Formation of globular clusters (GCs), the Galactic bulge, or galaxy bulges in general is an important unsolved problem in Galactic astronomy. Homogeneous infrared observations of large samples of ...stars belonging to GCs and the Galactic bulge field are one of the best ways to study these problems. We report the discovery by APOGEE (Apache Point Observatory Galactic Evolution Experiment) of a population of field stars in the inner Galaxy with abundances of N, C, and Al that are typically found in GC stars. The newly discovered stars have high N/Fe, which is correlated with Al/Fe and anticorrelated with C/Fe. They are homogeneously distributed across, and kinematically indistinguishable from, other field stars within the same volume. Their metallicity distribution is seemingly unimodal, peaking at Fe/H ~ -1, thus being in disagreement with that of the Galactic GC system. Our results can be understood in terms of different scenarios. N-rich stars could be former members of dissolved GCs, in which case the mass in destroyed GCs exceeds that of the surviving GC system by a factor of ~8. In that scenario, the total mass contained in so-called 'first-generation' stars cannot be larger than that in 'second-generation' stars by more than a factor of ~9 and was certainly smaller. Conversely, our results may imply the absence of a mandatory genetic link between 'second-generation' stars and GCs. Last, but not least, N-rich stars could be the oldest stars in the Galaxy, the by-products of chemical enrichment by the first stellar generations formed in the heart of the Galaxy.
We report chemical abundances obtained by Sloan Digital Sky Survey (SDSS)-III/Apache Point Observatory Galactic Evolution Experiment for giant stars in five globular clusters located within 2.2 kpc ...of the Galactic Centre. We detect the presence of multiple stellar populations in four of those clusters (NGC 6553, NGC 6528, Terzan 5 and Palomar 6) and find strong evidence for their presence in NGC 6522. All clusters with a large enough sample present a significant spread in the abundances of N, C, Na and Al, with the usual correlations and anticorrelations between various abundances seen in other globular clusters. Our results provide important quantitative constraints on theoretical models for self-enrichment of globular clusters, by testing their predictions for the dependence of yields of elements such as Na, N, C and Al on metallicity. They also confirm that, under the assumption that field N-rich stars originate from globular cluster destruction, they can be used as tracers of their parental systems in the high-metallicity regime.
We have determined Li abundances for eleven metal-poor turnoff stars, among which eight have Fe/H <-3, based on LTE analyses of high-resolution spectra obtained with the High Dispersion Spectrograph ...on the Subaru Telescope. The Li abundances for four of these eight stars are determined for the first time by this study. Effective temperatures are determined by a profile analysis of H alpha and H beta . While seven stars have Li abundances as high as the Spite Plateau value, the remaining four objects with Fe/H <-3 have A(Li) =log (Li/H)+ 12 2.0, confirming the existence of extremely metal-poor (EMP) turnoff stars having low Li abundances, as reported by previous work. The average of the Li abundances for stars with Fe/H<-3 is lower by 0.2 dex than that of the stars with higher metallicity. No clear constraint on the metallicity dependence or scatter of the Li abundances is derived from our measurements for the stars with Fe/H<-3. Correlations of the Li abundance with effective temperatures, with abundances of Na, Mg, and Sr, and with the kinematical properties are investigated, but no clear correlation is seen in the EMP star sample.
We employ the first two years of data from the near-infrared, high-resolution SDSS-III/APOGEE spectroscopic survey to investigate the distribution of metallicity and alpha-element abundances of stars ...over a large part of the Milky Way disk. Using a sample of approximately 10,000 kinematically unbiased red-clump stars with ~5% distance accuracy as tracers, the alpha/Fe versus Fe/H distribution of this sample exhibits a bimodality in alpha/Fe at intermediate metallicities, -0.9 < Fe/H < -0.2, but at higher metallicities (Fe/H ~ +0.2) the two sequences smoothly merge. We investigate the effects of the APOGEE selection function and volume filling fraction and find that these have little qualitative impact on the alpha-element abundance patterns. The described abundance pattern is found throughout the range 5 < R < 11 kpc and 0 < |Z| < 2 kpc across the Galaxy. The alpha/Fe trend of the high-alpha sequence is surprisingly constant throughout the Galaxy, with little variation from region to region (~10%). Using simple galactic chemical evolution models, we derive an average star-formation efficiency (SFE) in the high-alpha sequence of ~4.5x10 super(-10) yr super(-1), which is quite close to the nearly constant value found in molecular-gas-dominated regions of nearby spirals. This result suggests that the early evolution of the Milky Way disk was characterized by stars that shared a similar star-formation history and were formed in a well-mixed, turbulent, and molecular-dominated ISM with a gas consumption timescale (SFE super(-1)) of ~2 Gyr. Finally, while the two alpha-element sequences in the inner Galaxy can be explained by a single chemical evolutionary track, this cannot hold in the outer Galaxy, requiring, instead, a mix of two or more populations with distinct enrichment histories.
Abstract
The measurement of the structure of stellar populations in the Milky Way disc places fundamental constraints on models of galaxy formation and evolution. Previously, the disc's structure has ...been studied in terms of populations defined geometrically and/or chemically, but a decomposition based on stellar ages provides a more direct connection to the history of the disc, and stronger constraint on theory. Here, we use positions, abundances and ages for 31 244 red giant branch stars from the Sloan Digital Sky Survey (SDSS)-APOGEE survey, spanning 3 < R
gc < 15 kpc, to dissect the disc into mono-age and mono-Fe/H populations at low and high
$\mathrm{ \alpha \mathrm{/Fe}}$
. For each population, with Δage < 2 Gyr and ΔFe/H < 0.1 dex, we measure the structure and surface-mass density contribution. We find that low
$\mathrm{ \alpha \mathrm{/Fe}}$
mono-age populations are fit well by a broken exponential, which increases to a peak radius and decreases thereafter. We show that this profile becomes broader with age, interpreted here as a new signal of disc heating and radial migration. High
$\mathrm{ \alpha \mathrm{/Fe}}$
populations are well fit as single exponentials within the radial range considered, with an average scalelength of 1.9 ± 0.1 kpc. We find that the relative contribution of high to low
$\mathrm{ \alpha \mathrm{/Fe}}$
populations at R
0 is
$f_\Sigma = 18\hbox{ per cent} \pm 5\hbox{ per cent}$
; high
$\mathrm{ \alpha \mathrm{/Fe}}$
contributes most of the mass at old ages, and low
$\mathrm{ \alpha \mathrm{/Fe}}$
at young ages. The low and high
$\mathrm{ \alpha \mathrm{/Fe}}$
populations overlap in age at intermediate Fe/H, although both contribute mass at R
0 across the full range of Fe/H. The mass-weighted scaleheight hZ
distribution is a smoothly declining exponential function. High
$\mathrm{ \alpha \mathrm{/Fe}}$
populations are thicker than low
$\mathrm{ \alpha \mathrm{/Fe}}$
, and the average hZ
increases steadily with age, between 200 and 600 pc.
ABSTRACT The Apache Point Observatory Galactic Evolution Experiment (APOGEE), part of the Sloan Digital Sky Survey III, explores the stellar populations of the Milky Way using the Sloan 2.5-m ...telescope linked to a high resolution (R ∼ 22,500), near-infrared (1.51-1.70 m) spectrograph with 300 optical fibers. For over 150,000 predominantly red giant branch stars that APOGEE targeted across the Galactic bulge, disks and halo, the collected high signal-to-noise ratio (>100 per half-resolution element) spectra provide accurate (∼0.1 km s−1) RVs, stellar atmospheric parameters, and precise ( 0.1 dex) chemical abundances for about 15 chemical species. Here we describe the basic APOGEE data reduction software that reduces multiple 3D raw data cubes into calibrated, well-sampled, combined 1D spectra, as implemented for the SDSS-III/APOGEE data releases (DR10, DR11 and DR12). The processing of the near-IR spectral data of APOGEE presents some challenges for reduction, including automated sky subtraction and telluric correction over a 3°-diameter field and the combination of spectrally dithered spectra. We also discuss areas for future improvement.
We present the latitude-normalized radial velocity (upsilon sub(b)) distribution of 3318 subsolar metallicity, V <, ~ 13.5 stars from the Grid Giant Star Survey (GGSS) in southern hemisphere fields. ...The sample includes giants mostly within ~5 kpc from the Galactic disks and halo. The nearby halo is found to (1) exhibit significant kinematical substructure, and (2) be prominently represented by several velocity coherent structures, including a very retrograde "cloud" of stars at l ~ 285degrees and extended, retrograde "streams" visible as relatively tight l-upsilon sub(b) sequences. One sequence in the fourth Galactic quadrant lies within the l-upsilon sub(b) space expected to contain tidal debris from the "star cluster" omega Centauri. Not only does omega Cen lie precisely in this l-upsilon sub(b) sequence, but the positions and upsilon sub(b) of member stars match those of N-body simulations of tidally disrupting dwarf galaxies on orbits ending with omega Cen's current position and space motion. But the ultimate proof that we have very likely found extended parts of the ?Cen tidal stream comes from echelle spectroscopy of a subsample of the stars that reveals a very particular chemical abundance signature known to occur only in omega Cen. The newly discovered omega Cen debris accounts for almost all fourth Galactic quadrant retrograde stars in the southern GGSS, which suggests omega Cen is a dominant contributor of retrograde giant stars in the inner Galaxy.
We report the peculiar chemical abundance patterns of 11 atypical Milky Way (MW) field red giant stars observed by the Apache Point Observatory Galactic Evolution Experiment (APOGEE). These atypical ...giants exhibit strong Al and N enhancements accompanied by C and Mg depletions, strikingly similar to those observed in the so-called second-generation (SG) stars of globular clusters (GCs). Remarkably, we find low Mg abundances (Mg/Fe < 0.0) together with strong Al and N overabundances in the majority (5/7) of the metal-rich (Fe/H −1.0) sample stars, which is at odds with actual observations of SG stars in Galactic GCs of similar metallicities. This chemical pattern is unique and unprecedented among MW stars, posing urgent questions about its origin. These atypical stars could be former SG stars of dissolved GCs formed with intrinsically lower abundances of Mg and enriched Al (subsequently self-polluted by massive AGB stars) or the result of exotic binary systems. We speculate that the stars Mg-deficiency as well as the orbital properties suggest that they could have an extragalactic origin. This discovery should guide future dedicated spectroscopic searches of atypical stellar chemical patterns in our Galaxy, a fundamental step forward to understanding the Galactic formation and evolution.
Despite its importance for understanding the nature of early stellar generations and for constraining Galactic bulge formation models, at present little is known about the metal-poor stellar content ...of the central Milky Way. This is a consequence of the great distances involved and intervening dust obscuration, which challenge optical studies. However, the Apache Point Observatory Galactic Evolution Experiment (APOGEE), a wide-area, multifiber, high-resolution spectroscopic survey within Sloan Digital Sky Survey III, is exploring the chemistry of all Galactic stellar populations at infrared wavelengths, with particular emphasis on the disk and the bulge. An automated spectral analysis of data on 2403 giant stars in 12 fields in the bulge obtained during APOGEE commissioning yielded five stars with low metallicity (Fe/H < or =, slant -1.7), including two that are very metal-poor Fe/H ~ -2.1 by bulge standards. Luminosity-based distance estimates place the 5 stars within the outer bulge, where 1246 of the other analyzed stars may reside. A manual reanalysis of the spectra verifies the low metallicities, and finds these stars to be enhanced in the alpha -elements O, Mg, and Si without significant alpha -pattern differences with other local halo or metal-weak thick-disk stars of similar metallicity, or even with other more metal-rich bulge stars. While neither the kinematics nor chemistry of these stars can yet definitively determine which, if any, are truly bulge members, rather than denizens of other populations co-located with the bulge, the newly identified stars reveal that the chemistry of metal-poor stars in the central Galaxy resembles that of metal-weak thick-disk stars at similar metallicity.
Little is known about IMP-producing Enterobacterales (IMP-Ent) in Europe. We analyzed at genomic and phenotypic level IMP-Ent isolates circulating in Spain in a 9-year period.
IMP-Ent isolates ...submitted to our reference laboratory were included. Antibiotic susceptibility was performed using microdilution method (EUCAST), and IMP-carbapenemase activity was measured with carbapenemase inhibitors, the β-CARBA method, the modified Hodge test (MHT), and the modified carbapenemase inhibition method (mCIM). All isolates collected were sequenced for high-resolution single-nucleotide polymorphism (SNP) typing, core genome multilocus sequence typing (cgMLST), and resistome analysis.
Fifty IMP-Ent isolates, collected from 19 hospitals in 13 Spanish provinces, were detected:
(IMP-Kpn) (24; 48%),
(13; 26%),
(8, 16%),
(two; 4%),
(one, 2%),
(one; 2%) and
(one; 2%). All isolates were positive by the MHT and β-CARBA tests; 48 (96%) were mCIM positive; 12 (24%) and 26 (52%) displayed positive inhibition with dipicolinic (meropenem) and EDTA (ertapenem), respectively. Five IMP-carbapenemase types were identified: IMP-8 (22; 44%), IMP-22 (17; 34%), IMP-13 (7; 14%), IMP-28 (two; 4%), and IMP-15 (two; 4%), predominating IMP-8 in
and IMP-22 in
. IMP-28 was exclusively identified in
and IMP-15 in
. Predominant STs were ST405 (29.2%), ST15 (25%) and ST464 (20.8%) in IMP-Kpn; ST96 (100%) in
and ST182 (62.5%) in
. Colistin and amikacin were the most active non-carbapenem antibiotics against IMP-Ent.
IMP-Ent isolates remain infrequent in Spain, although in recent years have been circulating causing nosocomial outbreaks, being IMP-8-producing
and IMP-22-producing
the most frequently detected in this study. Inhibition with EDTA or dipicolinic acid presented false negative results in some IMP-producing strains. Active microbiological and molecular surveillance is essential for a better comprehension and control of IMP-Ent dissemination.
PDF
