2,160 research outputs found
Impact of gaps in the asteroseismic characterization of pulsating stars. I. On the efficiency of pre-whitening
It is known that the observed distribution of frequencies in CoRoT and Kepler
{\delta} Scuti stars has no parallelism with any theoretical model.
Pre-whitening is a widespread technique in the analysis of time series with
gaps from pulsating stars located in the classical instability strip such as
{\delta} Scuti stars. However, some studies have pointed out that this
technique might introduce biases in the results of the frequency analysis. This
work aims at studying the biases that can result from pre-whitening in
asteroseismology. The results will depend on the intrinsic range and
distribution of frequencies of the stars. The periodic nature of the gaps in
CoRoT observations, just in the range of the pulsational frequency content of
the {\delta} Scuti stars, is shown to be crucial to determine their oscillation
frequencies, the first step to perform asteroseismolgy of these objects. Hence,
here we focus on the impact of pre-whitening on the asteroseismic
characterization of {\delta} Scuti stars. We select a sample of 15 {\delta}
Scuti stars observed by the CoRoT satellite, for which ultra-high quality
photometric data have been obtained by its seismic channel. In order to study
the impact on the asteroseismic characterization of {\delta} Scuti stars we
perform the pre-whitening procedure on three datasets: gapped data, linearly
interpolated data, and ARMA interpolated data. The different results obtained
show that at least in some cases pre-whitening is not an efficient procedure
for the deconvolution of the spectral window. therefore, in order to reduce the
effect of the spectral window to the minimum it is necessary to interpolate
with an algorithm that is aimed to preserve the original frequency content, and
not only to perform a pre-whitening of the data.Comment: 27 pages, 47 figures Tables and typos fixe
Fractal analysis applied to light curves of Scuti stars
Fractal behaviour, i.e. scale invariance in spatio-temporal dynamics, have
been found to describe and model many systems in nature, in particular fluid
mechanics and geophysical related geometrical objects, like the convective
boundary layer of cumulus cloud fields, topographic landscapes, solar
granulation patterns, and observational astrophysical time series, like light
curves of pulsating stars. The main interest in the study of fractal properties
in such physical phenomena lies in the close relationships they have with
chaotic and turbulent dynamic. In this work we introduce some statistical tools
for fractal analysis of light curves: Rescaled Range Analysis (R/S),
Multifractal Spectra Analysis, and Coarse Graining Spectral Analysis (CGSA), an
FFT based algorithm, which can discriminate in a time series the stochastic
fractal power spectra from the harmonic one. An interesting application of
fractal analysis in asteroseismology concerns the joint use of all these tools
in order to develop classification criteria and algorithms for {\delta}-Scuti
pulsating stars. In fact from the fractal and multi-fractal fingerprints in
background noise of light curves we could infer on different mechanism of
stellar dynamic, among them rotation, modes excitation and magnetic activity.Comment: 13 pages, 10 figure
Relationship between meditative practice and self-reported mindfulness: The MINDSENS composite index
Mindfulness has been described as an inherent human capability that can be learned and trained, and its improvement has been associated with better health outcomes in both medicine and psychology. Although the role of practice is central to most mindfulness programs, practice-related improvements in mindfulness skills is not consistently reported and little is known about how the characteristics of meditative practice affect different components of mindfulness. The present study explores the role of practice parameters on self-reported mindfulness skills. A total of 670 voluntary participants with and without previous meditation experience (n = 384 and n = 286, respectively) responded to an internet-based survey on various aspects of their meditative practice (type of meditation, length of session, frequency, and lifetime practice). Participants also completed the Five Facets Mindfulness Questionnaire (FFMQ), and the Experiences Questionnaire (EQ). The group with meditation experience obtained significantly higher scores on all facets of FFMQ and EQ questionnaires compared to the group without experience. However different effect sizes were observed, with stronger effects for the Observing and Non-Reactivity facets of the FFMQ, moderate effects for Decentering in EQ, and a weak effect for Non-judging, Describing, and Acting with awareness on the FFMQ. Our results indicate that not all practice variables are equally relevant in terms of developing mindfulness skills. Frequency and lifetime practice - but not session length or meditation type - were associated with higher mindfulness skills. Given that these 6 mindfulness aspects show variable sensitivity to practice, we created a composite index (MINDSENS) consisting of those items from FFMQ and EQ that showed the strongest response to practice. The MINDSENS index was able to correctly discriminate daily meditators from non-meditators in 82.3% of cases. These findings may contribute to the understanding of the development of mindfulness skills and support trainers and researchers in improving mindfulness-oriented practices and programs
Role of the electric field in surface electron dynamics above the vacuum level
Scanning tunneling spectroscopy (STS) is used to study the dynamics of hot
electrons trapped on a Cu(100) surface in field emission resonances (FER) above
the vacuum level. Differential conductance maps show isotropic electron
interference wave patterns around defects whenever their energy lies within a
surface projected band gap. Their Fourier analysis reveals a broad wave vector
distribution, interpreted as due to the lateral acceleration of hot electrons
in the inhomogeneous tip-induced potential. A line-shape analysis of the
characteristic constant-current conductance spectra permits to establish the
relation between apparent width of peaks and intrinsic line-width of FERs, as
well as the identification of the different broadening mechanisms.Comment: 7 pages, 4 figures, to appear in Phys. Rev.
The PL diagram for Sct stars: back in business as distance estimators
In this work, we focus on the period-luminosity relation (PLR) of
Sct stars, in which mode excitation and selection mechanisms are still poorly
constrained, and whose structure and oscillations are affected by rotation. We
review the PLRs in the recent literature, and add a new inference from a large
sample of Sct. We highlight the difficulty in identifying the
fundamental mode and show that rotation-induced surface effects can impact the
measured luminosities, explaining the broadening of the PLR. We derive a tight
relation between the low-order large separation and the fundamental radial mode
frequency (F0) that holds for rotating stars, thus paving the way towards mode
identification. We show that the PLRs we obtain for different samples are
compatible with each other and with the recent literature, and with most
observed Sct stars when taking rotation effects into account. We also
find that the highest-amplitude peak in the frequency spectrum corresponds to
the fundamental mode in most Sct, thus shedding some light on their
elusive mode selection mechanism.Comment: 10 pages, 5 figures, 1 table, IAU conference proceedin
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