CHEOPS finds KELT-1b darker than expected in visible light: Discrepancy between the CHEOPS and TESS eclipse depths

Abstract

Recent TESS-based studies have suggested that the dayside of KELT-1b, a strongly-irradiated brown dwarf, is significantly brighter in visible light than what would be expected based on Spitzer observations in infrared. We observe eight eclipses of KELT-1b with CHEOPS (CHaracterising ExOPlanet Satellite) to measure its dayside brightness temperature in the bluest passband observed so far, and model the CHEOPS photometry jointly with the existing optical and NIR photometry from TESS, LBT, CFHT, and Spitzer. Our modelling leads to a self-consistent dayside spectrum for KELT-1b covering the CHEOPS, TESS, H , Ks, and Spitzer IRAC 3.6 and 4.5 $\mu$m bands, where our TESS, H , Ks, and Spitzer band estimates largely agree with the previous studies, but we discover a strong discrepancy between the CHEOPS and TESS bands. The CHEOPS observations yield a higher photometric precision than the TESS observations, but do not show a significant eclipse signal, while a deep eclipse is detected in the TESS band. The derived TESS geometric albedo of $0.36_{-0.13}^{+0.12}$ is difficult to reconcile with a CHEOPS geometric albedo that is consistent with zero because the two passbands have considerable overlap. Variability in cloud cover caused by the transport of transient nightside clouds to the dayside could provide an explanation for reconciling the TESS and CHEOPS geometric albedos, but this hypothesis needs to be tested by future observations.

Accepted to A&A

References in corpus (25)

• The Transiting Exoplanet Survey Satellite
• CLES, Code Liegeois d'Evolution Stellaire
• PyTransit: Fast and Easy Exoplanet Transit Modelling in Python
• Balancing the Energy Budget of Short-Period Giant Planets: Evidence for Reflective Clouds and Optical Absorbers
• Self-luminous and irradiated exoplanetary atmospheres explored with HELIOS
• Revising the ages of planet-hosting stars
• KELT-20b: A giant planet with a period of P~ 3.5 days transiting the V~ 7.6 early A star HD 185603
• Optical Albedo Theory of Strongly-Irradiated Giant Planets: The Case of HD 209458b
• Helios-r2 -- A new Bayesian, open-source retrieval model for brown dwarfs and exoplanet atmospheres
• Transit detection of the long-period volatile-rich super-Earth ${\nu }^2$ Lupi d with $CHEOPS$
• CHEOPS observations of the HD 108236 planetary system: A fifth planet, improved ephemerides, and planetary radii
• Near-infrared Thermal Emission Detections of a number of hot Jupiters and the Systematics of Ground-based Near-infrared Photometry
• WASP-186 and WASP-187: two hot Jupiters discovered by SuperWASP and SOPHIE with additional observations by TESS
• The atmosphere and architecture of WASP-189 b probed by its CHEOPS phase curve
• A pair of Sub-Neptunes transiting the bright K-dwarf TOI-1064 characterised with CHEOPS
• MuSCAT2 multicolour validation of TESS candidates: an ultra-short-period substellar object around an M dwarf
• Reinvestigating $\alpha$ Cen AB in light of asteroseismic forward and inverse methods
• CHEOPS Precision Phase Curve of the Super-Earth 55 Cnc e
• Detection of the tidal deformation of WASP-103b at $3\sigma$ with CHEOPS
• Investigating the architecture and internal structure of the TOI-561 system planets with CHEOPS, HARPS-N and TESS
• The EBLM project -- VIII. First results for M-dwarf mass, radius and effective temperature measurements using CHEOPS light curves
• A CHEOPS White Dwarf Transit Search
• Going back to basics: accelerating exoplanet transit modelling using Taylor-series expansion of the orbital motion
• Doppler beaming factors for white dwarfs, main sequence stars, and giant stars Limb-darkening coefficients for 3D (DA and DB) white dwarf models
• RoadRunner: a fast and flexible exoplanet transit model

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