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SUMMARY:White dwarfs as probes of convective overshoot and evolved exoplan
 etary systems - Tim Cunningham\, University of Warwick
DTSTART:20221004T121500Z
DTEND:20221004T131500Z
UID:TALK182558@talks.cam.ac.uk
CONTACT:Dr Emily Sandford
DESCRIPTION:Using the 3D radiation-hydrodynamics code\, CO5BOLD\, I have m
 odelled the surface convection zones of hydrogen atmosphere white dwarfs. 
 In particular\, probing the effective temperature range 11\,400K – 18\,0
 00K where convection is existent\, yet confined to a region small enough t
 o allow modelling of the full vertical extent of the convective and oversh
 oot layers. I will present the first 3D simulations of degenerate stars wi
 th passive scalar particles that provide a statistical characterisation of
  the macroscopic diffusion of metals in the overshoot layers below the con
 vective zone. Our results suggest that macroscopic diffusion\, driven by c
 onvective overshoot\, decays over at least 2.5 pressure scale heights bene
 ath the unstable layers\, leading to much larger mixed masses. I will disc
 uss the implications of this result for the inferred accretion rates\, mas
 ses and compositions of evolved planetary systems\, and recent X-ray obser
 vations with the Chandra X-ray Observatory which provide a test of these m
 odels and confirm metal-polluted white dwarfs as a new class of X-ray sour
 ce. In addition\, combined with photometry from the Sloan Digital Sky Surv
 ey\, the Galaxy Evolution Explorer and Gaia\, our CO5BOLD simulations have
  improved constraints on the primordial mass of hydrogen in white dwarfs. 
 I will present these results\, which have implications for e.g. nuclear bu
 rning during the asymptotic giant branch and asteroseismological studies\,
  as well as the prospects for detecting variability at actively accreting 
 white dwarfs.\n\n 
LOCATION:HOYLE LECTURE THEATRE + ONLINE - Details to be sent by email
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