FUV variability of HD 189733. Is the star accreting material from its hot Jupiter?

TL;DR

This study uses time-resolved UV spectroscopy to investigate star-planet interactions in HD 189733, revealing variability likely caused by planetary material accreting onto the star, with implications for system evolution.

Contribution

First detection of UV line variability linked to planetary accretion processes in a hot Jupiter system using HST COS observations.

Findings

Detected variability in ion lines of Si, C, N, O during HST observations.

FUV variability correlates with planetary orbit, indicating star-planet interaction.

Proposed gas stream from planet accreting onto star, impacting ahead of sub-planetary point.

Abstract

Hot Jupiters are subject to strong irradiation from the host stars and, as a consequence, they do evaporate. They can also interact with the parent stars by means of tides and magnetic fields. Both phenomena have strong implications for the evolution of these systems. Here we present time resolved spectroscopy of HD~189733 observed with the Cosmic Origin Spectrograph (COS) on board to HST. The star has been observed during five consecutive HST orbits, starting at a secondary transit of the planet ($\phi$ ~0.50-0.63). Two main episodes of variability of ion lines of Si, C, N and O are detected, with an increase of line fluxes. Si IV lines show the highest degree of variability. The FUV variability is a signature of enhanced activity in phase with the planet motion, occurring after the planet egress, as already observed three times in X-rays. With the support of MHD simulations, we propose the following interpretation: a stream of gas evaporating from the planet is actively and almost steadily accreting onto the stellar surface, impacting at $70-90\deg$ ahead of the sub-planetary point.