5,122 research outputs found
Revised element abundances for WC-type central stars
According to previous spectral analyses of Wolf-Rayet type central stars,
late [WC] subtypes show systematically higher carbon-to-helium abundance ratios
than early [WC] subtypes. If this were true, it would rule out that these stars
form an evolutionary sequence. However, due to the different parameter domains
and diagnostic lines, one might suspect systematic errors being the source of
this discrepancy. In an ongoing project we are therefore checking the [WC]
analyses by means of the last generation of non-LTE models for expanding
stellar atmospheres which account for line-blanketing and wind clumping. So
far, the abundance discrepancy is not resolved. Further element abundances (H,
N, Fe) are determined and compared with evolutionary predictions.Comment: 4 pages, 5 figures, in conference proceedings of "Planetary Nebulae
in our Galaxy and Beyond" IAU Symposion 234, 2006, editors: Michael J.
Barlow, Roberto H. M\'ende
Hydrodynamic model atmospheres for WR stars: Self-consistent modeling of a WC star wind
We present the first non-LTE atmosphere models for WR stars that incorporate
a self-consistent solution of the hydrodynamic equations. The models account
for iron-group line-blanketing and clumping, and compute the hydrodynamic
structure of a radiatively driven wind consistently with the non-LTE radiation
transport in the co-moving frame. We construct a self-consistent wind model
that reproduces all observed properties of an early-type WC star (WC5). We find
that the WR-type mass-loss is initiated at high optical depth by the so-called
`Hot Iron Bump' opacities (Fe IX-XVI). The acceleration of the outer wind
regions is performed by iron-group ions of lower excitation in combination with
C and O. Consequently, the wind structure shows two acceleration regions, one
close to the hydrostatic wind base in the optically thick part of the
atmosphere, and another farther out in the wind. In addition to the radiative
acceleration, the `Iron Bump' opacities are responsible for an intense heating
of deep atmospheric layers. We find that the observed narrow OVI-emissions in
the optical spectra of WC stars originate from this region. By their dependence
on the clumping factor we gain important information about the location where
the density inhomogeneities in WR-winds start to develop.Comment: accepted by A&
Detecting sterile neutrinos with KATRIN like experiments
A sterile neutrino with mass in the eV range, mixing with the electron
antineutrino, is allowed and possibly even preferred by cosmology and
oscillation experiments. If such eV-mass neutrinos exist they provide a much
better target for direct detection in beta decay experiments than the active
neutrinos which are expected to have sub-eV masses. Their relatively high mass
would allow for an easy separation from the primary decay signal in experiments
such as KATRIN.Comment: 23 pages, 7 figures. References & Figures updated. Text reviewed and
revised. Accepted for publication JCA
Cosmological axion bounds
We discuss current cosmological constraints on axions, as well as future
sensitivities. Bounds on axion hot dark matter are discussed first, and
subsequently we discuss both current and future sensitivity to models in which
axions play the role as cold dark matter, but where the Peccei-Quinn symmetry
is not restored during reheating.Comment: 4 pages, 2 figures, To appear in the proceedings of 5th Patras
Workshop on Axions, WIMPs and WISPs, Durham 13-17 July 200
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