537 research outputs found
HLA class II antibodies at the time of kidney transplantation and cardiovascular outcome : a retrospective cohort study
Background.
The negative role of HLA class II donor-specific antibody on graft outcome is well recognized. However, the potentially negative cardiovascular effects of preformed HLA class II antibodies and donor HLA in kidney transplant recipients (KTRs) remain unestablished.
Methods.
We conducted a single-center, retrospective cohort study including 1115 KTRs (2003–2016) with up to 4449 person-years of follow-up after transplantation and a median follow-up time of 5.1 years (interquartile range, 2.7–7.6). We evaluated the unadjusted and multivariable-adjusted association between pretransplant HLA class I and II antibodies, as well as HLA-DR1 donor/recipient genotype and the primary (major adverse cardiac and cerebrovascular event [MACCE] or all-cause mortality) and secondary (MACCE or cardiovascular mortality) outcome.
Results.
In a multivariate Cox proportional hazard model, HLA class II antibodies before transplantation were associated with increased adjusted hazard ratio (aHR) for MACCE or all-cause mortality (aHR, 1.71 [1.13–2.60]; P = 0.012) even after adjustment for time-varying covariate graft loss (aHR, 1.68 [1.08–2.62]; P = 0.022) and biopsy-proven acute rejection (aHR, 1.71 [1.13–2.60]; P = 0.012). HLA class II antibodies were also associated with increased aHR for the secondary outcome, MACCE, or cardiovascular mortality (aHR, 1.92 [1.12–3.30]; P = 0.018). We investigated the effect of donor and recipient HLA-DR1 on these outcome parameters and demonstrated that KTRs with HLA-DR1 positive donors had an increased aHR for MACCE with all-cause (aHR, 1.45 [1.09–1.94]; P = 0.012) and cardiovascular mortality (aHR, 1.49 [1.00–2.22]; P = 0.05).
Conclusions.
Prior sensitization against HLA class II antigens is associated with unfavorable long-term cardiovascular outcome in KTRs independent of graft loss or rejection. Recipients of an HLA-DR1 donor also have an impaired cardiovascular outcome
Disks around Hot Stars in the Trifid Nebula
We report on mid-IR observations of the central region in the Trifid nebula,
carried out with ISOCAM in several broad-band infrared filters and in the low
resolution spectroscopic mode provided by the circular variable filter.
Analysis of the emission indicates the presence of a hot dust component (500 to
1000 K) and a warm dust component at lower temperatures (150-200 K) around
several members of the cluster exciting the HII region, and other stars
undetected at optical wavelengths. Complementary VLA observations suggest that
the mid-IR emission could arise from a dust cocoon or a circumstellar disk,
evaporated under the ionization of the central source and the exciting star of
the nebula. In several sources the silicate band is seen in
emission. One young stellar source shows indications of crystalline silicates
in the circumstellar dust.Comment: 4 pages with 1 figur
Near-Infrared Photometric Survey of Herbig Ae/Be Candidate Stars
We report near-infrared photometric measurements of 35 Herbig Ae/Be candidate
stars obtained with direct imaging and aperture photometry. Observations were
made through the broadband J, H, and K' filters, with each source imaged in at
least one of the wavebands. We achieved subarcsecond angular resolution for all
observations, providing us with the opportunity to search for close binary
candidates and extended structure. The imaging revealed five newly identified
binary candidates and one previously resolved T Tauri binary among the target
sources with separations of <~2.5". Separate photometry is provided for each of
the binary candidate stars. We detect one extended source that has been
identified as a protoplanetary nebula. Comparing our magnitudes to past
measurements yields significant differences for some sources, possibly
indicating photometric variability. H-band finding charts for all of our
sources are provided to aid follow-up high-resolution imaging.Comment: 22 pages, 1 figure, accepted for publication in A
ISO spectroscopy of circumstellar dust in 14 Herbig Ae/Be systems: towards an understanding of dust processing
We present Infrared Space Observatory (ISO) spectra of fourteen isolated
Herbig Ae/Be (HAEBE) stars, to study the characteristics of their circumstellar
dust. These spectra show large star-to-star differences, in the emission
features of both carbon-rich and oxygen-rich dust grains. The IR spectra were
combined with photometric data ranging from the UV through the optical into the
sub-mm region. We defined two key groups, based upon the spectral shape of the
infrared region. The derived results can be summarized as follows: (1) the
continuum of the IR to sub-mm region of all stars can be reconstructed by the
sum of a power-law and a cool component, which can be represented by a black
body. Possible locations for these components are an optically thick,
geometrically thin disc (power-law component) and an optically thin flared
region (black body); (2) all stars have a substantial amount of cold dust
around them, independent of the amount of mid-IR excess they show; (3) also the
near-IR excess is unrelated to the mid-IR excess, indicating different
composition/location of the emitting material; (4) remarkably, some sources
lack the silicate bands; (5) apart from amorphous silicates, we find evidence
for crystalline silicates in several stars, some of which are new detections;
(6) PAH bands are present in at least 50% of our sample, and their appearance
is slightly different from PAHs in the ISM; (7) PAH bands are, with one
exception, not present in sources which only show a power-law continuum in the
IR; their presence is unrelated to the presence of the silicate bands; (8) the
dust in HAEBE stars shows strong evidence for coagulation; this dust processing
is unrelated to any of the central star properties (such as age, spectral type
and activity).Comment: 15 pages, accepted by A&
Silicate Emission in the TW Hydrae Association
The TW Hydrae Association is the nearest young stellar association. Among its
members are HD 98800, HR 4796A, and TW Hydrae itself, the nearest known
classical T Tauri star. We have observed these three stars spectroscopically
between 3 and 13 microns. In TW Hya the spectrum shows a silicate emission
feature that is similar to many other young stars with protostellar disks. The
11.2 micron feature indicative of significant amounts of crystalline olivine is
not as strong as in some young stars and solar system comets. In HR 4796A, the
thermal emission in the silicate feature is very weak, suggesting little in the
way of (small silicate) grains near the star. The silicate band of HD 98800
(observed by us but also reported by Sylvester and Skinner (1996)) is
intermediate in strength between TW Hya and HR 4796.Comment: 22 pages, 11 figures, LaTeX2e and AAS LaTeX macros v5.0. Accepted for
publication in A
SPH modelling of companion-perturbed AGB outflows including a new morphology classification scheme
CONTEXT: Asymptotic giant branch (AGB) stars are known to lose a significant amount of mass by a stellar wind, which controls the remainder of their stellar lifetime. High angular-resolution observations show that the winds of these cool stars typically exhibit mid- to small-scale density perturbations such as spirals and arcs, believed to be caused by the gravitational interaction with a (sub-)stellar companion. AIMS: We aim to explore the effects of the wind-companion interaction on the 3D density and velocity distribution of the wind, as a function of three key parameters: wind velocity, binary separation and companion mass. For the first time, we compare the impact on the outflow of a planetary companion to that of a stellar companion. We intend to devise a morphology classification scheme based on a singular parameter. METHODS: We ran a small grid of high-resolution polytropic models with the smoothed particle hydrodynamics (SPH) numerical code PHANTOM to examine the 3D density structure of the AGB outflow in the orbital and meridional plane and around the poles. By constructing a basic toy model of the gravitational acceleration due to the companion, we analysed the terminal velocity reached by the outflow in the simulations. RESULTS: We find that models with a stellar companion, large binary separation and high wind speed obtain a wind morphology in the orbital plane consisting of a single spiral structure, of which the two edges diverge due to a velocity dispersion caused by the gravitational slingshot mechanism. In the meridional plane the spiral manifests itself as concentric arcs, reaching all latitudes. When lowering the wind velocity and/or the binary separation, the morphology becomes more complex: in the orbital plane a double spiral arises, which is irregular for the closest systems, and the wind material gets focussed towards the orbital plane, with the formation of an equatorial density enhancement (EDE) as a consequence. Lowering the companion mass from a stellar to a planetary mass, reduces the formation of density perturbations significantly. CONCLUSIONS: With this grid of models we cover the prominent morphology changes in a companion-perturbed AGB outflow: slow winds with a close, massive binary companion show a more complex morphology. Additionally, we prove that massive planets are able to significantly impact the density structure of an AGB wind. We find that the interaction with a companion affects the terminal velocity of the wind, which can be explained by the gravitational slingshot mechanism. We distinguish between two types of wind focussing to the orbital plane resulting from distinct mechanisms: global flattening of the outflow as a result of the AGB star’s orbital motion and the formation of an EDE as a consequence of the companion’s gravitational pull. We investigate different morphology classification schemes and uncover that the ratio of the gravitational potential energy density of the companion to the kinetic energy density of the AGB outflow yields a robust classification parameter for the models presented in this paper
SPH modelling of wind-companion interactions in eccentric AGB binary systems
The late evolutionary stages of low- and intermediate-mass stars are
characterised by mass loss through a dust-driven stellar wind. Recent
observations reveal complex structures within these winds, that are believed to
be formed primarily via interaction with a companion. How these complexities
arise, and which structures are formed in which type of systems, is still
poorly understood. Particularly, there is a lack of studies investigating the
structure formation in eccentric systems. We aim to improve our understanding
of the wind morphology of eccentric AGB binary systems by investigating the
mechanism responsible for the different small-scale structures and global
morphologies that arise in a polytropic wind with different velocities. Using
the smoothed particle hydrodynamics (SPH) code Phantom, we generate nine
different high-resolution, 3D simulations of an AGB star with a solar-mass
companion with various wind velocity and eccentricity combinations. The models
assume a polytropic gas, with no additional cooling. We conclude that for
models with a high wind velocity, the short interaction with the companion
results in a regular spiral morphology, that is flattened. In the case of a
lower wind velocity, the stronger interaction results in the formation of a
high-energy region and bow-shock structure that can shape the wind into an
irregular morphology if instabilities arise. High-eccentricity models show a
complex, phase-dependent interaction leading to wind structures that are
irregular in three dimensions. However, the significant interaction with the
companion compresses matter into an equatorial density enhancement,
irrespective of eccentricity.Comment: 23 pages, 22 figure
Recent Results of Solid-State Spectroscopy
Solid state spectroscopy continues to be an important source of information
on the mineralogical composition and physical properties of dust grains both in
space and on planetary surfaces. With only a few exceptions, artificially
produced or natural terrestrial analog materials, rather than 'real' cosmic
dust grains, are the subject of solid state astrophysics. The Jena laboratory
has provided a large number of data sets characterizing the UV, optical and
infrared properties of such cosmic dust analogs. The present paper highlights
recent developments and results achieved in this context, focussing on
'non-standard conditions' such as very low temperatures, very high temperatures
and very long wavelengths.Comment: 15 pages, 10 figures. Contribution to an IAU Conference "The
Molecular Universe" held in Toledo in June 201
Cometary Dust in the Debris Disks of HD 31648 and HD 163296: Two ``Baby'' beta Pics
The debris disks surrounding the pre-main sequence stars HD 31648 and HD
163296 were observed spectroscopically between 3 and 14 microns. Both possess a
silicate emission feature at 10 microns which resembles that of the star beta
Pictoris and those observed in solar system comets. The structure of the band
is consistent with a mixture of olivine and pyroxene material, plus an
underlying continuum of unspecified origin. The similarity in both size and
structure of the silicate band suggests that the material in these systems had
a processing history similar to that in our own solar system prior to the time
that the grains were incorporated into comets.Comment: 17 pages, AASTeX, 5 eps figures, accepted for publication in Ap.
- …