD 102195b is then extracted by cross-correlating the residual GIANO spectra with models of the planetary atmosphere. Results. We detect molecular absorption from water vapor at the 4.4σ level of statistical significance. We also find convincing evidence for the presence of methane, which is detected at the 4.1σ level. This is the first detection of methane obtained with the HRS technique. The two molecules are detected with a combined significance of 5.3σ, at a semi-amplitude of the planet radial velocity KP = 128 ± 6 km s−1. We estimate a true planet mass of MP = 0.46 ± 0.03 MJ and constrain the orbital inclination in the range 72.5° < i < 84.79° (1σ). Our analysis indicates a noninverted atmosphere for HD 102195b. This is expected given the relatively low temperature of the planet, inefficient to keep TiO/VO in gas phase. Moreover, a comparison with theoretical model expectations corroborates our detection of methane, and a cursory confrontation with chemical model predictions published in the literature suggests that the detected methane and water signatures could be consistent with a low C/O ratio for HD 102195b. Finally, as HD 102195 is one to three magnitudes fainter in the K-band than the nontransiting systems studied until now with 8 m telescopes, our study opens up the possibility for atmospheric characterization of a larger sample of exoplanets.

HyDRA-H: Simultaneous Hybrid Retrieval of Exoplanetary Emission Spectra

“…Secondly, a wealth of high-resolution observations is expected with the commissioning of CRIRES+ at the VLT (Follert et al 2014) as well as other high throughput instruments such as CARMENES (Quirrenbach et al 2014). The use of smaller telescopes with high throughput spectrographs such as GI-ANO has been shown to prove fruitful in HRS exoplanet spectroscopy (Brogi et al 2018;Guilluy et al 2019). Hybrid retrieval methods exploiting synergies between high and low-resolution data will be vital in fully exploiting the high-resolution spectra obtained with these facilities.…”

Detection of Fe i in the atmosphere of the ultra-hot Jupiter WASP-121b, and a new likelihood-based approach for Doppler-resolved spectroscopy

“…This technique has so far confirmed the presence of molecules such as CO, H 2 O, TiO, HCN, CH 4 and atomic species such as Fe, Ti, Mg and Ca (e.g. Snellen et al 2010;Brogi et al 2012;Birkby et al 2013;Nugroho et al 2017;Hoeijmakers et al 2019;Hawker et al 2018;Guilluy et al 2019;Turner et al 2019;Yan et al 2019). For a recent review see Birkby (2018).…”

Biosignatures Search in Habitable Planets

“…A detailed review of the high spectral dispersion Doppler correlation technique for characterize the planet atmospheres is given in Birkby [160]. So far, this technique was applied with success to hot Jupiter and other giant planets, transiting or not (e.g., [161][162][163][164][165][166][167][168]) and has provided some upper limits on mini-Neptune and super-Earth atmospheres [169,170].…”