Can radio emission escape from the magnetosphere of υ Andromedae b – a new method to constrain the minimum mass of Hot Jupiters

Abstract

ABSTRACT We investigate the atmospheric and magnetospheric conditions of the massive, close-in exoplanet υ Andromedae b (hereafter ups And b). In particular, we explore whether radio emission can be produced by the Cyclotron Maser Instability (CMI), and whether this emission can escape from its source region. For this, we compare the local cyclotron frequency to the local plasma frequency. The planetary mass has a decisive impact on both of these frequencies: the cyclotron frequency depends on the (mass-dependent) estimate of the planetary magnetic moment, and the plasma frequency is determined by the (gravity-dependent) atmospheric profile. For this reason, the planetary mass is one of the decisive parameters determining whether the CMI can operate efficiently. As the precise planetary mass is unknown in the case of ups And b, we compare the plasma conditions for a range of hypothetical masses of the planet in order to determine at which mass the atmosphere becomes ‘compact’, i.e. is not strongly extended, and thus provides favourable conditions for the CMI. In the case of detected planetary radio emission, this approach can provide a new way to constrain the mass of an exoplanet for which only a minimum mass is known.