Follow-up LOFAR observations of the $τ$ Boötis exoplanetary system

Kavli Affiliate: Xiang Zhang

| First 5 Authors: Jake D. Turner, Jean-Mathias Grießmeier, Philippe Zarka, Xiang Zhang, Emilie Mauduit

| Summary:

Context. Observing the radio emission from exoplanets is among the most
promising methods to detect their magnetic fields and a measurement of an
exoplanetary magnetic field will help constrain the planet’s interior
structure, star-planet interactions, atmospheric escape and dynamics, and
habitability. Recently, circularly polarized bursty and slow emission from the
$tau$ Bo"{o}tis ($tau$ Boo) exoplanetary system was tentatively detected
using LOFAR (LOW-Frequency ARray) beamformed observations. If confirmed, this
detection will be a major contribution to exoplanet science. However, follow-up
observations are required to confirm this detection.
Aims. Here, we present such follow-up observations of the $tau$ Boo system
using LOFAR. These observations cover 70$%$ of the orbital period of $tau$
Boo b including the orbital phases of the previous tentative detections.
Methods. We used the BOREALIS pipeline to mitigate radio frequency
interference and to search for bursty and slowing varying radio signals.
BOREALIS was previously used to find the tentative radio signals from $tau$
Boo.
Results. Our new observations do not show any signs of bursty or slow
emission from the $tau$ Bo"{o}tis exoplanetary system.
Conclusions. The cause for our non-detection is currently degenerate. It is
possible that the tentative radio signals were an unknown instrumental
systematic or that we are observing variability in the planetary radio emission
due to changes in its host star. More radio data (preferably multi-site) and
ancillary observations (e.g. magnetic maps) are required to further investigate
the potential radio emission from the $tau$ Bo"{o}tis exoplanetary system.

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