GIANO-B allows to conduct a detailed HeI survey of close-in giant planets hosted by M-K dwarf stars

Exoplanets orbiting very close to their host stars are strongly irradiated. This can cause the upper layers of their atmospheres to expand and potentially evaporate. Atmospheric escape plays a pivotal role in determining the characteristics of these exoplanets. The metastable near-infrared (nIR) helium triplet at 1083.3 nm (HeI) serves as a powerful indicator of extended and evaporating atmospheres.
The Italian researchers from the GAPS collaboration (Global Architecture of Planetary Systems) searched helium absorption in the upper atmospheres of five close-in giant planets orbiting K and M dwarf stars within the GAPS-ATMO (the atmospheric package of the GAPS project) sample. This survey includes five planets: the warm Saturn WASP-69 b, the super Neptune WASP-107 b, and the warm Neptunes HAT-P-11 b, GJ 436 b, and GJ 3470 b.

They utilized the Telescopio Nazionale Galileo in the GIARPS (GIANO-B + HARPS-N) observing mode and employed the 'transmission spectroscopy' technique. This method involves comparing the out-of-transit observations (the stellar spectrum without the planetary contribution) with the in-transit observations (the combined stellar and planetary spectrum). By doing so, it enables the potential detection of signals originating from the planetary atmosphere. As the dataset under investigation includes multiple observing nights for each target, the researchers were able to examine nightly variability. Astronomers explored the potential impact of stellar magnetic activity on the true planetary absorption signal by examining variations in the Hα transmission spectrum (in the visible HARPS-N range). The He I and Hα diagnostics display indeed opposite behaviours in response to stellar activity

Astronomers spectrally resolved the He I triplet and confirmed the previously published detections for 4 of the 5 planets with different measured contrast of the excess absorption. However, GJ 436 b did not exhibit evidence of additional He absorption. For WASP-69 b the researchers observed night-to-night variations in the He I absorption signal which were correlated with changes in Hα, likely indicating the influence of pseudo-signals associated with stellar activity. Furthermore, their findings suggested that the He I signal of GJ 3470 b originated from a single transit observation, thus confirming inconsistencies reported in previous literature. Examination of the Hα line revealed an absorption signal during the same transit event.

Finally, the authors placed their results in the context of previous GIANO-B He I measurements of planets orbiting K dwarfs and examined potential trends with planetary and stellar parameters believed to influence the absorption of metastable He I. However, the analysis did not reveal clear patterns, highlighting the need for further measurements and exploration of additional parameters that may play a crucial role in regulating He I absorption in planetary upper atmospheres.

Link to the paper.

Known exoplanets as a function of their radius and period from the NASA Exoplanet Archive (Akeson et al. 2013). Targets analysed in this work are highlighted. The marker colour reflects the HeI absorption signal we found in this work.
The transmission spectra centred on the HeI triplet (in the planet rest frame) after removing the Gaussian process model are overplotted. For each target, different colours refer to the different visits, while the black points show the weighted average over the observations. See fig. 1 and 5 of the paper for more information.