Where is the Water? Jupiter-like C/H ratio but strong H$_2$O depletion found on $τ$ Boötis b using SPIRou

Stefan Pelletier; Björn Benneke; Antoine Darveau-Bernier; Anne Boucher; Neil J. Cook; Caroline Piaulet; Louis-Philippe Coulombe; Étienne Artigau; David Lafrenière; Simon Delisle; Romain Allart; René Doyon; Jean-François Donati; Pascal Fouqué; Claire Moutou; Charles Cadieux; Xavier Delfosse; Guillaume Hébrard; Jorge H. C. Martins; Eder Martioli; Thomas Vandal

doi:10.3847/1538-3881/ac0428

paper

Where is the Water? Jupiter-like C/H ratio but strong H $_{2}$ O depletion found on $τ$ Boötis b using SPIRou

arXiv:2105.10513 · doi:10.3847/1538-3881/ac0428

Abstract

The present-day envelope of gaseous planets is a relic of how these giant planets originated and evolved. Measuring their elemental composition therefore presents a powerful opportunity to answer long-standing questions regarding planet formation. Obtaining precise observational constraints on the elemental inventory of giant exoplanets has, however, remained challenging due to the limited simultaneous wavelength coverage of current space-based instruments. Here, we present thermal emission observations of the non-transiting hot Jupiter $τ$ Boo b using the new wide wavelength coverage (0.95 $-$ 2.50 $μ$ m) and high spectral resolution ( $R = 70000$ ) SPIRou spectrograph. By combining a total of 20 hours of SPIRou data obtained over five nights in a full atmospheric retrieval framework designed for high-resolution data, we constrain the abundances of all the major oxygen- and carbon-bearing molecules and recover a non-inverted temperature structure using a new free-shape, nonparametric TP profile retrieval approach. We find a volume mixing ratio of log(CO) $= - 2.4 6_{- 0.29}^{+ 0.25}$ and a highly depleted water abundance of less than $0.0072$ times the value expected for a solar composition envelope. Combined with upper limits on the abundances of CH $_{4}$ , CO $_{2}$ , HCN, TiO, and C $_{2}$ H $_{2}$ , this results in a gas-phase C/H ratio of 5.85 $_{- 2.82}^{+ 4.44} \times$ solar, consistent with the value of Jupiter, and an envelope C/O ratio robustly greater than 0.60, even when taking into account the oxygen that may be sequestered out of the gas-phase. Combined, the inferred super-solar C/H, O/H, and C/O ratios on $τ$ Boo b support a formation scenario beyond the water snowline in a disk enriched in CO due to pebble drift.

27 pages, 14 figures, 3 tables, Accepted for publication in The Astronomical Journal

Where is the Water? Jupiter-like C/H ratio but strong H $_{2}$ O depletion found on $τ$ Boötis b using SPIRou

Abstract

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Where is the Water? Jupiter-like C/H ratio but strong H2​O depletion found on τ Boötis b using SPIRou

Abstract

References in corpus (59)

Cited by in corpus (65)

Where is the Water? Jupiter-like C/H ratio but strong H $_{2}$ O depletion found on $τ$ Boötis b using SPIRou