On the generation of gravity waves in astrophysical environments

Details On the generation of gravity waves in astrophysical environments On the generation of gravity waves in astrophysical environments

Dec 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004phdt.........7a&link_type=abstract

Thesis (PhD). THE UNIVERSITY OF CHICAGO, Source DAI-B 65/06, p. 2982, Dec 2004, 133 pages.

Computer Science

Scientific paper

Typical ejecta of classical nova explosions (thermonuclear runaways of accreted H/He envelopes on the surfaces of a white dwarfs) are enriched in CNO and Ne, elements that are not product of the nuclear reactions involved. We investigate how this enrichment might originate from mixing of the white dwarf material (mainly composed of CNO&Ne) to the He/H envelope, due to large-scale flow and gravity wave interaction, prior to the explosion. In our simplified mixing model shear flow amplifies the waves, which eventually form cusps and break. This wave breaking injects a spray of C/O into the superincumbent H/He forming a layer with mixed material. Material from this layer are mixed through out the white dwarfs envelope by convective motions. We perform an extensive study of the interaction shear flows with interfacial gravity modes by (a)examining the stability properties of such flows using linear theory, (b)investigating the evolution of marginally unstable modes using weakly non-linear theory and (c)using two-dimensional numerical simulations to follow the non-linear evolution of the system. Our results allow us to formulate a quantitative expression for the amount of C/O per unit area that can be entrained into the H/He. The fraction of the envelope that is enriched depends on the horizontal distribution of shear velocity and the density contrast between the C/O white dwarf and the H/He layer. Using this parameterization to model the mixed mass, we then perform several one- dimensional Lagrangian calculations of an accreting white dwarf envelope. Our final results indicate that the envelope can be enriched by ˜25% of C/O by mass (consistent with that observed in some ejecta) for shear velocities, over the surface, with Mach numbers ˜0.4.

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