5,884 research outputs found
Abundance ratios of red giants in low mass ultra faint dwarf spheroidal galaxies
Low mass dwarf spheroidal galaxies are key objects for our understanding of
the chemical evolution of the pristine Universe and the Local Group of
galaxies. Abundance ratios in stars of these objects can be used to better
understand their star formation and chemical evolution. We report on the
analysis of a sample of 11 stars belonging to 5 different ultra faint dwarf
spheroidal galaxies (UfDSph) based on X-Shooter spectra obtained at the VLT.
Medium resolution spectra have been used to determine the detailed chemical
composition of their atmosphere. We performed a standard 1D LTE analysis to
compute the abundances.
Considering all the stars as representative of the same population of low
mass galaxies, we found that the [alpha/Fe] ratios vs [Fe/H] decreases as the
metallicity of the star increases in a way similar to what is found for the
population of stars belonging to dwarf spheroidal galaxies. The main difference
is that the solar [alpha/Fe] is reached at a much lower metallicity for the
UfDSph than the dwarf spheroidal galaxies.
We report for the first time the abundance of strontium in CVnI. The star we
analyzed in this galaxy has a very high [Sr/Fe] and a very low upper limit of
barium which makes it a star with an exceptionally high [Sr/Ba] ratio.
Our results seem to indicate that the galaxies which have produced the bulk
of their stars before the reionization (fossil galaxies) have lower [X/Fe]
ratios at a given metallicity than the galaxies that have experienced a
discontinuity in their star formation rate (quenching).Comment: 22 pages, 12 figures, submitted to A&
Attributions Made By Students In Learning Groups
Student groups are widely used for major projects in the business capstone course. Increasingly, students are expressing difficulties with such groups primarily involving arrangements for meet-ings outside of class and group relationships. This preliminary research explored social loafing and the attributions made by students about its causes. It was widespread, but just talking about social loafing improved the group’s reaction to it. Satisfaction with the group experience was not adversely affected by the presence of social loafing in groups
Ca II TRIPLET SPECTROSCOPY OF SMALL MAGELLANIC CLOUD RED GIANTS. IV. ABUNDANCES FOR A LARGE SAMPLE OF FIELD STARS AND COMPARISON WITH THE CLUSTER SAMPLE
This paper represents a major step forward in the systematic and homogeneous study of Small Magellanic Cloud (SMC) star clusters and field stars carried out by applying the calcium triplet technique. We present in this work the radial velocity and metallicity of approximately 400 red giant stars in 15 SMC fields, with typical errors of about 7 km s-1 and 0.16 dex, respectively. We added to this information our previously determined metallicity values for 29 clusters and approximately 350 field stars using the identical techniques. Using this enlarged sample, we analyze the metallicity distribution and gradient in this galaxy. We also compare the chemical properties of the clusters and of their surrounding fields. We find a number of surprising results. While the clusters, taken as a whole, show no strong evidence for a metallicity gradient (MG), the field stars exhibit a clear negative gradient in the inner region of the SMC, consistent with the recent results of Dobbie et al. For distances to the center of the galaxy less than 4\ub0, field stars show a considerably smaller metallicity dispersion than that of the clusters. However, in the external SMC regions, clusters and field stars exhibit similar metallicity dispersions. Moreover, in the inner region of the SMC, clusters appear to be concentrated in two groups: one more metal-poor and another more metal-rich than field stars. Individually considered, neither cluster group presents an MG. Most surprisingly, the MG for both stellar populations (clusters and field stars) appears to reverse sign in the outer regions of the SMC. The difference between the cluster metallicity and the mean metallicity of the surrounding field stars turns out to be a strong function of the cluster metallicity. These results could be indicating different chemical evolution histories for these two SMC stellar populations. They could also indicate variations in the chemical behavior of the SMC in its internal and external regions
Strategic Planning Under Severe Constraints In A State College
This paper examines the difficulties of strategic planning under severe constraints in a state college. Constraints include the planning models available, the governance structure of the college and other externalities, and a not-for-profit model of constraints by Newman and Wallender. After presenting the planning challenges, we discuss approaches to be used by institutions facing similarly constrained environments. 
Detailed abundances in stars belonging to ultra-faint dwarf spheroidal galaxies
We report preliminary results concerning the detailed chemical composition of
metal poor stars belonging to close ultra-faint dwarf galaxies (hereafter
UfDSphs). The abundances have been determined thanks to spectra obtained with
X-Shooter, a high efficiency spectrograph installed on one of the ESO VLT
units. The sample of ultra-faint dwarf spheroidal stars have abundance ratios
slightly lower to what is measured in field halo star of the same
metallicity.We did not find extreme abundances in our Hercules stars as the one
found by Koch for his 2 Hercules stars. The synthesis of the neutron capture
elements Ba and Sr seems to originate from the same nucleosynthetic process in
operation during the early stages of the galactic evolution.Comment: 3 pages, 1 figure; OMEG11 conference (Tokyo, Nov 2011
DNA methylation at the mu-1 opioid receptor gene (OPRM1) promoter predicts preoperative, acute, and chronic postsurgical pain after spine fusion.
INTRODUCTION:The perioperative pain experience shows great interindividual variability and is difficult to predict. The mu-1 opioid receptor gene (OPRM1) is known to play an important role in opioid-pain pathways. Since deoxyribonucleic acid (DNA) methylation is a potent repressor of gene expression, DNA methylation was evaluated at the OPRM1 promoter, as a predictor of preoperative, acute, and chronic postsurgical pain (CPSP). METHODS:A prospective observational cohort study was conducted in 133 adolescents with idiopathic scoliosis undergoing spine fusion under standard protocols. Data regarding pain, opioid consumption, anxiety, and catastrophizing (using validated questionnaires) were collected before and 2-3 months postsurgery. Outcomes evaluated were preoperative pain, acute postoperative pain (area under curve [AUC] for pain scores over 48 hours), and CPSP (numerical rating scale >3/10 at 2-3 months postsurgery). Blood samples collected preoperatively were analyzed for DNA methylation by pyrosequencing of 22 CpG sites at the OPRM1 gene promoter. The association of each pain outcome with the methylation percentage of each CpG site was assessed using multivariable regression, adjusting for significant (P<0.05) nongenetic variables. RESULTS:Majority (83%) of the patients reported no pain preoperatively, while CPSP occurred in 36% of the subjects (44/121). Regression on dichotomized preoperative pain outcome showed association with methylation at six CpG sites (1, 3, 4, 9, 11, and 17) (P<0.05). Methylation at CpG sites 4, 17, and 18 was associated with higher AUC after adjusting for opioid consumption and preoperative pain score (P<0.05). After adjusting for postoperative opioid consumption and preoperative pain score, methylation at CpG sites 13 and 22 was associated with CPSP (P<0.05). DISCUSSION:Novel CPSP biomarkers were identified in an active regulatory region of the OPRM1 gene that binds multiple transcription factors. Inhibition of binding by DNA methylation potentially decreases the OPRM1 gene expression, leading to a decreased response to endogenous and exogenous opioids, and an increased pain experience
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
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