Origin of α-rich young stars: clues from C, N, and O

Hekker, S.; Johnson, Jennifer A.

doi:10.1093/mnras/stz1554

Cited by 47 publications

(29 citation statements)

References 44 publications

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“…However, a detailed binary evolution modelling of the non-degenerate channel is needed to make any conclusive predictions. It may also be possible that the second-branch objects are members of a peculiar Galactic subpopulation with a metallicity of about [Fe/H] ≈ −1 and a broad range of ages between 5 and 10 Gyr not included in the Besanćon model, for example Chiappini et al (2015), Martig et al (2015) and Hekker & Johnson (2019). However, it seems unlikely that a separate unidentified population comparable in size to that of the thin disc would be present in the solar neighbourhood.…”

Section: Constraining Stellar Evolution With Sdb Binariesmentioning

confidence: 99%

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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Section: Constraining Stellar Evolution With Sdb Binariesmentioning

confidence: 99%

Observed binary populations reflect the Galactic history

Vos

Bobrick

Vučković

2020

A&A

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“…There is also likely evidence of such products among field stars that are enriched in α elements, hence supposedly belonging to an old population [50,98,107,108,134,219].…”

Section: Occurrence Of Mergers / Products Of Binary Evolutionmentioning

confidence: 99%

Haydn

Miglio

Girardi

Grundahl³

et al. 2021

Exp Astron

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In the last decade, the Kepler and CoRoT space-photometry missions have demonstrated the potential of asteroseismology as a novel, versatile and powerful tool to perform exquisite tests of stellar physics, and to enable precise and accurate characterisations of stellar properties, with impact on both exoplanetary and Galactic astrophysics. Based on our improved understanding of the strengths and limitations of such a tool, we argue for a new small/medium space mission dedicated to gathering high-precision, high-cadence, long photometric series in dense stellar fields. Such a mission will lead to breakthroughs in stellar astrophysics, especially in the metal poor regime, will elucidate the evolution and formation of open and globular clusters, and aid our understanding of the assembly history and chemodynamics of the Milky Way’s bulge and a few nearby dwarf galaxies.

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“…The origins of young, high-α stars are still debated: Chiappini et al (2015) postulated that these stars could arise from inert gas near the ends of the Galactic bar; other authors note that they are frequently found in binary systems (Jofré et al 2016) and show evidence of mass transfer (Yong et al 2016; see also Hekker & Johnson 2019) which suggests that these stars are truly Blue Straggler stars (Matsuno et al 2018;Sun et al 2020). This could lead to an observationally young population of stars which is kinematically old and similar in chemistry to the older thick disk.…”

Section: Evolution Of the Metallicity Gradient In The Thick Diskmentioning

confidence: 99%

The Flattening Metallicity Gradient in the Milky Way's Thin Disk

Vickers,

Shen,

2021

Preprint

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We calculate the ages, orbits and phase-space coordinates for a sample of ∼4 million LAMOST and Gaia stars. The ages are crossmatched and compared with values from two other popular age catalogs which derive the ages using different methods. Of these ∼4 million stars, we select a sample of 1.3 million stars and investigate their radial metallicity gradients (as determined by orbital radii) as a function of their ages. This analysis is performed on various subsets of the data split by chemistry and orbital parameters. We find that commonly used selections for "thin disk" stars (such as low-α chemistry or vertically thin orbits) yield radial metallicity gradients which generally grow shallower for the oldest stars. We interpret this as a hallmark feature of radial migration (churning). Constraining our sample to very small orbital Z max (the maximal height of a star's integrated orbit) makes this trend most pronounced. A chemistry-based "thin disk" selection of α-poor stars displays the same trend, but to a lesser extent. Intruigingly, we find that "thick disk" selections in chemistry and Z max reveal a slightly positive radial metallicity gradients which seem similar in magnitude at all ages. This may imply that the thick disk population is well mixed in age, but not in radius. This finding could help constrain conditions during the early epochs of Milky Way formation, and shed light on processes such as the accretion and reaccretion of gasses of different metallicities.

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Origin of α-rich young stars: clues from C, N, and O

Cited by 47 publications

References 44 publications

Observed binary populations reflect the Galactic history

Observed binary populations reflect the Galactic history

Haydn

The Flattening Metallicity Gradient in the Milky Way's Thin Disk

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