Hydrodynamic Models of Classical Novae and Type I X-Ray Bursts

Abstract

Classical nova outbursts are powered by thermonuclear runaways that take place in the H‐rich accreted envelopes of white dwarfs in close binary systems. Extensive numerical simulations of nova outbursts have shown that the accreted envelopes attain peak temperatures ranging between 108 and 4×108 K, for about several hundred seconds, and therefore, their ejecta is expected to show signatures of a significant nuclear activity. Indeed, it has been claimed that novae can play a certain role in the enrichment of the interstellar medium through a number of intermediate‐mass elements. This includes 17O, 15N, and 13C, systematically overproduced in huge amounts with respect to solar abundances, with a lower contribution in a number of other species with A<40, such as 7Li, 19F, or 26Al. X‐ray bursts, in turn, constitute the most frequent source of stellar explosions in the Galaxy (and the third most energetic events after supernovae and nova outbursts). They take place in the H/He‐rich envelopes accreted onto neutron stars in binary systems. In this paper, we will present new hydrodynamic models (1D) of both classical nova outbursts and X‐ray bursts, from the onset of accretion up to the explosion phase, with special emphasis on their gross observational properties and on their associated nucleosynthesis. Two‐dimensional models of mixing at the core‐envelope interface during nova outbursts will also be presented. The impact of nuclear uncertainties on the final nucleosynthetic yields will be discussed in detail for the two astrophysical scenarios.