6,758 research outputs found
Non-Gaussian Foreground Residuals of the WMAP First Year Maps
We investigate the effect of foreground residuals in the WMAP data (Bennet et
al. 2004) by adding foreground contamination to Gaussian ensembles of CMB
signal and noise maps. We evaluate a set of non-Gaussian estimators on the
contaminated ensembles to determine with what accuracy any residual in the data
can be constrained using higher order statistics. We apply the estimators to
the raw and cleaned Q, V, and W band first year maps. The foreground
subtraction method applied to clean the data in Bennet et al. (2004a) appears
to have induced a correlation between the power spectra and normalized
bispectra of the maps which is absent in Gaussian simulations. It also appears
to increase the correlation between the dl=1 inter-l bispectrum of the cleaned
maps and the foreground templates. In a number of cases the significance of the
effect is above the 98% confidence level.Comment: 9 pages, 4 figure
Nonextensivity in the solar magnetic activity during the increasing phase of solar Cycle 23
In this paper we analyze the behavior of the daily Sunspot Number from the
Sunspot Index Data Center (SIDC), the mean Magnetic Field strength from the
National Solar Observatory/Kitt Peak (NSO/KP) and Total Solar Irradiance means
from Virgo/SoHO, in the context of the --Triplet which emerges within
nonextensive statistical mechanics. Distributions for the mean solar Magnetic
Field show two different behaviors, with a --Gaussian for scales of 1 to 16
days and a Gaussian for scales longer than 32 days. The latter corresponds to
an equilibrium state. Distributions for Total Solar Irradiance also show two
different behaviors (approximately Gaussian) for scales of 128 days and longer,
consistent with statistical equilibrium and --Gaussian for scales 128
days. Distributions for the Sunspot Number show a --Gaussian independent of
timescales, consistent with a nonequilibrium state. The values obtained
("--Triplet",,)
demonstrate that the Gaussian or --Gaussian behavior of the aforementioned
data depends significantly on timescales. These results point to strong
multifractal behavior of the dataset analyzed, with the multifractal level
decreasing from Sunspot Number to Total Solar Irradiance. In addition, we found
a numerically satisfied dual relation between and .Comment: 6 pages, 4 figure
Power-law statistics and stellar rotational velocities in the Pleiades
In this paper we will show that, the non-gaussian statistics framework based
on the Kaniadakis statistics is more appropriate to fit the observed
distributions of projected rotational velocity measurements of stars in the
Pleiades open cluster. To this end, we compare the results from the
and -distributions with the Maxwellian.Comment: 13 pages, 3 figure
Wavelets: a powerful tool for studying rotation, activity, and pulsation in Kepler and CoRoT stellar light curves
Aims. The wavelet transform has been used as a powerful tool for treating
several problems in astrophysics. In this work, we show that the time-frequency
analysis of stellar light curves using the wavelet transform is a practical
tool for identifying rotation, magnetic activity, and pulsation signatures. We
present the wavelet spectral composition and multiscale variations of the time
series for four classes of stars: targets dominated by magnetic activity, stars
with transiting planets, those with binary transits, and pulsating stars.
Methods. We applied the Morlet wavelet (6th order), which offers high time and
frequency resolution. By applying the wavelet transform to the signal, we
obtain the wavelet local and global power spectra. The first is interpreted as
energy distribution of the signal in time-frequency space, and the second is
obtained by time integration of the local map. Results. Since the wavelet
transform is a useful mathematical tool for nonstationary signals, this
technique applied to Kepler and CoRoT light curves allows us to clearly
identify particular signatures for different phenomena. In particular, patterns
were identified for the temporal evolution of the rotation period and other
periodicity due to active regions affecting these light curves. In addition, a
beat-pattern signature in the local wavelet map of pulsating stars over the
entire time span was also detected.Comment: Accepted for publication on A&
Measuring stellar differential rotation with high-precision space-borne photometry
We introduce a method of measuring a lower limit to the amplitude of surface
differential rotation from high-precision, evenly sampled photometric time
series. It is applied to main-sequence late-type stars whose optical flux
modulation is dominated by starspots. An autocorrelation of the time series was
used to select stars that allow an accurate determination of starspot rotation
periods. A simple two-spot model was applied together with a Bayesian
information criterion to preliminarily select intervals of the time series
showing evidence of differential rotation with starspots of almost constant
area. Finally, the significance of the differential rotation detection and a
measurement of its amplitude and uncertainty were obtained by an a posteriori
Bayesian analysis based on a Monte Carlo Markov Chain approach. We applied our
method to the Sun and eight other stars for which previous spot modelling had
been performed to compare our results with previous ones. We find that
autocorrelation is a simple method for selecting stars with a coherent
rotational signal that is a prerequisite for successfully measuring
differential rotation through spot modelling. For a proper Monte Carlo Markov
Chain analysis, it is necessary to take the strong correlations among different
parameters that exist in spot modelling into account. For the planet-hosting
star Kepler-30, we derive a lower limit to the relative amplitude of the
differential rotation of \Delta P / P = 0.0523 \pm 0.0016. We confirm that the
Sun as a star in the optical passband is not suitable for measuring
differential rotation owing to the rapid evolution of its photospheric active
regions. In general, our method performs well in comparison to more
sophisticated and time-consuming approaches.Comment: Accepted to Astronomy and Astrophysics, 15 pages, 13 figures, 4
tables and an Appendi
Introduction: A handbook on territorial impact assessment (TIA)
Territorial Impact Assessment (TIA) is a relatively ‘new kid on the block’ of policy evaluation. Resting upon the holistic notion of territory, which encompasses multiple analytic dimensions (economy, society, environment, governance, spatial planning), TIA is the most complex, yet with the policy evaluation procedure with the largest potential to assess projects, programmes and policies. Indeed, policy evaluation procedures are now deeply rooted in sub-national, national and transnational territorial development strategies and processes. However, unlike the plethora of published books on Environmental Impact Assessment (EIA) and other Impact Assessment (IA) methodologies, presently no TIA handbook has been published by any major international publisher. As such, this one intends to add a substantial contribution to available literature by presenting to the interested reader the most relevant TIA methodologies that have been produced so far. Furthermore, all the chapters, written by the authors of each TIA methodology presented, provide a detailed, updated and scientifically accurate explanation of their particular purpose and methodological operation. In the end, the reader is presented with a complete set of TIA methodologies to select from based on their advantages/disadvantages for a particular case-study. For a better understanding of how all the presented TIA methodologies work, concrete examples are presented in each chapter.info:eu-repo/semantics/acceptedVersio
- …