21,433 research outputs found
Automated preparation of Kepler time series of planet hosts for asteroseismic analysis
One of the tasks of the Kepler Asteroseismic Science Operations Center
(KASOC) is to provide asteroseismic analyses on Kepler Objects of Interest
(KOIs). However, asteroseismic analysis of planetary host stars presents some
unique complications with respect to data preprocessing, compared to pure
asteroseismic targets. If not accounted for, the presence of planetary transits
in the photometric time series often greatly complicates or even hinders these
asteroseismic analyses. This drives the need for specialised methods of
preprocessing data to make them suitable for asteroseismic analysis. In this
paper we present the KASOC Filter, which is used to automatically prepare data
from the Kepler/K2 mission for asteroseismic analyses of solar-like planet host
stars. The methods are very effective at removing unwanted signals of both
instrumental and planetary origins and produce significantly cleaner
photometric time series than the original data. The methods are automated and
can therefore easily be applied to a large number of stars. The application of
the filter is not restricted to planetary hosts, but can be applied to any
solar-like or red giant stars observed by Kepler/K2.Comment: Accepted for publication in MNRA
Space-charge transport limits of ion beams in periodic quadrupole focusing channels
It has been empirically observed in both experiments and particle-in-cell
simulations that space-charge-dominated beams suffer strong growth in
statistical phase-space area (degraded quality) and particle losses in
alternating gradient quadrupole transport channels when the undepressed phase
advance sigma_0 increases beyond about 85 degrees per lattice period. Although
this criterion has been used extensively in practical designs of strong
focusing intense beam transport lattices, the origin of the limit has not been
understood. We propose a mechanism for the transport limit resulting from
classes of halo particle resonances near the core of the beam that allow
near-edge particles to rapidly increase in oscillation amplitude when the
space-charge intensity and the flutter of the matched beam envelope are both
sufficiently large. When coupled with a diffuse beam edge and/or perturbations
internal to the beam core that can drive particles outside the edge, this
mechanism can result in large and rapid halo-driven increases in the
statistical phase-space area of the beam, lost particles, and degraded
transport. A core-particle model is applied to parametrically analyze this
process. Extensive self-consistent particle in cell simulations are employed to
better quantify space-charge limit and verify core-particle model predictions.Comment: 17 pages, 5 figures. Submitted to Nuclear Instruments and Methods A.
Includes a long version of a conference talk (trans_limits_talk.pdf)
presented on the topic at the "Coulomb'05 -- High Intensity Beam Dynamics"
workshop (Senigallia, Italy, 12-16 September 2005). This talk presents
further supporting information/plots not included in the abbreviated,
draft-format manuscrip
K2P: Reduced data from campaigns 0-4 of the K2 mission
Context: After the loss of a second reaction wheel the Kepler mission was
redesigned as the K2 mission, pointing towards the ecliptic and delivering data
for new fields approximately every 80 days. The steady flow of data obtained
with a reduced pointing stability calls for dedicated pipelines for extracting
light curves and correcting these for use in, e.g., asteroseismic analysis.
Aims: We provide corrected light curves for the K2 fields observed until now
(campaigns 0-4), and provide a comparison with other pipelines for K2 data
extraction/correction. Methods: Raw light curves are extracted from K2 pixel
data using the "K2-pixel-photometry" (K2P) pipeline, and corrected using
the KASOC filter. Results: The use of K2P allows for the extraction of the
order of 90.000 targets in addition to 70.000 targets proposed by the community
- for these, other pipelines provide no data. We find that K2P in general
performs as well as, or better than, other pipelines for the tested metrics of
photometric quality. In addition to stars, pixel masks are properly defined
using K2P for extended objects such as galaxies for which light curves are
also extracted.Comment: Accepted for publication in Astronomy and Astrophysic
SPS phase control studies
To properly point and form the satellite microwave power beam, the outputs of the power amplifiers in the transmitting array must be phased in a specific and coherent fashion. A retrodirective CW phase conjugating system using a spread spectrum uplink signal and a reference phase signal that is distributed via fiber optics, was selected as the control system for SPS. The design details are presented and applications of the system are discussed
Damping rates and frequency corrections of Kepler LEGACY stars
Linear damping rates and modal frequency corrections of radial oscillation
modes in selected LEGACY main-sequence stars are estimated by means of a
nonadiabatic stability analysis. The selected stellar sample covers stars
observed by Kepler with a large range of surface temperatures and surface
gravities. A nonlocal, time-dependent convection model is perturbed to assess
stability against pulsation modes. The mixing-length parameter is calibrated to
the surface-convection-zone depth of a stellar model obtained from fitting
adiabatic frequencies to the LEGACY observations, and two of the nonlocal
convection parameters are calibrated to the corresponding LEGACY linewidth
measurements. The remaining nonlocal convection parameters in the 1D
calculations are calibrated so as to reproduce profiles of turbulent pressure
and of the anisotropy of the turbulent velocity field of corresponding 3D
hydrodynamical simulations. The atmospheric structure in the 1D stability
analysis adopts a temperature-optical-depth relation derived from 3D
hydrodynamical simulations. Despite the small number of parameters to adjust,
we find good agreement with detailed shapes of both turbulent pressure profiles
and anisotropy profiles with depth, and with damping rates as a function of
frequency. Furthermore, we find the absolute modal frequency corrections,
relative to a standard adiabatic pulsation calculation, to increase with
surface temperature and surface gravity.Comment: accepted for publication in Monthly Notices of the Royal Astronomical
Society (MNRAS); 15 pages, 8 figure
Review of literature relating to the modeling of soil temperatures based on meteorological factors
Abstracts of 72 papers, journal articles, and other publications are presented. The applicabilities of each is assessed for use in improving winterkill parameters for a winter wheat model
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