1,485 research outputs found
The Lithium test for multiple populations in Globular Clusters: Lithium in NGC 2808
In the globular cluster NGC2808, a quasi-standard initial lithium abundance
is derived for a red giant belonging to the `extreme' population, characterized
by a large helium overabundance, and by abundances of proton capture elements
typical of nuclear processing in gas at very high temperatures, where the
initial lithium has been fully destroyed. The observations of lithium in such
extreme cluster stars are important to test different models for the formation
of multiple populations in old Globular Clusters. In the asymptotic giant
branch (AGB) scenario, fresh lithium is synthetized during the initial phases
of hot bottom burning which, afterwards, synthetize the other p-capture
elements. We model the abundance of lithium in the ejecta of superAGB models,
finding values consistent or larger than observed in the `extreme' giant; these
same models describe correctly the magnesium depletion and silicon enrichment
of the extreme population of NGC 2808, so the overall agreement provides
further support to the AGB scenario. In the models involving massive or
supermassive stars, the Lithium observed requires a mixture of the lithium-free
ejecta of the polluting population with more than 40% of standard-lithium
pristine gas. The extended chemical anomalies of NGC 2808 stars are then to be
all explained within at most 60% of the possible dilution range, the initial
helium mass fraction in the ejecta should be Y >= 0.5, to account for the Ye
0.38-0.40 of the extreme population, and further observations of p-process
elements are needed to check the model.Comment: accepted for publication in The Astrophysical Journal Letter
Discovery of Extended Main Sequence Turnoffs in Galactic Open Clusters
The color-magnitude diagrams (CMDs) of Galactic open clusters are widely considered to be the prototypes of single stellar populations. By using photometry in ultraviolet and optical bands we discovered that the nearby young cluster NGC 6705 (M11) exhibits an extended main-sequence turnoff (eMSTO) and a broadened main sequence (MS). This is the first evidence of multiple stellar populations in a Galactic open cluster. By using high-resolution Very Large Telescope (VLT) spectra we provide direct evidence that the multiple sequences along the CMD correspond to stellar populations with different rotation rates. Specifically, the blue MS (bMS) is formed of slow-rotating stars, while red-MS (rMS) stars are fast rotators. Moreover, we exploit photometry from Gaia data release 2 (DR2) to show that three Galactic open clusters, namely NGC 2099, NGC 2360, and NGC 2818, exhibit the eMSTO, thus suggesting that it is a common feature among these objects. Our previous work on the Large Magellanic Cloud star cluster NGC 1818 shows that slowly and rapidly rotating stars populate the bMS and rMS observed in its CMD. The similarities between M11 and the young clusters of the Magellanic Clouds (MCs) suggest that rotation is responsible for the appearance of multiple populations in the CMDs of both Milky Way open clusters and MCs young clusters.A.F.M.
and L.C. acknowledge support by the Australian Research
Council through Discovery Early Career Researcher Award
DE160100851 and the Future Fellowship FT160100402.
A.P.M. has been supported by the European Research Council
through the Starting Grant âGALFORâ (716082) and the FAREMIUR project R164RM93XW âSEMPLICEâ. A.S., L.B.N., and
F.V. are partially supported by the MINECO (Spanish Ministry of
Economy) through grants ESP2017-82674-R and ESP2016-
80079-C2-1-R (MINECO/FEDER, UE), SGR-1131 (Generalitat
Catalunya), and MDM-2014-0369 of ICCUB (Unidad de
Excelencia âMarĂa de Maeztuâ)
Gaia unveils the kinematics of multiple stellar populations in 47 Tucanae
The series of events, which occurred at high redshift and originated multiple stellar populations in Globular Clusters (GCs) are still poorly understood. Theoretical work suggests that the present-day dynamics of stars in nearby GCs, including the rotation and velocity dispersion, may retain important clues on the formation of multiple populations. So far, the dynamics of multiple populations have been investigated either from radial velocities of a relatively small sample of stars, or from relative proper motions of stars in the small field of view provided by the Hubble Space Telescope. In this context, Gaia provides the unique opportunity to investigate the dynamics of thousands of GC stars over a wide field of view. For the first time, we combine Gaia DR2 proper motions and multiband photometry to study the internal motions of the two main stellar populations of 47 Tucanae in a wide field of view. We confirm that this cluster exhibits high rotation on the plane of the sky and find that both stellar generations share similar rotation patterns. Second-generation stars show stronger anisotropies and smaller tangential-velocity dispersion than the first-generation stars, while there is no significant difference between their radial-velocity dispersion profiles. We discuss the impact of these results in the context of the formation scenarios for multiple stellar populations in GCs.AFM acknowledges support by the Australian Research Council
through Discovery Early Career Researcher Award DE160100851.
This work has been supported by the European Research Council through the ERC-StG 2016 project 716082 âGALFORâ (http:
//progetti.dfa.unipd.it/GALFOR) and by the MIUR through the
FARE project R164RM93XW âSEMPLICEâ. AMB acknowledges
support by Sonderforschungsbereich (SFB) 881 âThe Milky Way
Systemâ of the German Research Foundation (DFG)
Multiple stellar populations along the red Horizontal Branch and Red Clump of Globular Clusters
We exploit multi-band Hubble Space Telescope photometry to investigate
multiple populations (MPs) along the red horizontal branches (HBs) and red
clumps of fourteen metal-rich Globular Clusters (GCs), including twelve Milky
Way GCs and the Magellanic Cloud GCs NGC 1978 and NGC 416. Based on appropriate
two-color diagrams we find that the fraction of 1G stars in Galactic GCs
correlates with cluster mass, confirming previous results based on red-giant
branch (RGB) stars. Magellanic-Cloud GCs show higher fractions of 1G stars than
Galactic GCs with similar masses, thus suggesting that the environment affects
the MP phenomenon. We compared and combined our population fractions based on
HB with previous estimates from MS and RGB, and we used ground-based UBVI
photometry (available for NGC 104, NGC 5927, NGC 6366, NGC 6838) to extend the
investigation over a wide field of view. All studied GCs are consistent with
flat distributions of 1G and 2G stars within ~1 arcmin from the cluster center
except NGC 416, where the 2G is more centrally concentrated. 2G stars of NGC
104 and NGC 5927 are more centrally-concentrated than the 1G, whereas the
distribution is flat for NGC 6366 and NGC 6838. We discover that most of the
analyzed GCs exhibit extended sequences of 1G stars along the red HB, not
consistent with a simple population. The comparison between appropriate
synthetic and observed CMDs reveals that these extended distributions are
consistent with either star-to-star variation in helium or with an internal
metallicity spread, recalling the inhomogeneity of 1G stars along the ChMs.Comment: 27 pages, 20 figures, 5 tables, accepted for pubblication in Ap
HLA-C genotype and TCR vÎČ expression analysis in Mexican patients with Psoriasis
"Genetic background and T-cell expansion have been associated as the most important factors for psoriasis susceptibility in the Caucasian population. This study was performed to identify the T cell receptor VÎČ repertoire and HLA-Cw genotype in two Mexican groups with severe chronic plaque-type psoriasis. HLA-C typing was performed to detect the allele pattern associated with the disease by sequence-specific primer-polymerase chain reaction. In parallel, RT-PCR and Western blot were used for the identification of the TCR VÎČ repertoire. We found a wide variety of HLA-C alleles displayed with a preference to HLA-Cw *07 as the most representative allele in the group of patients. TCR VÎČ-2 and VÎČ-7 clone-type frequencies were statistically significant (p of 0.0280) when compared to other TCR VÎČ expressed in the two groups. We found notable differences both in the HLA-C genotype and TCR VÎČ repertoire in the groups of patients studied. Since Mexican individuals are genetically different from the Caucasian population, we suggest that due to these differences the susceptibility to disease and activation of T-cells for a proper immune response may be affected.
Long-term culture of patient-derived cardiac organoids recapitulated Duchenne muscular dystrophy cardiomyopathy and disease progression
Duchenne Muscular Dystrophy (DMD) is an X-linked neuromuscular disease which to date is incurable. The major cause of death is dilated cardiomyopathy however, its pathogenesis is unclear as existing cellular and animal models do not fully recapitulate the human disease phenotypes. In this study, we generated cardiac organoids from patient-derived induced pluripotent stem cells (DMD-COs) and isogenic-corrected controls (DMD-Iso-COs) and studied if DMD-related cardiomyopathy and disease progression occur in the organoids upon long-term culture (up to 93 days). Histological analysis showed that DMD-COs lack initial proliferative capacity, displayed a progressive loss of sarcoglycan localization and high stress in endoplasmic reticulum. Additionally, cardiomyocyte deterioration, fibrosis and aberrant adipogenesis were observed in DMD-COs over time. RNA sequencing analysis confirmed a distinct transcriptomic profile in DMD-COs which was associated with functional enrichment in hypertrophy/dilated cardiomyopathy, arrhythmia, adipogenesis and fibrosis pathways. Moreover, five miRNAs were identified to be crucial in this dysregulated gene network. In conclusion, we generated patient-derived cardiac organoid model that displayed DMD-related cardiomyopathy and disease progression phenotypes in long-term culture. We envision the feasibility to develop a more complex, realistic and reliable in vitro 3D human cardiac-mimics to study DMD-related cardiomyopathies
Extreme Rainfall Events Alter the Trophic Structure in Bromeliad Tanks Across the Neotropics
Changes in global and regional precipitation regimes are among the most pervasive components of climate change. Intensification of rainfall cycles, ranging from frequent downpours to severe droughts, could cause widespread, but largely unknown, alterations to trophic structure and ecosystem function. We conducted multi-site coordinated experiments to show how variation in the quantity and evenness of rainfall modulates trophic structure in 210 natural freshwater microcosms (tank bromeliads) across Central and South America (18°N to 29°S). The biomass of smaller organisms (detritivores) was higher under more stable hydrological conditions. Conversely, the biomass of predators was highest when rainfall was uneven, resulting in top-heavy biomass pyramids. These results illustrate how extremes of precipitation, resulting in localized droughts or flooding, can erode the base of freshwater food webs, with negative implications for the stability of trophic dynamics
Multiple stellar populations in Magellanic Cloud clusters - V. The split main sequence of the young cluster NGC 1866
One of the most unexpected results in the field of stellar populations of the last few years is the discovery that some Magellanic Cloud globular clusters younger than ~400 Myr exhibit bimodal main sequences (MSs) in their colour-magnitude diagrams (CMDs). Moreover, these young clusters host an extended main-sequence turn-off(eMSTO) in close analogy with what is observed in most ~1-2 Gyr old clusters of both Magellanic Clouds. We use high-precision Hubble Space Telescope photometry to study the young star cluster NGC 1866 in the Large Magellanic Cloud. We discover an eMSTO and a split MS. The analysis of the CMD reveals that (i) the blue MS is the less populous one, hosting about one-third of the total number of MS stars; (ii) red MS stars are more centrally concentrated than blue MS stars; (iii) the fraction of blue MS stars with respect to the total number of MS stars drops by a factor of ~2 in the upper MS with mF814W âČ 19.7. The comparison between the observed CMDs and stellar models reveals that the observations are consistent with ~200 Myr old highly rotating stars on the red MS, with rotation close to critical value, plus a non-rotating stellar population spanning an age interval between ~140 and 220 Myr, on the blue MS. Noticeable, neither stellar populations with different ages only, nor coeval stellar models with different rotation rates, properly reproduce the observed split MS and eMSTO. We discuss these results in the context of the eMSTO and multiple MS phenomenonAPM, AFM, and HJ acknowledge support by the Australian Research Council through Discovery Early Career Researcher Awards DE150101816 and DE160100851 and Discovery project DP150100862
Keck HIRES spectroscopy of SkyMapper commissioning survey candidate extremely metal-poor stars
We present results from the analysis of high-resolution spectra obtained with the Keck HIRES spectrograph for a sample of 17 candidate extremely metal-poor (EMP) stars originally selected from commissioning data obtained with the SkyMapper telescope. Fourteen of the stars have not been observed previously at high dispersion. Three have [Fe/H] †â3.0, while the remainder, with two more metal-rich exceptions, have â3.0 †[Fe/H] †â2.0 dex. Apart from Fe, we also derive abundances for the elements C, N, Na, Mg, Al, Si, Ca, Sc, Ti, Cr, Mn, Co, Ni, and Zn, and for n-capture elements Sr, Ba, and Eu. None of the current sample of stars is found to be carbon-rich. In general, our chemical abundances follow previous trends found in the literature, although we note that two of the most metal-poor stars show very low [Ba/Fe] (âŒâ1.7) coupled with low [Sr/Ba] (âŒâ0.3). Such stars are relatively rare in the Galactic halo. One further star, and possibly two others, meet the criteria for classification as a r-I star. This study, together with that of Jacobson et al. (2015), completes the outcomes of the SkyMapper commissioning data survey for EMP stars.SkyMapper research on EMP stars has been supported in part
through the Australian Research Council (ARC) Discovery Grant
programs DP120101237 and DP150103294 (Lead-CI Da Costa).
A. F. M., A. R. C., and A. D. M. have been in part supported
by ARC through the Discovery Early Career Researcher Award
DE160100851, the Discovery Project DP160100637, and the Future
Fellowship FT160100206, respectively. M. A. gratefully acknowledges generous funding from an ARC Laureate Fellowship (grant
FL110100012). Parts of this research were conducted under the
auspices of the Australian Research Council Centre of Excellence
for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), which
is supported through project number CE170100013. This project
has received funding from the European Unionâs Horizon 2020
research and innovation programme under the Marie SkĆodowskaCurie Grant Agreement No. (797100; Beneficiary: A. F. M.). The national facility capability for SkyMapper has been funded
through ARC LIEF grant LE130100104 from the Australian Research Council, awarded to the University of Sydney, the Australian
National University, Swinburne University of Technology, the
University of Queensland, the University of Western Australia,
the University of Melbourne, Curtin University of Technology,
Monash University, and the Australian Astronomical Observator
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