Chemical evolution of the Galactic bulge as traced by microlensed dwarf and subgiant stars. VI. Age and abundance structure of the stellar populations in the central sub-kpc of the Milky Way
Lund University1, Ohio State University2, Korea Astronomy and Space Science Institute3, Max Planck Society4, Smithsonian Astrophysical Observatory5, Australian National University6, University of São Paulo7, INAF8, Carnegie Learning9, University of Warsaw10, University of Warwick11, Nagoya University12, University of Notre Dame13, Massey University14, Goddard Space Flight Center15, Osaka University16
TL;DR: In this paper, a detailed elemental abundance study of 90 F and G dwarfs, turn-off, and subgiant stars in the Galactic bulge has been presented, based on high-resolution spectra acquired during gravitational microlensing events.
Abstract: We present a detailed elemental abundance study of 90 F and G dwarf, turn-off, and subgiant stars in the Galactic bulge. Based on high-resolution spectra acquired during gravitational microlensing events, stellar ages and abundances for 11 elements (Na, Mg, Al, Si, Ca, Ti, Cr, Fe, Zn, Y and Ba) have been determined. Four main findings are presented: (1) a wide metallicity distribution with distinct peaks at [Fe/H] = -1.09, -0.63, -0.20, + 0.12, + 0.41; (2) a highfraction of intermediate-age to young stars where at [Fe/H] > 0 more than 35% are younger than 8 Gyr, and for [Fe/H] ≲-0.5 most stars are 10 Gyr or older; (3) several episodes of significant star formation in the bulge has been identified: 3, 6, 8, and 11 Gyr ago; (4) tentatively the "knee" in the α-element abundance trends of the sub-solar metallicity bulge is located at a slightly higher [Fe/H] than in the local thick disk. These findings show that the Galactic bulge has complex age and abundance properties that appear to be tightly connected to the main Galactic stellar populations. In particular, the peaks in the metallicity distribution, the star formation episodes, and the abundance trends, show similarities with the properties of the Galactic thin and thick disks. At the same time, the star formation rate appears to have been slightly faster in the bulge than in the local thick disk, which most likely is an indication of the denser stellar environment closer to the Galactic centre. There are also additional components not seen outside the bulge region, and that most likely can be associated with the Galactic bar. Our results strengthen the observational evidence that support the idea of a secular origin for the Galactic bulge, formed out of the other main Galactic stellar populations present in the central regions of our Galaxy. Additionally, our analysis of this enlarged sample suggests that the (V-I)0 colour of the bulge red clump should be revised to 1.09. (Less)
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TL;DR: In this paper, the authors calculate the evolution of heavy element abundances from C to Zn in the solar neighborhood adopting their new nucleosynthesis yields, based on the light curve and spectra fitting of individual supernovae.
Abstract: We calculate the evolution of heavy element abundances from C to Zn in the solar neighborhood adopting our new nucleosynthesis yields. Our yields are calculated for wide ranges of metallicity (Z=0-Z_\odot) and the explosion energy (normal supernovae and hypernovae), based on the light curve and spectra fitting of individual supernovae. The elemental abundance ratios are in good agreement with observations. Among the alpha-elements, O, Mg, Si, S, and Ca show a plateau at [Fe/H] < -1, while Ti is underabundant overall. The observed abundance of Zn ([Zn/Fe] ~ 0) can be explained only by the high energy explosion models, which requires a large contribution of hypernovae. The observed decrease in the odd-Z elements (Na, Al, and Cu) toward low [Fe/H] is reproduced by the metallicity effect on nucleosynthesis. The iron-peak elements (Cr, Mn, Co, and Ni) are consistent with the observed mean values at -2.5 < [Fe/H] < -1$, and the observed trend at the lower metallicity can be explained by the energy effect. We also show the abundance ratios and the metallicity distribution functions of the Galactic bulge, halo, and thick disk. Our results suggest that the formation timescale of the thick disk is ~ 1-3 Gyr.
500 citations
TL;DR: Poulopoulos and Nissen as discussed by the authors reported support for this work from the NSF through the Graduate Research Fellowships Program (grant #DGE1144082), the Josephine de Karman Fellowship Trust, the Illinois Space Grant Consortium, and the Lewis and Clark Fund for Exploration and Field Research in Astrobiology.
Abstract: Poul
Nissen, and the anonymous referee for valuable input. M.B.
acknowledges support for this work from the NSF through the
Graduate Research Fellowships Program (grant #DGE1144082),
the Josephine de Karman Fellowship Trust, the
Illinois Space Grant Consortium, and the Lewis and Clark Fund
for Exploration and Field Research in Astrobiology. J.L.B.
acknowledges support for this work from the NSF (grant
number AST-1313119), the Alfred P. Sloan Foundation, and
the David and Lucile Packard Foundation. J.M. and L.S.
acknowledge the support from FAPESP (2012/24392-2 and
2014/15706-9)
147 citations
Cites background from "Chemical evolution of the Galactic ..."
...Sodium, as an odd-Z light element, follows a similar trend but shows hints of more complex evolution, as has been previously noted in studies of sodium abundance as a function of metallicity (Bensby et al. 2017)....
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TL;DR: In this paper, the trend of copper and zinc abundances as a function of the metallicity [Fe/H] is discussed and compared to that of other heavy elements beyond iron.
Abstract: We present new observations of copper and zinc abundances in 90 metal-poor stars, belonging to the metallicity range -3 100). The trend of Cu and Zn abundances as a function of the metallicity [Fe/H] is discussed and compared to that of other heavy elements beyond iron. We also estimate spatial velocities and galactic orbital parameters for our target stars in order to disentangle the population of disk stars from that of halo stars using kinematic criteria. In the absence of a firm a priori knowledge of the nucleosynthesis mechanisms controlling Cu and Zn production, and of the relative stellar sites, we derive constraints on these last from the trend of the observed ratios [Cu/Fe] and [Zn/Fe] throughout the history of the Galaxy, as well as from a few well established properties of basic nucleosynthesis processes in stars. We thus confirm that the production of Cu and Zn requires a number of different sources (neutron captures in massive stars, s-processing in low and intermediate mass stars, explosive nucleosynthesis in various supernova types). We also attempt a ranking of the relative roles played by different production mechanisms, and verify these hints through a simple estimate of the galactic enrichment in Cu and Zn. In agreement with suggestions presented earlier, we find evidence that Type Ia Supernovae must play a relevant role, especially for the production of Cu.
126 citations
Leibniz Institute for Astrophysics Potsdam1, University of Barcelona2, Universidade Federal do Rio Grande do Sul3, University of Birmingham4, University of Porto5, University of São Paulo6, Millennium Institute7, Andrés Bello National University8, University of La Laguna9, Spanish National Research Council10, Carnegie Learning11, University of Notre Dame12, Apache Corporation13, Sternberg Astronomical Institute14, University of Utah15, University of Arizona16, Centre national de la recherche scientifique17, Texas Christian University18, Pontifical Catholic University of Chile19, University of Atacama20, University of Virginia21, Johns Hopkins University22, University of Antofagasta23, University of La Serena24, University of Washington25, University of Colorado Boulder26
TL;DR: The StarHorse code as mentioned in this paper is written in python 3.6 and makes use of several community-developed python packages, among them astropy (Astropy Collaboration 2013), ezpadova (https://github.com/mfouesneau/ezpadova), numpy and scipy (Virtanen et al. 2020), and matplotlib (Hunter 2007).
Abstract: The StarHorse code is written in python 3.6 and makes use of several community-developed python packages, among them astropy (Astropy Collaboration 2013), ezpadova (https://github.com/ mfouesneau/ezpadova), numpy and scipy (Virtanen et al. 2020), and matplotlib (Hunter 2007). The code also makes use of the photometric filter database of VOSA (Bayo et al. 2008), developed under the Spanish Virtual Observatory project supported from the Spanish MICINN through grant AyA2011-24052. Funding for the SDSS Brazilian Participation Group has been provided by the Ministerio de Ciencia e Tecnologia (MCT), Fundacao Carlos Chagas Filho de Amparo a Pesquisa do Estado do Rio de Janeiro (FAPERJ), Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq), and Financiadora de Estudos e Projetos (FINEP). Funding for the Sloan Digital Sky Survey IV has been provided by the Alfred P. Sloan Foundation, the US Department of Energy Office of Science, and the Participating Institutions. SDSS-IV acknowledges support and resources from the Center for High-Performance Computing at the University of Utah. The SDSS web site is www.sdss. org. SDSS-IV is managed by the Astrophysical Research Consortium for the Participating Institutions of the SDSS Collaboration including the Brazilian Participation Group, the Carnegie Institution for Science, Carnegie Mellon University, the Chilean Participation Group, the French Participation Group, Harvard-Smithsonian Center for Astrophysics, Instituto de Astrofisica de Canarias, The Johns Hopkins University, Kavli Institute for the Physics and Mathematics of the Universe (IPMU)/University of Tokyo, Lawrence Berkeley National Laboratory, Leibniz-Institut fur Astrophysik Potsdam (AIP), Max-Planck-Institut fur Astronomie (MPIA Heidelberg), Max-Planck-Institut fur Astrophysik (MPA Garching), Max-Planck-Institut fur Extraterrestrische Physik (MPE), National Astronomical Observatory of China, New Mexico State University, New York University, University of Notre Dame, Observatario Nacional/MCTI, The Ohio State University, Pennsylvania State University, Shanghai Astronomical Observatory, United Kingdom Participation Group, Uni-versidad Nacional Autonoma de Mexico, University of Arizona, University of Colorado Boulder, University of Oxford, University of Portsmouth, University of Utah, University of Virginia, University of Washington, University of Wisconsin, Vanderbilt University, and Yale University. Guoshoujing Telescope (the Large Sky Area Multi-Object Fiber Spectroscopic Telescope LAMOST) is a National Major Scientific Project built by the Chinese Academy of Sciences. Funding for the project has been provided by the National Development and Reform Commission. LAMOST is operated and managed by the National Astronomical Observatories, Chinese Academy of Sciences. Funding for RAVE has been provided by: the Australian Astronomical Observatory; the Leibniz-Institut fur Astrophysik Potsdam (AIP); the Australian National University; the Australian Research Council; the French National Research Agency; the German Research Foundation (SPP 1177 and SFB 881); the European Research Council (ERC-StG 240271 Galactica); the Istituto Nazionale di Astrofisica at Padova; The Johns Hopkins University; the National Science Foundation of the USA (AST-0908326); the W. M. Keck foundation; the Macquarie University; the Netherlands Research School for Astronomy; the Natural Sciences and Engineering Research Council of Canada; the Slovenian Research Agency; the Swiss National Science Foundation; the Science & Technology Facilities Council of the UK; Opticon; Strasbourg Observatory; and the Universities of Groningen, Heidelberg and Sydney. The RAVE web site is at https://www.rave-survey. org. This work has made use of data from the European Space Agency (ESA) mission Gaia (http://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, http://www.cosmos.esa. int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. This work has also made use of data from Gaia-ESO based on data products from observations made with ESO Telescopes at the La Silla Paranal Observatory under programme ID 188.B-3002. FA is grateful for funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 800502 H2020-MSCA-IF-EF-2017. CC acknowledges support from DFG Grant CH1188/2-1 and from the ChETEC COST Action (CA16117)
114 citations
Cites background from "Chemical evolution of the Galactic ..."
...Additionally, for the first time, ages of large numbers of field stars are being determined with sufficient precision, at least within ' 2 kpc, to impose strong direct constraints on the Galactic star formation history (Ness et al. 2019; Bensby et al. 2017)....
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Uppsala University1, Columbia University2, Monash University3, INAF4, University of New South Wales5, Macquarie University6, University of Ljubljana7, Harvard University8, University of Sydney9, University of Western Australia10, Johns Hopkins University11, Carnegie Learning12, Princeton University13
TL;DR: In this paper, the authors investigated correlations between chemical compositions, ages, and kinematics for a subset of the overlap between the spectroscopic Galactic Archaeology with HERMES (GALAH) survey and $Gaia$ provides a high-dimensional chemodynamical space of unprecedented size.
Abstract: The overlap between the spectroscopic Galactic Archaeology with HERMES (GALAH) survey & $Gaia$ provides a high-dimensional chemodynamical space of unprecedented size. We present a first analysis of a subset of this overlap, of 7066 dwarf, turn-off, & sub-giant stars. [...] We investigate correlations between chemical compositions, ages, & kinematics for this sample. Stellar parameters & elemental abundances are derived from the GALAH spectra with the spectral synthesis code SME. [...] We report Li, C, O, Na, Mg, Al, Si, K, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Y, as well as Ba & we note that we employ non-LTE calculations for Li, O, Al, & Fe. We show that the use of astrometric & photometric data improves the accuracy of the derived spectroscopic parameters, especially $\log g$. [...] we recover the result that stars of the high-$\alpha$ sequence are typically older than stars in the low-$\alpha$ sequence, the latter spanning $-0.7 8$ Gyr have lower angular momenta $L_z$ than the Sun, which implies that they are on eccentric orbits & originate from the inner disk. Contrary to some previous smaller scale studies we find a continuous evolution in the high-$\alpha$-sequence up to super-solar [Fe/H] rather than a gap, which has been interpreted as a separate "high-$\alpha$ metal-rich" population. Stars in our sample that are younger than 10 Gyr, are mainly found on the low $\alpha$-sequence & show a gradient in $L_z$ from low [Fe/H] ($L_z>L_{z,\odot}$) towards higher [Fe/H] ($L_z
99 citations
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TL;DR: In this paper, the nucleosynthetic yield of isotopes lighter than A = 66 (zinc) is determined for a grid of stellar masses and metallicities including stars of 11, 12, 13, 15, 18, 19, 20, 22, 25, 30, 35, and 40 M{sub {circle_dot}} and metals Z = 0, 10{sup {minus}4}, 0.01, 0.1, and 1 times solar (a slightly reduced mass grid is employed for non-solar metallicities).
Abstract: The nucleosynthetic yield of isotopes lighter than A = 66 (zinc) is determined for a grid of stellar masses and metallicities including stars of 11, 12, 13, 15, 18, 19, 20, 22, 25, 30, 35, and 40 M{sub {circle_dot}} and metallicities Z = 0, 10{sup {minus}4}, 0.01, 0.1, and 1 times solar (a slightly reduced mass grid is employed for non-solar metallicities). Altogether 78 different model supernova explosions are calculated. In each case nucleosynthesis has already been determined for 200 isotopes in each of 600 to 1200 zones of the presupernova star, including the effects of time dependent convection. Here each star is exploded using a piston to give a specified final kinetic energy at infinity (typically 1.2 {times} 10{sup 51} erg), and the explosive modifications to the nucleosynthesis, including the effects of neutrino irradiation, determined. A single value of the critical {sup 12}C({sub {alpha},{gamma}}){sup 16}O reaction rate corresponding to S(300 keV) = 170 keV barns is used in all calculations. The synthesis of each isotope is discussed along with its sensitivity to model parameters. In each case, the final mass of the collapsed remnant is also determined and often found not to correspond to the location of the pistonmore » (typically the edge of the iron core), but to a ``mass cut`` farther out. This mass cut is sensitive not only to the explosion energy, but also to the presupernova structure, stellar mass, and the metallicity. Unless the explosion mechanism, for unknown reasons, provides a much larger characteristic energy in more massive stars, it appears likely that stars larger than about 30 M{sub {center_dot}} will experience considerable reimplosion of heavy elements following the initial launch of a successful shock. While such explosions will produce a viable, bright Type II supernova light curve, lacking the radioactive tail, they will have dramatically reduced yields of heavy elements and may leave black hole remnants of up to 10 and more solar masses.« less
3,649 citations
"Chemical evolution of the Galactic ..." refers background in this paper
...…are useful tracers of Galactic chemical evolution as they are believed to mainly come from one type of source, core-collapse supernovae (e.g. Arnett 1996; Woosley & Weaver 1995), even though some of them might have significant contributions from low-mass stars as well (e.g. Thielemann et al. 2002)....
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...Na is partly made in massive stars, in the C-burning phase (e.g. Woosley & Weaver 1995), and partly from low-mass stars through the Ne-Na and Mg-Al cycles and mixed to the surface when ascending the red giant branch (e.g. Karakas 2010)....
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3,633 citations
"Chemical evolution of the Galactic ..." refers background in this paper
...…and A.2 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/XXX/AXX. a so called “classical bulge” (e.g. White & Rees 1978; Matteucci & Brocato 1990; Ferreras et al. 2003; Rahimi et al. 2010)....
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TL;DR: In this article, an extensive grid of spherically-symmetric models (supplemented with plane-parallel ones for the highest surface gravities), built on up-to-date atomic and molecular data, is presented.
Abstract: Context. In analyses of stellar spectra and colours, and for the analysis of integrated light from galaxies, a homogeneous grid of model atmospheres of late-type stars and corresponding flux spectra is needed. Aims. We construct an extensive grid of spherically-symmetric models (supplemented with plane-parallel ones for the highest surface gravities), built on up-to-date atomic and molecular data, and make it available for public use. Methods. The most recent version of the MARCS program is used. Results. We present a grid of about 104 model atmospheres for stars with 2500K <= T-eff <= 8000 K, -1 <= log g = log (GM/R-2) <= 5 (cgs) with various masses and radii, -5 <= [Me/H] <= + 1, with [alpha/Fe] = 0.0 and 0.4 and different choices of C and N abundances. This includes "CN-cycled" models with C/N=4.07 (solar), 1.5 and 0.5, C/O ranging from 0.09 to (normally) 5.0 to also represent stars of spectral types R, S and N, and with 1.0 <= xi(t) = 5km s(-1). We also list thermodynamic quantities (T, P-g, P-e, rho, partial pressures of molecules, etc.) and provide them on the World Wide Web, as well as calculated fluxes in approximately 108 000 wavelength points. Underlying assumptions in addition to 1D stratification (spherical or plane-parallel) include hydrostatic equilibrium, mixing-length convection and local thermodynamic equilibrium. We discuss a number of general properties of the models, in particular in relation to the effects of changing abundances, of blanketing, and of sphericity. We illustrate positive and negative feedbacks between sphericity and molecular blanketing. We compare the models with those of other available grids and find excellent agreement with planeparallel models of Castelli & Kurucz (if convection is treated consistently) within the overlapping parameter range. Although there are considerable departures from the spherically-symmetric NextGen models, the agreement with more recent PHOENIX models is gratifying. Conclusions. The models of the grid show considerable regularities, but some interesting departures from general patterns occur for the coolest models due to the molecular opacities. We have tested a number of approximate "rules of thumb" concerning effects of blanketing and sphericity and often found them to be astonishingly accurate. Some interesting new phenomena have been discovered and explored, such as the intricate coupling between blanketing and sphericity, and the strong effects of carbon enhancement on metal-poor models. We give further details of line absorption data for molecules, as well as details of models and comparisons with observations in subsequent papers.
2,411 citations
TL;DR: In the far future, evolution will mostly be secular, the slow rearrangement of energy and mass that results from interactions involving collective phenomena such as bars, oval disks, spiral structure, and triaxial dark halos as mentioned in this paper.
Abstract: ▪ Abstract The Universe is in transition. At early times, galactic evolution was dominated by hierarchical clustering and merging, processes that are violent and rapid. In the far future, evolution will mostly be secular—the slow rearrangement of energy and mass that results from interactions involving collective phenomena such as bars, oval disks, spiral structure, and triaxial dark halos. Both processes are important now. This review discusses internal secular evolution, concentrating on one important consequence, the buildup of dense central components in disk galaxies that look like classical, merger-built bulges but that were made slowly out of disk gas. We call these pseudobulges. We begin with an “existence proof”—a review of how bars rearrange disk gas into outer rings, inner rings, and stuff dumped onto the center. The results of numerical simulations correspond closely to the morphology of barred galaxies. In the simulations, gas is transported to small radii, where it reaches high densities and...
1,767 citations
"Chemical evolution of the Galactic ..." refers background in this paper
...It is now widely believed that the bulge is a boxy peanut-shaped (e.g. Dwek et al. 1995; Wegg & Gerhard 2013) pseudo-bulge of a secular origin (Kormendy & Kennicutt 2004) rather than being a classical spheroid....
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1,649 citations
"Chemical evolution of the Galactic ..." refers background in this paper
...…a long time been regarded as the oldest components of spiral galaxies (see review by e.g. Wyse et al. 1997), formed during the initial monolithic collapse era of galaxy formation (Eggen et al. 1962), or merging of clumps within the disk at high red-shift (e.g. Noguchi 1999; Bournaud et al. 2009)....
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