2,249 research outputs found
Unevenly-sampled signals: a general formalism of the Lomb-Scargle periodogram
The periodogram is a popular tool that tests whether a signal consists only
of noise or if it also includes other components. The main issue of this method
is to define a critical detection threshold that allows identification of a
component other than noise, when a peak in the periodogram exceeds it. In the
case of signals sampled on a regular time grid, determination of such a
threshold is relatively simple. When the sampling is uneven, however, things
are more complicated. The most popular solution in this case is to use the
"Lomb-Scargle" periodogram, but this method can be used only when the noise is
the realization of a zero-mean, white (i.e. flat-spectrum) random process. In
this paper, we present a general formalism based on matrix algebra, which
permits analysis of the statistical properties of a periodogram independently
of the characteristics of noise (e.g. colored and/or non-stationary), as well
as the characteristics of sampling.Comment: 10 pages, 11 figures, Astronomy and Astrophysics, in pres
A Survey of European Regional Adaptation in Italian Ryegrass Varieties
Ryegrass is widely adapted to cool temperate eco-zones and breeders often submit individual varieties for testing in a number of EU countries. National testing programmes often combine data from several trial sites that may differ climatically, but not from sites in other member states, despite the possibility of high ecological similarity. Given increasing interest in ‘animal value’ characters (soluble sugars, lipids, sward geometry), additional testing for these would be valuable but is prohibited by capped or declining funding. Data sharing between EU national authorities could be advantageous but is inhibited by the lack of statistically valid data on the sensitivity of each performance parameter to agro-climatic conditions across the EU. This paper, reports the preliminary stages of the ‘EuroVCU’ (herbage) desktop study of ryegrass variety performances across an extensive range of EU national test centres. Analysis of the resulting data sets quantifies the genotype by environment responses of current varieties and could provide a validated protocol for future data sharing
NICMOS Observations of the Transiting Hot Jupiter XO-1b
We refine the physical parameters of the transiting hot Jupiter planet XO-1b
and its stellar host XO-1 using HST NICMOS observations. XO-1b has a radius
Rp=1.21+/-0.03 RJup, and XO-1 has a radius Rs=0.94+/-0.02 RSun, where the
uncertainty in the mass of XO-1 dominates the uncertainty of Rp and Rs. There
are no significant differences in the XO-1 system properties between these
broad-band NIR observations and previous determinations based upon ground-based
optical observations. We measure two transit timings from these observations
with 9 s and 15 s precision. As a residual to a linear ephemeris model, there
is a 2.0 sigma timing difference between the two HST visits that are separated
by 3 transit events (11.8 days). These two transit timings and additional
timings from the literature are sufficient to rule out the presence of an Earth
mass planet orbiting in 2:1 mean motion resonance coplanar with XO-1b. We
identify and correct for poorly understood gain-like variations present in
NICMOS time series data. This correction reduces the effective noise in time
series photometry by a factor of two, for the case of XO-1.Comment: 13 pages, 8 figures, submitted to Ap
Precise Estimates of the Physical Parameters for the Exoplanet System HD-17156 Enabled by HST FGS Transit and Asteroseismic Observations
We present observations of three distinct transits of HD 17156b obtained with
the Fine Guidance Sensors (FGS) on board the Hubble Space Telescope} (HST). We
analyzed both the transit photometry and previously published radial velocities
to find the planet-star radius ratio R_p/R_s = 0.07454 +/- 0.00035, inclination
i=86.49 +0.24/-0.20 deg, and scaled semi-major axis a/R = 23.19 +0.32/-0.27.
This last value translates directly to a mean stellar density determination of
0.522 +0.021/-0.018 g cm^-3. Analysis of asteroseismology observations by the
companion paper of Gilliland et al. (2009) provides a consistent but
significantly refined measurement of the stellar mean density. We compare
stellar isochrones to this density estimate and find M_s = 1.275 +/- 0.018
M_sun and a stellar age of $3.37 +0.20/-0.47 Gyr. Using this estimate of M_s
and incorporating the density constraint from asteroseismology, we model both
the photometry and published radial velocities to estimate the planet radius
R_p= 1.0870 +/- 0.0066 Jupiter radii and the stellar radius R_s = 1.5007 +/-
0.0076 R_sun. The planet radius is larger than that found in previous studies
and consistent with theoretical models of a solar-composition gas giant of the
same mass and equilibrium temperature. For the three transits, we determine the
times of mid-transit to a precision of 6.2 s, 7.6 s, and 6.9 s, and the transit
times for HD 17156 do not show any significant departures from a constant
period. The joint analysis of transit photometry and asteroseismology presages
similar studies that will be enabled by the NASA Kepler Mission.Comment: Accepted for publication to Ap
Kepler Mission Stellar and Instrument Noise Properties
Kepler Mission results are rapidly contributing to fundamentally new
discoveries in both the exoplanet and asteroseismology fields. The data
returned from Kepler are unique in terms of the number of stars observed,
precision of photometry for time series observations, and the temporal extent
of high duty cycle observations. As the first mission to provide extensive time
series measurements on thousands of stars over months to years at a level
hitherto possible only for the Sun, the results from Kepler will vastly
increase our knowledge of stellar variability for quiet solar-type stars. Here
we report on the stellar noise inferred on the timescale of a few hours of most
interest for detection of exoplanets via transits. By design the data from
moderately bright Kepler stars are expected to have roughly comparable levels
of noise intrinsic to the stars and arising from a combination of fundamental
limitations such as Poisson statistics and any instrument noise. The noise
levels attained by Kepler on-orbit exceed by some 50% the target levels for
solar-type, quiet stars. We provide a decomposition of observed noise for an
ensemble of 12th magnitude stars arising from fundamental terms (Poisson and
readout noise), added noise due to the instrument and that intrinsic to the
stars. The largest factor in the modestly higher than anticipated noise follows
from intrinsic stellar noise. We show that using stellar parameters from
galactic stellar synthesis models, and projections to stellar rotation,
activity and hence noise levels reproduces the primary intrinsic stellar noise
features.Comment: Accepted by ApJ; 26 pages, 20 figure
Assessing the effectiveness of a naturally occurring population-level physical activity intervention for children
Objectives The aim of the study was to assess the impact of a recreation access pass on grade 5 children\u27s physical activity (PA) levels. Study design This is a pre-post evaluation of a population-level community-based intervention. Methods All grade 5 students in (London, Ontario, Canada) were invited to participate in the [ACT-i-Pass] program (G5AP) in May 2014. A total of 643 children completed surveys, that included Physical Activity Questionnaire for Children (PAQ-C), at baseline (October 2014) and 6-month follow-up (April 2015). Difference in the means t-test compared PAQ-C scores between baseline and follow-up for the sample and subgroups. Multiple regression analysis tested associations between change in PAQ-C scores and intrapersonal-, interpersonal-, and physical environment-level variables. Results PA increased significantly from baseline to 6-month follow-up. Girls, visible minorities, immigrants, and children with low parental support experienced significant increases in PA. Regression found girls benefitted from the G5AP significantly more than boys, and lower parental support is related to increases in PA. Conclusion The findings indicate that collaboratively developed, community-based interventions can significantly increase children\u27s PA levels, particularly among subgroups with traditionally lower PA. The pre-post evaluation of this community-based intervention provides useful evidence for developing policies and programs aimed at making population-level improvements in children\u27s PA levels
A comparative analysis of place branding in Michigan and Ontario
Place branding has increasingly been adopted as a municipal initiative to change the trajectory of local economic development. Specifically, local municipalities and communities have used place branding not only as a response to the influence of globalization and neo-liberalism, but also economic challenges and restructuring. Like any other initiative, the ultimate goal is to enhance the economic and social well-being of local jurisdictions. Although a popular strategy, it is not clear if and how locally specific factors mediate the process. By comparing two cross-border geographical areas, this study attempts to identify how regional variability in the manifestation of politicaleconomic forces, as well as geographical influences, affects the use of place branding at local scales. Every municipality in Michigan (n = 1774) and Ontario (n = 414) was systematically examined for the presence and message of local place brands as presented through logos and slogans. The comparative analysis demonstrated that Ontario’s municipalities utilized place branding to a greater extent, and that the dominant messages differ by region. Further, this analysis shows that – beyond political differences – geographical context appears to have an effect on both local place branding usage and message
Asteroseismic classification of stellar populations among 13000 red giants observed by Kepler
Of the more than 150000 targets followed by the Kepler Mission, about 10%
were selected as red giants. Due to their high scientific value, in particular
for Galaxy population studies and stellar structure and evolution, their Kepler
light curves were made public in late 2011. More than 13000 (over 85%) of these
stars show intrinsic flux variability caused by solar-like oscillations making
them ideal for large scale asteroseismic investigations. We automatically
extracted individual frequencies and measured the period spacings of the dipole
modes in nearly every red giant. These measurements naturally classify the
stars into various populations, such as the red giant branch, the low-mass
(M/Msol
1.8) secondary clump. The period spacings also reveal that a large fraction of
the stars show rotationally induced frequency splittings. This sample of stars
will undoubtedly provide an extremely valuable source for studying the stellar
population in the direction of the Kepler field, in particular when combined
with complementary spectroscopic surveys.Comment: 6 page, 5 figures, accepted by ApJ
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