A Search for Water in the Atmosphere of HAT-P-26b Using LDSS-3C

TL;DR

This study uses advanced ground-based and space telescopes to detect water vapor in the atmosphere of exoplanet HAT-P-26b, providing insights into its atmospheric composition and structure.

Contribution

It demonstrates the effectiveness of LDSS-3C combined with Spitzer data in detecting atmospheric water vapor and constrains the planet's atmospheric properties.

Findings

Evidence of water vapor in HAT-P-26b's atmosphere

Absence of potassium in the spectrum

Degeneracy between high-metallicity and cloud deck scenarios

Abstract

The characterization of a physically-diverse set of transiting exoplanets is an important and necessary step towards establishing the physical properties linked to the production of obscuring clouds or hazes. It is those planets with identifiable spectroscopic features that can most effectively enhance our understanding of atmospheric chemistry and metallicity. The newly-commissioned LDSS-3C instrument on Magellan provides enhanced sensitivity and suppressed fringing in the red optical, thus advancing the search for the spectroscopic signature of water in exoplanetary atmospheres from the ground. Using data acquired by LDSS-3C and the Spitzer Space Telescope, we search for evidence of water vapor in the transmission spectrum of the Neptune-mass planet HAT-P-26b. Our measured spectrum is best explained by the presence of water vapor, a lack of potassium, and either a high-metallicity, cloud-free atmosphere or a solar-metallicity atmosphere with a cloud deck at ~10 mbar. The emergence of multi-scale-height spectral features in our data suggests that future observations at higher precision could break this degeneracy and reveal the planet's atmospheric chemical abundances. We also update HAT-P-26b's transit ephemeris, t_0 = 2455304.65218(25) BJD_TDB, and orbital period, p = 4.2345023(7) days.