88 research outputs found
Abundance Patterns in Stars in the Bulge and Galactic Center
We discuss oxygen and iron abundance patterns in K and M red-giant members of
the Galactic bulge and in the young and massive M-type stars inhabiting the
very center of the Milky Way. The abundance results from the different bulge
studies in the literature, both in the optical and the infrared, indicate that
the [O/Fe]-[Fe/H] relation in the bulge does not follow the disk relation, with
[O/Fe] values falling above those of the disk. Based on these elevated values
of [O/Fe] extending to large Fe abundances, it is suggested that the bulge
underwent a rapid chemical enrichment with perhaps a top-heavy initial mass
function. The Galactic Center stars reveal a nearly uniform and slightly
elevated (relative to solar) iron abundance for a studied sample which is
composed of 10 red giants and supergiants. Perhaps of more significance is the
fact that the young Galactic Center M-type stars show abundance patterns that
are reminiscent of those observed for the bulge population and contain enhanced
abundance ratios of alpha-elements relative to either the Sun or Milky Way disk
at near-solar metallicities.Comment: requires iaus.cls; to appear in Formation and Evolution of Galaxy
Bulges, Proceedings IAU Symposium No. 245, 2007, M. Bureau et al. eds., in
pres
Oxygen abundances in the Galactic Bulge: evidence for fast chemical enrichment
AIMS: We spectroscopically characterize the Galactic Bulge to infer its star
formation timescale, compared to the other Galactic components, through the
chemical signature on its individual stars.
METHODS: We derived iron and oxygen abundances for 50 K giants in four fields
towards the Galactic bulge. High resolution (R=45,000) spectra for the target
stars were collected with FLAMES-UVES at the VLT.
RESULTS: Oxygen, as measured from the forbidden line at 6300 \AA, shows a
well-defined trend with [Fe/H], with [O/Fe] higher in bulge stars than in thick
disk ones, which were known to be more oxygen enhanced than thin disk stars.
CONCLUSIONS: These results support a scenario in which the bulge formed
before and more rapidly than the disk, and therefore the MW bulge can be
regarded as a prototypical old spheroid, with a formation history similar to
that of early-type (elliptical) galaxies.Comment: A&A Letters, in pres
Chemical similarities between Galactic bulge and local thick disk red giant stars
The evolution of the Milky Way bulge and its relationship with the other
Galactic populations is still poorly understood. The bulge has been suggested
to be either a merger-driven classical bulge or the product of a dynamical
instability of the inner disk. To probe the star formation history, the initial
mass function and stellar nucleosynthesis of the bulge, we performed an
elemental abundance analysis of bulge red giant stars. We also completed an
identical study of local thin disk, thick disk and halo giants to establish the
chemical differences and similarities between the various populations.
High-resolution infrared spectra of 19 bulge giants and 49 comparison giants in
the solar neighborhood were acquired with Gemini/Phoenix. All stars have
similar stellar parameters but cover a broad range in metallicity. A standard
1D local thermodynamic equilibrium analysis yielded the abundances of C, N, O
and Fe. A homogeneous and differential analysis of the bulge, halo, thin disk
and thick disk stars ensured that systematic errors were minimized. We confirm
the well-established differences for [O/Fe] (at a given metallicity) between
the local thin and thick disks. For the elements investigated, we find no
chemical distinction between the bulge and the local thick disk, which is in
contrast to previous studies relying on literature values for disk dwarf stars
in the solar neighborhood. Our findings suggest that the bulge and local thick
disk experienced similar, but not necessarily shared, chemical evolution
histories. We argue that their formation timescales, star formation rates and
initial mass functions were similar.Comment: Accepted for publication in A&A, 5 page
Alpha element abundances and gradients in the Milky Way bulge from FLAMES-GIRAFFE spectra of 650 K giants
We obtained FLAMES-GIRAFFE spectra (R=22,500) at the ESO Very Large Telescope
for 650 bulge red giant branch (RGB) stars and performed spectral synthesis to
measure Mg, Ca, Ti, and Si abundances. This sample is composed of 474 giant
stars observed in 3 fields along the minor axis of the Galactic bulge and at
latitudes b=-4, b=-6, b=-12. Another 176 stars belong to a field containing the
globular cluster NGC 6553, located at b=-3 and 5 degrees away from the other
three fields along the major axis. Our results confirm, with large number
statistics, the chemical similarity between the Galactic bulge and thick disk,
which are both enhanced in alpha elements when compared to the thin disk. In
the same context, we analyze [alpha/Fe] vs. [Fe/H] trends across different
bulge regions. The most metal rich stars, showing low [alpha/Fe] ratios at b=-4
disappear at higher Galactic latitudes in agreement with the observed
metallicity gradient in the bulge. Metal-poor stars ([Fe/H]<-0.2) show a
remarkable homogeneity at different bulge locations. We have obtained further
constrains for the formation scenario of the Galactic bulge. A metal-poor
component chemically indistinguishable from the thick disk hints for a fast and
early formation for both the bulge and the thick disk. Such a component shows
no variation, neither in abundances nor kinematics, among different bulge
regions. A metal-rich component showing low [alpha/Fe] similar to those of the
thin disk disappears at larger latitudes. This allows us to trace a component
formed through fast early mergers (classical bulge) and a disk/bar component
formed on a more extended timescale.Comment: 13 pages, 17 figures. Accepted for publication in Astronomy and
Astrophysic
The metallicity distribution of bulge clump giants in Baade's Window
We seek to constrain the formation of the Galactic bulge by means of
analysing the detailed chemical composition of a large sample of red clump
stars in Baade's window. We measure [Fe/H] in a sample of 219 bulge red clump
stars from R=20000 resolution spectra obtained with FLAMES/GIRAFFE at the VLT,
using an automatic procedure, differentially to the metal-rich local reference
star muLeo. For a subsample of 162 stars, we also derive [Mg/H] from spectral
synthesis around the MgI triplet at 6319A. The Fe and Mg metallicity
distributions are both asymmetric, with median values of +0.16 and +0.21
respectively. The iron distribution is clearly bimodal, as revealed both by a
deconvolution (from observational errors) and a Gaussian decomposition. The
decomposition of the observed Fe and Mg metallicity distributions into Gaussian
components yields two populations of equal sizes (50% each): a metal-poor
component centred around [Fe/H]=-0.30 and [Mg/H]=-0.06 with a large dispersion
and a narrow metal-rich component centred around [Fe/H]=+0.32 and [Mg/H]=+0.35.
The metal poor component shows high [Mg/Fe] ratios (around 0.3) whereas stars
in the metal rich component are found to have near solar ratios. Babusiaux et
al. (2010) also find kinematical differences between the two components: the
metal poor component shows kinematics compatible with an old spheroid whereas
the metal rich component is consistent with a population supporting a bar. In
view of their chemical and kinematical properties, we suggest different
formation scenarios for the two populations: a rapid formation timescale as an
old spheroid for the metal poor component (old bulge) and for the metal rich
component, a formation over a longer time scale driven by the evolution of the
bar (pseudo-bulge).Comment: Accepted for publication in Astronomy & Astrophysic
The Milky Way Bulge: Observed properties and a comparison to external galaxies
The Milky Way bulge offers a unique opportunity to investigate in detail the
role that different processes such as dynamical instabilities, hierarchical
merging, and dissipational collapse may have played in the history of the
Galaxy formation and evolution based on its resolved stellar population
properties. Large observation programmes and surveys of the bulge are providing
for the first time a look into the global view of the Milky Way bulge that can
be compared with the bulges of other galaxies, and be used as a template for
detailed comparison with models. The Milky Way has been shown to have a
box/peanut (B/P) bulge and recent evidence seems to suggest the presence of an
additional spheroidal component. In this review we summarise the global
chemical abundances, kinematics and structural properties that allow us to
disentangle these multiple components and provide constraints to understand
their origin. The investigation of both detailed and global properties of the
bulge now provide us with the opportunity to characterise the bulge as observed
in models, and to place the mixed component bulge scenario in the general
context of external galaxies. When writing this review, we considered the
perspectives of researchers working with the Milky Way and researchers working
with external galaxies. It is an attempt to approach both communities for a
fruitful exchange of ideas.Comment: Review article to appear in "Galactic Bulges", Editors: Laurikainen
E., Peletier R., Gadotti D., Springer Publishing. 36 pages, 10 figure
Role of Organic Cation Transporter 1, OCT1 in the Pharmacokinetics and Toxicity of cis-Diammine(pyridine)chloroplatinum(II) and Oxaliplatin in Mice
PurposeThe goal of this study was to test the hypothesis that by controlling intracellular uptake, organic cation transporter 1, Oct1 is a key determinant of the disposition and toxicity of cis-diammine(pyridine)chloroplatinum(II)(CDPCP) and oxaliplatin.MethodsPharmacokinetics, tissue accumulation and toxicity of CDPCP and oxaliplatin were compared between Oct1-/- and wild-type mice.ResultsAfter intravenous administration, hepatic and intestinal accumulation of CDPCP was 2.7-fold and 3.9-fold greater in Oct1 wild-type mice (p < 0.001). Deletion of Oct1 resulted in a significantly decreased clearance (0.444 ± 0.0391 ml/min*kg versus 0.649 ± 0.0807 ml/min*kg in wild-type mice, p < 0.05) and volume distribution (1.90 ± 0.161 L/kg versus 3.37 ± 0.196 L/kg in wild-type mice, p < 0.001). Moreover, Oct1 deletion resulted in more severe off-target toxicities in CDPCP-treated mice. Histologic examination of the liver and measurements of liver function indicated that the level of hepatic toxicity was mild and reversible, but was more apparent in the wild-type mice. In contrast, the effect of Oct1 on the pharmacokinetics and toxicity of oxaliplatin in the mice was minimal.ConclusionsOur study suggests that Oct1 plays an important role in the pharmacokinetics, tissue distribution and toxicity of CDPCP, but not oxaliplatin
Chemical abundances and kinematics of a sample of metal-rich barium stars
We determined the atmospheric parameters and abundance pattern for a sample
of metal-rich barium stars. We used high-resolution optical spectroscopy.
Atmospheric parameters and abundances were determined using the local
thermodynamic equilibrium atmosphere models of Kurucz and the spectral analysis
code MOOG. We show that the stars have enhancement factors, [s/Fe], from 0.25
to 1.16. Their abundance pattern of the Na, Al, alpha-elements, and iron group
elements as well as their kinematical properties are similar to the
characteristics of the other metal-rich and super metal-rich stars already
analyzed. We conclude that metal-rich barium stars do not belong to the bulge
population. We also show that metal-rich barium stars are useful targets for
probing the s-process enrichment in high-metallicity environments.Comment: 21 pages, 9 figures, accepted for publication in in Astronomy and
Astrophysic
VLT-FLAMES Analysis of 8 giants in the Bulge Metal-poor Globular Cluster NGC 6522: Oldest Cluster in the Galaxy?
NGC 6522 has been the first metal-poor globular cluster identified in the
bulge by W. Baade. Despite its importance, very few high resolution abundance
analyses of stars in this cluster are available in the literature. The bulge
metal-poor clusters may be important tracers of the early chemical enrichment
of the Galaxy. The main purpose of this study is the determination of
metallicity and elemental ratios in individual stars of NGC 6522. High
resolution spectra of 8 giants of the bulge globular cluster NGC 6522 were
obtained at the 8m VLT UT2-Kueyen telescope with the FLAMES+GIRAFFE
spectrograph. Multiband V,I,J,Ks} photometry was used to derive effective
temperatures as reference values. Spectroscopic parameters are derived from FeI
and FeII lines, and adopted for the derivation of abundance ratios. The present
analysis provides a metallicity [Fe/H] = -1.0+-0.2. The alpha-elements Oxygen,
Magnesium and Silicon show [O/Fe]=+0.4, [Mg/Fe]=[Si/Fe]= +0.25, whereas Calcium
and Titanium show shallower ratios of [Ca/Fe]=[Ti/Fe]=+0.15. The
neutron-capture r-process element Europium appears to be overabundant by
[Eu/Fe]=+0.4. The neutron-capture s-elements La and Ba are enhanced by
[La/Fe]=+0.35 and [Ba/Fe]=+0.5. The large internal errors, indicating the large
star-to-star variationin the Ba and Eu abundances, are also discussed. The
moderate metallicity combined to a blue Horizontal Branch (BHB), are
characteristics similar to those of HP~1 and NGC 6558, pointing to a population
of very old globular clusters in the Galactic bulge. Also, the abundance ratios
in NGC 6522 resemble those in HP 1 and NGC 6558. The ultimate conclusion is
that the bulge is old, and went through an early prompt chemical enrichment.Comment: 18 pages, 16 figures. Astronomy & Astrophysics, accepte
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