Star-Planet Interactions

Radio and Radiocarbon

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/astron22/astron22.html

Solar Archaeology

Carrington Event

Aurora

F.E. Church, "Aurora Borealis", 1865.

774-775 AD

Miyake Figure

Miyake et al, 2012

To model these time series, you have to model the entire global carbon cycle!

carbon cycle diagram

First Open Source Carbon Cycle Model

sharmallama.github.io/ticktack

posterior samples
corner plot

Radio Exoplanets

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 will the SKA do for exoplanet science?

LOFAR Exoplanets

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

Active stars

Quiescent stars

Güdel-Benz Diagram

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!