Planet(esimal)s Around Stars with TESS (PAST) III: A Search for Triplet He I in the Atmospheres of Two 200 Myr-old Planets

Abstract

We report a search for excess absorption in the 1083.2 nm line of ortho (triplet) helium during transits of TOI-1807b and TOI-2076b, 1.25 and 2.5R${}_{\mathrm{Earth}}$ planets on 0.55- and 10.4-day orbits around nearby $\sim$200~Myr-old K dwarf stars. We limit the equivalent width of any transit-associated absorption to $<$4 and $<$8 mA, respectively. We limit the escape of solar-composition atmospheres from TOI-1807b and TOI-2076b to $\lesssim$1 and $\lesssim$0.1M${}_{\mathrm{Earth}}$ Gyr${}^{-1}$, respectively, depending on wind temperature. The absence of a H/He signature for TOI-1807b is consistent with a measurement of mass indicating a rocky body and the prediction by a hydrodynamic model that any H-dominated atmosphere would be unstable and already have been lost. Differential spectra obtained during the transit of TOI-2076b contain a He I-like feature, but this closely resembles the stellar line and extends beyond the transit interval. Until additional transits are observed, we suspect this to be the result of variation in the stellar He I line produced by rotation of active regions and/or flaring on the young, active host star. Non-detection of escape could mean that TOI-2076b is more massive than expected, the star is less EUV-luminous, the models overestimate escape, or the planet has a H/He-poor atmosphere that is primarily molecules such as H${}_2$O. Photochemical models of planetary winds predict a semi-major axis at which triplet He I observations are most sensitive to mass loss: TOI-2076b orbits near this optimum. Future surveys could use a distance criterion to increase the yield of detections.

Accepted to MNRAS

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Cited by in corpus (15)

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• DREAM: III.A helium survey in exoplanets on the edge of the hot Neptune desert with GIANO-B@TNG
• On the origin of the non-detection of metastable HeI in the upper atmosphere of the hot Jupiter WASP-80b
• The open-source sunbather code: modeling escaping planetary atmospheres and their transit spectra
• Confirmation of an He I evaporating atmosphere around the 650-Myr-old sub-Neptune HD235088 b (TOI-1430 b) with CARMENES
• Probing atmospheric escape through metastable He I triplet lines in 15 exoplanets observed with SPIRou
• NEID Reveals that The Young Warm Neptune TOI-2076 b Has a Low Obliquity
• Non-detection of Helium in the Hot Jupiter WASP-48b
• Helium in Exoplanet Exospheres: Orbital and Stellar Influences
• Evolution of helium triplet transits of close-in gas giants orbiting K-dwarfs
• The GAPS Programme at TNG. LXV. Precise density measurement of TOI-1430 b, a young planet with an evaporating atmosphere
• The GAPS Programme at TNG. LIX. A characterisation study of the $\sim$300 Myr old multi-planetary system orbiting the star BD+40 2790 (TOI-2076)
• The effects of stellar activity cycles on planetary atmospheric escape and the HeI 1083nm transit signature