Hubble Space Telescope observations of the NUV transit of WASP-12b

Abstract

We present new observations of four closely-spaced NUV transits of the hot Jupiter-like exoplanet WASP-12b using HST/COS, significantly increasing the phase resolution of the observed NUV light curve relative to previous observations, while minimising the temporal variation of the system. We observe significant excess NUV absorption during the transit, with mean normalised in-transit fluxes of $F_{\mathrm{norm}}\simeq 0.97$, i.e. $\simeq$2-5 $\sigma$ deeper than the optical transit level of $\simeq 0.986$ for a uniform stellar disk (the exact confidence level depending on the normalisation method used). We further observe an asymmetric transit shape, such that the post-conjunction fluxes are overall $\simeq$2-3 $\sigma$ higher than pre-conjunction values, and characterised by rapid variations in count rate between the pre-conjunction and out of transit levels. We do not find evidence for an early ingress to the NUV transit as suggested by earlier HST observations. However, we show that the NUV count rate observed prior to the optical transit is highly variable, but overall $\simeq$2.2-3.0 $\sigma$ below the post-transit values and comparable in depth to the optical transit, possibly forming a variable region of NUV absorption from at least phase $\varphi \simeq$0.83, limited by the data coverage.

Accepted into the Astrophysical Journal

References in corpus (5)

• Near-UV Absorption, Chromospheric Activity, and Star-Planet Interactions in the WASP-12 system
• Early UV Ingress in WASP-12b: Measuring Planetary Magnetic Fields
• Exoplanet HD 209458b : Evaporation strengthened
• The shocking transit of WASP-12b: Modelling the observed early ingress in the near ultraviolet
• Mass-Loss Rates of "Hot-Jupiter" Exoplanets with Various Types of Gaseous Envelopes

Cited by in corpus (11)

• The Orbit of WASP-12b is Decaying
• Decaying Orbit of the Hot Jupiter WASP-12b: Confirmation with TESS Observations
• TESS Revisits WASP-12: Updated Orbital Decay Rate and Constraints on Atmospheric Variability
• Swift UVOT near-UV transit observations of WASP-121 b
• The Colorado Ultraviolet Transit Experiment (CUTE) Mission Overview
• TASTE V. A new ground-based investigation of orbital decay in the ultra-hot Jupiter WASP-12b
• Extrasolar giant magnetospheric response to steady-state stellar wind pressure at 10, 5, 1, and 0.2 AU
• The on-orbit performance of the Colorado Ultraviolet Transit Experiment (CUTE) Mission
• Cold day-side winds shape large leading streams in evaporating exoplanet atmospheres
• Impact of MgII interstellar medium absorption on near-ultraviolet exoplanet transit measurements
• Characterizing the WASP-4 system with TESS and radial velocity data: Constraints on the cause of the hot Jupiter's changing orbit and evidence of an outer planet