Abstract
Recent observations of the ultra-hot Jupiter WASP-76b have revealed a
diversity of atmospheric species. Here we present new high-resolution
transit spectroscopy of WASP-76b with GRACES at the Gemini North
Observatory, serving as a baseline for the Large and Long Program
"Exploring the Diversity of Exoplanet Atmospheres at High Spectral
Resolution" (Exoplanets with Gemini Spectroscopy, or ExoGemS for short).
With a broad spectral range of 400-1050 nm, these observations allow us
to search for a suite of atomic species. We recover absorption features
due to neutral sodium (Na I), and report a new detection of the ionized
calcium (Ca II) triplet at ~850 nm in the atmosphere of WASP-76b,
complementing a previous detection of the Ca II H and K lines. The
triplet has line depths of 0.295% ± 0.034% at ~849.2 nm, 0.574%
± 0.041% at ~854.2 nm, and 0.454% ± 0.024% at ~866.2 nm,
corresponding to effective radii close to (but within) the planet's
Roche radius. These measured line depths are significantly larger than
those predicted by model LTE and NLTE spectra obtained on the basis of a
pressure-temperature profile computed assuming radiative equilibrium.
The discrepancy suggests that the layers probed by our observations are
either significantly hotter than predicted by radiative equilibrium
and/or in a hydrodynamic state. Our results shed light on the exotic
atmosphere of this ultra-hot world, and will inform future analyses from
the ExoGemS survey.
Original language | English |
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Article number | L15 |
Journal | The Astrophysical Journal Letters |
Volume | 919 |
Issue number | 2 |
Early online date | 28 Sept 2021 |
DOIs | |
Publication status | Published - 01 Oct 2021 |
Keywords
- Exoplanet atmospheres
- Transmission spectroscopy
- Hot Jupiters
- High resolution spectroscopy
- Optical astronomy
- Exoplanet atmospheric composition
- Exoplanet atmospheric variability
- Transits