Homogeneous search for helium in the atmosphere of 11 gas giant exoplanets with SPIRou

TL;DR

This study uses high-resolution spectroscopy with SPIRou to detect and analyze metastable helium in the atmospheres of 11 gas giant exoplanets, confirming some previous detections and setting new constraints on atmospheric escape.

Contribution

It provides a homogeneous analysis of helium in diverse exoplanets, confirming some detections, setting upper limits, and highlighting the need for larger, repeatable studies for robust conclusions.

Findings

Confirmed helium detections in HAT-P-11b, HD189733b, and WASP-69b.

Set upper limits on helium and mass-loss rates for non-detections.

Demonstrated correlation between helium presence and stellar XUV flux.

Abstract

The metastable helium triplet in the near-infrared (10833{\AA}) is among the most important probes of exoplanet atmospheres. It can trace their extended outer layers and constrain mass-loss. We use the near-infrared high-resolution spectropolarimeter SPIRou on the CFHT to search for the spectrally resolved helium triplet in the atmospheres of eleven exoplanets, ranging from warm mini-Neptunes to hot Jupiters and orbiting G, K, and M dwarfs. Observations were obtained as part of the SPIRou Legacy Survey and complementary open-time programs. We apply a homogeneous data reduction to all datasets and set constraints on the presence of metastable helium, despite the presence of systematics in the data. We confirm published detections for HAT-P-11b, HD189733b, and WASP-69b and set upper limits for the other planets. We apply the p-winds open source code to set upper limits on the mass-loss rate for the non-detections and to constrain the thermosphere temperature, mass-loss rate, line-of-sight velocity, and the altitude of the thermosphere for the detections. We confirm that the presence of metastable helium correlates with the stellar mass and the XUV flux received by the planets. We investigated the correlation between the mass-loss rate and the presence of metastable helium, but it remains difficult to draw definitive conclusions. Finally, some of our results are in contradiction with previous results in the literature, therefore we stress the importance of repeatable, homogeneous, and larger-scale analyses of the helium triplet to obtain robust statistics, study temporal variability, and better understand how the helium triplet can be used to explore the evolution of exoplanets.