1,655 research outputs found
A study of binary constraints for seismology of delta Scuti stars
Seismology of single delta Scuti stars has mainly been inhibited by failing
to detect many of the theoretically predicted pulsation modes, resulting in
difficulties with mode identification. Theoretical and observational advances
have, however, helped to overcome this problem, but the following questions
then remain: do we know enough about the star to either use the (few)
identified mode(s) to probe the structure of the star? or improve the
determination of the stellar parameters? It is now generally accepted that for
the observed frequencies to be used successfully as seismic probes for these
objects, we need to concentrate on stars where we can constrain the number of
free parameters in the problem, such as in binary systems or open clusters. The
work presented here, investigates how much is gained in our understanding of
the star, by comparing the information we obtain from a single star with that
of an eclipsing binary system. Singular Value Decomposition is the technique
used to explore the precision we expect in terms of stellar parameters (such as
mass, age and chemical composition).Comment: v2: error in equation corrected. HELAS II Conference:
Helioseismology, Asteroseismology and MHD Connections, August 2007
Goettingen, German
A Stellar Model-fitting Pipeline for Solar-like Oscillations
Over the past two decades, helioseismology has revolutionized our
understanding of the interior structure and dynamics of the Sun.
Asteroseismology will soon place this knowledge into a broader context by
providing structural data for hundreds of Sun-like stars. Solar-like
oscillations have already been detected from the ground in several stars, and
NASA's Kepler mission is poised to unleash a flood of stellar pulsation data.
Deriving reliable asteroseismic information from these observations demands a
significant improvement in our analysis methods. We report the initial results
of our efforts to develop an objective stellar model-fitting pipeline for
asteroseismic data. The cornerstone of our automated approach is an
optimization method using a parallel genetic algorithm. We describe the details
of the pipeline and we present the initial application to Sun-as-a-star data,
yielding an optimal model that accurately reproduces the known solar
properties.Comment: 5 pages, 2 figs, Stellar Pulsation: Challenges for Theory and
Observation (proceedings to be published by AIP
What Fraction of Boron-8 Solar Neutrinos arrive at the Earth as a nu_2 mass eigenstate?
We calculate the fraction of B^8 solar neutrinos that arrive at the Earth as
a nu_2 mass eigenstate as a function of the neutrino energy. Weighting this
fraction with the B^8 neutrino energy spectrum and the energy dependence of the
cross section for the charged current interaction on deuteron with a threshold
on the kinetic energy of the recoil electrons of 5.5 MeV, we find that the
integrated weighted fraction of nu_2's to be 91 \pm 2 % at the 95% CL. This
energy weighting procedure corresponds to the charged current response of the
Sudbury Neutrino Observatory (SNO). We have used SNO's current best fit values
for the solar mass squared difference and the mixing angle, obtained by
combining the data from all solar neutrino experiments and the reactor data
from KamLAND. The uncertainty on the nu_2 fraction comes primarily from the
uncertainty on the solar delta m^2 rather than from the uncertainty on the
solar mixing angle or the Standard Solar Model. Similar results for the
Super-Kamiokande experiment are also given. We extend this analysis to three
neutrinos and discuss how to extract the modulus of the Maki-Nakagawa-Sakata
mixing matrix element U_{e2} as well as place a lower bound on the electron
number density in the solar B^8 neutrino production region.Comment: 23 pages, 8 postscript figures, latex. Dedicated to the memory of
John Bahcall who championed solar neutrinos for many lonely year
Escherichia coli contamination and health aspects of soil and tomatoes (Solanum lycopersicum L.) subsurface drip irrigated with on-site treated domestic wastewater.
Faecal contamination of soil and tomatoes irrigated by sprinkler as well as surface and subsurface drip irrigation with treated domestic wastewater were compared in 2007 and 2008 at experimental sites in Crete and Italy. Wastewater was treated by Membrane Bio Reactor (MBR) technology, gravel filtration or UV-treatment before used for irrigation. Irrigation water, soil and tomato samples were collected during two cropping seasons and enumerated for the faecal indicator bacterium Escherichia coli and helminth eggs. The study found elevated levels of E. coli in irrigation water (mean: Italy 1753 cell forming unit (cfu) per 100 ml and Crete 488 cfu per 100 ml) and low concentrations of E. coli in soil (mean: Italy 95 cfu g(-1) and Crete 33 cfu g(-1)). Only two out of 84 tomato samples in Crete contained E. coli (mean: 2700 cfu g(-1)) while tomatoes from Italy were free of E. coli. No helminth eggs were found in the irrigation water or on the tomatoes from Crete. Two tomato samples out of 36 from Italy were contaminated by helminth eggs (mean: 0.18 eggs g(-1)) and had been irrigated with treated wastewater and tap water, respectively. Pulsed Field Gel Electrophoresis DNA fingerprints of E. coli collected during 2008 showed no identical pattern between water and soil isolates which indicates contribution from other environmental sources with E. coli, e.g. wildlife. A quantitative microbial risk assessment (QMRA) model with Monte Carlo simulations adopted by the World Health Organization (WHO) found the use of tap water and treated wastewater to be associated with risks that exceed permissible limits as proposed by the WHO (1.0 × 10(-3) disease risk per person per year) for the accidental ingestion of irrigated soil by farmers (Crete: 0.67 pppy and Italy: 1.0 pppy). The QMRA found that the consumption of tomatoes in Italy was deemed to be safe while permissible limits were exceeded in Crete (1.0 pppy). Overall the quality of tomatoes was safe for human consumption since the disease risk found on Crete was based on only two contaminated tomato samples. It is a fundamental limitation of the WHO QMRA model that it is not based on actual pathogen numbers, but rather on numbers of E. coli converted to estimated pathogen numbers, since it is widely accepted that there is poor correlation between E. coli and viral and parasite pathogens. Our findings also stress the importance of the external environment, typically wildlife, as sources of faecal contamination
Stability of latitudinal differential rotation in stars
The question is addressed whether stellar differentially rotating radiative
zones (like the solar tachocline) excite nonaxisymmetric r-modes which can be
observed. To this end the hydrodynamical stability of latitudinal differential
rotation is studied. The amount of rotational shear required for the
instability is estimated in dependence of the character of radial
stratification and the flow patterns excited by the instability are found. The
eigenvalue equations for the nonaxisymmetric disturbances are formulated in 3D
and then solved numerically. Radial displacements and entropy disturbances are
included. The equations contain the 2D approximation of strictly horizontal
displacements as a special limit. The critical magnitude of the latitudinal
differential rotation for onset of the instability is considerably reduced in
the 3D theory compared to the 2D approximation. The instability requires a
subadiabatic stratification. It does not exist in the bulk of convection zone
with almost adiabatic stratification but may switch on near its base in the
region of penetrative convection. Growth rates and symmetry types of the modes
are computed in dependence on the rotation law parameters. The S1 mode with its
transequatorial toroidal vortices is predicted as the dominating instability
mode. The vortices show longitudinal drift rates retrograde to the basic
rotation which are close to that of the observed weak r-mode signatures at the
solar surface.Comment: 5 pages, 6 figure
TarTar: A Timed Automata Repair Tool
We present TarTar, an automatic repair analysis tool that, given a timed
diagnostic trace (TDT) obtained during the model checking of a timed automaton
model, suggests possible syntactic repairs of the analyzed model. The suggested
repairs include modified values for clock bounds in location invariants and
transition guards, adding or removing clock resets, etc. The proposed repairs
are guaranteed to eliminate executability of the given TDT, while preserving
the overall functional behavior of the system. We give insights into the design
and architecture of TarTar, and show that it can successfully repair 69% of the
seeded errors in system models taken from a diverse suite of case studies.Comment: 15 pages, 7 figure
Determining global parameters of the oscillations of solar-like stars
Helioseismology has enabled us to better understand the solar interior, while
also allowing us to better constrain solar models. But now is a tremendous
epoch for asteroseismology as space missions dedicated to studying stellar
oscillations have been launched within the last years (MOST and CoRoT). CoRoT
has already proved valuable results for many types of stars, while Kepler,
which was launched in March 2009, will provide us with a huge number of seismic
data very soon. This is an opportunity to better constrain stellar models and
to finally understand stellar structure and evolution. The goal of this
research work is to estimate the global parameters of any solar-like
oscillating target in an automatic manner. We want to determine the global
parameters of the acoustic modes (large separation, range of excited pressure
modes, maximum amplitude, and its corresponding frequency), retrieve the
surface rotation period of the star and use these results to estimate the
global parameters of the star (radius and mass).To prepare the analysis of
hundreds of solar-like oscillating stars, we have developed a robust and
automatic pipeline. The pipeline consists of data analysis techniques, such as
Fast Fourier Transform, wavelets, autocorrelation, as well as the application
of minimisation algorithms for stellar-modelling. We apply our pipeline to some
simulated lightcurves from the asteroFLAG team and the Aarhus-asteroFLAG
simulator, and obtain results that are consistent with the input data to the
simulations. Our strategy gives correct results for stars with magnitudes below
11 with only a few 10% of bad determinations among the reliable results. We
then apply the pipeline to the Sun and three CoRoT targets.In particular we
determine the parameters of the Sun, HD49933, HD181906, and HD181420.Comment: 15 pages, 17 figures, accepted for publication in A&
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