Radio Observatons

of Star-Planet Magnetic Interaction

Benjamin Pope, UQ

Callingham et al. 2021: "The population of M dwarfs observed at low radio frequencies", Nature Astronomy

Pope et al. 2021: "The TESS View of LOFAR Radio-Emitting Stars", ApJL

Slides available at
benjaminpope.github.io/talks/csiro/csiro

Radio Astronomy

Many papers have discussed low-frequency searches for exoplanetary radio emission, with no detections so far.

Theorists now say that expanded ionospheres of hot Jupiters might self-absorb this emission down to undetectable levels.

The Square Kilometre Array (SKA) is a billion-dollar project to build a massive ~ GHz frequency SKA-Mid array in the Karoo Desert in South Africa and a ~ 100 MHz SKA-Low array in the Murchison Desert in Western Australia.
What can the SKA do for exoplanet science?
Callingham Sensitivities Figure

LOFAR

The LOw Frequency Aperture Array (LOFAR) in the Netherlands has been surveying the northern sky as a LOFAR Two-metre Sky Survey LoTSS.

Kepler showed us almost all stars have planets - so no point targeting known exoplanets!

Unbiased survey: cross-matching LOFAR Stokes V sources with Gaia DR2 50 pc sample we obtain many matches

GJ 1151

M dwarfs are known to be very variable in the radio, with wideband, circularly polarized flares.

... but GJ 1151 is inactive and this emission is steady during the epoch it is detected.

Scaled up from Jupiter-Io?

Simulations by Kavanagh et al predict radio emission from planets inside the 'Alfvén surface' (where Alfvén speed > wind speed)

Kavanagh et al lightcurve is consistent with GJ 1151 variability.

RV Followup inconclusive: Pope+ 2020, Mahadevan+ 2021, Perger+ 2021

Upper limit of 1.2m/s - about an Earth mass in a few day orbit.

The Whole Sample

Güdel-Benz Diagram

Active stars

Quiescent stars

The Future

As LOFAR continues its survey we expect dozens more detections.

With the SKA - hundreds!

Joint LOFAR+TESS observation to observe flaring stars - can we constrain CMEs?
Follow up all LOFAR candidates with RVs and look for transits!
Finally the dawn of exoplanet radio astronomy (!?)