156 research outputs found
High resolution optical spectroscopy of IRAS 09425-6040 (=GLMP 260)
We present high resolution optical spectroscopic observations of IRAS
09425-6040, a peculiar, extremely red, C-rich AGB star showing prominent O-rich
dust features in its ISO infrared spectrum attributed to crystalline silicates.
Our analysis shows that IRAS 09425-6040 is indeed a C-rich star slightly
enriched in lithium (log (Li/H) + 12 ~ 0.7) with a low 12C/13C = 15+-6 ratio.
We also found some evidence that it may be enriched in s-elements. Combining
our results with other observational data taken from the literature we conclude
that the star is possibly an intermediate-mass TP-AGB star (M > 3 M_sun) close
to the end of its AGB evolution which may have only very recently experienced a
radical change in its chemistry, turning into a carbon-rich AGB star.Comment: 5 pages, 2 figures, accepted for publication in A&
Measurement of the Higgs Boson Mass with a Linear e+e- Collider
The potential of a linear e+e- collider operated at a centre-of-mass energy
of 350 GeV is studied for the measurement of the Higgs boson mass. An
integrated luminosity of 500 fb-1 is assumed. For Higgs boson masses of 120,
150 and 180 GeV the uncertainty on the Higgs boson mass measurement is
estimated to be 40, 65 and 70 MeV, respectively. The effects of beam related
systematics, namely a bias in the beam energy measurement, the beam energy
spread and the luminosity spectrum due to beamstrahlung, on the precision of
the Higgs boson mass measurement are investigated. In order to keep the
systematic uncertainty on the Higgs boson mass well below the level of the
statistical error, the beam energy measurement must be controlled with a
relative precision better than 10-4.Comment: 19 pages, 10 Figure
The very lithium rich post-AGB SB2 binary HD172481
Double lined spectroscopic binaries in an evolved stage of evolution are
expected to be extremely rare since they must consist of equally luminous and
thus almost equally evolved objects, which requires an extremely similar
initial mass. In this contribution we discuss such rare double evolved SB2
system: HD172481. This binary includes an F-type post-AGB object and an M-type
AGB companion. The spectrum shows a surprisingly strong LiI 670.8nm line with
an equivalent width of 54mA yielding a lithium abundance of log(Li)=3.6.
Several explanations for this huge lithium content are explored.Comment: 7 pages, 5 figures, to appear in the proceedings of: "Post-AGB
Objects (Proto-Planetary Nebulae) as a Phase of Stellar Evolution", held in
Torun, Poland, July 5-7, 2000; eds. R. Szczerba, R. Tylenda, and S.K. Gorny.
See also the accepted A&A paper at http://xxx.lanl.gov/abs/astro-ph/001048
The effects of exogenous fatty acids and niacin on human monocyte-macrophage plasticity
Scope: Macrophage plasticity allows adapting to different environments, having a dual activity in inflammatory-related diseases. Our hypothesis is that the type of dietary fatty acids into human postprandial triglyceride-rich lipoproteins (TRLs), alone or in combination with niacin (vitamin B3), could modulate the plasticity of monocytes-macrophages. Methods and results: We isolated TRLs at the postprandial peak from blood samples of healthy volunteers after the ingestion of a meal rich in saturated fatty acids (SFAs), monounsaturated fatty acids (MUFAs) or MUFAs plus omega-3 long-chain polyunsaturated fatty acids (LCPUFAs). Autologous monocytes isolated at fasting were first induced to differentiate into naĂŻve macrophages. We observed that postprandial TRL-MUFAs, particularly in combination with niacin, enhance competence to monocytes to differentiate and polarise into M2 macrophages. Postprandial TRL-SFAs made polarised macrophages prone to an M1 phenotype. In contrast to dietary SFAs, dietary MUFAs in the meals plus immediate-release niacin primed circulating monocytes for a reduced postprandial pro-inflammatory profile. Conclusion: Our study underlines a role of postprandial TRLs as a metabolic entity in regulating the plasticity of the monocyte-macrophage lineage and also brings an understanding of the mechanisms by which dietary fatty acids are environmental factors fostering the innate immune responsiveness in humans.Ministerio de Ciencia e InnovaciĂłn AGL2011- 2900
Rb-rich Asymptotic Giant Branch stars in the Magellanic Clouds
We present high-resolution (R~60,000) optical spectra of a carefully selected
sample of heavily obscured and presumably massive O-rich Asymptotic Giant
Branch (AGB) stars in the Magellanic Clouds (MCs). We report the discovery of
strong Rb I lines at 7800 A in four Rb-rich LMC stars at luminosities equal to
or greater than the standard adopted luminosity limit for AGB stars
(Mbol~-7.1), confirming that "Hot Bottom Burning" (HBB) may produce a flux
excess in the more massive AGB stars. In the SMC sample, just one of the five
stars with Mbol<-7.1 was detected in Rb; the other stars may be massive red
supergiants. The Rb-rich LMC AGB stars might have stellar masses of at least
~6-7 Msun. Our abundance analysis show that these Rb-rich stars are extremely
enriched in Rb by up to 10^3-10^5 times solar but seem to have only mild Zr
enhancements. The high Rb/Zr ratios, if real, represent a severe problem for
the s-process, even if the 22Ne source is operational as expected for massive
AGB stars; it is not possible to synthesize copious amounts of Rb without also
overproducing Zr. The solution to the problem may lie with an incomplete
present understanding of the atmospheres of luminous AGB stars.Comment: accepted for publication in The Astrophysical Journal Letters (10
pages, 3 figures and 2 Tables
Determination of stellar parameters of C-rich hydrostatic stars from spectro-interferometric observations
Giant stars, and especially C-rich giants, contribute significantly to the
chemical enrichment of galaxies. The determination of precise parameters for
these stars is a necessary prerequisite for a proper implementation of this
evolutionary phase in the models of galaxies. Infrared interferometry opened
new horizons in the study of the stellar parameters of giant stars, and
provided new important constraints for the atmospheric and evolutionary
models.We aim to determine which stellar parameters can be constrained by using
infrared interferometry and spectroscopy, in the case of C-stars what is the
precision which can be achieved and what are the limitations. For this purpose
we obtained new infrared spectra and combined them with unpublished
interferometric measurements for five mildly variable carbon-rich asymptotic
giant branch stars. The observations were compared with a large grid of
hydrostatic model atmospheres and with new isochrones which include the
predictions of the thermally pulsing phase. For the very first time we are able
to reproduce spectra in the range between 0.9 and 4 m, and broad band
interferometry with hydrostatic model atmospheres. Temperature, mass, log,
C/O and a reasonable range for the distance were derived for all the objects of
our study. All our targets have at least one combination of best-fitting
parameters which lays in the region of the HR-diagram where C-stars are
predicted. We confirm that low resolution spectroscopy is not sensitive to the
mass and log determination. For hydrostatic objects the m feature
is very sensitive to temperature variations therefore it is a very powerful
tool for accurate temperature determinations. Interferometry can constrain
mass, radius and log but a distance has to be assumed. The large
uncertainty in the distance measurements available for C-rich stars remains a
major problem.Comment: 18 pages, 11 figures. Accepted for publication in A&
Analysis of the infrared spectra of the peculiar post-AGB stars EPLyr and HD52961
Aim: We aim to study in detail the peculiar mineralogy and structure of the
circumstellar environment of two binary post-AGB stars, EPLyr and HD52961. Both
stars were selected from a larger sample of evolved disc sources observed with
Spitzer and show unique solid-state and gas features in their infrared spectra.
Moreover, they show a very small infrared excess in comparison with the other
sample stars. Methods: The different dust and gas species are identified on the
basis of high-resolution Spitzer-IRS spectra. We fit the full spectrum to
constrain grain sizes and temperature distributions in the discs. This,
combined with our broad-band spectral energy distribution and interferometric
measurements, allows us to study the physical structure of the disc, using a
self-consistent 2D radiative-transfer disc model. Results: We find that both
stars have strong emission features due to CO_2 gas, dominated by
^{12}C^{16}O_2, but with clear ^{13}C^{16}O_2 and even ^{16}O^{12}C^{18}O
isotopic signatures. Crystalline silicates are apparent in both sources but
proved very hard to model. EP Lyr also shows evidence of mixed chemistry, with
emission features of the rare class-C PAHs. Whether these PAHs reside in the
oxygen-rich disc or in a carbon-rich outflow is still unclear. With the
strongly processed silicates, the mixed chemistry and the low ^{12}C/^{13}C
ratio, EP Lyr resembles some silicate J-type stars, although the depleted
photosphere makes nucleosynthetic signatures difficult to probe. We find that
the disc environment of both sources is, to a first approximation, well
modelled with a passive disc, but additional physics such as grain settling,
radial dust distributions, and an outflow component must be included to explain
the details of the observed spectral energy distributions in both stars.Comment: 14 pages, accepted for publication by A&
Study of Spin and Decay-Plane Correlations of W Bosons in the e+e- -> W+W- Process at LEP
Data collected at LEP at centre-of-mass energies \sqrt(s) = 189 - 209 GeV are
used to study correlations of the spin of W bosons using e+e- -> W+W- -> lnqq~
events. Spin correlations are favoured by data, and found to agree with the
Standard Model predictions. In addition, correlations between the W-boson decay
planes are studied in e+e- -> W+W- -> lnqq~ and e+e- -> W+W- -> qq~qq~ events.
Decay-plane correlations, consistent with zero and with the Standard Model
predictions, are measured
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