107 research outputs found
Oxygen Abundances in Two Metal-Poor Subgiants from the Analysis of the 6300 A Forbidden O I Line
Recent LTE analyses (Israelian et al. 1998 and Bosegaard et al. 1999) of the
OH bands in the optical-ultraviolet spectra of nearby metal-poor subdwarfs
indicate that oxygen abundances are generally higher than those previously
determined. The difference increases with decreasing metallicity and reaches
delta([O/Fe]) ~ +0.6 dex as [Fe/H] approaches -3.0.
Employing high resolution (R = 50000), high S/N (~ 250) echelle spectra of
the two stars found by Israelian et al. (1998) to have the highest
[O/Fe]-ratios, viz, BD +23 3130 and BD +37 1458, we conducted abundance
analyses based on about 60 Fe I and 7-9 Fe II lines. We determined from Kurucz
LTE models the values of the stellar parameters, as well as abundances of Na,
Ni, and the traditional alpha-elements, independent of the calibration of color
vs scales. We determined oxygen abundances from spectral synthesis of
the stronger line (6300 A) of the [O I] doublet.
The syntheses of the [O I] line lead to smaller values of [O/Fe], consistent
with those found earlier among halo field and globular cluster giants. We
obtain [O/Fe] = +0.35 +/- 0.2 for BD +23 3130 and +0.50 +/- 0.2 for BD +37
1458. In the former, the [O I] line is very weak (~ 1 mA), so that the quoted
[O/Fe] value may in reality be an upper limit.
Therefore in these two stars a discrepancy exists between the [O/Fe]- ratios
derived from [O I] and the OH feature, and the origin of this difference
remains unclear. Until the matter is clarified, we suggest it is premature to
conclude that the ab initio oxygen abundances of old, metal-poor stars need to
be revised drastically upward.Comment: 38 pages, 5 tables, 14 figures To appear in July 1999 AJ Updated
April 16, 1999. Fixed typo
Abundances and Kinematics of Field Halo and Disk Stars I: Observational Data and Abundance Analysis
We describe observations and abundance analysis of a high-resolution,
high-S/N survey of 168 stars, most of which are metal-poor dwarfs. We follow a
self-consistent LTE analysis technique to determine the stellar parameters and
abundances, and estimate the effects of random and systematic uncertainties on
the resulting abundances. Element-to-iron ratios are derived for key alpha,
odd, Fe-peak, r- and s-process elements. Effects of Non-LTE on the analysis of
Fe I lines are shown to be very small on the average. Spectroscopically
determined surface gravities are derived that are generally close to those
obtained from Hipparcos parallaxes.Comment: 41 pages, 7 Postscript figures. Accepted for publication in the A
Abundances In Very Metal Poor Dwarf Stars
We discuss the detailed composition of 28 extremely metal-poor dwarfs, 22 of
which are from the Hamburg/ESO Survey, based on Keck Echelle spectra. Our
sample has a median [Fe/H] of -2.7 dex, extends to -3.5 dex, and is somewhat
less metal-poor than was expected from [Fe/H](HK,HES) determined from low
resolution spectra. Our analysis supports the existence of a sharp decline in
the distribution of halo stars with metallicity below [Fe/H] = -3.0 dex. So far
no additional turnoff stars with [Fe/H]}<-3.5 have been identified in our
follow up efforts. For the best observed elements between Mg and Ni, we find
that the abundance ratios appear to have reached a plateau, i.e. [X/Fe] is
approximately constant as a function of [Fe/H], except for Cr, Mn and Co, which
show trends of abundance ratios varying with [Fe/H]. These abundance ratios at
low metallicity correspond approximately to the yield expected from Type II SN
with a narrow range in mass and explosion parameters; high mass Type II SN
progenitors are required. The dispersion of [X/Fe] about this plateau level is
surprisingly small, and is still dominated by measurement errors rather than
intrinsic scatter. The dispersion in neutron-capture elements, and the
abundance trends for Cr, Mn and Co are consistent with previous studies of
evolved EMP stars. Two dwarfs in the sample are carbon stars, while two others
have significant C enhancements, all with C12/C13 ~ 7 and with C/N between 10
and 150. Three of these C-rich stars have large enhancements of the heavy
neutron capture elements, including lead, which implies a strong s-process
contribution, presumably from binary mass transfer; the fourth shows no excess
of Sr or Ba.Comment: Accepted for publication in the Ap
Spectroscopic Analysis of Two Carbon Rich Post-AGB Stars
The chemical compositions of the C-rich pAGB stars IRAS 05113+1347 and IRAS
22272+5424 are determined from high-resolution optical spectra using standard
LTE model atmosphere-based techniques. The stars are C, N, and -process
enriched suggesting efficient operation of the third-dredge up in the AGB star
following a first dredge-up that increased the N abundance. Lithium is present
with an abundance requiring Li manufacture. With this pair, abundance analyses
are now available for 11 C-rich pAGBs. A common history is indicated and, in
particular, the -abundances, especially the relative abundances of light to
heavy -process elements, follow recent predictions for the third dredge-up
in AGB stars.Comment: 41 pages (including 10 figs). 2001, ApJ, Accepte
New Analyses of Star-to-Star Abundance Variations Among Bright Giants in the Mildly Metal-Poor Globular Cluster M5
We present a chemical composition analysis of 36 giant stars in the mildly
metal-poor globular cluster M5 (NGC 5904). The analysis makes use of high
resolution data acquired at the Keck I telescope as well as a re-analysis of
high resolution spectra acquired for an earlier study at Lick Observatory. We
employed two analysis techniques: one, adopting standard spectroscopic
constraints, and two, adopting an analysis consistent with the non-LTE precepts
as recently described by Thevenin & Idiart. The abundance ratios we derive for
magnesium, silicon, calcium, scandium, titanium, vanadium, nickel, barium and
europium in M5 show no significant abundance variations and the ratios are
comparable to those of halo field stars. However, large variations are seen in
the abundances of oxygen, sodium and aluminum, the elements that are sensitive
to proton-capture nucleosynthesis. In comparing the abundances of M5 and M4
(NGC 6121), another mildly metal-poor globular cluster, we find that silicon,
aluminum, barium and lanthanum are overabundant in M4 with respect to what is
seen in M5, confirming and expanding the results of previous studies. In
comparing the abundances between these two clusters and others having
comparable metallicities, we find that the anti-correlations observed in M5 are
similar to those found in more metal-poor clusters, M3, M10 and M13, whereas
the behavior in M4 is more like that of the more metal-rich globular cluster
M71. We conclude that among stars in Galactic globular clusters, there is no
definitive ``single'' value of [el/Fe] at a given [Fe/H] for at least some
alpha-capture, odd-Z and slow neutron-capture process elements, in this case,
silicon, aluminum, barium and lanthanum.Comment: 31 pages + 16 figures + 11 tables; accepted for publication in
Sept.2001 Astronomical Journa
Kidney Pathology Precedes and Predicts the Pathological Cascade of Cerebrovascular Lesions in Stroke Prone Rats
INTRODUCTION: Human cerebral small vessel disease (CSVD) has been hypothesized to be an age-dependent disease accompanied by similar vascular changes in other organs. SHRSP feature numerous vascular risk factors and may be a valid model of some aspects of human CSVD. Here we compare renal histopathological changes with the brain pathology of spontaneously hypertensive stroke-prone rats (SHRSP). MATERIAL AND METHODS: We histologically investigated the brains and kidneys of 61 SHRSP at different stages of age (12 to 44 weeks). The brain pathology (aggregated erythrocytes in capillaries and arterioles, microbleeds, microthromboses) and the kidney pathology (aggregated erythrocytes within peritubular capillaries, tubular protein cylinders, glomerulosclerosis) were quantified separately. The prediction of the brain pathology by the kidney pathology was assessed by creating ROC-curves integrating the degree of kidney pathology and age of SHRSP. RESULTS: Both, brain and kidney pathology, show an age-dependency and proceed in definite stages whereas an aggregation of erythrocytes in capillaries and arterioles, we parsimoniously interpreted as stases, represent the initial finding in both organs. Thus, early renal tubulointerstitial damage characterized by rather few intravasal erythrocyte aggregations and tubular protein cylinders predicts the initial step of SHRSPs' cerebral vascular pathology marked by accumulated erythrocytes. The combined increase of intravasal erythrocyte aggregations and protein cylinders accompanied by glomerulosclerosis and thrombotic renal microangiopathy in kidneys of older SHRSP predicts the final stages of SHRSPs' cerebrovascular lesions marked by microbleeds and thrombotic infarcts. CONCLUSION: Our results illustrate a close association between structural brain and kidney pathology and support the concept of small vessel disease to be an age-dependent systemic pathology. Further, an improved joined nephrologic and neurologic diagnostic may help to identify patients with CSVD at an early stage
Chemical Composition of the Planet-Harboring Star TrES-1
We present a detailed chemical abundance analysis of the parent star of the
transiting extrasolar planet TrES-1. Based on high-resolution Keck/HIRES and
HET/HRS spectra, we have determined abundances relative to the Sun for 16
elements (Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Y, and Ba).
The resulting average abundance of is in good
agreement with initial estimates of solar metallicity based on iron. We compare
the elemental abundances of TrES-1 with those of the sample of stars with
planets, searching for possible chemical abundance anomalies. TrES-1 appears
not to be chemically peculiar in any measurable way. We investigate possible
signs of selective accretion of refractory elements in TrES-1 and other stars
with planets, and find no statistically significant trends of metallicity
[/H] with condensation temperature . We use published abundances and
kinematic information for the sample of planet-hosting stars (including TrES-1)
and several statistical indicators to provide an updated classification in
terms of their likelihood to belong to either the thin disk or the thick disk
of the Milky Way Galaxy. TrES-1 is found to be a very likely member of the thin
disk population. By comparing -element abundances of planet hosts and a
large control sample of field stars, we also find that metal-rich
([Fe/H]) stars with planets appear to be systematically
underabundant in [/Fe] by dex with respect to comparison
field stars. The reason for this signature is unclear, but systematic
differences in the analysis procedures adopted by different groups cannot be
ruled out.Comment: 52 pages, 15 figures, 5 tables, accepted for publication in the
Astronomical Journa
Search for the standard model Higgs boson decaying to a pair in events with no charged leptons and large missing transverse energy using the full CDF data set
We report on a search for the standard model Higgs boson produced in
association with a vector boson in the full data set of proton-antiproton
collisions at TeV recorded by the CDF II detector at the
Tevatron, corresponding to an integrated luminosity of 9.45 fb. We
consider events having no identified charged lepton, a transverse energy
imbalance, and two or three jets, of which at least one is consistent with
originating from the decay of a quark. We place 95% credibility level upper
limits on the production cross section times standard model branching fraction
for several mass hypotheses between 90 and . For a Higgs
boson mass of , the observed (expected) limit is 6.7
(3.6) times the standard model prediction.Comment: Accepted by Phys. Rev. Let
Search for the standard model Higgs boson decaying to a bb pair in events with one charged lepton and large missing transverse energy using the full CDF data set
We present a search for the standard model Higgs boson produced in
association with a W boson in sqrt(s) = 1.96 TeV p-pbar collision data
collected with the CDF II detector at the Tevatron corresponding to an
integrated luminosity of 9.45 fb-1. In events consistent with the decay of the
Higgs boson to a bottom-quark pair and the W boson to an electron or muon and a
neutrino, we set 95% credibility level upper limits on the WH production cross
section times the H->bb branching ratio as a function of Higgs boson mass. At a
Higgs boson mass of 125 GeV/c2 we observe (expect) a limit of 4.9 (2.8) times
the standard model value.Comment: Submitted to Phys. Rev. Lett (v2 contains clarifications suggested by
PRL
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