1,251 research outputs found
Final Results from phase II of the Mainz Neutrino Mass Search in Tritium Decay
The paper reports on the improved Mainz experiment on tritum
spectroscopy which yields a 10 times' higher signal to background ratio than
before. The main experimental effects and systematic uncertainties have been
investigated in side experiments and possible error sources have been
eliminated. Extensive data taking took place in the years 1997 to 2001. A
residual analysis of the data sets yields for the square of the electron
antineutrino mass the final result of eV/c. We derive an upper limit of
eV/c at 95% confidence level for the mass itself.Comment: 22 pages, 22 figures submitted to EPJ
The CRESST Dark Matter Search
We present first competitive results on WIMP dark matter using the
phonon-light-detection technique. A particularly strong limit for WIMPs with
coherent scattering results from selecting a region of the phonon-light plane
corresponding to tungsten recoils. The observed count rate in the neutron band
is compatible with the rate expected from neutron background. CRESST is
presently being upgraded with a 66 channel SQUID readout system, a neutron
shield and a muon veto system. This results in a significant improvement in
sensitivity.Comment: 6 pages, 3 figures, to be published in the proceedings of the 5th
International Workshop on the Identification and Detection of Dark Matter IDM
2004, Edinburgh, Sept. 2004, World Scientifi
Ground--state energies and widths of He and Li
We extract energies and widths of the ground states of He and Li from
recent single--level R--matrix fits to the spectra of the H)He and the He)Li reactions. The widths
obtained differ significantly from the formal R--matrix values but they are
close to those measured as full widths at half maxima of the spectra in various
experiments. The energies are somewhat lower than those given by usual
estimates of the peak positions. The extracted values are close to the
S--matrix poles calculated previously from the multi--term analyses of the
N-He elastic scattering data.Comment: 3 pages, no figures, uses revtex.sty, accepted for publication in
PRC, uuencoded postscript and tex-files available at
ftp://is1.kph.tuwien.ac.at/pub/ohu/fwidth.u
Detection of the Natural Alpha Decay of Tungsten
The natural alpha decay of 180W has been unambiguously detected for the first
time. The alpha peak is found in a (gamma,beta and neutron)-free background
spectrum. This has been achieved by the simultaneous measurement of phonon and
light signals with the CRESST cryogenic detectors. A half-life of T1/2 = (1.8
+- 0.2) x 10^18 y and an energy release of Q = (2516.4 +- 1.1 (stat.) +- 1.2
(sys.)) keV have been measured. New limits are also set on the half-lives of
the other naturally occurring tungsten isotopes.Comment: Submitted to Physical Review C Revised versio
Visual/infrared interferometry of Orion Trapezium stars: Preliminary dynamical orbit and aperture synthesis imaging of the Theta 1 Orionis C system
Located in the Orion Trapezium cluster, Theta 1 Orionis C is one of the
youngest and nearest high-mass stars (O5-O7) and also known to be a close
binary system. Using new multi-epoch visual and near-infrared bispectrum
speckle interferometric observations obtained at the BTA 6 m telescope, and
IOTA near-infrared long-baseline interferometry, we trace the orbital motion of
the Theta 1 Ori C components over the interval 1997.8 to 2005.9, covering a
significant arc of the orbit. Besides fitting the relative position and the
flux ratio, we apply aperture synthesis techniques to our IOTA data to
reconstruct a model-independent image of the Theta 1 Ori C binary system.
The orbital solutions suggest a high eccentricity (e approx. 0.91) and
short-period (P approx. 10.9 yrs) orbit. As the current astrometric data only
allows rather weak constraints on the total dynamical mass, we present the two
best-fit orbits. From these orbital solutions one can be favoured, implying a
system mass of 48 M_sun and a distance to the Trapezium cluster of 434 pc. When
also taking the measured flux ratio and the derived location in the HR-diagram
into account, we find good agreement for all observables, assuming a spectral
type of O5.5 for Theta 1 Ori C1 (M=34.0 M_sun) and O9.5 for C2 (M=15.5 M_sun).
We find indications that the companion C2 is massive itself, which makes it
likely that its contribution to the intense UV radiation field of the Trapezium
cluster is non-negligible. Furthermore, the high eccentricity of the
preliminary orbit solution predicts a very small physical separation during
periastron passage (approx. 1.5 AU, next passage around 2007.5), suggesting
strong wind-wind interaction between the two O stars.Comment: 13 pages, 9 figures, Accepted for publication in Astronomy &
Astrophysic
Inner Rim of A Molecular Disk Spatially Resolved in Infrared CO Emission Lines
We present high-resolution infrared spectroscopy of the Herbig Ae star HD
141569 A in the CO v=2-1 transition. With the angular resolution attained by
the adaptive optics system, the gas disk around HD 141569 A is spatially
resolved down to its inner-rim truncation. The size of the inner clearing is
11+-2 AU in radius, close to the gravitational radius of the star. The rough
coincidence to the gravitational radius indicates that the viscous accretion
working together with the photoevaporation by the stellar radiation has cleared
the inner part of the disk.Comment: 6 pages, 3 figures, Accepted for publication in the Astrophysical
Journa
Dynamical masses of the primary Be star and the secondary sdB star in the single-lined binary kappa Dra (B6 IIIe)
Because many classical Be stars may owe their nature to mass and
angular-momentum transfer in a close binary, the present masses, temperatures,
and radii of their components are of high interest for comparison to stellar
evolution models. Kappa Dra is a 61.5-day single-lined binary with a B6 IIIe
primary. With the CHARA Array instruments MIRC/MIRC-X and MYSTIC, we detected
the secondary at (approximately photospheric) flux ratios of 1.49 +- 0.10% and
1.63 +- 0.09% in the H and K band, respectively. From a large and diverse
optical spectroscopic database only the radial velocity curve of the Be star
could be extracted. However, employing the parallaxes from Hipparcos and Gaia,
which agree within their nominal 1-sigma errors, we could derive the total mass
and found component masses of 3.65 +- 0.48 Msun and 0.426 +- 0.043 Msun for the
Be star and the companion, respectively. Previous cross-correlation of the
observed far-UV spectrum with sdO spectral model templates had not detected a
companion belonging to the hot O-type subdwarf (sdO) population known from ~20
earlier-type Be stars. Guided by our full 3D orbital solution, we found a
strong cross-correlation signal for a stripped subdwarf B-type companion
(far-UV flux ratio of 2.3 +- 0.5%), enabling the first firm characterization of
such a star, and making kappa Dra the first mid- to late-type Be star with a
directly-observed subdwarf companion.Comment: Accepted to ApJ. Figure sets available on reques
First AMBER/VLTI observations of hot massive stars
AMBER is the first near infrared focal instrument of the VLTI. It combines
three telescopes and produces spectrally resolved interferometric measures.
This paper discusses some preliminary results of the first scientific
observations of AMBER with three Unit Telescopes at medium (1500) and high
(12000) spectral resolution. We derive a first set of constraints on the
structure of the circumstellar material around the Wolf Rayet Gamma2 Velorum
and the LBV Eta Carinae
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