Chemical evolution of the Galactic bulge as traced by microlensed dwarf and subgiant stars - V. Evidence for a wide age distribution and a complex MDF
Thomas Bensby,Jennifer C. Yee,Sofia Feltzing,Jennifer A. Johnson,Andrew Gould,J. G. Cohen,Martin Asplund,Jorge Melendez,Sara Lucatello,C. Han,Ian B. Thompson,Avishay Gal-Yam,Andrzej Udalski,David P. Bennett,Ian A. Bond,W. Kohei,Takahiro Sumi,Daisuke Suzuki,K. Suzuki,S. Takino,Paul J. Tristram,N. Yamai,Atsunori Yonehara +22 more
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In this paper, a detailed elemental abundance analysis of 32 dwarfs and subgiant stars in the Galactic bulge is presented, based on high-resolution spectra obtained during gravitational microlensing events.Abstract:
Based on high-resolution spectra obtained during gravitational microlensing events we present a detailed elemental abundance analysis of 32 dwarf and subgiant stars in the Galactic bulge. Combined with the sample of 26 stars from the previous papers in this series, we now have 58 microlensed bulge dwarfs and subgiants that have been homogeneously analysed. The main characteristics of the sample and the findings that can be drawn are: (i) the metallicity distribution (MDF) is wide and spans all metallicities between [Fe/H] = −1.9 to +0.6; (ii) the dip in the MDF around solar metallicity that was apparent in our previous analysis of a smaller sample (26 microlensed stars) is no longer evident; instead it has a complex structure and indications of multiple components are starting to emerge. A tentative interpretation is that there could be different stellar populations at interplay, each with a different scale height: the thin disk, the thick disk, and a bar population; (iii) the stars with [Fe/H] ≲ −0.1 are old with ages between 10 and 12 Gyr; (iv) the metal-rich stars with [Fe/H] ≳ −0.1 show a wide variety of ages, ranging from 2 to 12 Gyr with a distribution that has a dominant peak around 4−5 Gyr and a tail towards higher ages; (v) there are indications in the [α/Fe]−[Fe/H] abundance trends that the “knee” occurs around [Fe/H] = −0.3 to −0.2, which is a slightly higher metallicity as compared to the “knee” for the local thick disk. This suggests that the chemical enrichment of the metal-poor bulge has been somewhat faster than what is observed for the local thick disk. The results from the microlensed bulge dwarf stars in combination with other findings in the literature, in particular the evidence that the bulge has cylindrical rotation, indicate that the Milky Way could be an almost pure disk galaxy. The bulge would then just be a conglomerate of the other Galactic stellar populations (thin disk, thick disk, halo, and ...?), residing together in the central parts of the Galaxy, influenced by the Galactic bar.read more
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The Galaxy in Context: Structural, Kinematic, and Integrated Properties
TL;DR: In this paper, the authors review the key integrated, structural and kinematic parameters of the Galaxy, and point to uncertainties as well as directions for future progress, and show that the Galaxy is a luminous (L⋆) barred spiral with a central box/peanut bulge, a dominant disk, and a diffuse stellar halo.
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Exploring the Milky Way stellar disk - A detailed elemental abundance study of 714 F and G dwarf stars in the solar neighbourhood
TL;DR: In this paper, a high-resolution spectroscopic study of 714 F and G dwarfs and subgiant stars in the Solar neighbourhood was conducted, where the star sample has been kinematically selected to trace the Galactic thin and thick disks to their extremes, the metal-rich stellar halo, sub-structures in velocity space such as the Hercules stream and the Arcturus moving group, as well as stars that cannot be associated with either the thin disk or the thick disk.
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Reconciling the Stellar and Nebular Spectra of High Redshift Galaxies
Charles C. Steidel,Allison L. Strom,Max Pettini,Gwen C. Rudie,Naveen A. Reddy,Ryan F. Trainor +5 more
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Dynamical modelling of the galactic bulge and bar: the Milky Way's pattern speed, stellar and dark matter mass distribution
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Spectroscopic Determination of Masses (And Implied Ages) for Red Giants
Melissa Ness,David W. Hogg,David W. Hogg,H-W. Rix,Marie Martig,Marc H. Pinsonneault,Anna Y. Q. Ho,Anna Y. Q. Ho +7 more
TL;DR: In this article, a data-driven spectral model using The Cannon, which can determine stellar masses to ~0.07 dex from apogee dr12 spectra of red giants, was presented.
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