The Leonard E Parker Center for Gravitation, Cosmology and Astrophysics holds frequent seminars on a broad range of ongoing cosmology and gravitation research topics. Unless otherwise noted, seminars are on Friday afternoons at 1:00 PM in KIRC 2175; there is a gathering for a brown bag lunch at 12:30.

Formation of low-mass white dwarfs orbiting millisecond pulsars
Dr. Alina Istrate, Research Associate, UWM

Millisecond pulsars (MSPs) belong to a class of radio pulsars characterized by high rotational spin rates and low magnetic fields. These neutron stars are believed to be the end-product of binary evolution, i.e. the recycling scenario, in which an old neutron star accretes matter and angular momentum from a close stellar companion for an extended period of time, while being observable as an X-ray binary. A handful of MSPs are detected in very compact orbits (orbital periods between 2 − 9 hr), around low-mass He WDs with masses below 0.25 Msun and surface gravities 5 < log g < 7, the so-called extremely low-mass helium white dwarfs (ELM WDs).

Today we know of the existence of more than 80 ELM WDs, with the majority of them in a binary system with a more massive CO WD. The increasing number of discovered ELM WDs reveals that they are formed in different environments, from the Galactic disk to open and globular clusters. ELM WDs are most likely the result of binary evolution as they cannot be formed from single stars within a Hubble time. The new wealth of data raises questions regarding the puzzling presence of metals in the atmospheres of young bloated ELM proto-WDs and the newly discovered pulsations in three ELM proto-WDs. The current available evolutionary models fail to explain such properties. In this talk, I will present the latest theoretical efforts regarding the formation and evolution of ELM WDs.