LBA observations for project V630 semester 2023OCTS

Full description

White dwarfs (WDs) are the final evolutionary stage of stars not massive enough to become a neutron star or black hole. Non-accreting white dwarfs are almost never detected at radio frequencies. Currently, the only known radio-bright white dwarf system (excluding cataclysmic variables) is AR Scorpii (AR Sco), which is a WD-star close binary. Its radio signal pulses with the WD's spin period, earning AR Sco the moniker ``white dwarf pulsar''. However, the exact radio emission mechanism remains unknown in the source, causing scepticism about whether such a moniker is warranted. Localising and resolving the emission region within a WD-star stellar system would determine the emission mechanism and validate current theoretical models for such systems. Unfortunately, the angular separation in AR Sco is too small to resolve with current VLBI facilities. Here, we propose LBA observations of a newly discovered radio-bright non-accreting WD-star system with properties that suggest it is similar to AR Sco. This system is significantly closer to us and possesses a larger separation (around 3.5 mas) between the star and the WD than AR Sco. The position of this system in the southern sky implies LBA is the only VLBI array that can resolve it. With our proposed observations, we will determine if the emitter remains unresolved on few-mas scales and search for the anticipated orbital motion of the emitter. This, when combined with Gaia data or followup radial velocity observations, will allow us to confidently localise the emitter within the system and determine its powering mechanism.