Exoplanets around LISA Verification Binaries

Recent years have seen the investigation of a novel detection method for exoplanets around gravitational wave (GW) emitting binary star systems. This technique proposed by Danileski & Tamanini (2020) is conceptually similar to that of radial velocity measurements, where the orbital motion of an exoplanet induces a detectable Doppler shift in the GW frequency of the binary system, rather than its electromagnetic spectrum. The Laser Interferometer Space Antenna (LISA) is expected to be up and running in 2030s, and will be sensitive to GWs in the mHz band. Dozens of galactic binaries have been identified as so called "LISA verification binaries"; loud, galactic, ultracompact GW sources with electromagnetic counterparts. We investigate whether the presence of an exoplanet could leave a detectable imprint for LISA measurements in the GW emission of verification binaries. We recover the uncertainties for a measurement of a hypothetical exoplanet’s period and minimum mass by means of a Fisher Matrix analysis, and constrain the parameter space of detectable exoplanets separately for each LISA verification binary. We find that Jupiter-like planets could be detectable by LISA for every verification binary with an SNR over ~50, provided that their period does not exceed the mission lifetime of 4 years. While this method is limited to a few possible targets, it is sensitive to a wide range of planetary masses, periods and inclinations