2,687 research outputs found
An Abundance Analysis for Five Red Horizontal Branch Stars in the Extremely Metal Rich Globular Cluster NGC 6553
We provide a high dispersion line-by-line abundance analysis of five red HB
stars in the extremely metal rich galactic globular cluster NGC 6553. These red
HB stars are significantly hotter than the very cool stars near the tip of the
giant branch in such a metal rich globular cluster and hence their spectra are
much more amenable to an abundance analysis than would be the case for red
giants.
We find that the mean [Fe/H] for NGC 6553 is -0.16 dex, comparable to the
mean abundance in the galactic bulge found by McWilliam & Rich (1994) and
considerably higher than that obtained from an analysis of two red giants in
this cluster by Barbuy etal (1999). The relative abundance for the best
determined alpha process element (Ca) indicates an excess of alpha process
elements of about a factor of two. The metallicity of NGC 6553 reaches the
average of the Galactic bulge and of the solar neighborhood.Comment: 29 pages, 6 figures, accepted for publication in the Ap
The Chemical Compositions of the SRd Variable Stars-- II. WY Andromedae, VW Eridani, and UW Librae
Chemical compositions are derived from high-resolution spectra for three
stars classed as SRd variables in the General Catalogue of Variable Stars.
These stars are shown to be metal-poor supergiants: WY And with [Fe/H] = -1.0,
VW Eri with [Fe/H] = -1.8, and UW Lib with [Fe/H] = -1.2. Their compositions
are identical to within the measurement errors with the compositions of
subdwarfs, subgiants, and less evolved giants of the same FeH. The stars are at
the tip of the first giant branch or in the early stages of evolution along the
asymptotic giant branch (AGB). There is no convincing evidence that these SRd
variables are experiencing thermal pulsing and the third dredge-up on the AGB.
The SRds appear to be the cool limit of the sequence of RV Tauri variables.Comment: 14 pages, 1 figure, 4 table
2-Methylpyrazine 1,4-dioxide
The title compound, C5H6N2O2, was prepared from 2-methylpyrazine, acetic acid and hydrogen peroxide. In the crystal, π–π stacking interactions between neighboring molecules are observed, with a centroid–centroid distance of 3.7370 Å, an interplanar distance of 3.167 Å, and a slippage of 1.984 Å. Each molecule is linked to four neighbors through C—H⋯O hydrogen-bonding interactions, forming one-dimensional ribbons
Visual loss and optic nerve head swelling in thiamine deficiency without prolonged dietary deficiency
Visual loss due to optic neuropathy is a rare manifestation of thiamine deficiency. We report a case of a 39-year-old woman with a body mass index (BMI) of 29 kg/m(2) who developed visual loss and bilateral optic nerve head swelling after a short, self-limited gastrointestinal illness. She was disoriented and inattentive and had absent ankle jerk reflexes, diminished sensation in both legs below the knees, and marked truncal ataxia. Magnetic resonance imaging (MRI) showed increased T2-signal in the medial thalami and mammillary bodies. The serum thiamine level was 8 nmol/L (normal 8–30). The diagnosis of thiamine deficiency was made, and the patient’s vision and neurologic symptoms improved significantly with intramuscular thiamine treatment. Thiamine deficiency can occur in the absence of an obvious predisposing factor such as alcoholism or low body weight. The clinician must be aware of the factors that govern vitamin availability and maintain a high index of suspicion to make the diagnosis in such cases
The First Detailed Abundances for M giants in Baade's Window from Infrared Spectroscopy
We report the first abundance analysis of 14 M giant stars in the Galactic
bulge, based on R=25,000 infrared spectroscopy (1.5-1.8um) using NIRSPEC at the
Keck II telescope. Because some of the bulge M giants reach high luminosities
and have very late spectral type, it has been suggested that they are the
progeny of only the most metal rich bulge stars, or possibly members of a
younger bulge population. We find the iron abundance and composition of the M
giants are similar to those of the K giants that have abundances determined
from optical high resolution spectroscopy: =-0.190 +/- 0.020 with a
1-sigma dispersion of 0.08 +/- 0.015. Comparing our bulge M giants to a control
sample of local disk M giants in the Solar vicinity, we find the bulge stars
are enhanced in alpha elements at the level of +0.3 dex relative to the Solar
composition stars, consistent with other studies of bulge globular clusters and
field stars. This small sample shows no dependence of spectral type on
metallicity, nor is there any indication that the M giants are the evolved
members of a subset of the bulge population endowed with special
characteristics such as relative youth or high metallicity. We also find low
12C/13C < 10, confirming the prsence of extra-mixing processes during the red
gaint phase of evolutionComment: 19 pages, 7 figures, accepted for publication in the Astrophysical
Journa
New Lithium Measurements in Metal-Poor Stars
We provide *lambda*6708 Li 1 measurements in 37 metal-poor stars, most of
which are poorly-studied or have no previous measurements, from high-resolution
and high-S/N spectroscopy obtained with the McDonald Observatory 2.1m and 2.7m
telescopes. The typical line strength and abundance uncertainties, confirmed by
the thinness of the Spite plateau manifested by our data and by comparison with
previous measurements, are <=4 mAng and <=0.07-0.10 dex respectively. Two rare
moderately metal-poor solar-Teff dwarfs, HIP 36491 and 40613, with
significantly depleted but still detectable Li are identified; future light
element determinations in the more heavily depeleted HIP 40613 may provide
constraints on the Li depletion mechanism acting in this star. We note two
moderately metal-poor and slightly evolved stars, HIP 105888 and G265-39, that
appear to be analogs of the low-Li moderately metal-poor subgiant HD 201889.
Preliminary abundance analysis of G 265-39 finds no abnormalities that suggest
the low Li content is associated with AGB mass-transfer or deep mixing and
p-capture. We also detect line doubling in HIP 4754, heretofore classified as
SB1.Comment: Accepted for publication in PASP, volume 912 (Feb 2012) 15 pages, 3
figures, 2 table
High resolution infrared spectra of NGC 6440 and NGC 6441: two massive Bulge Globular Clusters
Using the NIRSPEC spectrograph at Keck II, we have obtained infrared echelle
spectra covering the 1.5-1.8 micron range for giant stars in the massive bulge
globular clusters NGC6440 and NGC6441. We report the first high dispersion
abundance for NGC6440, [Fe/H]=-0.56+/-0.02 and we find [Fe/H]=-0.50+/-0.02 for
the blue HB cluster NGC6441. We measure an average -enhancement of
~+0.3 dex in both clusters, consistent with previous measurements of other
metal rich bulge clusters, and favoring the scenario of a rapid bulge formation
and chemical enrichment. We also measure very low 12C/13C isotopic ratios
(~5+/- 1), suggesting that extra-mixing mechanisms are at work during evolution
along the Red Giant Branch also in the high metallicity regime. We also measure
Al abundances, finding average [Al/Fe]=0.45+/-0.02 and [Al/Fe]=0.52+/-0.02 in
NGC6440 and NGC6441, respectively, and some Mg-Al anti-correlation in NGC6441.
We also measure radial velocities vr=-76+/-3 km/s and vr=+14+/-3 km/s and
velocity dispersions sigma=9+/-2 km/s and sigma=10+/-2 km/s, in NGC6440 and
NGC6441, respectively.Comment: 8 pages, 7 figure
Flying with the right principles at hand: An interactive lab to understand the physical origin of lift
A set of simple laboratory experiments aimed to understand the physical origin of lift is presented. The experiments are realized with simple materials and the use of multimedia reference sources (movies, computer simulations,
flow visualizations) is extensively applied in order to put forward otherwise complex fluid dynamical concepts. Emphasis is put in the individuation and correction of
commonly found misconceptions or wrong principles regarding, in particular, the concept of pressure, the role of viscosity, the flow behavior around an airfoil, the
domain of applicability of fluid dynamical principles, the role of flow curvature in attaining lift and the dynamical mechanisms at the basis of flight
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