A search for star-planet interactions in the upsilon Andromedae system at X-ray and optical wavelengths

TL;DR

This study investigates whether close-in giant planets influence their host star's activity by monitoring the upsilon Andromedae system in X-ray and optical wavelengths, finding no clear evidence of planet-induced variability.

Contribution

The paper provides multi-wavelength observational data on star-planet interactions, demonstrating the difficulty in detecting such effects with current instrumentation.

Findings

Stellar activity levels are low in X-ray and optical data.

No activity variations linked to the planet were observed.

Chromospheric variability is consistent with stellar rotation.

Abstract

Close-in, giant planets are expected to influence their host stars via tidal or magnetic interaction. But are these effects strong enough in suitable targets known so far to be observed with today's instrumentation? The upsilon And system, an F8V star with a Hot Jupiter, was claimed to undergo cyclic changes in chromospheric activity indicators with its innermost planet's period. We want to investigate the stellar chromospheric and coronal activity over several months. We therefore monitored the star in X-rays as well as at optical wavelengths to test coronal and chromospheric activity indicators for planet-induced variability, making use of the Chandra X-ray Observatory as well as the echelle spectrographs FOCES and HRS at Calar Alto (Spain) and the Hobby-Eberly Telescope (Texas, US). The stellar activity level is low, as seen both in X-rays as in Ca II line fluxes; the chromospheric data show variability with the stellar rotation period. We do not find activity variations in X-rays or in the optical which can be traced back to the planet. Gaining observational evidence for star-planet interactions in X-rays remains challenging.