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Detecting heavy atoms in the inflated atmospheres of giant exoplanets thatorbit close to their parent stars is a key factor for understanding their bulkcomposition, and the processes that drive their expansion and interaction withthe impinging stellar wind. Here, we use archive data obtained with the CosmicOrigins Spectrograph onboard the Hubble Space Telescope to report an absorptionof ~6.4+/-1.8% by neutral oxygen during the HD 189733b transit. Scalingpublished HI results from a simple hydrodynamic model of HD 189733b, a verticalOI column density of ~8x10^15/cm2 produces only a 3.5% attenuation, implyingthat non-thermal line broadening or super-solar abundances are required. Wealso report evidence of short-time variability in the measured stellar flux, avariability that we analyze and compare to solar flaring activity. In thatframe, we find that non-statistical uncertainties in the measured fluxes arenot negligible, which calls for caution when reporting transit absorptions.Despite these uncertainties, we also show a possible detection for both atransit and early-ingress absorption in the ion CII 133.5nm lines. Ifconfirmed, this would be the second exoplanet for which an early-ingressabsorption is reported. Assuming the HD 189733b magnetosphere to be at theorigin of the early absorption, we use the Parker model for the stellar windand a particle-in-cell code for the magnetosphere to show that its orientationshould be deflected ~10-30{\deg} from the planet-star line, while its nose'sposition should be at least ~16.7 Rp upstream of the exoplanet in order to fitthe CII transit light curve. The derived stand-off distance is consistent witha surface magnetic field strength of ~5.3 Gauss for the exoplanet, and asupersonic stellar wind impinging at ~250 km/s, with a temperature of 1.2x10^5Kand a density ~6.3x10^6/cm^3 at the planetary orbit, yet the fit is not unique.

Hubble Space Telescope detection of oxygen in the atmosphere of exoplanet HD189733b