New Revelations about White Dwarf Pulsations from Kepler and K2

Keaton Bell (UT Austin) - April 17, 2017 at 12:10 pm

Nearly 98% of all stars in the Galaxy will conclude their evolution as compact white dwarf stars, and the history of Galactic stellar evolution is revealed through white dwarf observations. White dwarfs with pure hydrogen atmospheres (80%) are observed as photometric variables while they cool from roughly 12,500 K to 10,800 K. These pulsating stars oscillate at numerous simultaneous eigenfrequencies, the measurements of which allow us a rare opportunity to constrain the details of their interior structures using the tools of asteroseismology.

Extensive Kepler and K2 photometry have recorded by far the most complete record of white dwarf pulsations to date. Besides enabling the precise determination of pulsation periods, they also reveal a new outburst-like phenomenon in stars near the cool edge of the instability strip. These quasiperiodic events recur on timescales of days and increase the overall stellar flux by up to 15% for many hours. The outbursts are observed to affect the pulsations in ways that can constrain theories for a physical mechanism. Since the cool edge of the instability strip is an empirically derived limit that nonadiabatic simulations have been unable to reproduce, this new behavior may represent missing physics from stellar pulsation theory. I review how the unprecedented coverage of short-cadence Kepler/K2 photometry has recently revolutionized our understanding of the characteristics of white dwarf pulsations.

The seminar will be held in 131A Campbell Hall.

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