7,422 research outputs found
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
BAL phosphorus abundance and evidence for immense ionic column densities in quasar outflows: VLT X-Shooter observations of quasar SDSS J1512+1119
We present spectroscopic analysis of the broad absorption line outflow in
quasar SDSS J1512+1119. In particular, we focus our attention on a kinematic
component in which we identify PV and SIV/SIV* absorption troughs. The shape of
the unblended phosphorus doublet troughs and the three SIV/SIV* troughs allow
us to obtain reliable column density measurements for these two ions.
Photoionization modelling using these column densities and those of HeI*
constrain the abundance of phosphorus to the range of 0.5-4 times the solar
value. The total column density, ionization parameter and metalicity inferred
from the PV and SIV column densities leads to large optical depth values for
the common transition observed in BAL outflows. We show that the true CIV
optical depth, is about 1000 times greater in the core of the absorption
profile than the value deduced from its apparent optical depth.Comment: Accepted for publication in ApJ on August 26, 2012; 33 pages, 8
figure
X-ray emission from hydrodynamical simulations in non-LTE wind models
Hot stars are sources of X-ray emission originating in their winds. Although
hydrodynamical simulations that are able to predict this X-ray emission are
available, the inclusion of X-rays in stationary wind models is usually based
on simplifying approximations. To improve this, we use results from
time-dependent hydrodynamical simulations of the line-driven wind instability
(seeded by the base perturbation) to derive the analytical approximation of
X-ray emission in the stellar wind. We use this approximation in our non-LTE
wind models and find that an improved inclusion of X-rays leads to a better
agreement between model ionization fractions and those derived from servations.
Furthermore, the slope of the L_x-L relation is in better agreement with
observations, however the X-ray luminosity is underestimated by a factor of
three. We propose a possible solution for this discrepancy.Comment: 9 pages, accepted for publication in Astronomy and Astrophysic
A High-Velocity Narrow Absorption Line Outflow in the Quasar J212329.46-005052.9
We report on a variable high-velocity narrow absorption line outflow in the
redshift 2.3 quasar J2123-0050. Five distinct outflow systems are detected with
velocity shifts from -9710 to -14,050 km/s and CIV 1548,1551 line widths of
FWHM = 62-164 km/s. These data require five distinct outflow structures with
similar kinematics, physical conditions and characteristic sizes of order
0.01-0.02 pc. The most likely location is ~5 pc from the quasar. The
coordinated line variations in <0.63 yr (rest) are best explained by global
changes in the outflow ionization caused by changes in the quasar's ionizing
flux. The absence of strong X-ray absorption shows that radiative shielding is
not needed to maintain the moderate ionizations and therefore, apparently, it
is not needed to facilitate the radiative acceleration to high speeds. The
kinetic energy yield of this flow is at least two orders of magnitude too low
to be important for feedback to the host galaxy's evolution.Comment: 20 pages. In press with MNRA
Axions and saxions from the primordial supersymmetric plasma and extra radiation signatures
We calculate the rate for thermal production of axions and saxions via
scattering of quarks, gluons, squarks, and gluinos in the primordial
supersymmetric plasma. Systematic field theoretical methods such as hard
thermal loop resummation are applied to obtain a finite result in a
gauge-invariant way that is consistent to leading order in the strong gauge
coupling. We calculate the thermally produced yield and the decoupling
temperature for both axions and saxions. For the generic case in which saxion
decays into axions are possible, the emitted axions can constitute extra
radiation already prior to big bang nucleosynthesis and well thereafter. We
update associated limits imposed by recent studies of the primordial helium-4
abundance and by precision cosmology of the cosmic microwave background and
large scale structure. We show that the trend towards extra radiation seen in
those studies can be explained by late decays of thermal saxions into axions
and that upcoming Planck results will probe supersymmetric axion models with
unprecedented sensitivity.Comment: 16 pages, 7 figures; v2: references added, minor clarifying
additions, matches published versio
Adherence to secondary stroke prevention strategies - Results from the German stroke data bank
Only very limited data are available concerning patient adherence to antithrombotic medication intended to prevent a recurrent stroke. Reduced adherence and compliance could significantly influence the effects of any stroke prevention strategies. This study from a large stroke data bank provides representative data concerning the rate of stroke victims adhering to their recommended preventive medication. During a 2-year period beginning January 1, 1998, all patients with acute stroke or TIA in 23 neurological departments with an acute stroke unit were included in the German Stroke Data Bank. Data were collected prospectively, reviewed, validated and processed in a central data management unit. Only 12 centers with a follow-up rate of 80% or higher were included in this evaluation. 3,420 patients were followed up after 3 months, and 2,640 patients were followed up one year after their stroke. After one year, 96% of all patients reported still adhere to at least one medical stroke prevention strategy. Of the patients receiving aspirin at discharge, 92.6% reported to use that medication after 3 months and 84% after one year, while 81.6 and 61.6% were the respective figures for clopidogrel, and 85.2 and 77.4% for oral anticoagulation. Most patients who changed medication switched from aspirin to clopidogrel. Under the conditions of this observational study, adherence to stroke prevention strategies is excellent. The highest adherence rate is noticed for aspirin and oral anticoagulation. After one year, very few patients stopped taking stroke preventive medication. Copyright (C) 2003 S. Karger AG, Basel
The Quasar-frame Velocity Distribution of Narrow CIV Absorbers
We report on a survey for narrow (FWHM < 600 km/s) CIV absorption lines in a
sample of bright quasars at redshifts in the Sloan Digital
Sky Survey. Our main goal is to understand the relationship of narrow CIV
absorbers to quasar outflows and, more generally, to quasar environments. We
determine velocity zero-points using the broad MgII emission line, and then
measure the absorbers' quasar-frame velocity distribution. We examine the
distribution of lines arising in quasar outflows by subtracting model fits to
the contributions from cosmologically intervening absorbers and absorption due
to the quasar host galaxy or cluster environment. We find a substantial number
( per cent) of absorbers with REW \AA in the velocity range
+750 km/s \la v \la +12000 km/s are intrinsic to the AGN outflow. This
`outflow fraction' peaks near km/s with a value of . At velocities below km/s the incidence
of outflowing systems drops, possibly due to geometric effects or to the
over-ionization of gas that is nearer the accretion disk. Furthermore, we find
that outflow-absorbers are on average broader and stronger than
cosmologically-intervening systems. Finally, we find that per cent of
the quasars in our sample exhibit narrow, outflowing CIV absorption with REW \AA, slightly larger than that for broad absorption line systems.Comment: 11 pages, 9 figures, accepted for publication in MNRA
A 10 kpc Scale Seyfert Galaxy Outflow: HST/COS Observations of IRAS F22456-5125
We present analysis of the UV-spectrum of the low-z AGN IRAS-F22456-5125
obtained with the Cosmic Origins Spectrograph on board the Hubble Space
Telescope. The spectrum reveals six main kinematic components, spanning a range
of velocities of up to 800 km s-1, which for the first time are observed in
troughs associated with CII, CIV, NV, SiII, SiIII, SiIV and SIV. We also obtain
data on the OVI troughs, which we compare to those available from an earlier
FUSE epoch. Column densities measured from these ions allow us to derive a
well-constrained photoionization solution for each outflow component. Two of
these kinematic components show troughs associated with transitions from
excited states of SiII\ and CII. The number density inferred from these
troughs, in combination with the deduced ioinization parameter, allows us to
determine the distance to these outflow components from the central source. We
find these components to be at a distance of ~ 10 kpc. The distances and the
number densities derived are consistent with the outflow being part of a
galactic wind.Comment: 52 pages, 15 figures, accepted for publication in ApJ March 25, 201
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