893 research outputs found
Chemodynamical history of the Galactic Bulge
The Galactic Bulge can uniquely be studied from large samples of individual
stars, and is therefore of prime importance for understanding the stellar
population structure of bulges in general. Here the observational evidence on
the kinematics, chemical composition, and ages of Bulge stellar populations
based on photometric and spectroscopic data is reviewed. The bulk of Bulge
stars are old and span a metallicity range -1.5<~[Fe/H]<~+0.5. Stellar
populations and chemical properties suggest a star formation timescale below ~2
Gyr. The overall Bulge is barred and follows cylindrical rotation, and the more
metal-rich stars trace a Box/Peanut (B/P) structure. Dynamical models
demonstrate the different spatial and orbital distributions of metal-rich and
metal-poor stars. We discuss current Bulge formation scenarios based on
dynamical, chemical, chemodynamical and cosmological models. Despite impressive
progress we do not yet have a successful fully self-consistent chemodynamical
Bulge model in the cosmological framework, and we will also need more extensive
chrono-chemical-kinematic 3D map of stars to better constrain such models.Comment: 9 figures, 55 pages final version to appear in the Annual Reviews of
Astronomy & Astrophysics, volume 5
Abundances in the Galactic bulge: results from planetary nebulae and giant stars
Our understanding of the chemical evolution of the Galactic bulge requires
the determination of abundances in large samples of giant stars and planetary
nebulae (PNe). We discuss PNe abundances in the Galactic bulge and compare
these results with those presented in the literature for giant stars. We
present the largest, high-quality data-set available for PNe in the direction
of the Galactic bulge (inner-disk/bulge). For comparison purposes, we also
consider a sample of PNe in the Large Magellanic Cloud (LMC). We derive the
element abundances in a consistent way for all the PNe studied. By comparing
the abundances for the bulge, inner-disk, and LMC, we identify elements that
have not been modified during the evolution of the PN progenitor and can be
used to trace the bulge chemical enrichment history. We then compare the PN
abundances with abundances of bulge field giant. At the metallicity of the
bulge, we find that the abundances of O and Ne are close to the values for the
interstellar medium at the time of the PN progenitor formation, and hence these
elements can be used as tracers of the bulge chemical evolution, in the same
way as S and Ar, which are not expected to be affected by nucleosynthetic
processes during the evolution of the PN progenitors. The PN oxygen abundance
distribution is shifted to lower values by 0.3 dex with respect to the
distribution given by giants. A similar shift appears to occur for Ne and S. We
discuss possible reasons for this PNe-giant discrepancy and conclude that this
is probably due to systematic errors in the abundance derivations in either
giants or PNe (or both). We issue an important warning concerning the use of
absolute abundances in chemical evolution studies.Comment: 23 pages, 15 figures, 16 pages of online material, A&A in pres
Nonlinear dispersion relation in anharmonic periodic mass-spring and mass-in-mass systems
The study of wave propagation in chains of anharmonic periodic systems is of
fundamental importance to understand the response of dynamical absorbers of
vibrations and acoustic metamaterials working in nonlinear regime. Here, we
derive an analytical nonlinear dispersion relation for periodic chains of
anharmonic mass-spring and mass-in-mass systems resulting from considering the
hypothesis of weak anharmonic energy and a periodic distribution function as
ansatz of a general solution of the nonlinear equations of motion. Numerical
simulations show that this expression is valid for anharmonic potential energy
up to 50% of the harmonic one. This work provides a simple tool to design and
study nonlinear dynamics for a class of seismic metamaterials.Comment: 18 pages, 5 figure
A new method for estimating the pattern speed of spiral structure in the Milky Way
In the last few decades many efforts have been made to understand the effect
of spiral arms on the gas and stellar dynamics in the Milky Way disc. One of
the fundamental parameters of the spiral structure is its angular velocity, or
pattern speed , which determines the location of resonances in the
disc and the spirals' radial extent. The most direct method for estimating the
pattern speed relies on backward integration techniques, trying to locate the
stellar birthplace of open clusters. Here we propose a new method based on the
interaction between the spiral arms and the stars in the disc. Using a sample
of around 500 open clusters from the {\it New Catalogue of Optically Visible
Open Clusters and Candidates}, and a sample of 500 giant stars observed by
APOGEE, we find km s kpc, for a local
standard of rest rotation ~km s and solar radius ~kpc.
Exploring a range in and within the acceptable values, 200-240 km
s and 7.5-8.5 kpc, respectively, results only in a small change in our
estimate of , that is within the error. Our result is in close
agreement with a number of studies which suggest values in the range 20-25 km
s kpc. An advantage of our method is that we do not need
knowledge of the stellar age, unlike in the case of the birthplace method,
which allows us to use data from large Galactic surveys. The precision of our
method will be improved once larger samples of disk stars with spectroscopic
information will become available thanks to future surveys such as 4MOST.Comment: 10 pages, 6 figures, 4 tables, accepted for publication in MNRA
Reduce, Reuse, Recycle: Planetary Nebulae as Green Galactic Citizens
We review gas-phase abundances in PNe and describe their dual utility as
archives of original progenitor metallicity via the alpha elements, as well as
sources of processed material from nucleosynthesis during the star's evolution,
i.e., C, N, and s-process elements. We describe the analysis of PN spectra to
derive abundances and discuss the discrepancies that arise from different
choices at each step. Abundance results for the Milky Way and Magellanic Clouds
from various groups of investigators are presented; the observational results
are compared with theoretical predictions of AGB stellar yields. Finally, we
suggest areas where more work is needed to improve our abilities to determine
abundances in PNe.Comment: 8 pages, 7 figures, 1 table. Invited review presented at the IAU
Symposium No. 283, Planetary Nebulae: an Eye to the Futur
Mathematical modeling of oxygen control in biocell composting plants
We propose an optimal control problem to determine the best aeration strategy for aerobic biodegradation in a composting cell. The goal is to minimize the deviation of the oxygen level from its reference value for the entire duration of the biodegradation process. The mathematical model includes several chemical phenomena, like the aerobic biodegradation of the soluble substrate by means of a bacterial biomass, the hydrolysis of insoluble substrate and the biomass decay. The oxygen and the optimal mechanical aeration time profiles are obtained and discussed. Finally, the plant performance is evaluated in absence and presence of external aeration by means of several specific indices
Innovative Micro- and Nanostructured Materials and Devices for Energy Applications
1 Dipartimento di Ingegneria Elettrica e dell'Informazione (DEI), Politecnico di Bari, Via E. Orabona 4, 70125 Bari, Italy 2 Consiglio Nazionale delle Ricerche-Istituto di Fotonica e Nanotecnologie (CNRIFN), Via alla Cascata 56/C, 38123 Trento, Italy 3 Istituto Italiano di Tecnologia (IIT), Center for Biomolecular Nanotechnologies (CBN), Via Barsanti 1, 73010 Arnesano, Italy 4Department of Physics and Meteorology, Indian Institute of Technology Kharagpur, Kharagpur 721302, Indi
Looking for imprints of the first stellar generations in metal-poor bulge field stars
© 2016 ESO. Context. Efforts to look for signatures of the first stars have concentrated on metal-poor halo objects. However, the low end of the bulge metallicity distribution has been shown to host some of the oldest objects in the Milky Way and hence this Galactic component potentially offers interesting targets to look at imprints of the first stellar generations. As a pilot project, we selected bulge field stars already identified in the ARGOS survey as having [Fe/H] 1 and oversolar [α/Fe] ratios, and we used FLAMES-UVES to obtain detailed abundances of key elements that are believed to reveal imprints of the first stellar generations. Aims. The main purpose of this study is to analyse selected ARGOS stars using new high-resolution (R ∼ 45 000) and high-signal-tonoise (S=N > 100) spectra. We aim to derive their stellar parameters and elemental ratios, in particular the abundances of C, N, the α-elements O, Mg, Si, Ca, and Ti, the odd-Z elements Na and Al, the neutron-capture s-process dominated elements Y, Zr, La, and Ba, and the r-element Eu. Methods. High-resolution spectra of five field giant stars were obtained at the 8 m VLT UT2-Kueyen telescope with the UVES spectrograph in FLAMES-UVES configuration. Spectroscopic parameters were derived based on the excitation and ionization equilibrium of Fe i and Fe ii. The abundance analysis was performed with a MARCS LTE spherical model atmosphere grid and the Turbospectrum spectrum synthesis code. Results.We confirm that the analysed stars are moderately metal-poor (-1:04≤[Fe/H]≤-0:43), non-carbon-enhanced (non-CEMP) with [C/Fe] ≤+0:2, and α-enhanced.We find that our three most metal-poor stars are nitrogen enhanced. The α-enhancement suggests that these stars were formed from a gas enriched by core-collapse supernovae, and that the values are in agreement with results in the literature for bulge stars in the same metallicity range. No abundance anomalies (Na-O, Al-O, Al-Mg anti-correlations) were detected in our sample. The heavy elements Y, Zr, Ba, La, and Eu also exhibit oversolar abundances. Three out of the five stars analysed here show slightly enhanced [Y/Ba] ratios similar to those found in other metal-poor bulge globular clusters (NGC 6522 and M 62). Conclusions. This sample shows enhancement in the first-to-second peak abundance ratios of heavy elements, as well as dominantly s-process element excesses. This can be explained by different nucleosynthesis scenarios: (a) the main r-process plus extra mechanisms, such as the weak r-process; (b) mass transfer from asymptotic giant branch stars in binary systems; (c) an early generation of fast-rotating massive stars. Larger samples of moderately metal-poor bulge stars, with detailed chemical abundances, are needed to better constrain the source of dominantly s-process elements in the early Universe
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