10 Gyr of classical nova explosions

Abstract

Classical novae are stellar explosions in cataclysmic binary systems, consisting of a compact white dwarf star (CO or ONe-rich) and a low-mass, main-sequence companion (typically, a K or M dwarf of solar composition). The system is close enough (orbital periods ranging between 1 and 15 h), hence allowing mass transfer episodes driven by overflows of the companion star. This matter flow forms an accretion disk that surrounds the white dwarf, and ultimately accumulates on its surface (at a rate M = 10−9–10−10 M⊙ yr−1), building up an envelope under semi-degenerate conditions until a violent thermonuclear runaway ensues. Classical novae are believed to be major sources of the Galactic 15N, 17O and 13C, with a minor contribution on a number of additional species, mainly 7Li and 26Al. But there are reasons to believe that these nucleosynthetic features have varied during the overall 10 Gyr of Galactic history. In this paper, we review recent progress on the characterization of primordial novae, that is, novae exploding in primordial cataclysmic binaries, and will compare their expected nucleosynthetic pattern with that of classical novae. Emphasis is made on the dominant nuclear paths during the explosion and on a thorough comparison with other explosive sites, such as type-I x-ray bursts.