Constraints on Metastable Helium in the Atmospheres of WASP-69b and WASP-52b with Ultranarrowband Photometry

Abstract

Infrared observations of metastable 2 3 S helium absorption with ground-and space-based spectroscopy are rapidly maturing, as this species is a unique probe of exoplanet atmospheres. Specifically, the transit depth in the triplet feature (with vacuum wavelengths near 1083.3 nm) can be used to constrain the temperature and mass-loss rate of an exoplanet's upper atmosphere. Here, we present a new photometric technique to measure metastable 2 3 S helium absorption using an ultranarrowband filter (FWHM 0.635 nm) coupled to a beam-shaping diffuser installed in the Wide-field Infrared Camera on the 200 inch Hale Telescope at Palomar Observatory. We use telluric OH lines and a helium arc lamp to characterize refractive effects through the filter and to confirm our understanding of the filter transmission profile. We benchmark our new technique by observing a transit of WASP-69b and detect an excess absorption of 0.498%±0.045% (11.1σ), consistent with previous measurements after considering our bandpass. We then use this method to study the inflated gas giant WASP-52b and place a 95th percentile upper limit on excess absorption in our helium bandpass of 0.47%. Using an atmospheric escape model, we constrain the massloss rate for WASP-69b to be-+-M 5.25 10 Gyr 0.46

Nondetection of Helium in the Upper Atmospheres of Three Sub-Neptune Exoplanets

“…Our observations target the 10833 Å He triplet feature, which has recently emerged as a way to probe the escaping atmospheres of larger planets (Allart et al 2018(Allart et al , 2019Kreidberg & Oklopčić 2018;Mansfield et al 2018;Nortmann et al 2018;Salz et al 2018;Spake et al 2018;Alonso-Floriano et al 2019;dos Santos et al 2020;Gaidos et al 2020;Kirk et al 2020;Ninan et al 2020;Palle et al 2020;Vissapragada et al 2020). The He triplet feature arises from a metastable transition.…”

Metastable Helium Absorptions with 3D Hydrodynamics and Self-consistent Photochemistry. I. WASP-69b, Dimensionality, X-Ray and UV Flux Level, Spectral Types, and Flares

“…We synthesize both the transmission line profiles (Nortmann et al 2018) and the narrowband light curves (Vissapragada et al 2020) of He * transitions using our simulations. At each wavelength λ and a particular orbital phase, the optical depth along a line of sight (LOS) is given by where we have transformed from our planet-centered coordinate systems in the simulations to a star-centered coordinate system for the synthetic observations.…”

“…The result is a transit light curve near the He * transitions. In this work, we use the bandpass function provided by Vissapragada et al (2020) for a direct comparison with their results.…”

“…Notably, Nortmann et al (2018) reported an asymmetric transit profile characterized by a longer-thanexpected egress that could be caused by a comet-like tail associated with the mass loss. However, Vissapragada et al (2020) suggest a symmetric shape of transit using bettersampled light curves with higher precision and signal-to-noise ratio. Another interesting point about WASP-69b is the apparent temporal variability of the He * transit depth seen in Nortmann et al (2018).…”

“…By the time of the writing this paper, several close-in exoplanets have transmission He * line profiles resolved by ground-based spectrographs (e.g., Allart et al 2018;Nortmann et al 2018;Salz et al 2018;Kirk et al 2020;Ninan et al 2020). More recently, Vissapragada et al (2020) made a narrowband filter specifically for the He * transitions on the diffuser-based photometric system on Palomar/WIRC. The resultant precise light curves of He * are complementary to the line profiles from the near-infrared spectrographs.…”