Searching for Star-Planet interactions within the magnetosphere of HD 189733

TL;DR

This study investigates the magnetic field and activity of HD 189733 to detect star-planet interactions, finding no clear evidence but predicting potentially detectable radio emissions from the planet.

Contribution

First detailed magnetic field mapping of HD 189733 using spectropolarimetry, exploring star-planet magnetic interactions and predicting radio emissions.

Findings

HD 189733 has a mainly toroidal magnetic field up to 40 G.

Stellar activity is mainly modulated by stellar rotation.

No clear evidence of star-planet magnetic interactions was found.

Abstract

HD 189733 is a K2 dwarf, orbited by a giant planet at 8.8 stellar radii. In order to study magnetospheric interactions between the star and the planet, we explore the large-scale magnetic field and activity of the host star. We collected spectra using the ESPaDOnS and the NARVAL spectropolarimeters, installed at the 3.6-m Canada-France-Hawaii telescope and the 2-m Telescope Bernard Lyot at Pic du Midi, during two monitoring campaigns (June 2007 and July 2008). HD 189733 has a mainly toroidal surface magnetic field, having a strength that reaches up to 40 G. The star is differentially rotating, with latitudinal angular velocity shear of domega = 0.146 +- 0.049 rad/d, corresponding to equatorial and polar periods of 11.94 +- 0.16 d and 16.53 +- 2.43 d respectively. The study of the stellar activity shows that it is modulated mainly by the stellar rotation (rather than by the orbital period or the beat period between the stellar rotation and the orbital periods). We report no clear evidence of magnetospheric interactions between the star and the planet. We also extrapolated the field in the stellar corona and calculated the planetary radio emission expected for HD 189733b given the reconstructed field topology. The radio flux we predict in the framework of this model is time variable and potentially detectable with LOFAR.