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Context.Although current observations indicate that there are two distinct sequences of disk stars in the [α/M] versus [M/H] parameter space, further complexity is evident in the chemical makeup of the Milky Way and consequently suggests a complicated evolutionary history. Aims.We developed two-infall galactic chemical evolution (GCE) models consistent with the Galactic chemical map. Methods.We obtained new GCE models simulating the chemical evolution of the Milky Way, as constrained by a golden sample of 394 000 stellar abundances of the Milky Way Mapper survey from data release 19 of SDSS-V. The separation between the chemical thin and thick disks was defined using [Mg/M]. We used the chemical evolution environmentOMEGA+combined with Levenberg-Marquardt (LM) and bootstrapping algorithms for the optimization and error estimation. We simulated the entire Galactic disk and considered six galactocentric regions, allowing for a more detailed analysis of the formation of the inner, middle, and outer Galaxy. We investigated the evolution ofα, odd-Z, and iron-peak elements, covering 15 species altogether. Results.The chemical thin and thick disks are separated by Mg observations, which the otherα-elements show similar trends with, while odd-Z species demonstrate different patterns as functions of metallicity. In the inner Galactic disk regions, the locus of the low-Mg sequence is gradually shifted toward higher metallicity, while the high-Mg phase is less populated. The best-fit GCE models show a well-defined peak in the rate of the infalling matter as a function of the Galactic age, confirming a merger event about 10 Gyr ago. We show that the timescale of gas accretion, the exact time of the second infall and the ratio between the surface mass densities associated with the second infall event and the formation event vary with the distance from the Galactic center. According to the models, the disk was assembled within a timescale of (0.32±0.02) Gyr during a primary formation phase, followed by an increasing accretion rate over a (0.55±0.06) Gyr-timescale and a relaxation phase that lasted (2.86±0.70) Gyr, with a second peak seen for the infall rate at (4.13±0.19) Gyr. Conclusions.Our best Galaxy evolution models are consistent with an inside-out formation scenario of the Milky Way disk and in agreement with the findings of recent chemodynamical simulations.
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This content will become publicly available on September 1, 2026
Binary stellar evolution yields in galactic chemical evolution calculations
Context.Galactic chemical evolution (GCE) models aim to bring together stellar yields and galactic evolution models to make predictions for the chemical evolution of real stellar environments. Until recently, stellar yields accounting for binary stellar evolution were unavailable, leading to an inability for GCE calculations to account for most binary stellar evolution effects. Fortunately, effective stellar yields that account for binary stellar evolution at a population level can be pre-computed and then used as if they were single yields. Aims.We present a framework for the computation of effective stellar yields that accounts for a mixed population of binary and single stars under an adjustable mix of binary evolution settings: the binary fraction, the accretion efficiencies of winds, Roche-lobe overflow, and supernovae. We emphasise the critical need for more complete yield coverage of the binary nucleosynthesis and evolution, without which the ability to make accurate predictions on the true role of binarity on GCE calculations is hamstrung. We also provide clear guidelines for future stellar modelling works to ensure their results are maximally useful to the wider community. Methods.We compute effective stellar yields using detailed binary stellar yields accounting for binary induced mass-loss from a solar-metallicity donor star. We study the effect of varying the binary mixture and accretion efficiencies, and consider a range of models for the treatment of accreted material on the secondary in detail. Results.In the absence of detailed binary yields for the secondary, we put forth a model for the composition of accreted material that preserves the signature of the primary’s nuclear processing within the post-mass-transfer secondary yields. This model includes special treatment for isotopes of the light elements Li, Be, and B and accreted radioisotopes. Among the binary parameters, we find that the binary fraction, which determines the ratio of binary and single star systems, has the most significant effect on the effective stellar yields, with widespread impact across most isotopes. In contrast, varying the accretion efficiencies produces comparatively minor changes. We also find that the binary fraction has a significant influence on the logarithmic elemental abundance ratios relative to H present in the effective yield; this impact is the largest for the lower-mass primaries. Conclusions.Comprehensive coverage of binary systems is essential for advancing our understanding of the role of binary stellar evolution in galactic chemical evolution. Priority areas include low-mass stellar evolution, binary mergers, and supernova yields coupled with the evolution of their binary progenitors with nuclear post-processing. The low-metallicity regime is also largely unexplored, offering great opportunity for novel and impactful research in this area.
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- Award ID(s):
- 1927130
- PAR ID:
- 10649167
- Publisher / Repository:
- EDP Sciences
- Date Published:
- Journal Name:
- Astronomy & Astrophysics
- Volume:
- 701
- ISSN:
- 0004-6361
- Page Range / eLocation ID:
- A177
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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