2 research outputs found
Novae -The study of the reactive flow
There is a wide consensus in the astrophysics community that the mechanism
underlying the observed Classical Nova eruptions is a surface thermonuclear
runaway. We start this short review with the main observational facts that lead
to the theoretical model of a thermonuclear runaway that takes place in an
accreted hydrogen rich envelope placed on top of a cool degenerate core of a
white dwarf. According to the theory, the accreted envelope becomes unstable to
convection days to weeks prior to the runaway. During the extreme stages of the
runaway itself, when the burning is most efficient, the envelope is fully
convective. Therefore, the elements processed under such extreme conditions are
lifted to the outermost regions of the star. A significant fraction of the
envelope is ejected during the outburst. The complicated combination of
hydrodynamic instabilities and explosive hydrogen burning, close to the surface
of the star, gives us a unique opportunity to study this complex reactive flow.
The range of core masses, core temperatures and accretion rates introduce a
whole range of burning temperatures and densities. Following the description of
the "standard" cases, we then focus on rare, but still possible, portions of
the relevant parameter space, in which "breakout" of the traditional CNO cycle
can occur and lead to heavy element enrichment patterns caused only by breakout
burning. We conclude our review with the main challenges that nova theorists
face today, with special emphasis on problems related to the nucleosynthesis
issues.Comment: Proceedings of: Nuclear Physics in Astrophysics-V,Eilat,April,201