Spatial variations in the Milky Way disc metallicity–age relation

Feuillet, Diane; Frankel, Neige; Lind, Karin; Frinchaboy, Peter M.; García-Hernández, D. A.; Lane, Richard R.; Nitschelm, Christian; Roman-Lopes, Alexandre

doi:10.1093/mnras/stz2221

Cited by 84 publications

(131 citation statements)

References 101 publications

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“…This is consistent with what is seen in the previous observational studies (e.g. Hayden et al 2017;Feuillet et al 2019). Our results provide more robust trends with more reliably measured relative ages.…”

Section: Implications For the Disc Formation And Evolutionsupporting

confidence: 93%

Unveiling the distinct formation pathways of the inner and outer discs of the Milky Way with Bayesian Machine Learning

Ciucă

Kawata

Miglio

et al. 2021

Monthly Notices of the Royal Astronomical Society

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We develop a Bayesian Machine Learning framework called BINGO (Bayesian INference for Galactic archaeOlogy) centred around a Bayesian neural network. After being trained on the APOGEE and Kepler asteroseismic age data, BINGO is used to obtain precise relative stellar age estimates with uncertainties for the APOGEE stars. We carefully construct a training set to minimise bias and apply BINGO to a stellar population that is similar to our training set. We then select the 17,305 stars with ages from BINGO and reliable kinematic properties obtained from Gaia DR2. By combining the age and chemo-kinematical information, we dissect the Galactic disc stars into three components, namely, the thick disc (old, high-[α/Fe], [α/Fe] ≳ 0.12), the thin disc (young, low-[α/Fe]) and the Bridge, which is a region between the thick and thin discs. Our results indicate that the thick disc formed at an early epoch only in the inner region, and the inner disc smoothly transforms to the thin disc. We found that the outer disc follows a different chemical evolution pathway from the inner disc. The outer metal-poor stars only start forming after the compact thick disc phase has completed and the star-forming gas disc extended outwardly with metal-poor gas accretion. We found that in the Bridge region the range of [Fe/H] becomes wider with decreasing age, which suggests that the Bridge region corresponds to the transition phase from the smaller chemically well-mixed thick to a larger thin disc with a metallicity gradient.

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Section: Implications For the Disc Formation And Evolutionsupporting

confidence: 93%

Unveiling the distinct formation pathways of the inner and outer discs of the Milky Way with Bayesian Machine Learning

Ciucă

Kawata

Miglio

et al. 2021

Monthly Notices of the Royal Astronomical Society

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“…We also note that the age-metallicity trends we see in our sample are broadly compatible with the findings reported in Feuillet et al (2018Feuillet et al ( , 2019, if one restricts to the region in the disc representative of the Kepler field. While Feuillet et al (2019) can extend the analysis to different locations in the Milky Way, our higher age resolution allows using individual points to investigate age-chemical-composition trends (instead of using the metallicity binning as it is the case in Feuillet et al 2019). The two approaches are thus complementary.…”

Section: The Old Metal-rich Stars In the Solar Neighbourhood: Radial Migration Efficiencysupporting

confidence: 90%

Age dissection of the Milky Way discs: Red giants in theKeplerfield

Miglio

Chiappini

Mackereth

et al. 2021

A&A

135

124

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Ensemble studies of red-giant stars with exquisite asteroseismic (Kepler), spectroscopic (APOGEE), and astrometric (Gaia) constraints offer a novel opportunity to recast and address long-standing questions concerning the evolution of stars and of the Galaxy. Here, we infer masses and ages for nearly 5400 giants with available Kepler light curves and APOGEE spectra using the code PARAM, and discuss some of the systematics that may affect the accuracy of the inferred stellar properties. We then present patterns in mass, evolutionary state, age, chemical abundance, and orbital parameters that we deem robust against the systematic uncertainties explored. First, we look at age-chemical-abundances ([Fe/H] and [α/Fe]) relations. We find a dearth of young, metal-rich ([Fe/H] > 0.2) stars, and the existence of a significant population of old (8−9 Gyr), low-[α/Fe], super-solar metallicity stars, reminiscent of the age and metallicity of the well-studied open cluster NGC 6791. The age-chemo-kinematic properties of these stars indicate that efficient radial migration happens in the thin disc. We find that ages and masses of the nearly 400 α-element-rich red-giant-branch (RGB) stars in our sample are compatible with those of an old (∼11 Gyr), nearly coeval, chemical-thick disc population. Using a statistical model, we show that the width of the observed age distribution is dominated by the random uncertainties on age, and that the spread of the inferred intrinsic age distribution is such that 95% of the population was born within ∼1.5 Gyr. Moreover, we find a difference in the vertical velocity dispersion between low- and high-[α/Fe] populations. This discontinuity, together with the chemical one in the [α/Fe] versus [Fe/H] diagram, and with the inferred age distributions, not only confirms the different chemo-dynamical histories of the chemical-thick and thin discs, but it is also suggestive of a halt in the star formation (quenching) after the formation of the chemical-thick disc. We then exploit the almost coeval α-rich population to gain insight into processes that may have altered the mass of a star along its evolution, which are key to improving the mapping of the current, observed, stellar mass to the initial mass and thus to the age. Comparing the mass distribution of stars on the lower RGB (R < 11 R⊙) with those in the red clump (RC), we find evidence for a mean integrated RGB mass loss ⟨ΔM⟩ = 0.10 ± 0.02 M⊙. Finally, we find that the occurrence of massive (M ≳ 1.1 M⊙) α-rich stars is of the order of 5% on the RGB, and significantly higher in the RC, supporting the scenario in which most of these stars had undergone an interaction with a companion.

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“…Our observed sample of sdB binaries and the locations of wide-period sdB binary candidates also belong to the solar neighbourhood and, therefore, should be well modelled by the age-metallicity correlation provided by the Besanćon model, also in agreement with Casagrande et al (2011) and Bensby et al (2014). The Milky Way, as a whole, has a broader spread in the age-metallicity correlation compared to the solar neighbourhood, for example Feuillet et al (2019). While this broader spread should not have much effect on the overall Galactic rates estimated in Table 3, we expect the P − q relation of sdB binaries to also become somewhat broader as larger parts of the Galaxy get included in the observed sample of sdB binaries.…”

Section: Galactic Formation Rates and Local Observationssupporting

confidence: 74%

Observed binary populations reflect the Galactic history

Vos

Bobrick

Vučković

2020

A&A

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Context. Wide hot subdwarf B (sdB) binaries with main-sequence companions are outcomes of stable mass transfer from evolved red giants. The orbits of these binaries show a strong correlation between their orbital periods and mass ratios. The origins of this correlation have, so far, been lacking a conclusive explanation. Aims. We aim to find a binary evolution model which can explain the observed correlation. Methods. Radii of evolved red giants, and hence the resulting orbital periods, strongly depend on their metallicity. We performed a small but statistically significant binary population synthesis study with the binary stellar evolution code MESA. We used a standard model for binary mass loss and a standard metallicity history of the Galaxy. The resulting sdB systems were selected based on the same criteria as was used in observations and then compared with the observed population. Results. We have achieved an excellent match to the observed period-mass ratio correlation without explicitly fine-tuning any parameters. Furthermore, our models produce a very good match to the observed period-metallicity correlation. We predict several new correlations, which link the observed sdB binaries to their progenitors, and a correlation between the orbital period, metallicity, and core mass for subdwarfs and young low-mass helium white dwarfs. We also predict that sdB binaries have distinct orbital properties depending on whether they formed in the Galactic bulge, thin or thick disc, or the halo. Conclusions. We demonstrate, for the first time, how the metallicity history of the Milky Way is imprinted in the properties of the observed post-mass transfer binaries. We show that Galactic chemical evolution is an important factor in binary population studies of interacting systems containing at least one evolved low-mass (Minit < 1.6 M⊙) component. Finally, we provide an observationally supported model of mass transfer from low-mass red giants onto main-sequence stars.

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Spatial variations in the Milky Way disc metallicity–age relation

Cited by 84 publications

References 101 publications

Unveiling the distinct formation pathways of the inner and outer discs of the Milky Way with Bayesian Machine Learning

Unveiling the distinct formation pathways of the inner and outer discs of the Milky Way with Bayesian Machine Learning

Age dissection of the Milky Way discs: Red giants in theKeplerfield

Observed binary populations reflect the Galactic history

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