5,404 research outputs found
The peculiar Na-O anticorrelation of the bulge globular cluster NGC 6440
Context. Galactic Globular Clusters (GCs) are essential tools to understand
the earliest epoch of the Milky Way, since they are among the oldest objects in
the Universe and can be used to trace its formation and evolution. Current
studies using high resolution spectroscopy for many stars in each of a large
sample of GCs allow us to develop a detailed observational picture about their
formation and their relation with the Galaxy. However, it is necessary to
complete this picture by including GCs that belong to all major Galactic
components, including the Bulge. Aims. Our aim is to perform a detailed
chemical analyses of the bulge GC NGC 6440 in order to determine if this object
has Multiple Populations (MPs) and investigate its relation with the Bulge of
the Milky Way and with the other Galactic GCs, especially those associated with
the Bulge, which are largely poorly studied. Methods. We determined the stellar
parameters and the chemical abundances of light elements (Na, Al), iron-peak
elements (Fe, Sc, Mn, Co, Ni), -elements (O, Mg, Si, Ca, Ti) and heavy
elements (Ba, Eu) in seven red giant members of NGC 6440 using high resolution
spectroscopy from FLAMES@UVES. Results. We found a mean iron content of
[Fe/H]=-0.500.03 dex in agreement with other studies. We found no internal
iron spread. On the other hand, Na and Al show a significant intrinsic spread,
but the cluster has no significant O-Na anticorrelation nor exhibits a Mg-Al
anticorrelation. The -elements show good agreement with the Bulge field
star trend, although they are at the high alpha end and are also higher than
those of other GCs of comparable metallicity. The heavy elements are dominated
by the r-process, indicating a strong contribution by SNeII. The chemical
analysis suggests an origin similar to that of the Bulge field stars.Comment: 12 pages, 13 figures, Accepted for publication in A&
Globular Cluster Systems in Brightest Cluster Galaxies. III: Beyond Bimodality
We present new deep photometry of the rich globular cluster (GC) systems
around the Brightest Cluster Galaxies UGC 9799 (Abell 2052) and UGC 10143
(Abell 2147), obtained with the HST ACS and WFC3 cameras. For comparison, we
also present new reductions of similar HST/ACS data for the Coma supergiants
NGC 4874 and 4889. All four of these galaxies have huge cluster populations (to
the radial limits of our data, comprising from 12000 to 23000 clusters per
galaxy). The metallicity distribution functions (MDFs) of the GCs can still be
matched by a bimodal-Gaussian form where the metal-rich and metal-poor modes
are separated by ~0.8 dex, but the internal dispersions of each mode are so
large that the total MDF becomes very broad and nearly continuous from [Fe/H] =
-2.4 to Solar. There are, however, significant differences between galaxies in
the relative numbers of \emph{metal-rich} clusters, suggesting that they
underwent significantly different histories of mergers with massive, gas-rich
halos. Lastly, the proportion of metal-poor GCs rises especially rapidly
outside projected radii R > 4 R_eff, suggesting the importance of accreted
dwarf satellites in the outer halo. Comprehensive models for the formation of
GCs as part of the hierarchical formation of their parent galaxies will be
needed to trace the systematic change in structure of the MDF with galaxy mass,
from the distinctly bimodal form in smaller galaxies up to the broad continuum
that we see in the very largest systems.Comment: In press for Astrophysical Journa
Digital modulation of the nickel valence state in a cuprate-nickelate heterostructure
Layer-by-layer oxide molecular beam epitaxy has been used to synthesize
cuprate-nickelate multilayer structures of composition
(LaCuO)/LaO/(LaNiO). In a combined experimental and
theoretical study, we show that these structures allow a clean separation of
dopant and doped layers. Specifically, the LaO layer separating cuprate and
nickelate blocks provides an additional charge that, according to density
functional theory calculations, is predominantly accommodated in the
interfacial nickelate layers. This is reflected in an elongation of bond
distances and changes in valence state, as observed by scanning transmission
electron microscopy and x-ray absorption spectroscopy. Moreover, the predicted
charge disproportionation in the nickelate interface layers leads to a
thickness-dependent metal-to-insulator transition for , as observed in
electrical transport measurements. The results exemplify the perspectives of
charge transfer in metal-oxide multilayers to induce doping without introducing
chemical and structural disorder
Chemical analysis of NGC 6528: one of the most metal-rich bulge globular cluster
The Bulge Globular Clusters (GCs) are key tracers of this central ancient
component of our Galaxy. It is essential to understand their formation and
evolution to study that of the bulge, as well as their relationship with the
other Galactic GC systems (halo and disk GCs). Our main goals are to obtain
detailed abundances for a sample of seven red giant members of NGC 6528 in
order to characterize its chemical composition and study the relationship of
this GC with the bulge, and with other bulge, halo and disk GCs. Moreover, we
analyze this clusters behavior associated with the Multiple Populations
(MPs) phenomenon. We obtained the stellar parameters and chemical abundances of
light elements (Na, Al), iron-peak elements (V, Cr, Mn, Fe, Co, Ni, Cu),
{\alpha}-elements (O, Mg, Si, Ca, Ti) and heavy elements (Zr, Ba, Eu) in seven
red giant members of NGC 6528 using high resolution spectroscopy from
FLAMES-UVES. We obtained in six stars of our sample a mean iron content of
[Fe/H]=-0.14+/-0.03 dex, in good agreement with other studies. We found no
significant internal iron spread. We detected one candidate variable star,
which was excluded from the mean in iron content, we derived a metallicity in
this star of [Fe/H]=-0.55+/-0.04 dex. Moreover, we found no extended O-Na
anticorrelation but instead only an intrinsic Na spread. In addition, NGC 6528
does not exhibit a Mg-Al anticorrelation, and no significant spread in either
Mg or Al. The {\alpha} and iron-peak elements show good agreement with the
bulge field star trend. The heavy elements are slightly dominated by the
r-process. The chemical analysis suggests an origin and evolution similar to
that of typical old Bulge field stars. Finally, we find remarkable agreement in
the chemical patterns of NGC 6528 and another bulge GC, NGC 6553, suggesting a
similar origin and evolution.Comment: Accepted for publication in A&A. 12 pages, 13 figures, 4 table
Large-scale study of the NGC 1399 globular cluster system in Fornax
We present a Washington C and Kron-Cousins R photometric study of the
globular cluster system of NGC 1399, the central galaxy of the Fornax cluster.
A large areal coverage of 1 square degree around NGC 1399 is achieved with
three adjoining fields of the MOSAIC II Imager at the CTIO 4-m telescope.
Working on such a large field, we can perform the first indicative
determination of the total size of the NGC 1399 globular cluster system. The
estimated angular extent, measured from the NGC 1399 centre and up to a
limiting radius where the areal density of blue globular clusters falls to 30
per cent of the background level, is 45 +/- 5 arcmin, which corresponds to 220
- 275 kpc at the Fornax distance. The bimodal colour distribution of this
globular cluster system, as well as the different radial distribution of blue
and red clusters, up to these large distances from the parent galaxy, are
confirmed. The azimuthal globular cluster distribution exhibits asymmetries
that might be understood in terms of tidal stripping of globulars from NGC
1387, a nearby galaxy. The good agreement between the areal density profile of
blue clusters and a projected dark-matter NFW density profile is emphasized.Comment: 9 pages, 9 figures. Accepted for publication in A&
Ultra-deep GEMINI near-infrared observations of the bulge globular cluster NGC 6624
We used ultra-deep and images secured with the near-infrared GSAOI
camera assisted by the multi-conjugate adaptive optics system GeMS at the
GEMINI South Telescope in Chile, to obtain a (, ) color-magnitude
diagram (CMD) for the bulge globular cluster NGC 6624. We obtained the deepest
and most accurate near-infrared CMD from the ground for this cluster, by
reaching 21.5, approximately 8 magnitudes below the horizontal
branch level. The entire extension of the Main Sequence (MS) is nicely sampled
and at 20 we detected the so-called MS "knee" in a purely
near-infrared CMD. By taking advantage of the exquisite quality of the data, we
estimated the absolute age of NGC 6624 ( = 12.0 0.5 Gyr), which
turns out to be in good agreement with previous studies in the literature. We
also analyzed the luminosity and mass functions of MS stars down to M
0.45 M finding evidence of a significant increase of low-mass stars
at increasing distances from the cluster center. This is a clear signature of
mass segregation, confirming that NGC 6624 is in an advanced stage of dynamical
evolution.Comment: Accepted for publication by ApJ. 39 pages, 19 figures, 1 tabl
A panchromatic view of the bulge globular cluster NGC 6569
We used high-resolution optical HST/WFC3 and multi-conjugate adaptive optics
assisted GEMINI GeMS/GSAOI observations in the near-infrared to investigate the
physical properties of the globular cluster NGC 6569 in the Galactic bulge. We
have obtained the deepest purely NIR color-magnitude diagram published so far
for this cluster using ground-based observations, reaching
21.0 mag (two magnitudes below the main-sequence turn-off point). By combining
the two datasets secured at two different epochs, we determined relative proper
motions for a large sample of individual stars in the center of NGC 6569,
allowing a robust selection of cluster member stars. Our proper motion analysis
solidly demonstrates that, despite its relatively high metal content, NGC 6569
hosts some blue horizontal branch stars. A differential reddening map has been
derived in the direction of the system, revealing a maximum color excess
variation of about 0.12 mag in the available field of
view. The absolute age of NGC 6569 has been determined for the first time. In
agreement with the other few bulge globular clusters with available age
estimates, NGC 6569 turns out to be old, with an age of about 12.8 Gyr, and a
typical uncertainty of 0.8-1.0 Gyr.Comment: 25 pages, 16 Figures, 1 Table. Accepted for publication in Ap
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