2,411 research outputs found
Beryllium abundances in stars hosting giant planets
We have derived beryllium abundances in a wide sample of stars hosting
planets, with spectral types in the range F7V-K0V, aimed at studying in detail
the effects of the presence of planets on the structure and evolution of the
associated stars. Predictions from current models are compared with the derived
abundances and suggestions are provided to explain the observed
inconsistencies. We show that while still not clear, the results suggest that
theoretical models may have to be revised for stars with Teff<5500K. On the
other hand, a comparison between planet host and non-planet host stars shows no
clear difference between both populations. Although preliminary, this result
favors a ``primordial'' origin for the metallicity ``excess'' observed for the
planetary host stars. Under this assumption, i.e. that there would be no
differences between stars with and without giant planets, the light element
depletion pattern of our sample of stars may also be used to further
investigate and constraint Li and Be depletion mechanisms.Comment: A&A in press -- accepted on the 22/02/2002 (11 pages, 6 figures
included
Are beryllium abundances anomalous in stars with giant planets?
In this paper we present beryllium (Be) abundances in a large sample of 41
extra-solar planet host stars, and for 29 stars without any known
planetary-mass companion, spanning a large range of effective temperatures. The
Be abundances were derived through spectral synthesis done in standard Local
Thermodynamic Equilibrium, using spectra obtained with various instruments. The
results seem to confirm that overall, planet-host stars have ``normal'' Be
abundances, although a small, but not significant, difference might be present.
This result is discussed, and we show that this difference is probably not due
to any stellar ``pollution'' events. In other words, our results support the
idea that the high-metal content of planet-host stars has, overall, a
``primordial'' origin. However, we also find a small subset of planet-host
late-F and early-G dwarfs that might have higher than average Be abundances.
The reason for the offset is not clear, and might be related either to the
engulfment of planetary material, to galactic chemical evolution effects, or to
stellar-mass differences for stars of similar temperature.Comment: 15 pages, 9 figures, accepted for publication in Astronomy &
Astrophysic
Beryllium anomalies in solar-type field stars
We present a study of beryllium (Be) abundances in a large sample of field
solar-type dwarfs and sub-giants spanning a large range of effective
temperatures. The analysis shows that Be is severely depleted for F stars, as
expected by the light-element depletion models. However, we also show that
Beryllium abundances decrease with decreasing temperature for stars cooler than
6000 K, a result that cannot be explained by current theoretical models
including rotational mixing, but that is, at least in part, expected from the
models that take into account internal wave physics. In particular, the light
element abundances of the coolest and youngest stars in our sample suggest that
Be, as well as lithium (Li), has already been burned early during their
evolution. Furthermore, we find strong evidence for the existence of a Be-gap
for solar-temperature stars. The analysis of Li and Be abundances in the
sub-giants of our sample also shows the presence of one case that has still
detectable amounts of Li, while Be is severely depleted. Finally, we compare
the derived Be abundances with Li abundances derived using the same set of
stellar parameters. This gives us the possibility to explore the temperatures
for which the onset of Li and Be depletion occurs.Comment: 16 pages, 13 figures, accepted for publication in Astronomy &
Astrophysic
Behaviour of the Absorptive Part of the W Electromagnetic Vertex
The absorptive part of the vertex induced by massive fermion loops
is considered for different kinematical configurations. We show that the axial
part of this vertex is different from zero not only when massive fermions are
involved but also for massless fermion loops, if one of the W bosons is
space-like and the other is time-like. We also discuss in what sense Low's soft
photon theorem is satisfied.Comment: 17 pages, 1 figure, LaTe
Constant probe orientation for fast contact-based inspection of 3D free-form surfaces using (3+2)-axis inspection machines
A new probe optimization method for contact based (3+2)-axis inspection machines is proposed. Given an inspection path of a stylus on a free-form surface, an optimal orientation of the stylus is computed such that (i) the inclination angle of the stylus is within a given angular range with respect to the surface normal, (ii) the motion of the stylus is globally collision free, and (iii) the stylus remains constant in the coordinate system of the measuring machine. The last condition guarantees that the inspection motion requires only the involvement of the three translational axes of the measuring machine. The numerical simulations were validated through physical experiments on a testcase of a tooth of a bevel gear due to the surface complexity and probe accessibility. This optimized method was compared to 3-axis and 5-axis inspection strategies, showing that the fixed (3+2)-axis stylus returns more accurate inspection results compared to the traditional 3-axis approach and similar to 5-axis approach
Nitrogen abundances in Planet-harbouring stars
We present a detailed spectroscopic analysis of nitrogen abundances in 91
solar-type stars, 66 with and 25 without known planetary mass companions. All
comparison sample stars and 28 planet hosts were analysed by spectral synthesis
of the near-UV NH band at 3360 \AA observed at high resolution with the
VLT/UVES,while the near-IR NI 7468 \AA was measured in 31 objects. These two
abundance indicators are in good agreement. We found that nitrogen abundance
scales with that of iron in the metallicity range -0.6 <[Fe/H]< +0.4 with the
slope 1.08 \pm 0.05. Our results show that the bulk of nitrogen production at
high metallicities was coupled with iron. We found that the nitrogen abundance
distribution in stars with exoplanets is the high [Fe/H] extension of the curve
traced by the comparison sample of stars with no known planets. A comparison of
our nitrogen abundances with those available in the literature shows a good
agreement.Comment: 15 pages, 7 figures, Accepted for publication in A&
Galactic Evolution of Nitrogen
We present detailed spectroscopic analysis of nitrogen abundances in 31
unevolved metal-poor stars analysed by spectral synthesis of the near-UV NH
band at 3360 A observed at high resolution with various telescopes. We found
that [N/Fe] scales with that of iron in the metallicity range -3.1 < [Fe/H] <0
with the slope 0.01+-0.02. Furthermore, we derive uniform and accurate (N/O)
ratios using oxygen abundances from near-UV OH lines obtained in our previous
studies. We find that a primary component of nitrogen is required to explain
the observations. The NH lines are discovered in the VLT/UVES spectra of the
very metal-poor subdwarfs G64-12 and LP815-43 indicating that these stars are N
rich. The results are compared with theoretical models and observations of
extragalactic HII regions and Damped Ly systems. This is the first
direct comparison of the (N/O) ratios in these objects with those in Galactic
stars.Comment: 10 pages, 6 figures, to appear in Astronomy and Astrophysic
Coexistence of Two Rare Sarcomas: Primary Leiomyosarcoma of Bone and Epithelioid Hemangioendothelioma of the Liver
A 33-year-old woman sought medical attention for a painful swelling of the left
ankle. Plain radiographs revealed an osteolytic lesion involving the left distal tibia.
An excisional biopsy provided the diagnosis of leiomyosarcoma in the tibia. A
staging work-up was performed and an abdominal CT showed 4 liver hypodense
lesions in both lobes with peripheral contrast enhancement. A liver biopsy
confirmed the diagnosis of epithelioid hemangioendothelioma of the liver. No
association between these two entities has been described before. This case
introduces the importance of the pathological confirmation of apparent metastatic
lesions in low grade sarcomas and provides a review of the literature of both
tumours
Chemical abundances of planet-host stars: Results for alpha and Fe-group elements
In this paper, we present a study of the abundances of Si, Ca, Sc, Ti, V, Cr,
Mn, Co, and Ni in a large set of stars known to harbor giant planets, as well
as in a comparison sample of stars not known to have any planet ary-mass
companions. We have checked for possible chemical differences between planet
hosts and field stars without known planets. Our results show that overall, and
for a given value of [Fe/H], the abundance trends for the planet hosts are
nearly indistinguishable from those of the field stars. In general, the trends
show no discontinuities,and the abundance distributions of stars with giant
planets are high [Fe/H] extensions to the curves traced by the field dwarfs
without planets. The only elements that might present slight differences
between the two groups of stars are V, Mn, and to a lesser extent Ti and Co. We
also use the available data to describe galactic chemical evolution trends for
the elements studied. When comparing the results with former studies, a few
differences emerge for the high [Fe/H] tail of the distribution, a region that
is sampled with unprecedented detail in our analysis.Comment: Accepted for publication in Astronomy & Astrophysic
The blaSHV-5 gene is encoded in a compound transposon duplicated in tandem in Enterobacter cloacae
AbstractThe presence of blaSHV-5 is described in a compound transposon, duplicated in tandem and flanked by IS26 copies on a 70-kb conjugative plasmid (pHNM1), in an Enterobacter cloacae strain associated with a nosocomial outbreak that occurred in Mexico
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