Exoplanets, -moons, -comets

Studying The Variability Of The He Triplet To Understand The Detection Limits Of Evaporating Exoplanet Atmospheres

By Keith Cowing
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astro-ph.EP
July 31, 2025
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Studying The Variability Of The He Triplet To Understand The Detection Limits Of Evaporating Exoplanet Atmospheres
Time series of atmospheric temperature and He column density for the observation day January 26, 2023. Blue and gray points represent the 20x binned and unbinned best-fit planetary parameters obtained from fitting the planetary absorption spectra as described in Sect. 3.3.2. The red line marks the weighted average of each retrieved parameter and the orange band represents the 1 σ region around this average. The black line shows the input values used in the simulation. We provide axes for the width in km/s and depth in % to facilitate the understanding of the analogy between temperature and width, and column density and depth. — astro-ph.EP

With more than a dozen significant detections, the helium triplet has emerged as a key tracer of evaporating exoplanet atmospheres.

This near-infrared feature can be observed from the ground and holds great promise, especially with upcoming observations provided by new-generation instruments such as the Near Infrared Planet Searcher (NIRPS).

However, as the helium triplet is also present in stellar spectra, careful removal of the average stellar contribution is necessary to accurately characterize the atmospheres of transiting exoplanets.

In this study, we analyze multi-epoch observations of the Sun obtained with NIRPS to investigate the temporal variability of the helium triplet. Our findings reveal significant variability across different timescales, ranging from minutes to days.

We identify telluric contamination and stellar activity as likely sources for the short-term and long-term variability, respectively. Importantly, we demonstrate that this variability has minimal impact on the retrieval of planetary parameters crucial to the study of atmospheric escape.

Samson J. Mercier, Xavier Dumusque, Vincent Bourrier, Khaled Al Moulla, Michael Cretignier, William Dethier, Gaspare Lo Curto, Pedro Figueira, Christophe Lovis, Francesco Pepe, Nuno C. Santos, Stéphane Udry, François Wildi, Romain Allart, Frédérique Baron, François Bouchy, Andres Carmona, Marion Cointepas, René Doyon, Yolanda Frensch, Nolan Grieves, Lucile Mignon, Louise D. Nielsen

Comments: 16 pages, including 10 figures and 3 tables. Submitted 04 November 2024 and accepted 15 January 2025 to Astronomy & Astrophysics (A&A)
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2507.21290 [astro-ph.EP] (or arXiv:2507.21290v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2507.21290
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Related DOI:
https://doi.org/10.1051/0004-6361/202452856
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Submission history
From: Samson Mercier
[v1] Mon, 28 Jul 2025 19:24:49 UTC (30,936 KB)
https://arxiv.org/abs/2507.21290
Astrobiology,

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

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