Monday

AM CVn-type binary systems are helium-dominated cataclysmic variables with orbital periods of 5 to 65 minutes. They are bright emitters of gravitational waves at the frequency range detectable by LISA, as well as sources of dwarf novae and possible sources of type IA supernovae. The nature and evolutionary channels of these systems are currently poorly constrained due to the small number of systems with reliable parameter measurements.

We present high-speed photometry of Gaia14aae, the first AM CVn in which the central white dwarf is fully eclipsed. Modelling of this system's eclipse lightcurves allows for the most precise measurement to date of the stellar masses within an AM CVn, while relying only on geometric assumptions. The measured donor mass differs from the masses predicted by previously modelled evolutionary tracks, and lies in a region of parameter space not possible for systems descended from double white dwarf binaries. We discuss the implications of this for the system's nature and for its previous evolution.