1,010 research outputs found
Lithium abundances in extremely metal-poor turn-off stars
We discuss the current status of the sample of Lithium abundances in
extremely metal poor (EMP) turn-off (TO) stars collected by our group, and
compare it with the available literature results. In the last years, evidences
have accumulated of a progressive disruption of the Spite plateau in stars of
extremely low metallicity. What appears to be a flat, thin plateau above
[Fe/H]\sim-2.8 turns, at lower metallicities, into a broader distribution for
which the plateau level constitutes the upper limit, but more and more stars
show lower Li abundances. The sample we have collected currently counts
abundances or upper limits for 44 EMP TO stars between [Fe/H]=-2.5 and -3.5,
plus the ultra-metal poor star SDSS J102915+172927 at [Fe/H]=-4.9. The
"meltdown" of the Spite plateau is quite evident and, at the current status of
the sample, does not appear to be restricted to the cool end of the effective
temperature distribution. SDSS J102915+172927 displays an extreme Li depletion
that contrasts with its otherwise quite ordinary set of [X/Fe] ratios.Comment: 6 pages, 4 figures, proceedings of the "Lithium in the Cosmos"
conference, Paris, 27-29 February 201
Clinical survey of neurosensory side-effects of mandibular parasymphyseal bone harvesting
The aim of the present survey was to assess neurosensory disturbances and/or tooth-pulp sensitivity losses after mandibular parasymphyseal bone-harvesting procedures. Twenty-eight harvesting areas in 16 patients were surveyed. Mucosal and skin sensitivity of the chin/lower lip, divided into four regions, were determined via Pointed-Blunt and Two-Point-Discrimination Tests. Pulp sensitivity of the mandibular teeth from the left second bicuspid to the right second bicuspid was tested by cold vitality preoperatively and 12 months postoperatively. Teeth were grouped according to sensitivity alterations and distance from the harvesting defects, as measured on CT scans, and statistically significant differences sought. At 12 months, 29% of preoperatively vital cuspids overlying the harvesting defects revealed pulp-sensitivity losses; no patient reported anaesthesia or analgesia; hypoaesthesia was present in 4% (8 sites; 2 patients), hypoalgesia was present in 3% (5 sites; 2 patients) and Two-Point-Discrimination Tests yielded pathologic responses in 5% of tested areas (10 sites; 4 patients). Teeth with and without pulp sensitivity changes were statistically indistinguishable regarding distances between root apices or mental foramen and the harvesting defect. The loss of pulp sensitivity in any tooth cannot be predicted simply on the basis of the distance between its apex and the harvesting osteotomy line
MyGIsFOS: an automated code for parameter determination and detailed abundance analysis in cool stars
The current and planned high-resolution, high-multiplexity stellar
spectroscopic surveys, as well as the swelling amount of under-utilized data
present in public archives have led to an increasing number of efforts to
automate the crucial but slow process to retrieve stellar parameters and
chemical abundances from spectra. We present MyGIsFOS, a code designed to
derive atmospheric parameters and detailed stellar abundances from medium -
high resolution spectra of cool (FGK) stars. We describe the general structure
and workings of the code, present analyses of a number of well studied stars
representative of the parameter space MyGIsFOS is designed to cover, and
examples of the exploitation of MyGIsFOS very fast analysis to assess
uncertainties through Montecarlo tests. MyGIsFOS aims to reproduce a
``traditional'' manual analysis by fitting spectral features for different
elements against a precomputed grid of synthetic spectra. Fe I and Fe II lines
can be employed to determine temperature, gravity, microturbulence, and
metallicity by iteratively minimizing the dependence of Fe I abundance from
line lower energy and equivalent width, and imposing Fe I - Fe II ionization
equilibrium. Once parameters are retrieved, detailed chemical abundances are
measured from lines of other elements. MyGIsFOS replicates closely the results
obtained in similar analyses on a set of well known stars. It is also quite
fast, performing a full parameter determination and detailed abundance analysis
in about two minutes per star on a mainstream desktop computer. Currently, its
preferred field of application are high-resolution and/or large spectral
coverage data (e.g UVES, X-Shooter, HARPS, Sophie).Comment: 15 pages, 14 figures, accepted for publication by A&
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&
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