Physics Seminar
Wednesday, October 9, 4:10 PM - 5:30 PM
Biology 19
This event is open to the public.
Anjun Mukadam, University of Washington, on "Evolutionary Rate of Cooling of the White Dwarf Pulsator ZZ Ceti."
We have finally measured the evolutionary rate of cooling of the pulsating hydrogen atmosphere (DA) white dwarf ZZ Ceti (Ross 548), as reflected by the drift rate of the 213.13260694 s period. Using 41 years of time-series photometry from November 1970 to January 2012, we determine the rate of change of this period with time to be dP/dt = (5.5 ± 1.0) x 10^{-15} s/s. After correcting for proper motion, the evolutionary rate of cooling of ZZ Ceti is computed to be (3.3 ± 1.1) x 10^{-15} s/s. This value is consistent within uncertainties with the measurement of (4.19 ± 0.73) x 10^{-15} s/s for another similar pulsating DA white dwarf, G117-B15A.
Measuring the cooling rate of ZZ Ceti helps us refine our stellar structure and evolutionary models, as cooling depends mainly on the core composition and stellar mass. Calibrating white dwarf cooling curves with this measurement will reduce the theoretical uncertainties involved in white dwarf cosmochronometry. Should the 213.13 s period be trapped in the hydrogen envelope, then our determination of its drift rate compared to the expected evolutionary rate suggests an additional source of stellar cooling. Attributing the excess cooling to the emission of axions imposes a constraint on the mass of the hypothetical axion particle.
Submitted by Mary Sullivan.
Posted on Oct 3, 2013