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SEQUENCE:0
UID:UW-Physics-Event-4929
DTSTART:20181018T203000Z
DTEND:20181018T220000Z
DTSTAMP:20260307T173416Z
LAST-MODIFIED:20181012T160137Z
LOCATION:4421 Sterling Hall\, Coffee and cookies 3:30 PM. Talk Begins 
 at 3:45 PM
SUMMARY:Pulsating White Dwarfs and Orbital Decay in Binaries\, Astrono
 my Colloquium\, Meng Sun\, UW Astronomy Department
DESCRIPTION:Motivated by the discovery of a handful of pulsating\, ext
 remely low-mass white dwarfs in compact binaries\, a formation model w
 as developed for these systems. Evolutionary models are constructed us
 ing the MESA code. Magnetic braking torques are used to shrink the orb
 it and remove the envelope before the helium core can significantly gr
 ow in size. The resulting models for the stellar structure are used to
  understand the properties of g and p-mode oscillations.<br>
\n<br>
\n
 WASP-12b is a hot Jupiter with an orbital period of only 1.1 days\, ma
 king it one of the shortest-period giant planets known. Recent transit
  timing observations measure the orbital period to decrease on a 3.2 M
 yr timescale. These observations imply that a Gyr-old planet is now ab
 out to be destroyed by its star over the next few Myr. One mechanism t
 o produce orbital decay is through tidal friction. Calculations are pr
 esented for the dynamical tide excitation of internal gravity waves by
  the tidal force. I show that sufficient tidal friction to explain the
  observations may be possible if the star is near the end of its main 
 sequence lifetime.<br>
\n<br>
\nIndirect evidence of orbital decay in 
 binaries comes from the lack of binaries with close orbital separation
 s\, as they have already suffered orbital decay and merged. A broad pa
 rameter study of orbital decay due to tides is presented for a range o
 f primary and secondary stars as well as orbital separation. The focus
  is on the red giant branch phase of the primary star. Both the dynami
 cal tide\, damped by nonlinear wave breaking or radiative diffusion\, 
 and the equilibrium tide\, damped by the turbulent viscosity in the co
 nvective envelope\, are included in the calculations of tidal friction
 . The calculations of orbital decay are compared to the sample of clos
 e APOGEE binaries with red giant branch primaries and substellar compa
 nions\, as well as the sample of exoplanet host stars.<br>
\n
URL:https://www.physics.wisc.edu/events/?id=4929
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