tokens: star has an initial mass within a given mass range is given by the Kroupa ( 2002 ) IMF, with a slope x = 1.7 for high masses, normalized to unity in the 0.1–100 M ⊙ range. For the starbursts, we also investigate the effects of an IMF skewed towards high masses ( x = 0.95 in the high-mass regime), similar to the one proposed by Ballero et al. ( 2007 ) for the Galactic bulge. All our computations avoid the instantaneous recycling approximation by detailed accounting of the finite stellar lifetimes. This is a necessary prerequisite for a proper treatment of elements that are produced on different time-scales by stars of different initial masses and chemical compositions. The nucleosynthetic outcomes of binary stars exploding as Type Ia supernovae (SNe Ia) and novae are included in our computations, adopting the single-degenerate scenario for their progenitors (Matteucci Recchi 2001 , and references therein) for SNe Ia and our previous work (Romano et al. 1999 , 2001 ; based on D'Antona Matteucci 1991 ) for novae. Since CNO elements are produced in negligible amounts in SN Ia explosions (Iwamoto et al. 1999 ), the exact choice of the route leading to such events does not affect the results presented in this paper. Classical novae, instead, are thought to significantly overproduce 13 C, 15 N and 17 O with respect to their solar abundances (e.g. José Hernanz 2007 ) making assumptions about their precursors a much more thorny problem (see the next section). The adopted nucleosynthesis prescriptions are summarized in Table 2 . The stellar yields for low- and intermediate-mass stars are from Karakas ( 2010 ). For massive stars, we adopt the grid of yields suggested by Nomoto, Kobayashi Tominaga ( 2013 , Models 1, 2 and 5). However, since the important effects of stellar rotation are not accounted for in this case, we also consider the grid of CNO yields from fast-rotating massive stars provided by the Geneva group (Meynet Maeder 2002b ; Hirschi, Meynet Maeder 2005 ; Hirschi 2007 ; Ekström et al. 2008 , Models 3 and 4). Detailed yields for super-AGB stars (Doherty et al. 2014a , b ) – often neglected in chemical evolution studies – are implemented in Models 2, 4 and 5, while nova nucleosynthesis – also disregarded in most studies – is included in one case (Model 5). All the adopted yields for single stars are dependent on mass and metallicity. For novae, we assume average yields, independent of mass and metallicity (see discussion in Section 4.1 ). The different sets of yields were all tested against the Milky Way data, while only the set labelled ‘1’ was used in the models for the other galaxies. Table 2. Prescriptions for nucleosynthesis. 4 RESULTS 4.1 Milky Way galaxy In this section, we present the results of our chemical evolution models for the Milky Way. These models differ in their adopted nucleosynthesis prescriptions (see Table 2 ). First, we discuss the predictions of Models 1, 2, 3 and 4, where the CNO elements come only from single stars.
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