Exoplanet atmospheres with GIANO

Abstract

Context. High-resolution spectroscopy (R ≥ 20 000) at near-infrared wavelengths can be used to investigate the composition, structure, and circulation patterns of exoplanet atmospheres. However, up to now it has been the exclusive dominion of the biggest telescope facilities on the ground, due to the large amount of photons necessary to measure a signal in high-dispersion spectra. Aims. Here we show that spectrographs with a novel design – in particular a large spectral range – can open exoplanet characterisation to smaller telescope facilities too. We aim to demonstrate the concept on a series of spectra of the exoplanet HD 189 733 b taken at the Telescopio Nazionale Galileo with the near-infrared spectrograph GIANO during two transits of the planet. Methods. In contrast to absorption in the Earth’s atmosphere (telluric absorption), the planet transmission spectrum shifts in radial velocity during transit due to the changing orbital motion of the planet. This allows us to remove the telluric spectrum while preserving the signal of the exoplanet. The latter is then extracted by cross-correlating the residual spectra with template models of the planet atmosphere computed through line-by-line radiative transfer calculations, and containing molecular absorption lines from water and methane. Results. By combining the signal of many thousands of planet molecular lines, we confirm the presence of water vapour in the atmosphere of HD 189 733 b at the 5.5σ level. This signal was measured only in the first of the two observing nights. By injecting and retrieving artificial signals, we show that the non-detection on the second night is likely due to an inferior quality of the data. The measured strength of the planet transmission spectrum is fully consistent with past CRIRES observations at the VLT, excluding a strong variability in the depth of molecular absorption lines.

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

“…We first compute a rough detection significance (sometimes referred to as signal-to-noise rather than detection significance, e.g. Brogi et al 2018) by dividing the map through by its standard deviation taken from a K p of 150 to 250 km/s and a v sys from -120 to -40 and 40 to -120 km/s, i.e avoiding the peak of the cross-correlation map and zero K p (where we expect slightly different noise properties). This results in a detection significance of 9.2 σ, with no other significant peaks present in the CCF map, although the exact detection significance will slightly vary with the (arbitrarily chosen) noise regions.…”

Detection of neutral atomic species in the ultra-hot Jupiter WASP-121b

“…We can search for these species by cross-correlating with a model transmission spectrum, which stacks the signal from all of the absorption lines. This approach has been used successfully in the optical regime (Nugroho et al 2017;Hoeijmakers et al 2018Hoeijmakers et al , 2019, as well as the near-infrared (Snellen et al 2010;Brogi et al 2012;Rodler et al 2013;Lockwood et al 2014;Birkby et al 2013;Piskorz et al 2016;Birkby et al 2017;Brogi et al 2018;Hawker et al 2018). We use the X-COR pipeline, which was previously used to detect CO, H 2 O, and HCN in the dayside atmospheres of hot Jupiters (Hawker et al 2018;Cabot et al 2019).…”

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.…”