Predicting radio emission from the newborn hot Jupiter V830 Tauri b and its host star

Abstract

Magnetised exoplanets are expected to emit at radio frequencies analogously to the radio auroral emission of Earth and Jupiter. We predict the radio emission from V830 Tau b, the youngest (2 Myr) detected exoplanet to date. We model the host star wind using 3DMHD simulations that take into account its surface magnetism. With this, we constrain the local conditions around V830 Tau b that we use to then compute its radio emission. We estimate average radio flux densities of 6 to 24mJy, depending on the assumed radius of the planet (one or two Rjupiter). These radio fluxes are present peaks that are up to twice the average values. We show here that these fluxes are weakly dependent (a factor of 1.8) on the assumed polar planetary magnetic field (10 to 100G), opposed to the maximum frequency of the emission, which ranges from 18 to 240MHz. We also estimate the thermal radio emission from the stellar wind. By comparing our results with VLA and VLBA observations of the system, we constrain the stellar mass-loss rate to be <3e-9 Msun/yr, with likely values between ~1e-12 and 1e-10 Msun/yr. The frequency-dependent extension of the radio-emitting wind is around ~ 3 to 30 Rstar for frequencies in the range of 275 to 50MHz, implying that V830 Tau b, at an orbital distance of 6.1 Rstar, could be embedded in the regions of the host star's wind that are optically thick to radio wavelengths, but not deeply so. Planetary emission can only propagate in the stellar wind plasma if the frequency of the cyclotron emission exceeds the stellar wind plasma frequency. For that, we find that for planetary radio emission to propagate through the host star wind, planetary magnetic field strengths larger than ~1.3 to 13 G are required. The V830 Tau system is a very interesting system for conducting radio observations from both the perspective of radio emission from the planet as well as from the host star's wind.