New Accreting White Dwarfs Determined from X-ray Observations (Timothy Cunningham)

X-rays provide a unique fingerprint of accretion onto compact objects. We have recently made the first direct detection of planetary material accreting onto a white dwarf using X-ray observations with Chandra. This discovery confirmed G29-38 - the prototype of all metal-polluted white dwarfs with detected debris disks - as a significant source of soft X-rays. Our detection provided the first direct evidence of ongoing accretion of planetary material onto a white dwarf and allowed the first independent constraint on the accretion rate at such a system, finding an instantaneous accretion rate consistent with modelling of observed photospheric abundances. I will present this system along with recent results from an ongoing search for more isolated white dwarfs with soft X-ray emission, including a new metal-polluted white dwarf and two low-state, long-period period-bounce polars. From an evolutionary perspective, these new polars - both with 2-hour periods and cool sub-stellar companions - are particularly interesting since angular momentum loss driven only by gravitational wave emission may not be sufficient to explain their evolution to such long periods, perhaps requiring additional angular momentum loss mechanisms such as residual magnetic braking.