Constraining the reflective properties of WASP-178b using Cheops photometry

TL;DR

This study measures the reflective and thermal properties of exoplanet WASP-178b using Cheops and Tess photometry, providing insights into its atmosphere and energy transport mechanisms.

Contribution

First measurement of geometric albedo and recirculation efficiency for WASP-178b using multiwavelength photometry from Cheops and Tess.

Findings

WASP-178b has a geometric albedo between 0.1 and 0.35.

The planet's recirculation efficiency exceeds 0.7.

The dayside brightness temperature is between 2250 K and 2800 K.

Abstract

Multiwavelength photometry of the secondary eclipses of extrasolar planets is able to disentangle the reflected and thermally emitted light radiated from the planetary dayside. This leads to the measurement of the planetary geometric albedo $A_g$, which is an indicator of the presence of clouds in the atmosphere, and the recirculation efficiency $\epsilon$, which quantifies the energy transport within the atmosphere. In this work we aim to measure $A_g$ and $\epsilon$ for the planet WASP-178 b, a highly irradiated giant planet with an estimated equilibrium temperature of 2450 K.} We analyzed archival spectra and the light curves collected by Cheops and Tess to characterize the host WASP-178, refine the ephemeris of the system and measure the eclipse depth in the passbands of the two respective telescopes. We measured a marginally significant eclipse depth of 70$\pm$40 ppm in the Tess passband and statistically significant depth of 70$\pm$20 ppm in the Cheops passband. Combining the eclipse depth measurement in the Cheops (lambda_eff=6300 AA) and Tess (lambda_eff=8000 AA) passbands we constrained the dayside brightness temperature of WASP-178 b in the 2250-2800 K interval. The geometric albedo 0.1<$\rm A_g$<0.35 is in general agreement with the picture of poorly reflective giant planets, while the recirculation efficiency $\epsilon>$0.7 makes WASP-178 b an interesting laboratory to test the current heat recirculation models.