387 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&
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
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
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
Sulfur abundances in three Galactic clusters: Ruprecht 106, Trumpler 5 and Trumpler 20
Context. Sulfur (S) is one of the lesser-studied -elements. Published
investigations of its behavior have so far focused on local stars, and only a
few clusters of the Milky Way have been considered to study this topic. We aim
to study the S content of the globular cluster Ruprecht 106 -- which has never
before been studied for this purpose, but is known to present low levels of the
[/Fe] abundance ratio -- and the open cluster Trumpler 5. The only star
studied so far in Trumpler 5 shows an unexpectedly low abundance of S. Aims.
With this work, we aim to provide the first S abundance in Ruprecht 106 and to
investigate the S content of Trumpler 5 with a larger sample of stars. The open
cluster Trumpler 20 is considered as a reference object. Methods. We performed
a standard abundance analysis based on 1D model atmospheres in local
thermodynamical equilibrium (LTE) and on high-resolution and
high-signal-to-noise-ratio UVES-slit and UVES/FLAMES spectra. We also applied
corrections for nonLTE. The metallicities of the targets were obtained by
studying equivalent widths. Sulfur abundances were derived from multiplets 1,
6, and 8 by spectrosynthesis. Results. We find that the metallicities of
Ruprecht 106 and Trumpler 5 are [Fe/H]= -1.37+/-0.11 and [Fe/H]= -0.49+/-0.14,
respectively. Ruprecht 106 is less S-rich than the other Galactic clusters at
similar metallicity. The low S content of Ruprecht 106, [S/Fe]NLTE=
-0.52+/-0.13, is consistent with its shortage of -elements. This
supports an extra-galactic origin of this cluster. We obtained a new and more
robust S content value of Trumpler 5 of about [S/Fe]NLTE= 0.05+/-0.20.
According to our results, Trumpler 5 follows the trend of the Galactic disk in
the [S/Fe]LTE versus [Fe/H] diagram. Our results for Trumpler 20, of namely
[Fe/H]= 0.06+/-0.15 and [S/Fe]NLTE= -0.28+/-0.21, are in agreement with those
in the literature.Comment: 15 pages, 7 figures, 5 table
Non-Abelian Discrete Symmetries and Neutrino Masses: Two Examples
Two recent examples of non-Abelian discrete symmetries (S_3 and A_4) in
understanding neutrino masses and mixing are discussed.Comment: 16 pages, no figure, invited contribution to NJP focus issue on
neutrino
A See-Saw model for fermion masses and mixings
We present a supersymmetric see-saw model giving rise to the most
general neutrino mass matrix compatible with Tri-Bimaximal mixing. We adopt the
flavour symmetry, broken by suitable vacuum expectation values
of a small number of flavon fields. We show that the vacuum alignment is a
natural solution of the most general superpotential allowed by the flavour
symmetry, without introducing any soft breaking terms. In the charged lepton
sector, mass hierarchies are controlled by the spontaneous breaking of the
flavour symmetry caused by the vevs of one doublet and one triplet flavon
fields instead of using the Froggatt-Nielsen U(1) mechanism. The next to
leading order corrections to both charged lepton mass matrix and flavon vevs
generate corrections to the mixing angles as large as .
Applied to the quark sector, the symmetry group can give a
leading order proportional to the identity as well as a matrix with
coefficients in the Cabibbo submatrix. Higher order
corrections produce non vanishing entries in the other entries which
are generically of .Comment: 30 pages, 3 figures, minor changes to match the published versio
The Gaia-ESO Survey: Detailed Abundances in the Metal-poor Globular Cluster NGC 4372
We present the abundance analysis for a sample of 7 red giant branch stars in
the metal-poor globular cluster NGC 4372 based on UVES spectra acquired as part
of the Gaia-ESO Survey. This is the first extensive study of this cluster from
high resolution spectroscopy. We derive abundances of O, Na, Mg, Al, Si, Ca,
Sc, Ti, Fe, Cr, Ni, Y, Ba, and La. We find a metallicity of [Fe/H] = -2.19
0.03 and find no evidence for a metallicity spread. This metallicity
makes NGC 4372 one of the most metal-poor galactic globular clusters. We also
find an {\alpha}-enhancement typical of halo globular clusters at this
metallicity. Significant spreads are observed in the abundances of light
elements. In particular we find a Na-O anti-correlation. Abundances of O are
relatively high compared with other globular clusters. This could indicate that
NGC 4372 was formed in an environment with high O for its metallicity. A Mg-Al
spread is also present which spans a range of more than 0.5 dex in Al
abundances. Na is correlated with Al and Mg abundances at a lower significance
level. This pattern suggests that the Mg-Al burning cycle is active. This
behavior can also be seen in giant stars of other massive, metal-poor clusters.
A relation between light and heavy s-process elements has been identified.Comment: 14 pages, 14 figures, accepted for publication in A&
A Simplest A4 Model for Tri-Bimaximal Neutrino Mixing
We present a see-saw model for Tri-Bimaximal mixing which is based on a
very economical flavour symmetry and field content and still possesses all the
good features of models. In particular the charged lepton mass
hierarchies are determined by the flavour symmetry itself
without invoking a Froggatt-Nielsen U(1) symmetry. Tri-Bimaximal mixing is
exact in leading order while all the mixing angles receive corrections of the
same order in next-to-the-leading approximation. As a consequence the predicted
value of is within the sensitivity of the experiments which will
take data in the near future. The light neutrino spectrum, typical of
see-saw models, with its phenomenological implications, also including
leptoproduction, is studied in detail.Comment: 20 pages, 2 figure
VLT multi-epoch radial velocity survey toward NGC 6253. Analysis of three transiting planetary candidates
We measured the radial velocity of 139 stars in the region of NGC 6253,
discussing cluster's membership and binarity in this sample, complementing our
analysis with photometric, proper motion, and radial velocity data available
from previous studies of this cluster, and analyzing three planetary transiting
candidates we found in the field of NGC 6253. Spectra were obtained with the
UVES and GIRAFFE spectrographs at the VLT, during three epochs in August 2008.
The mean radial velocity of the cluster is -29.11+/-0.85 km/s. Using both
radial velocities and proper motions we found 35 cluster's members, among which
12 are likely cluster's close binary systems. One star may have a sub-stellar
companion, requiring a more intensive follow-up. Our results are in good
agreement with past radial velocity and photometric measurements. Furthermore,
using our photometry, astrometry and spectroscopy we identified a new sub-giant
branch eclipsing binary system, member of the cluster. The cluster's close
binary frequency at 29% +/- 9% (34% +/-10% once including long period
binaries), appears higher than the field binary frequency equal to (22% +/- 5%,
though these estimates are still consistent within the uncertainties. Among the
three transiting planetary candidates the brightest one (V=15.26) is worth to
be more intensively investigated with higher percision spectroscopy. We
discussed the possibility to detect sub-stellar companions (brown dwarfs and
planets) with the radial velocity technique (both with UVES/GIRAFFE and HARPS)
around turn-off stars of old open clusters [abridged].Comment: 25 pages, 18 figures, 8 tables. Accepted for publication in A&
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