1,584 research outputs found
The origin of the spurious iron spread in the globular cluster NGC 3201
NGC 3201 is a globular cluster suspected to have an intrinsic spread in the
iron content. We re-analysed a sample of 21 cluster stars observed with
UVES-FLAMES at the Very Large Telescope and for which Simmerer et al. found a
0.4 dex wide [Fe/H] distribution with a metal-poor tail. We confirmed that when
spectroscopic gravities are adopted, the derived [Fe/H] distribution spans ~0.4
dex. On the other hand, when photometric gravities are used, the metallicity
distribution from Fe I lines remains large, while that derived from Fe II lines
is narrow and compatible with no iron spread. We demonstrate that the
metal-poor component claimed by Simmerer et al. is composed by asymptotic giant
branch stars that could be affected by non local thermodynamical equilibrium
effects driven by iron overionization. This leads to a decrease of the Fe I
abundance, while leaving the Fe II abundance unaltered. A similar finding has
been already found in asymptotic giant branch stars of the globular clusters M5
and 47 Tucanae. We conclude that NGC 3201 is a normal cluster, with no evidence
of intrinsic iron spread.Comment: Accepted for publication by ApJ, 7 pages, 4 figure
Ileocecal appendix involvement in fabry disease mimicking an acute abdomen
Anderson-Fabry disease (AFD) is a rare, X-linked, lysosomal storage disorder due to a deficiency of alphagalactosidase A. The direct consequence is a lipid storage with the accumulation of glycosphingolipids throughout the body. The clinical picture is highly variable and depends on cellular storage deposition ranging from neurological, cutaneous and renal symptoms to cardiac and gastrointestinal ones. We are reporting about the case of a young female carrier of alpha-galactosidase A (agalA) gene mutation who was treated at our out-clinic practice for minimal neurological involvement (achroparaestesia). She was subsequently admitted in order to undergo appendectomy because of an acute severe abdominal pain. The histological examination of her appendix revealed only a deposition of globotriaosylceramide (Gb3) without any sign of acute inflammation. This case confirms the extreme clinical variability of Fabry disease and how the gastrointestinal involvement diagnosis can be misse
No evidence of mass segregation in the low mass Galactic globular cluster NGC 6101
We used a combination of Hubble Space Telescope and ground based data to
probe the dynamical state of the low mass Galactic globular cluster NGC 6101.
We have re-derived the structural parameters of the cluster by using star
counts and we find that it is about three times more extended than thought
before. By using three different indicators, namely the radial distribution of
Blue Straggler Stars, that of Main Sequence binaries and the luminosity (mass)
function, we demonstrated that NGC 6101 shows no evidence of mass segregation,
even in the innermost regions. Indeed, both the BSS and the binary radial
distributions fully resemble that of any other cluster population. In addition
the slope of the luminosity (mass) functions does not change with the distance,
as expected for non relaxed stellar systems. NGC 6101 is one of the few
globulars where the absence of mass segregation has been observed so far. This
result provides additional support to the use of the "dynamical clock"
calibrated on the radial distribution of the Blue Stragglers as a powerful
indicator of the cluster dynamical age.Comment: Accepted for publication by ApJ; 33 pages, 13 figure
A chemical trompe-l'\oe{}il: no iron spread in the globular cluster M22
We present the analysis of high-resolution spectra obtained with UVES and
UVES-FLAMES at the Very Large Telescope of 17 giants in the globular cluster
M22, a stellar system suspected to have an intrinsic spread in the iron
abundance. We find that when surface gravities are derived spectroscopically
(by imposing to obtain the same iron abundance from FeI and FeII lines) the
[Fe/H] distribution spans ~0.5 dex, according to previous analyses. However,
the gravities obtained in this way correspond to unrealistic low stellar masses
(0.1-0.5 Msun) for most of the surveyed giants. Instead, when photometric
gravities are adopted, the [FeII/H] distribution shows no evidence of spread at
variance with the [FeI/H] distribution. This difference has been recently
observed in other clusters and could be due to non-local thermodynamical
equilibrium effects driven by over-ionization mechanisms, that mainly affect
the neutral species (thus providing lower [FeI/H]) but leave [FeII/H]
unaltered. We confirm that the s-process elements show significant star-to-star
variations and their abundances appear to be correlated with the difference
between [FeI/H] and [FeII/H]. This puzzling finding suggests that the peculiar
chemical composition of some cluster stars may be related to effects able to
spuriously decrease [FeI/H]. We conclude that M22 is a globular cluster with no
evidence of intrinsic iron spread, ruling out that it has retained the
supernovae ejecta in its gravitational potential well.Comment: Accepted for publication to ApJ; 33 pages, 10 figures, 6 table
Probing the MSP prenatal stage: the optical identification of the X-ray burster EXO 1745-248 in Terzan 5
We report on the optical identification of the neutron star burster EXO
1745-248 in Terzan 5. The identification was performed by exploiting HST/ACS
images acquired in Director's Discretionary Time shortly after (approximately 1
month) the Swift detection of the X-ray burst. The comparison between these
images and previous archival data revealed the presence of a star that
currently brightened by ~3 magnitudes, consistent with expectations during an
X-ray outburst. The centroid of this object well agrees with the position, in
the archival images, of a star located in the Turn-Off/Sub Giant Branch region
of Terzan 5. This supports the scenario that the companion should has recently
filled its Roche Lobe. Such a system represents the pre-natal stage of a
millisecond pulsar, an evolutionary phase during which heavy mass accretion on
the compact object occurs, thus producing X-ray outbursts and re-accelerating
the neutron star.Comment: ApJ Letter, in pres
The Terzan 5 puzzle: discovery of a third, metal-poor component
We report on the discovery of 3 metal-poor giant stars in Terzan 5, a complex
stellar system in the the Galactic bulge, known to have two populations at
[Fe/H]=-0.25 and +0.3. For these 3 stars we present new echelle spectra
obtained with NIRSPEC at Keck II, which confirm their radial velocity
membership and provide average [Fe/H]=-0.79 dex iron abundance and
[alpha/Fe]=+0.36 dex enhancement. This new population extends the metallicity
range of Terzan~5 0.5 dex more metal poor, and it has properties consistent
with having formed from a gas polluted by core collapse supernovae.Comment: Accepted for publication on ApJ Lette
M13 multiple stellar populations seen with the eyes of Stromgren photometry
We present a photometric study of M13 multiple stellar populations over a wide field of view, covering approximately 6.5 half-light radii, using archival Isaac Newton Telescope observations to build an accurate multiband Strömgren catalogue. The use of the Strömgren index cy permits us to separate the multiple populations of M13 on the basis of their position on the red giant branch. The comparison with medium and high resolution spectroscopic analysis confirms the robustness of our selection criterion. To determine the radial distribution of stars in M13, we complemented our data set with Hubble Space Telescope observations of the cluster core, to compensate for the effect of incompleteness affecting the most crowded regions. From the analysis of the radial distributions, we do not find any significant evidence of spatial segregation. Some residuals may be present in the external regions where we observe only a small number of stars. This finding is compatible with the short dynamical time-scale of M13 and represents, to date, one of the few examples of fully spatially mixed multiple populations in a massive globular cluster
First evidence of fully spatially mixed first and second generations in globular clusters: the case of NGC 6362
We present the first evidence of multiple populations in the Galactic
globular cluster NGC 6362. We used optical and near-UV Hubble Space Telescope
and ground based photometry, finding that both the sub giant and red giant
branches are split in two parallel sequences in all color magnitude diagrams
where the F336W filter (or U band) is used. This cluster is one of the least
massive globulars (M_tot~5x10^4 M_sun) where multiple populations have been
detected so far. Even more interestingly and at odds with any previous finding,
we observe that the two identified populations share the same radial
distribution all over the cluster extension. NGC 6362 is the first system where
stars from different populations are found to be completely spatially mixed.
Based on N-body and hydrodynamical simulations of multiple stellar generations,
we argue that, to reproduce these findings, NGC 6362 should have lost up to the
80% of its original massComment: Accepted for publication by ApJ Letters; 6 pages, 5 figure
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