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2017 Fall Science Colloquia

Asteroseismology As Probe of Internal Rotation in Pulsating White Dwarf Stars

Presented by: Gilles Fontaine (University of Montreal)
Category: Science Colloquia   Duration: 1 hour   Broadcast date: December 13, 2017
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A few years ago, Charpinet, Fontaine, & Brassard (2009, Nature, 461, 501) developed a new approach to test for solid body rotation (and deviations thereof) in pulsating stars. The method was successfully applied to the prototype of the GW Vir class of pulsating white dwarfs, PG 1159-035, for which the internal rotation profile was mapped over 99% of its mass (92% of its radius), a much better coverage than can currently be achieved from either helioseismology or asteroseismology of normal or giant stars. Similar results were obtained since for the four other GW Vir pulsators with available and suitable seismic rotational data. These stars are all found to rotate rigidly but, more importantly, to rotate extremely slowly, not only at the surface but *globally*. Since the internal rotation profile is available over 99% of the mass of each of these pulsators, it is possible to compute the global rotation energy as well as the total angular momentum in each case. This leads to ratios of the global rotation energy to the internal thermal energy ranging from 1.E-08 to 1.E-06, and to total angular momentum that is 200 to 25 times smaller than that of the actualSun. In essence, these post-AGB objects have lost *all* of their initial angular momentum. This finding has a direct impact on the question of angular momentum transfer that must exist between the radiative core and the convective envelope in the red giant phases of stellar evolution. While the distribution of rotation kernels is exceptionally favorable for mapping the full structure of a GW Vir star, mode confinement below the outer envelope can also help in probing an unexpectedly large fraction of the mass in some cooler, more degenerate pulsating white dwarfs of the V777 Her and ZZ Ceti types.