WASP-South detection of HD219666b transits provides an accurate ephemeris

Abstract

The hot-Neptune HD219666b (= TOI-118.01) was an early discovery from Sector 1 of the TESS transit survey. Being a rare "Neptune desert" planet, and transiting a bright, V = 9.9 star, it is a prime target for further study including atmospheric characterisation. Targeting exoplanet transits with major facilities such as HST and the imminent JWST depends on an accurate ephemeris. Here we report a recovery of the transit in WASP-South data, enabling an ephemeris from data spanning 8 years that has a period uncertainty which is smaller by a factor 60 compared to the discovery paper.