Probing the Cloudy Sky of the Inflated Hot Jupiter WASP-13b with GIARPS at the TNG

A new study led by the GAPS (Global Architecture of Planetary Systems) collaboration has provided unprecedented observational constraints on the atmosphere of WASP-13b, an extremely low-density and inflated hot Jupiter orbiting a G1-type star every 4.35 days. Using the GIARPS observing mode at the Telescopio Nazionale Galileo (TNG), the team performed high-resolution transmission spectroscopy across multiple transits to search for atomic and molecular signatures in both the optical and near-infrared domains.

WASP-13b represents a fascinating laboratory for exoplanetary atmospheric physics. Due to its large radius and low mass, its atmosphere was expected to exhibit strong, extended spectral signatures. However, high-sensitivity cross-correlation techniques applied to the high-resolution optical spectra from HARPS-N and near-infrared spectra from GIANO-B revealed no statistically significant absorption signals from key atmospheric species, including H2O,CO, and sodium.

To interpret these non-detections, the authors conducted extensive injection-recovery tests and compared the data against physical atmospheric models. The results rule out clear, low-metallicity atmospheres and point towards the presence of a high-altitude cloud deck at the planet's terminator. These condensates effectively mute the spectral line contrasts, shielding the deeper atmospheric layers from view.

This work highlights the unique capability of GIARPS at the TNG to simultaneously probe exoplanetary atmospheres over a broad wavelength baseline (0.38 to 2.45µm). By placing tight upper limits on the atmospheric properties of WASP-13b, this study contributes a vital piece to the puzzle of low-density hot Jupiters, setting the stage for future characterization with space missions like Ariel and next-generation ground-based facilities such as ANDES at the ELT.

More details in the paper: https://doi.org/10.1093/mnras/stag1927

Cross-correlation maps obtained by using the dataset of N3 (left panels) and N4 (right panels), for the H2O and CO templates (using only the K band of GIANO-B for the CO), respectively. Top: Planes of Kp-Δ𝑣sys, in which a peak of cross-correlation is visible close to the expected planetary RV for both species but the signals are not sufficiently robust to be claimed as detections (see the text for more details). Bottom: Cross-correlation as a function of the orbital phase in the planet rest-frame. The dashed white (dash-dotted black) line represents the planet (stellar) RV. See paper for more details