13,090 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
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
Search for heavy antinuclei in the cosmic radiation
The existence of significant amounts of antimatter in the Universe is demonstrated through cosmic radiation. The data from the Danish-French Cosmic Ray Spectrometer on the HEAO-3 satellite offers an opportunity to search for heavy antinuclei, since all the relevant parameters (charge, velocity, arrival direction, and satellite position at the time of arrival) are measured for each recorded nucleus. Using the 22676 positive only events in the data seletion corresponding to L 1.5 as a measure of our exposure factor to heavy antinuclei and noting that no corresponding antinuclei were found, an upper limit (95% confidence) is given to the ratio of antinuclei to nuclei as 1.4 x .0001 for particles with Z 9. The upper limit resulting from this work is compared with previous results of searches for heavy antimatter in the cosmic radiation. It is seen that, if one regards only antiparticles heavier than fluorine, then the present result represents a reduced upper limit over previous data. When taken together, all the available experiment data now push the upper limit for the ratio of antiparticles to particles well below .0001
Magnetic activity, differential rotation and dynamo action in the pulsating F9IV star KIC 5955122
We present photometric spot modeling of the nearly four-year long light-curve
of the Kepler target KIC 5955122 in terms of persisting dark circular surface
features. With a Bayesian technique, we produced a plausible surface map that
shows dozens of small spots. After some artifacts are removed, the residuals
are at \,mmag. The shortest rotational period found is days. The equator-to-pole extrapolated differential rotation is rad/d. The spots are roughly half as bright as the unperturbed stellar
photosphere. Spot latitudes are restricted to the zone latitude.
There is no indication for any near-pole spots. In addition, the p-mode
pulsations enabled us to determine the evolutionary status of the star, the
extension of the convective zone, and its radius and mass. We discuss the
possibility that the clear signature of active regions in the light curve of
the F9IV star KIC 5955122 is produced by a flux-transport dynamo action at the
base of the convection zone. In particular, we argue that this star has evolved
from an active to a quiet status during the Q0--Q16 period of observation, and
we predict, according to our dynamo model, that the characteristic activity
cycle is of the order of the solar one.Comment: 9 pages, 12 figures, to be published on A&
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
A number or a person?: perspectives on credit scoring and fair mortgage lending: article four in a five-part series
This fourth article in a five-part series on credit scoring showcases three different perspectives. Up for debate is how lenders can ensure fair treatment to all mortgage applicants and how consumers can be educated about the effect their credit score has on loan pricing.Mortgage loans
PDB42 INCRETIN-THERAPY IN ADDITION TO METFORMIN AND/OR SULFONYLUREA FOR TYPE 2 DIABETES MELLITUS (T2DM): COSTEFFECTIVENESS OF LIRAGLUTIDE VERSUS EXENATIDE FROM THE PERSPECTIVE OF THE GERMAN STATUTORY HEALTH INSURANCE (SHI)
Review of NGO performance research published in academic journals between 1996 and 2008
Globally, literature on the performance of development non-governmental organisations (NGOs) has increased. However, little is known regarding the distinctive characteristics of academic articles on factors influencing NGO performance. In a recent systematic review of research, published in English-language academic journals between 1996 and 2008, factors influencing NGO performance were investigated. From the 31 journal articles that met the inclusion criteria, this study examined the salient characteristics of NGO performance research in terms of, (1) the number of publications, (2) publication outlets (journals and journal cluster), (3) author collaboration (sole or joint authors), (4) author affiliation, (5) study location, (6) study period, (7) study topics and (8) method and sources of information. Findings showed a steady increase in the number of articles, published in a wide array of journals with over half of the articles published in development studies journals. Of the 31 articles, 21 were sole authored. Data were mainly sought from NGO directors, programme staff and donors; comparatively fewer studies collected data from beneficiaries. Studies were mainly conducted in developing countries, whilst most authors were affiliated to institutions in developed countries. Of the 13 authors who conducted studies in Africa only 3 were affiliated to an institution in Africa. This study confirmed the continued need for increased research on factors influencing NGO performance; revealed the low seeking of beneficiaries’ perspectives in NGO performance research despite the rhetoric of participatory development; and revealed the low number of published researchers in Africa an
The LOFT (Large Observatory for X-ray Timing) background simulations
The Large Observatory For X-ray Timing (LOFT) is an innovative medium-class
mission selected for an assessment phase in the framework of the ESA M3 Cosmic
Vision call. LOFT is intended to answer fundamental questions about the
behaviour of matter in the very strong gravitational and magnetic fields around
compact objects. With an effective area of ~10 m^2 LOFT will be able to measure
very fast variability in the X-ray fluxes and spectra. A good knowledge of the
in-orbit background environment is essential to assess the scientific
performance of the mission and to optimize the instrument design. The two main
contributions to the background are cosmic diffuse X-rays and high energy
cosmic rays; also, albedo emission from the Earth is significant. These
contributions to the background for both the Large Area Detector and the Wide
Field Monitor are discussed, on the basis of extensive Geant-4 simulations of a
simplified instrumental mass model.Comment: Proceedings of SPIE, Vol. 8443, Paper No. 8443-209, 201
Registration of the First Thermonuclear X-ray Burst from AX J1754.2-2754
During the analysis of the INTEGRAL observatory archival data we found a
powerful X-ray burst, registered by JEM-X and IBIS/ISGRI telescopes on April
16, 2005 from a weak and poorly known source AX J1754.2-2754. Analysis of the
burst profiles and spectrum shows, that it was a type I burst, which result
from thermonuclear explosion on the surface of nutron star. It means that we
can consider AX J1754.2-2754 as an X-ray burster. Certain features of burst
profile at its initial stage witness of a radiation presure driven strong
expansion and a corresponding cooling of the nutron star photosphere. Assuming,
that the luminosity of the source at this phase was close to the Eddington
limit, we estimated the distance to the burst source d=6.6+/-0.3 kpc (for
hidrogen atmosphere of the neutron star) and d=9.2+/-0.4 kpc (for helium
atmosphere).Comment: 12 pages, 6 figure
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