Speaker: Peter Garnavich

Title: White Dwarf Pulsars and Cataclysmic Propellers

Abstract: 

Cataclysmic variables (CVs) are close binary stars consisting of a white dwarf accreting, or trying to accrete, mass from a cool companion. An accretion disk typically forms in normal CVs, but a strong magnetic field on the white dwarf can truncate the disk or block its development. How a significant magnetic field is generated from the white dwarf remains a problem. One scenario is that during a common envelope phase, a high accretion rate spins-up the white dwarf and a field is generated through a magnetic dynamo. Here, I will discuss the properties of two unusual CVs that may have recently had their white dwarfs spun-up and are now shedding this accumulated rotational energy through magnetic interaction with its secondary star.  In the white dwarf pulsar AR Scorpii, the white dwarf spin energy is being converted into electromagnetic radiation through generation of synchrotron emission - although the details of this process remain uncertain. In the propeller LAMOST-J0240, the white dwarf is spinning once every 25 seconds, close to the limit of stability. Combined with a significant magnetic field, the star shocks and ejects gas approaching from its secondary star. The spin-down time scale for these systems is only tens of millions of years, suggesting that they quickly blend back into the normal CV population.