Neutrino luminosity from oxygen depletion to core collapse for the 15 M_⊙ model run with the V-NJ scheme and η = 1.0. This shows that variations in the nuclear burning rate cause the oscillations in ξ_2.5. The red curve shows only neutrinos coming from nuclear reactions, the cyan curve shows thermal neutrinos, and the blue curve is the sum of the two. The dotted line shows the compactness parameter (right hand side vertical axis). The vertical dot-dashed line indicates the approximate time of core silicon depletion. The ξ_2.5 oscillations are driven by variations in silicon and oxygen shell burning.