534 research outputs found
Sensitivity of measured fission yields on prompt-neutron corrections
The amount of emitted prompt neutrons from the fission fragments increases as
a function of excitation energy. Yet it is not fully understood whether the
increase in \nu(A) as a function of E_{n} is mass dependent. The share of
excitation energies among the fragments is still under debate, but there are
reasons to believe that the excess in neutron emission originates only from the
heavy fragments, leaving \nu_{light}(A) almost unchanged. In this work we
investigated the consequences of a mass-dependent increase in \nu(A) on the
final mass and energy distributions. The assumptions on \nu(A) are essential
when analysing measurements based on the 2E-technique. This choice showed to be
significant on the measured observables. For example, the post-neutron emission
mass yield distribution revealed changes up to 10-30%. The outcome of this work
pinpoint the urgent need to determine \nu(A) experimentally, and in particular,
how \nu(A) changes as a function of incident-neutron energy. Until then, many
fission yields in the data libraries could be largely affected, since they were
analysed based on another assumption on the neutron emission.Comment: 4 pages, 3 figures, Proc. 2013 International Conference on Nuclear
Data for Science & Technology (ND2013), March 4-8, 2013, New York, USA, to be
published in Nuclear Data Sheet
Spectroscopic and photometric oscillatory envelope variability during the S Doradus outburst of the Luminous Blue Variable R71
To better understand the LBV phenomenon, we analyze multi-epoch and
multi-wavelength spectra and photometry of R71. Pre-outburst spectra are
analyzed with the radiative transfer code CMFGEN to determine the star's
fundamental stellar parameters. During quiescence, R71 has an effective
temperature of and a luminosity of
log = 5.78 and is thus a classical LBV, but at the lower
luminosity end of this group. We determine its mass-loss rate to yr. We present R71's spectral energy distribution
from the near-ultraviolet to the mid-infrared during its present outburst.
Mid-infrared observations suggest that we are witnessing dust formation and
grain evolution. Semi-regular oscillatory variability in the star's light curve
is observed during the current outburst. Absorption lines develop a second blue
component on a timescale twice that length. The variability may consist of one
(quasi-)periodic component with P ~ 425/850 d with additional variations
superimposed. During its current S Doradus outburst, R71 occupies a region in
the HR diagram at the high-luminosity extension of the Cepheid instability
strip and exhibits similar irregular variations as RV Tau variables. LBVs do
not pass the Cepheid instability strip because of core evolution, but they
develop comparable cool, low-mass, extended atmospheres in which convective
instabilities may occur. As in the case of RV Tau variables, the occurrence of
double absorption lines with an apparent regular cycle may be due to shocks
within the atmosphere and period doubling may explain the factor of two in the
lengths of the photometric and spectroscopic cycles.Comment: 18 pages, 14 figures, submitted to A&
- …