High velocity stars are messengers of violent astrophysical phenomena.
Either unleashed from the Galactic centre (hypervelocity stars), or ejected
from stellar clusters and binary supernova explosions (runaway stars),
these stars are powerful tools to study distant stellar populations and
rare physics. Thermonuclear explosions, like those
occurring in Type Ia supernovae, are expected to entirely disrupt an
accreting white dwarf in a compact binary system, leading to the
ejection of their companion stars at high velocities.
Recent observations, also guided by the astrometric Gaia mission, have
revealed new exotic objects that may form via the (failed) thermonuclear
explosion of white dwarfs. Among the new discoveries we find unusual
white dwarfs with carbon or oxygen-dominated atmospheres,
as well as stars with neon-dominated atmospheres that could be the formerly
accreting white dwarf survivors of peculiar thermonuclear supernovae.
As we are just starting to discover these rare objects, the accurate
characterisation of their unusual atmospheres is improving our understanding
of the formation scenarios and evolution, having an impact theoretical
works that aim to constrain the pathways to thermonuclear supernovae,
birth rates, and nucleosynthetic yields.
1st February 2021: High-velocity Thermonuclear Supernova Survivors
Speaker: Roberto Raddi (Universitat Politècnica de Catalunya, Castelldefels). Location: Virtually; 3 pm