The Fall of a Giant. Chemical evolution of Enceladus, alias the Gaia Sausage

Vincenzo, Fiorenzo; Spitoni, E.; Calura, F.; Matteuccí, F.; Aguirre, V. Silva; Miglio, A.; Cescutti, G.

doi:10.1093/mnrasl/slz070

Cited by 136 publications

(132 citation statements)

References 61 publications

(76 reference statements)

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“…This Plume is largely responsible for the marked change in radial anisotropy with increasing [Fe/H] in the RRL sample, which resembles the one Belokurov et al (2018) found in a sample of main-sequence stars. In all respects, the kinematics of the Plume RRL closely resemble as the 'Gaia-Sausage' or 'Gaia-Enceladus' , which appear to have their origin in a large dwarf galaxy that merged with the MW (see also Myeong et al 2018;Kruijssen et al 2019;Mackereth et al 2019a;Vincenzo et al 2019;Fattahi et al 2019). The MDF of the Plume RRL is skewed towards higher metallicity than the MDF of other high-energy RRL, many of which are members of either the prograde Helmi-Stream or retrograde groups that may be part of the 'Sequoia' galaxy (Myeong et al 2019).…”

Section: Discussionmentioning

confidence: 91%

Local RR Lyrae stars: native and alien

Zinn

Chen

Layden

et al. 2019

Monthly Notices of the Royal Astronomical Society

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Measurements of [Fe/H] and radial velocity are presented for 89 RR Lyrae (RRL) candidates within 6 kpc of the Sun. After the removal of two suspected non-RRL, these stars were added to an existing database, which yielded 464 RRL with [Fe/H] on a homogeneous scale. Using data from the Gaia satellite (Data Release 2), we calculated the positions and space velocities for this sample. These data confirm the existence of a thin-disc of RRL with [α/Fe]∼ solar. The majority of the halo RRL with large total energies have near zero angular momenta about the Z axis. Kinematically these stars closely resemble the Gaia-Sausage/Gaia-Enceladus stars that others have proposed are debris from the merger of a large galaxy with the Milky Way. The metallicity and period distributions of the RRL and their positions in the period-amplitude diagram suggest that this disrupted galaxy was as massive as the Large Magellanic Cloud and possibly greater.

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Section: Discussionmentioning

confidence: 91%

Local RR Lyrae stars: native and alien

Zinn

Chen

Layden

et al. 2019

Monthly Notices of the Royal Astronomical Society

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“…Tolstoy et al 2009). Recent Galactic chemical evolution modelling suggest that this knee could be at around [Fe/H] ≈ −2.5 (Vincenzo et al 2019). The corresponding plateau value of [O/Fe] ≈ 0.7 at the lowest metallicities [Fe/H] −2.5 in the unclassified stars, is roughly 0.1 dex higher than that of the high-α halo population.…”

Section: The Low-metallicity Starsmentioning

confidence: 95%

Carbon, oxygen, and iron abundances in disk and halo stars

Amarsi

Nissen

Skúladóttir

2019

A&A

127

106

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The abundances of carbon, oxygen, and iron in late-type stars are important parameters in exoplanetary and stellar physics, as well as key tracers of stellar populations and Galactic chemical evolution. However, standard spectroscopic abundance analyses can be prone to severe systematic errors, based on the assumption that the stellar atmosphere is one-dimensional (1D) and hydrostatic, and by ignoring departures from local thermodynamic equilibrium (LTE). In order to address this, we carried out three-dimensional (3D) non-LTE radiative transfer calculations for C I and O I, and 3D LTE radiative transfer calculations for Fe II, across the STAGGER-grid of 3D hydrodynamic model atmospheres. The absolute 3D non-LTE versus 1D LTE abundance corrections can be as severe as − 0.3 dex for C I lines in low-metallicity F dwarfs, and − 0.6 dex for O I lines in high-metallicity F dwarfs. The 3D LTE versus 1D LTE abundance corrections for Fe II lines are less severe, typically less than + 0.15 dex. We used the corrections in a re-analysis of carbon, oxygen, and iron in 187 F and G dwarfs in the Galactic disk and halo. Applying the differential 3D non-LTE corrections to 1D LTE abundances visibly reduces the scatter in the abundance plots. The thick disk and high-α halo population rise in carbon and oxygen with decreasing metallicity, and reach a maximum of [C/Fe] ≈ 0.2 and a plateau of [O/Fe] ≈ 0.6 at [Fe/H] ≈ −1.0. The low-α halo population is qualitatively similar, albeit offset towards lower metallicities and with larger scatter. Nevertheless, these populations overlap in the [C/O] versus [O/H] plane, decreasing to a plateau of [C/O] ≈ −0.6 below [O/H] ≈ −1.0. In the thin-disk, stars having confirmed planet detections tend to have higher values of C∕O at given [O/H]; this potential signature of planet formation is only apparent after applying the abundance corrections to the 1D LTE results. Our grids of line-by-line abundance corrections are publicly available and can be readily used to improve the accuracy of spectroscopic analyses of late-type stars.

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“…Even though this is in fact the main tenet of the popular sub-field of Astrophysics known as Galactic Archaeology, not many such forensic studies are currently on record. Large numbers of detailed chemical abundances have so far only been collected and analysed for two stellar halo structures: the Sagittarius stream (see Monaco et al 2007;Chou et al 2007;de Boer et al 2015;Carlin et al 2018;Hayes et al 2020) and the Gaia Sausage (see Nissen & Schuster 2010;Helmi et al 2018;Mackereth et al 2019;Vincenzo et al 2019;Molaro et al 2020;Feuillet et al 2020). Additionally, a small number of stars in globular cluster streams have been under the magnifying glass of high-resolution spectroscopy (e.g.…”

Section: Introductionmentioning

confidence: 99%

The S2 Stream: the shreds of a primitive dwarf galaxy.*

Aguado

Belokurov

Evans

et al. 2020

Monthly Notices of the Royal Astronomical Society

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The S2 stream is a kinematically cold stream that is plunging downwards through the Galactic disc. It may be part of a hotter and more diffuse structure called the Helmi stream. We present a multi-instrument chemical analysis of the stars in the metal-poor S2 stream using both high- and low-resolution spectroscopy, complemented with a re-analysis of the archival data to give a total sample of 62 S2 members. Our high-resolution program provides α-elements (C, Mg, Si, Ca and Ti), iron-peak elements (V, Cr, Mn, Fe, Ni), n-capture process elements (Sr, Ba) and other elements such as Li, Na, Al, and Sc for a subsample of S2 objects. We report coherent abundance patterns over a large metallicity spread (∼1 dex) confirming that the S2 stream was produced by a disrupted dwarf galaxy. The combination of S2’s α-elements displays a mildly decreasing trend with increasing metallicity which can be tentatively interpreted as a “knee” at [Fe/H]<−2. At the low metallicity end, the n-capture elements in S2 may be dominated by r-process production however several stars are Ba-enhanced, but unusually poor in Sr. Moreover, some of the low-[Fe/H] stars appear to be carbon-enhanced. We interpret the observed abundance patterns with the help of chemical evolution models that demonstrate the need for modest star-formation efficiency and low wind efficiency confirming that the progenitor of S2 was a primitive dwarf galaxy.

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The Fall of a Giant. Chemical evolution of Enceladus, alias the Gaia Sausage

Cited by 136 publications

References 61 publications

Local RR Lyrae stars: native and alien

Local RR Lyrae stars: native and alien

Carbon, oxygen, and iron abundances in disk and halo stars

The S2 Stream: the shreds of a primitive dwarf galaxy.*

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