Nova contributions to the chemical evolution of the Milky Way

¹ Institute for Astronomy (IvS), KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
² School of Physics & Astronomy, Monash University, Clayton, 3800 Victoria, Australia
³ Centre of Excellence for Astrophysics in Three Dimensions (ASTRO-3D), Melbourne, Victoria, Australia
⁴ Center for Computational Astrophysics, Flatiron Institute, New York City, New York, USA
⁵ Department of Physics and Astronomy, University of Victoria, Victoria, BC, V8P 5C2 Canada
⁶ Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Eötvös Loránd Research Network (ELKH), Konkoly Thege Miklós út 15-17, 1121 Budapest, Hungary
⁷ Astrophysics Research Group, University of Surrey, Guildford, Surrey, GU2 7XH UK

Received: 20 May 2024
Accepted: 25 June 2024

Abstract

Context. 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.

Aims. 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.

Methods. We combine populations of novae computed using the binary population synthesis code binary_c 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.

Results. 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 ¹³C and ¹⁵N 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 ¹⁵N. Predictions for [¹³C/Fe], [¹⁵N/Fe], ¹²C/¹³C, and ¹⁴N/¹⁵N abundances ratios vary by up to 0.2 dex at [Fe/H] = 0 and by up to 0.7 dex in [¹⁵N/Fe] and ¹⁴N/¹⁵N 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: ³He (especially at high M_WD), ⁷Li, ¹⁸O, ¹⁸F, and the > 1.3 M_⊙ regime of ²⁹Si, ³³S, ³⁴S, ³⁵Cl, and ³⁶Ar.