77 research outputs found
Application of Monte Carlo-based statistical significance determinations to the Beta Cephei stars V400 Car, V401 Car, V403 Car and V405 Car
We have used Lomb-Scargle periodogram analysis and Monte Carlo significance
tests to detect periodicities above the 3-sigma level in the Beta Cephei stars
V400 Car, V401 Car, V403 Car and V405 Car. These methods produce six previously
unreported periodicities in the expected frequency range of excited pulsations:
one in V400 Car, three in V401 Car, one in V403 Car and one in V405 Car. One of
these six frequencies is significant above the 4-sigma level. We provide
statistical significances for all of the periodicities found in these four
stars.Comment: 11 pages, 17 figure
JPWL - an Extension of JPEG 2000 for Wireless Imaging
In this paper, we present an overview of the JPWL standardization activity. JPWL is an extension of JPEG 2000 for the efficient transmission of JPEG 2000 images over an error-prone wireless network. More specifically, JPWL supports a set of tools for error protection and correction, including Forward Error Correcting codes (FEC), Unequal Error Protection (UEP), data partitioning and interleaving
Real-Time Generation of Standard-Compliant DVB-T Signals
This paper proposes and discusses two software implementations of the DVB-T modulator, using C++ and MATLAB, respectively. All the key features of the DVB-T standard are included. The C++ DVB-T modulator, incorporated into the Iris framework developed by Trinity College of Dublin, works in real time on an Intel Core i7 2.4 GHz CPU with the Iris testbed. The MATLAB-based DVB-T modulator is coupled with a receiver implementation with channel estimation, equalization, soft-output demapping and channel decoding. The validation step demonstrates that the proposed DVB-T software implementations generate standard-compliant DVB-T signals that are correctly received by commercially available TV sets and USB dongles. The software code for the Iris-based C++ modulator, and for the MATLAB-based modulator and receiver, has been made publicly available under the GNU license
Ostial plication: a rarely reported cause of sudden death
We report a rare case of ostial plication as a potential cause of sudden death. Very few reports and images are available in the specialized literature regarding this anomaly. Ostial plication may be a source of sudden death or cause of death when no other significant autopsy findings are present
Determination of rotation periods in solar-like stars with irregular sampling: the Gaia case
We present a study on the determination of rotation periods (P) of solar-like
stars from the photometric irregular time-sampling of the ESA Gaia mission,
currently scheduled for launch in 2013, taking into account its dependence on
ecliptic coordinates. We examine the case of solar-twins as well as thousands
of synthetic time-series of solar-like stars rotating faster than the Sun. In
the case of solar twins we assume that the Gaia unfiltered photometric passband
G will mimic the variability of the total solar irradiance (TSI) as measured by
the VIRGO experiment. For stars rotating faster than the Sun, light-curves are
simulated using synthetic spectra for the quiet atmosphere, the spots, and the
faculae combined by applying semi-empirical relationships relating the level of
photospheric magnetic activity to the stellar rotation and the Gaia
instrumental response. The capabilities of the Deeming, Lomb-Scargle, and Phase
Dispersion Minimisation methods in recovering the correct rotation periods are
tested and compared. The false alarm probability (FAP) is computed using Monte
Carlo simulations and compared with analytical formulae. The Gaia scanning law
makes the rate of correct detection of rotation periods strongly dependent on
the ecliptic latitude (beta). We find that for P ~ 1 d, the rate of correct
detection increases with ecliptic latitude from 20-30 per cent at beta ~
0{\deg} to a peak of 70 per cent at beta=45{\deg}, then it abruptly falls below
10 per cent at beta > 45{\deg}. For P > 5 d, the rate of correct detection is
quite low and for solar twins is only 5 per cent on average.Comment: 12 pages, 18 figures, accepted by MNRA
The Gran Sasso muon puzzle
We carry out a time-series analysis of the combined data from three
experiments measuring the cosmic muon flux at the Gran Sasso laboratory, at a
depth of 3800 m.w.e. These data, taken by the MACRO, LVD and Borexino
experiments, span a period of over 20 years, and correspond to muons with a
threshold energy, at sea level, of around 1.3 TeV. We compare the best-fit
period and phase of the full muon data set with the combined DAMA/NaI and
DAMA/LIBRA data, which spans the same time period, as a test of the hypothesis
that the cosmic ray muon flux is responsible for the annual modulation detected
by DAMA. We find in the muon data a large-amplitude fluctuation with a period
of around one year, and a phase that is incompatible with that of the DAMA
modulation at 5.2 sigmas. Aside from this annual variation, the muon data also
contains a further significant modulation with a period between 10 and 11 years
and a power well above the 99.9% C.L threshold for noise, whose phase
corresponds well with the solar cycle: a surprising observation for such high
energy muons. We see no corresponding long-period oscillation in the
stratospheric temperature data.Comment: Minor changes and clarifications, matches version accepted at JCAP. 5
pages, 3 figure
Plaskett's Star: Analysis of the CoRoT photometric data
The SRa02 of the CoRoT space mission for Asteroseismology was partly devoted
to stars belonging to the Mon OB2 association. An intense monitoring was
performed on Plaskett's Star (HD47129) and the unprecedented quality of the
light curve allows us to shed new light on this very massive, non-eclipsing
binary system. We particularly aimed at detecting periodic variability which
might be associated with pulsations or interactions between both components. We
also searched for variations related to the orbital cycle which could help to
constrain the inclination and the morphology of the binary system. A
Fourier-based prewhitening and a multiperiodic fitting procedure were applied
to analyse the time series and extract the frequencies of variations. We
describe the noise properties to tentatively define an appropriate significance
criterion, to only point out the peaks at a certain significance level. We also
detect the variations related to the orbital motion and study them by using the
NIGHTFALL program. The periodogram exhibits a majority of peaks at low
frequencies. Among these peaks, we highlight a list of about 43 values,
including notably two different sets of harmonic frequencies whose fundamental
peaks are located at about 0.07 and 0.82d-1. The former represents the orbital
frequency of the binary system whilst the latter could probably be associated
with non-radial pulsations. The study of the 0.07d-1 variations reveals the
presence of a hot spot most probably situated on the primary star and facing
the secondary. The investigation of this unique dataset constitutes a further
step in the understanding of Plaskett's Star. These results provide a first
basis for future seismic modelling. The existence of a hot region between both
components renders the determination of the inclination ambiguous.Comment: Accepted in A&A, 13 pages, 7 figures, 2 table
Kepler observations of variability in B-type stars
The analysis of the light curves of 48 B-type stars observed by Kepler is
presented. Among these are 15 pulsating stars, all of which show low
frequencies characteristic of SPB stars. Seven of these stars also show a few
weak, isolated high frequencies and they could be considered as SPB/beta Cep
hybrids. In all cases the frequency spectra are quite different from what is
seen from ground-based observations. We suggest that this is because most of
the low frequencies are modes of high degree which are predicted to be unstable
in models of mid-B stars. We find that there are non-pulsating stars within the
beta Cep and SPB instability strips. Apart from the pulsating stars, we can
identify stars with frequency groupings similar to what is seen in Be stars but
which are not Be stars. The origin of the groupings is not clear, but may be
related to rotation. We find periodic variations in other stars which we
attribute to proximity effects in binary systems or possibly rotational
modulation. We find no evidence for pulsating stars between the cool edge of
the SPB and the hot edge of the delta Sct instability strips. None of the stars
show the broad features which can be attributed to stochastically-excited modes
as recently proposed. Among our sample of B stars are two chemically peculiar
stars, one of which is a HgMn star showing rotational modulation in the light
curve.Comment: 19 pages, 11 figures, 4 table
CoRoT's view of newly discovered B-star pulsators: results for 358 candidate B pulsators from the initial run's exoplanet field data
We search for new variable B-type pulsators in the CoRoT data assembled
primarily for planet detection, as part of CoRoT's Additional Programme. We aim
to explore the properties of newly discovered B-type pulsators from the
uninterrupted CoRoT space-based photometry and to compare them with known
members of the Beta Cep and slowly pulsating B star (SPB) classes. We developed
automated data analysis tools that include algorithms for jump correction,
light-curve detrending, frequency detection, frequency combination search, and
for frequency and period spacing searches. Besides numerous new, classical,
slowly pulsating B stars, we find evidence for a new class of low-amplitude
B-type pulsators between the SPB and Delta Sct instability strips, with a very
broad range of frequencies and low amplitudes, as well as several slowly
pulsating B stars with residual excess power at frequencies typically a factor
three above their expected g-mode frequencies. The frequency data we obtained
for numerous new B-type pulsators represent an appropriate starting point for
further theoretical analyses of these stars, once their effective temperature,
gravity, rotation velocity, and abundances will be derived spectroscopically in
the framework of an ongoing FLAMES survey at the VLT.Comment: 22 pages, 30 figures, accepted for publication in A&
- …