Speaker
Description
Novae and X-Ray Bursts are among the most important stellar explosions in our Galaxy. Classical novae are driven by thermonuclear explosions in the envelopes accumulated through mass transfer onto white dwarf stars in close binary systems. During these events, approximately $10^{-7}-10^{-4}$ M$_\odot$ of material enriched in CNO nuclei, and in some cases in intermediate-mass elements such as Ne, Na, Mg, and Al, are ejected into the interstellar medium. Infrared and ultraviolet observations have also confirmed dust formation in the expanding nova ejecta, raising the possibility that novae may contribute to the inventory of presolar grains found in meteorites. Recent work on the subclass of recurrent novae, including studies of T CrB and other well-known systems, has focused on characterizing their accretion histories and white-dwarf masses. In many recurrent novae, the accreting white dwarf is inferred to be close to the Chandrasekhar mass because of the observed short recurrence periods. Numerical simulations suggest that such systems may experience net white-dwarf mass growth, making at least some recurrent novae plausible progenitors of thermonuclear supernovae.
X-ray bursts (XRBs) are another class of thermonuclear explosions that involve neutron stars rather than white dwarfs. These events constitute the most frequent type of thermonuclear stellar explosion in our Galaxy (the third, in terms of total energy output after novae and supernovae). To date, most of the efforts undertaken in the modeling of XRBs have relied on non-rotating, 1D hydrodynamic simulations. We will report on pioneering XRB models computed with different angular velocities (up to 80% of the critical value) and discuss the differences obtained in the lightcurves and in the associated nucleosynthesis with respect to non-rotating models. It is worth noting that, while all XRB hydro simulations performed to date report that ejection from a neutron star is unlikely, radiation-driven winds during photospheric radius expansion have been suggested to lead to the ejection of a tiny fraction of the accreted envelope. Here, we will report the results of the coupling of a non-relativistic, radiative wind model with a series of XRB hydrodynamic simulations, quantifying the expected contribution of XRBs to the Galactic abundances.
This invited talk will review the current understanding of novae and XRB, with empasis on the explosion mechanisms, the main nuclear processes involved and their associated uncertainties. Particular attention will be devoted to the impact of nuclear reaction rates and weak interactions on abundance predictions and observational diagnostics.