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Description
Hot Jupiters are surrounded by extended atmospheres of neutral hydrogen. Observations have provided evidence for in-transit hydrogen H{alpha} absorption as well as variable pre-transit absorption signals. These have been interpreted in terms of a bow shock or an accretion stream that transits the host star before the planet. We test the hypothesis of planetary related H{alpha} absorption by studying the time variability of the H{alpha} and stellar activity-sensitive calcium lines in high-resolution spectra of the planet host HD189733. In the framework of an observing campaign spanning several months, the host star was observed several times per week randomly sampling the orbital phases of the planet. We determine the equivalent width in the H{alpha}, Ca H&K and Ca IRT lines, and subtract stellar rotationally induced activity from the H{alpha} time series via its correlation with the IRT evolution. The residuals are explored for significant differences between the pre-, in-, and out-of-transit phases. We find strong stellar rotational variation with a lifetime of about 20-30 days in all activity indicators, but the corrected H{alpha} time series exhibits no significant periodic variation. We exclude the presence of more than 6.2m{AA}A pre-transit absorption and 5.6m{AA} in-transit absorption in the corrected H{alpha} data at a 99% confidence level. Previously observed H{alpha} absorption signals exceed our upper limits, but they could be related to excited atmospheric states. The H{alpha} variability in the HD189733 system is dominated by stellar activity, and observed signals around the planetary transit may well be caused by short term stellar variability.
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