Nova contributions to the chemical evolution of the Milky Way

Abstract

The explosive burning that drives nova eruptions results in unique nucleosynthesis that heavily over-produces certain isotopes relative to the solar abundance. However, novae are often ignored when considering the chemical evolution of our Galaxy due to their low ejecta masses. Galactic chemical evolution studies including novae are rare and have previously relied upon simplified treatments for the behaviour of nova populations. In this work, we use previously computed synthetic nova populations and the galactic chemical evolution code OMEGA+ to assess the impact that novae have on the evolution of stable elemental and isotopic abundances. We combine populations of novae computed using the binary population synthesis code with the galactic chemical evolution code OMEGA+ and detailed, white dwarf mass-dependent nova yields to model the nucleosynthetic contributions of novae to the evolution of the Milky Way. We consider three different nova yield profiles, each corresponding to a different set of nova yield calculations. We examine which nova sites contribute most to which isotopes. Despite novae from low-mass white dwarfs (WDs) dominating nova ejecta contributions, we find that novae occurring on massive WDs are still able to contribute significantly to many isotopes, particularly those with high mass numbers. We find that novae can produce up to 35 of the Galactic C and N mass by the time the model Galaxy reaches Fe/H = 0, and earlier in the evolution of the Galaxy (between Fe/H = -2 and -1) novae may have been the dominant source of N. Predictions for C/Fe N/Fe C/ C, and N/ N abundances ratios vary by up to 0.2 dex at Fe/H = 0 and by up to 0.7 dex in N/Fe and N/ N between Fe/H = -2 and -1 (corresponding approximately to Galactic ages of 170 Myr and 1 Gyr in our model). The Galactic evolution of other stable isotopes (excluding Li) is not noticeably affected by including novae. For most isotopes, agreement is generally good between the three different yield profiles we consider. Isotopes where agreement is relatively poor include: He (especially at high Li O F, and the >1.3 M regime of Si S S Cl, and Ar.