Star Formation Timescales of the Halo Populations from Asteroseismology and Chemical Abundances*

Matsuno, Tadafumi; Aoki, Wako; Casagrande, Luca; Ishigaki, Miho N.; Shi, Jianrong; Takata, Masasuke; Xiang, Maosheng; Yong, David; Li, Haining; Suda, Takuma; Xing, Qianfan; Zhao, Jingkun

doi:10.3847/1538-4357/abeab2

Cited by 22 publications

(32 citation statements)

References 194 publications

(285 reference statements)

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“…Cu: We find depleted [Cu/Fe] abundances for the blob stars with mean of −0.35 dex, where the trend is essentially flat for [Fe/H] > −1.5 dex but is decreasing with decreasing [Fe/H] below this value. Our Cu result agrees with that of Nissen & Schuster ( 2011 ) as well as the more recent study from Matsuno et al ( 2020 ), where both show [Cu/Fe] abundances below 0 dex for low-α accreted halo stars. Taking into account the difference between our solar Cu abundance and that of Asplund et al ( 2009 ) (Reddy et al 2003(Reddy et al , 2006Yong et al 2013 ;Bensby 2014 ;Battistini & Bensby 2015 ), gold pentagons for accreted stars (Nissen & Schuster 2010, 2011Fishlock et al 2017 ), and green triangles for LMC (Van der Swaelmen et al 2013 ).…”

Section: Light and Odd-z Elementssupporting

confidence: 92%

“…More recent studies (e.g. Matsuno et al 2020Matsuno et al , 2021Aguado et al 2021 ) also find r-process enhancement in GES stars. Most of the studies aforementioned have samples of 10-30 low-α stars, but as been shown with more recent studies using large surv e ys (e.g.…”

mentioning

confidence: 75%

“…These authors find that the low-α stars have higher [Eu/Fe] compared to the high-α stars that have in situ origins. Matsuno et al ( 2020Matsuno et al ( , 2021 and Aguado et al ( 2021 ) all find enhanced Eu abundances for their respective samples of low-α accreted stars, pointing to the pre v alence of r-process in their progenitor. It is worth noting that r-process sites are rare and so the r-process abundance trends in lowmass systems are mostly due to stochastic effects (e.g.…”

Section: Neutr On-captur E Elementsmentioning

confidence: 90%

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The detailed chemical abundance patterns of accreted halo stars from the optical to infrared

Carrillo

Hawkins

Jofré

et al. 2022

Monthly Notices of the Royal Astronomical Society

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Understanding the assembly of our Galaxy requires us to also characterize the systems that helped build it. In this work, we accomplish this by exploring the chemistry of accreted halo stars from the Gaia-Enceladus/Gaia-Sausage (GES) selected in the infrared from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) Data Release 16. We use high resolution optical spectra for 62 GES stars to measure abundances in 20 elements spanning the α, Fe-peak, light, odd-Z, and notably, the neutron-capture groups of elements to understand their trends in the context of and in contrast to the Milky Way and other stellar populations. Using these derived abundances we find that the optical and the infrared abundances agree to within 0.15 dex except for O, Co, Na, Cu, and Ce. These stars have enhanced neutron-capture abundance trends compared to the Milky Way, and their [Eu/Mg] and neutron-capture abundance ratios (e.g. [Y/Eu], [Ba/Eu], [Zr/Ba], [La/Ba], and [Nd/Ba]) point to r-process enhancement and a delay in s-process enrichment. Their [α/Fe] trend is lower than the Milky Way trend for [Fe/H]>-1.5 dex, similar to previous studies of GES stars and consistent with the picture that these stars formed in a system with a lower rate of star formation. This is further supported by their depleted abundances in Ni, Na, and Cu abundances, again, similar to previous studies of low-α stars with accreted origins.

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Section: Light and Odd-z Elementssupporting

confidence: 92%

mentioning

confidence: 75%

Section: Neutr On-captur E Elementsmentioning

confidence: 90%

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The detailed chemical abundance patterns of accreted halo stars from the optical to infrared

Carrillo

Hawkins

Jofré

et al. 2022

Monthly Notices of the Royal Astronomical Society

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“…The mean age of GSE stars is found to be ≈ 10 Gyr (e.g. Kilic et al 2019;Borre et al 2021;Montalbán et al 2021;Matsuno et al 2021b). On the other hand, Sequoia stars are found to be slightly older than GSE (e.g.…”

Section: Sequoia and Other Very Retrograde Substructuresmentioning

confidence: 99%

GASTRO library I: the simulated chemodynamical properties of several GSE-like stellar halos

Amarante,

Debattista,

Silva

et al. 2022

Preprint

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The Milky Way stellar halo contains relics of ancient mergers that tell the story of our Galaxy's formation. Some of them are identified due to their similarity in energy, actions and chemistry, referred to as the "chemodynamical space", and are often attributed to distinct merger events. It is also known that our Galaxy went through a significant merger event that shaped the local stellar halo during its first Gyr. Previous studies using N -body only and cosmological hydrodynamical simulations have shown that such single massive merger can produce several "signatures" in the chemodynamical space, which can potentially be misinterpreted as distinct merger events. Motivated by these, in this work we use a subset of the GASTRO library which consists of several SPH+N -body models of single accretion event in a Milky Way-like galaxy. Here, we study models with orbital properties similar to the main merger event of our Galaxy and explore the implications to known stellar halo substructures. We find that: i. supernova feedback efficiency influences the satellite's structure and orbital evolution, resulting in distinct chemodynamical features for models with the same initial conditions, ii. very retrograde high energy stars are the most metal-poor of the accreted dwarf galaxy and could be misinterpreted as a distinct merger iii. the most bound stars are more metal-rich in our models, the opposite of what is observed in the Milky Way, suggesting a secondary massive merger, and finally iv. our models can reconcile other known substructures to an unique progenitor.

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“…In the present study we compare Eu abundances of stars in Gaia-Enceladus with those of stars formed in the Milky Way (the in situ stars having high-[Mg/Fe]) with the aim of obtaining constraints on r-process enrichment processes. Although Ishigaki et al (2013), Fishlock et al (2017), andMatsuno et al (2021) presented hints of Eu enhancements of the low-Mg halo stars, their samples were of limited size. Thanks to the Gaia mission and the recent data release from the optical high-resolution spectroscopic survey, the Galactic Archaeology with HERMES (GALAH; De Silva et al 2015), we can now study this phenomenon with a larger sample analysed homogeneously.…”

Section: Introductionmentioning

confidence: 98%

R-process enhancements of Gaia-Enceladus in GALAH DR3

Matsuno

Hirai

Tarumi

et al. 2021

A&A

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Context. The dominant site of production of r-process elements remains unclear despite recent observations of a neutron star merger. Observational constraints on the properties of the sites can be obtained by comparing r-process abundances in different environments. The recent Gaia data releases and large samples from high-resolution optical spectroscopic surveys are enabling us to compare r-process element abundances between stars formed in an accreted dwarf galaxy, Gaia-Enceladus, and those formed in the Milky Way. Aims. Our aim is to understand the origin of r-process elements in Gaia-Enceladus. Methods. We first constructed a sample of stars so that our study on Eu abundance is not affected by the detection limit. We then kinematically selected 76 Gaia-Enceladus stars and 81 in situ stars from the Galactic Archaeology with HERMES (GALAH) DR3, of which 47 and 55 stars, respectively, can be used to study Eu reliably. Results. Gaia-Enceladus stars clearly show higher ratios of [Eu/Mg] than in situ stars. High [Eu/Mg] along with low [Mg/Fe] are also seen in relatively massive satellite galaxies such as the LMC, Fornax, and Sagittarius dwarfs. On the other hand, unlike these galaxies, Gaia-Enceladus does not show enhanced [Ba/Eu] or [La/Eu] ratios suggesting a lack of significant s-process contribution. From comparisons with simple chemical evolution models, we show that the high [Eu/Mg] of Gaia-Enceladus can naturally be explained by considering r-process enrichment by neutron-star mergers with delay time distribution that follows a power-law similar to type Ia supernovae but with a shorter minimum delay time.

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Star Formation Timescales of the Halo Populations from Asteroseismology and Chemical Abundances*

Cited by 22 publications

References 194 publications

The detailed chemical abundance patterns of accreted halo stars from the optical to infrared

The detailed chemical abundance patterns of accreted halo stars from the optical to infrared

GASTRO library I: the simulated chemodynamical properties of several GSE-like stellar halos

R-process enhancements of Gaia-Enceladus in GALAH DR3

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