Two distinct halo populations in the solar neighborhood. II. Evidence from stellar abundances of Mn, Cu, Zn, Y, and Ba

By P. Nissen, W. Schuster. 2011

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A previous study (Nissen & Schuster 2010) of 94 dwarf stars with -1.6 < [Fe/H] < -0.4 has revealed the existence of two distinct halo populations with a systematic difference in [alpha/Fe] at a given metallicity. In continuation of that work, abundances of Mn, Cu, Zn, Y, and Ba are determined for the same sample of stars. Equivalent widths of atomic lines are measured from high resolution VLT/UVES and NOT/FIES spectra and used to derive precise abundance ratios from an LTE analysis based on MARCS model atmospheres. Systematic differences between the `high-alpha' and `low-alpha' halo populations are found for [Cu/Fe], [Zn/Fe], and [Ba/Y], whereas there is no significant difference in the case of [Mn/Fe]. At a given metallicity, [Cu/Fe] shows a large scatter that is closely correlated with a corresponding scatter in [Na/Fe] and [Ni/Fe]. The metallicity trends of [Cu/Fe], [Zn/Fe], and [Ba/Y] can be explained from existing nucleosynthesis calculations if the high-alpha stars formed in regions with such a high star formation rate that only massive stars and Type II supernovae contributed to the chemical enrichment. The low-alpha stars, on the other hand, most likely originate from systems with a slower chemical evolution, characterized by additional enrichment from Type Ia supernovae and low-mass AGB stars.

Subfields: Astronomy and Astrophysics, Global and Planetary Change

View Paper: https://www.semanticscholar.org/paper/df0b897178aa7ba83f8c6426ba351db71305f204

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Citations in the corpus

Through thick and thin: kinematic and chemical components in the solar neighbourhood (2010, methodology): “Guided by Nissen & Schuster (2010), we inspect the Na and Ni content of such stars for supporting evidence of this conclusion.”
HIGH-RESOLUTION SPECTROSCOPY OF EXTREMELY METAL-POOR STARS FROM SDSS/SEGUE. I. ATMOSPHERIC PARAMETERS AND CHEMICAL COMPOSITIONS (2012, background): “Recent abundance studies of halo stars with available full space motions suggest different trends in the [α/Fe] abundance ratios depending on kinematics (Zhang et al. 2009; Ishigaki et al. 2010; Nissen & Schuster 2010).”
The biggest splash (2019, background): “…et al. (2018b) and claim that the stars analysed by Bonaca et al. (2017), Haywood et al. (2018), Di Matteo et al. (2018) and earlier by Nissen & Schuster (2010), Nissen & Schuster (2011), and Schuster et al. (2012) are typically as old as the oldest accreted halo stars and…”
XHIP: An extended hipparcos compilation (2011, background): “J/AJ/124/1144 Two distinct halo populations in the solar neighborhood, Nissen & Schuster, 2010.”
OXYGEN ABUNDANCES IN NEARBY FGK STARS AND THE GALACTIC CHEMICAL EVOLUTION OF THE LOCAL DISK AND HALO (2013, background): “Thus, our oxygen abundance results for halo stars support the observations by Nissen & Schuster (2010) regarding α-element abundances, and therefore also suggest that there is a certain degree of heterogeneity in the abundances and kinematics of nearby halo stars.”
High-precision abundances of elements in solar twin stars - Trends with stellar age and elemental condensation temperature (2015, background): “A Ni-Na relation has, however, been found for thick-disk and halo stars with−1.6 < [Fe/H] − 0.4 (Nissen & Schuster 1997, 2010, 2011) and for stars in dwarf spheroidal galaxies in the same metallicity interval (Venn et al. 2004; Letarte 2010; Lemasle 2014).”
Non-LTE calculations for neutral Na in late-type stars using improved atomic data (2011, background): “Interestingly, Nissen & Schuster (2010) found evidence for systematic Na abundance differences of the order of 0.2 dex between α-poor and α-rich halo stars, with important implications for the presumably separate origin of these two Galactic components.”
Chemical signatures of formation processes in the stellar populations of simulated galaxies (2011, background): “There are also new observations suggesting differences in kinematics and α-enrichment for stars in the Milky Way stellar halo which might indicate the presence of two distinct stellar populations (e.g. Nissen & Schuster 2010; Beers et al. 2011).”
Extragalactic science, cosmology, and Galactic archaeology with the Subaru Prime Focus Spectrograph (2012, background): “The chemical abundances of stars reflect their past star-formation history and chemical evolution, possibly in association with the dynamical state of proto-galactic clouds such as their collision and merging (e. ., De Silva et al. 2007; Nissen & Schuster 2010).”
In Disguise or Out of Reach: First Clues about In Situ and Accreted Stars in the Stellar Halo of the Milky Way from Gaia DR2 (2018, background): “Fig 31 shows the [Fe/H]-[α/Fe] distribution of the sample of Nissen & Schuster (2010), with the high-α, low metallicity stars shown as blue square.”
THE MOST METAL-POOR STARS. II. CHEMICAL ABUNDANCES OF 190 METAL-POOR STARS INCLUDING 10 NEW STARS WITH [Fe/H] ⩽ −3.5,, (2012, background): “The reason for separating the dwarfs from giants is that we want to compare, as best we can, stars with similar stellar parameters to minimize systematic errors (e.g., Cayrel et al. 2004; Meléndez et al. 2008; Bonifacio et al. 2009; Alves-Brito et al. 2010; Nissen & Schuster 2010)16.”
The age structure of stellar populations in the solar vicinity Clues of a two-phase formation history of the Milky Way disk (2013, background): “All four stars are possible members of the so-called accreted halo (see Nissen & Schuster 2010)2.”
FORMATION AND EVOLUTION OF THE DISK SYSTEM OF THE MILKY WAY: [α/Fe] RATIOS AND KINEMATICS OF THE SEGUE G-DWARF SAMPLE (2011, background): “The recent study by Nissen & Schuster (2010) demonstrated that nearby dwarfs with halo kinematics could be separated into two groups on [α/Fe].”