1,497 research outputs found
Radio and IR interferometry of SiO maser stars
Radio and infrared interferometry of SiO maser stars provide complementary
information on the atmosphere and circumstellar environment at comparable
spatial resolution. Here, we present the latest results on the atmospheric
structure and the dust condensation region of AGB stars based on our recent
infrared spectro-interferometric observations, which represent the environment
of SiO masers. We discuss, as an example, new results from simultaneous VLTI
and VLBA observations of the Mira variable AGB star R Cnc, including VLTI near-
and mid-infrared interferometry, as well as VLBA observations of the SiO maser
emission toward this source. We present preliminary results from a monitoring
campaign of high-frequency SiO maser emission toward evolved stars obtained
with the APEX telescope, which also serves as a precursor of ALMA images of the
SiO emitting region. We speculate that large-scale long-period chaotic motion
in the extended molecular atmosphere may be the physical reason for observed
deviations from point symmetry of atmospheric molecular layers, and for the
observed erratic variability of high-frequency SiO maser emissionComment: 8 pages, 4 figures, submitted to Proc. IAU Symp. 287 "Cosmic masers -
from OH to H_0", R.S. Booth, E.M.L. Humphreys, W.H.T. Vlemmings (eds.),
invited pape
New insights into the dust formation of oxygen-rich AGB stars
We observed the AGB stars S Ori, GX Mon and R Cnc with the MIDI instrument at
the VLTI. We compared the data to radiative transfer models of the dust shells,
where the central stellar intensity profiles were described by dust-free
dynamic model atmospheres. We used Al2O3 and warm silicate grains. Our S Ori
and R Cnc data could be well described by an Al2O3 dust shell alone, and our GX
Mon data by a mix of an Al2O3 and a silicate shell. The best-fit parameters for
S Ori and R Cnc included photospheric angular diameters Theta(Phot) of
9.7+/-1.0mas and 12.3+/-1.0mas, optical depths tau(V)(Al2O3) of 1.5+/-0.5 and
1.35+/-0.2, and inner radii R(in) of 1.9+/-0.3R(Phot) and 2.2+/-0.3R(Phot),
respectively. Best-fit parameters for GX Mon were Theta(Phot)=8.7+/-1.3mas,
tau(V)(Al2O3)=1.9+/-0.6, R(in)(Al2O3)=2.1+/-0.3R(Phot),
tau(V)(silicate)=3.2+/-0.5, and R(in)(silicate)=4.6+/-0.2R(Phot). Our model
fits constrain the chemical composition and the inner boundary radii of the
dust shells, as well as the photospheric angular diameters. Our interferometric
results are consistent with Al2O3 grains condensing close to the stellar
surface at about 2 stellar radii, co-located with the extended atmosphere and
SiO maser emission, and warm silicate grains at larger distances of about 4--5
stellar radii. We verified that the number densities of aluminum can match that
of the best-fit Al2O3 dust shell near the inner dust radius in sufficiently
extended atmospheres, confirming that Al2O3 grains can be seed particles for
the further dust condensation. Together with literature data of the mass-loss
rates, our sample is consistent with a hypothesis that stars with low mass-loss
rates form primarily dust that preserves the spectral properties of Al2O3, and
stars with higher mass-loss rate form dust with properties of warm silicates.Comment: 20 pages, 10 figure
557 GHz Observations of Water Vapor Outflows from VY CMa and W Hydrae
We report the first detection of thermal water vapor emission in the 557 GHz,
ground state transition of ortho-HO toward VY Canis
Majoris. In observations obtained with the Submillimeter Wave Astronomy
Satellite (SWAS), we measured a flux of Jy, in a spectrally resolved
line centered on a velocity km s with a full width half
maximum of km s, somewhat dependent on the assumed line shape.
We analyze the line shape in the context of three different radial outflow
models for which we provide analytical expressions. We also detected a weaker
557 GHz emission line from W Hydrae. We find that these and other HO
emission line strengths scale as suggested by Zubko and Elitzur (2000).Comment: Astrophysical Journal Letters, accepte
Movement disorders and syndromic autism: a systematic review
Movement disorders are reported in idiopathic autism but the extent to which comparable movement disorders are found in syndromic/co-morbid autism is unknown. A systematic search of Medline, Embase, PsychINFO and CINAHL on the prevalence of specific movement disorder in syndromic autism associated with specific genetic syndromes identified 16 papers, all relating to Angelman syndrome or Rett syndrome. Prevalence rates of 72.7–100% and 25.0–27.3% were reported for ataxia and tremor, respectively, in Angelman syndrome. In Rett syndrome, prevalence rates of 43.6–50% were reported for ataxia and 27.3–48.3% for tremor with additional reports of dystonia, rigidity and pyramidal signs. However, reliable assessment measures were rarely used and recruitment was often not described in sufficient detail
Influence of transient pressure changes on speech intelligibility: Implications for nextgeneration train travel
High-speed trains are operated in increasingly complex railway networks and continual improvement of driver assistance systems is necessary to maintain safety. Speech offers the opportunity to provide information to the driver without disrupting visual attention. However, it is not known whether the transient pressure changes inside trains passing through tunnels interfere with speech intelligibility. Our primary goal was to test whether the most severe pressure variations occurring in high-speed trains (25 hPa in 2 s) affect speech intelligibility in individuals with normal hearing ability and secondly whether a potential effect would depend on the direction of the pressure change. A cross-over design was used to compare speech intelligibility, measured with the monosyllable word test by Wallenberg and Kollmeier, in steady ambient pressure versus subsequent to pressure events, both realised in a pressure chamber. Since data for a power calculation did not exist, we conducted a pilot study with 20 participants to estimate variance of intra-individual differences. The upper 80% confidence limit guided sample size of the main campaign, which was performed with 72 participants to identify a 10% difference while limiting alpha (5%) and beta error (10%). On average, a participant understood 0.7 fewer words following a pressure change event compared to listening in steady ambient pressure. However, this intra-individual differences varied strongly between participants, standard deviation (SD) +/- 4.5 words, resulting in a negligible effect size of 0.1 and the Wilcoxon signed rank test (Z = -1.26; p = 0.21) did not distinguish it from chance. When comparing decreasing and increasing pressure events an average of 0.2 fewer words were understood (+/- 3.9 SD). The most severe pressure changes expected to occur in high-speed trains passing through tunnels do not interfere with speech intelligibility and are in itself not a risk factor for loss of verbal information transmission
Structure and shaping processes within the extended atmospheres of AGB stars
We present recent studies using the near-infrared instrument AMBER of the VLT
Interferometer (VLTI) to investigate the structure and shaping processes within
the extended atmosphere of AGB stars. Spectrally resolved near-infrared AMBER
observations of the Mira variable S Ori have revealed wavelength-dependent
apparent angular sizes. These data were successfully compared to dynamic model
atmospheres, which predict wavelength-dependent radii because of geometrically
extended molecular layers. Most recently, AMBER closure phase measurements of
several AGB stars have also revealed wavelength-dependent deviations from 0/180
deg., indicating deviations from point symmetry. The variation of closure phase
with wavelength indicates a complex non-spherical stratification of the
extended atmosphere, and may reveal whether observed asymmetries are located
near the photosphere or in the outer molecular layers. Concurrent observations
of SiO masers located within the extended molecular layers provide us with
additional information on the morphology, conditions, and kinematics of this
shell. These observations promise to provide us with new important insights
into the shaping processes at work during the AGB phase. With improved imaging
capabilities at the VLTI, we expect to extend the successful story of imaging
studies of planetary nebulae to the photosphere and extended outer atmosphere
of AGB stars.Comment: 6 pages, Proc. of "Asymmetric Planetary Nebulae V", A.A. Zijlstra, F.
Lykou, I. McDonald, and E. Lagadec (eds.), Jodrell Bank Centre for
Astrophysics, Manchester, UK, 201
Phenotyping Genetic Diseases Using an Extension of μ-Scores for Multivariate Data
As the field of genomics matures, more complex genotypes and phenotypes are being studied. Fanconi anemia (FA), for example, is an inherited chromosome instability syndrome with a complex array of variable disease phenotypes including congenital malformations, hematological manifestations, and cancer. To better understand specific aspects of the genetic etiology of FA and other rare diseases with complex phenotypes, it is often necessary to reduce the dimensions of the disease phenotype information. Towards this end, we extend a novel non-parametric approach to include information about a hierarchical structure among disease phenotypes. The proposed extension increases information content of the phenotype scores obtained and, thereby, the power of genotype-phenotype relationships studies
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