Two distinct halo populations in the solar neighborhood - Evidence from stellar abundance ratios and kinematics

By P. Nissen, W. Schuster. 2010

175 citations recorded by the source corpus.

Aims. Precise abundance ratios are determined for 94 dwarf stars with 5200 < Teff < 6300 K, −1.6 < [Fe/H] < −0.4, and distances D < 335 pc. Most of them have halo kinematics, but 16 thick-disk stars are included. Methods. Equivalent widths of atomic lines are measured from VLT/UVES and NOT/FIES spectra with resolutions R � 55 000 and R � 40 000, respectively. An LTE abundance analysis based on MARCS models is applied to derive precise differential abundance ratios of Na, Mg, Si, Ca, Ti, Cr, and Ni with respect to Fe. Results. The halo stars fall into two populations, clearly separated in [α/Fe], where α refers to the average abundance of Mg, Si, Ca, and Ti. Differences in [Na/Fe] and [Ni/Fe] are also present with a remarkably clear correlation between these two abundance ratios. Conclusions. The “high-α” stars may be ancient disk or bulge stars “heated” to halo kinematics by merging satellite galaxies or they could have formed as the first stars during the collapse of a proto-Galactic gas cloud. The kinematics of the “low-α” stars suggest that they have been accreted from dwarf galaxies, and that some of them may originate from the ω Cen progenitor galaxy.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/1239208091d4a2dfca5b7d61fa68250a58df2d73

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In Astronomy and Astrophysics

1. D. Stello
2. I. Ramírez
3. G. Marcy
4. T. Bedding
5. Debra A. Fischer
6. A. Miglio
7. S. Hekker
8. C. Allende Prieto

In Instrumentation

1. D. Stello
2. G. Marcy
3. T. Bedding
4. I. Ramírez
5. H. Isaacson
6. A. Miglio
7. Debra A. Fischer
8. S. Hekker

Citations in the corpus

• Using chemical tagging to redefine the interface of the Galactic disc and halo (2015, methodology): “As noted by Nissen & Schuster (2011) the [Mn/Fe] ratio is comparable between the α-poor and α-rich halo sequences.”
• The biggest splash (2019, background): “…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 significantly older than the bulk of…”
• 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).”
• 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, result): “However, we note that ω Cen seems to have a peculiar barium abundance (Majewski et al. 2012) which appears not compatible with that of the low-α stars discussed here (see Nissen & Schuster 2011).”
• AN ANCIENT EXTRASOLAR SYSTEM WITH FIVE SUB-EARTH-SIZE PLANETS (2015, background): “Similarly favorable conditions to planet formation in iron-poor environments seem to be associated with a fraction of the halo stellar population, namely, the so-called high-α stars (Nissen & Schuster 2010).”
• OXYGEN ABUNDANCES IN NEARBY FGK STARS AND THE GALACTIC CHEMICAL EVOLUTION OF THE LOCAL DISK AND HALO (2013, background): “Low- and high-α halo stars have also separate Cu, Zn, and Ba to Fe abundance ratio trends (Nissen & Schuster 2011), but there is no significant difference regarding their lithium abundances (Nissen & Schuster 2012).”