306 research outputs found
Stellar Iron Abundances: non-LTE Effects
We report new statistical equilibrium calculations for Fe I and Fe II in the
atmosphere of Late-Type stars. We used atomic models for Fe I and Fe II having
respectively 256 and 190 levels, as well as 2117 and 3443 radiative
transitions. Photoionization cross-sections are from the Iron Project. These
atomic models were used to investigate non-LTE effects in iron abundances of
Late-Type stars with different atmospheric parameters.
We found that most Fe I lines in metal-poor stars are formed in conditions
far from LTE. We derived metallicity corrections of about 0.3 dex with respect
to LTE values, for the case of stars with [Fe/H] ~ -3.0. Fe II is found not to
be affected by significant non-LTE effects. The main non-LTE effect invoked in
the case of Fe I is overionization by ultraviolet radiation, thus classical
ionization equilibrium is far to be satisfied. An important consequence is that
surface gravities derived by LTE analysis are in error and should be corrected
before final abundances corrections.
This apparently solves the observed discrepancy between spectroscopic surface
gravities derived by LTE analyses and those derived from Hipparcos parallaxes.
A table of non-LTE [Fe/H] and log g values for a sample of metal-poor late-type
stars is given.Comment: 22 pages, 9 figures, 1 table, ApJ style, accepte
Abundances in Stars from the Red Giant Branch Tip to Near the Main Sequence Turn Off in M71: III. Abundance Ratios
We present abundance ratios for 23 elements with respect to Fe in a sample of
stars with a wide range in luminosity, from luminous giants to stars near the
turnoff, in the globular cluster M71. The analyzed spectra, obtained with HIRES
at the Keck Observatory, are of high dispersion (R=35,000). We find that the
neutron capture, the iron peak and the alpha-element abundance ratios show no
trend with Teff, and low scatter around the mean between the top of the RGB and
near the main sequence turnoff. The alpha-elements Mg, Ca, Si and Ti are
overabundant relative to Fe. The anti-correlation between O and Na abundances,
observed in other metal poor globular clusters, is detected in our sample and
extends to the main sequence. A statistically significant correlation between
Al and Na abundances is observed among the M71 stars in our sample, extending
to Mv = +1.8, fainter than the luminosity of the RGB bump in M5. Lithium is
varying, as expected, and Zr may be varying from star to star as well. M71
appears to have abundance ratios very similar to M5 whose bright giants were
studied by Ivans et al. (2001), but seems to have a smaller amplitude of
star-to-star variations at a given luminosity, as might be expected from its
higher metallicity. The results of our abundance analysis of 25 stars in M71
provide sufficient evidence of abundance variations at unexpectedly low
luminosities to rule out the mixing scenario. Either alone or, even more
powerfully, combined with other recent studies of C and N abundances in M71
stars, the existence of such abundance variations cannot be reproduced within
the context of our current understanding of stellar evolution.Comment: AJ, in press (June 2002), 18 figure
Abundances in Stars from the Red Giant Branch Tip to the Near Main Sequence in M71: II. Iron Abundance
We present [Ffe/H] abundance results that involve a sample of stars with a
wide range in luminosity from luminous giants to stars near the turnoff in a
globular cluster. Our sample of 25 stars in M71 includes 10 giant stars more
luminous than the RHB, 3 horizontal branch stars, 9 giant stars less luminous
than the RHB, and 3 stars near the turnoff. We analyzed both Fe I and Fe II
lines in high dispersion spectra observed with HIRES at the W. M. Keck
Observatory. We find that the [Fe/H] abundances from both Fe I and Fe II lines
agree with each other and with earlier determinations. Also the [Fe/H] obtained
from Fe I and Fe II lines is constant within the rather small uncertainties for
this group of stars over the full range in Teff and luminosity, suggesting that
NLTE effects are negligible in our iron abundance determination. In this
globular cluster, there is no difference among the mean [Fe/H] of giant stars
located at or above the RHB, RHB stars, giant stars located below the RHB and
stars near the turnoff.Comment: Minor changes to conform to version accepted for publication, with
several new figures (Paper 2 of a pair
A toolkit of mechanism and context independent widgets
Most human-computer interfaces are designed to run on a static platform (e.g. a workstation with a monitor) in a static environment (e.g. an office). However, with mobile devices becoming ubiquitous and capable of running applications similar to those found on static devices, it is no longer valid to design static interfaces. This paper describes a user-interface architecture which allows interactors to be flexible about the way they are presented. This flexibility is defined by the different input and output mechanisms used. An interactor may use different mechanisms depending upon their suitability in the current context, user preference and the resources available for presentation using that mechanism
Congenital tibial deficiencies: Treatment using the Ilizarov's external fixator
SummaryIntroductionCongenital longitudinal deficiency of the tibia is a rare and often syndromic anomaly. Amputation is usually the preferred treatment option in complete absence of the tibia; however, a conservative management might be implemented in partial forms or in case of amputation refusal. Our experience with the Ilizarov fixator, convinced us this device was the best suited for progressive correction of lower limbs length discrepancies and articular or bone angular limb deformities (ALD). The aim of this study is to highlight the interest of the Ilizarov fixator in the multistage conservative treatment of congenital tibial deficiencies.Material and methodsA retrospective study was conducted in nine patients suffering from Type I or II congenital tibial deficiencies (Jones) and sequentially managed using the Ilizarov technique. The functional outcome after treatment completion was then clinically assessed.ResultsThe different stages of correction were recorded for each individual patient. Patients were assessed at a mean follow-up of 18,3 years (4–32 years). The mean maximum knee flexion was 35° (0°–90°) in type I deficiencies and 118° (90°–140°) in type II deficiencies. One patient underwent amputation and a bilateral knee arthrodesis was performed in another case.DiscussionFew series in the literature report a comparable length of follow-up period in the conservative management of severe congenital tibial deficiencies. In our study, the Ilizarov fixator provided satisfactory progressive corrections of severe congenital tibial deficiencies.Level of EvidenceLevel IV therapeutic retrospective study
Abundance Analysis of Planetary Host Stars I. Differential Iron Abundances
We present atmospheric parameters and iron abundances derived from
high-resolution spectra for three samples of dwarf stars: stars which are known
to host close-in giant planets (CGP), stars for which radial velocity data
exclude the presence of a close-in giant planetary companion (no-CGP), as well
as a random sample of dwarfs with a spectral type and magnitude distribution
similar to that of the planetary host stars (control). All stars have been
observed with the same instrument and have been analyzed using the same model
atmospheres, atomic data and equivalent width modeling program. Abundances have
been derived differentially to the Sun, using a solar spectrum obtained with
Callisto as the reflector with the same instrumentation. We find that the iron
abundances of CGP dwarfs are on average by 0.22 dex greater than that of no-CGP
dwarfs. The iron abundance distributions of both the CGP and no-CGP dwarfs are
different than that of the control dwarfs, while the combined iron abundances
have a distribution which is very similar to that of the control dwarfs. All
four samples (CGP, no-CGP, combined, control) have different effective
temperature distributions. We show that metal enrichment occurs only for CGP
dwarfs with temperatures just below solar and approximately 300 K higher than
solar, whereas the abundance difference is insignificant at Teff around 6000 K.Comment: 52 pages (aastex 11pt, preprint style), including 17 figures and 13
tables; accepted for publication in AJ (scheduled for the October 2003 issue
Th Ages for Metal-Poor Stars
With a sample of 22 metal-poor stars, we demonstrate that the heavy element
abundance pattern (Z > 55) is the same as the r-process contributions to the
solar nebula. This bolsters the results of previous studies that there is a
universal r-process production pattern. We use the abundance of thorium in five
metal-poor stars, along with an estimate of the initial Th abundance based on
the abundances of stable r-process elements, to measure their ages. We have
four field red giants with errors of 4.2 Gyr in their ages and one M92 giant
with an error of 5.6 Gyr, based on considering the sources of observational
error only. We obtain an average age of 11.4 Gyr, which depends critically on
the assumption of an initial production ratio of Th/Eu of 0.496. If the
Universe is 15 Gyr old, then the initial Th/Eu value should be 0.590, in
agreement with some theoretical models of the r-process.Comment: 26 pages, to be published in Ap
The Carina dSph galaxy: where is the edge?
Recent cosmological N-body simulations suggest that current empirical
estimates of tidal radii in dSphs might be underestimated by at least one order
of magnitude. To constrain the plausibility of this theoretical framework, we
undertook a multiband (U,B,V,I) survey of the Carina dSph. Deep B,V data of
several fields located at radial distances from the Carina center ranging from
0.5 to 4.5 degrees show a sizable sample of faint blue objects with the same
magnitudes and colors of old, Turn-Off stars detected across the center. We
found that the (U-V,B-I) color-color plane is a robust diagnostic to split
stars from background galaxies. Unfortunately, current U,I-band data are too
shallow to firmly constrain the real extent of Carina.Comment: To be published on the proceedings of the XLIX meeting of the Italian
Astronomical Society. Requires mem.cl
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