5,843 research outputs found
Characterization of CoRoT target fields with BEST: Identification of periodic variable stars in the IR01 field
We report on observations of the CoRoT IR01 field with the Berlin Exoplanet
Search Telescope (BEST). BEST is a small aperture telescope with a wide field
of view (FOV). It is dedicated to search for variable stars within the target
fields of the CoRoT space mission to aid in minimizing false-alarm rates and
identify potential targets for additional science. CoRoT's observational
programm started in February 2007 with the "initial run" field (IR01) observed
for about two months. BEST observed this field for 12 nights spread over three
months in winter 2006. From the total of 30426 stars observed in the IR01 field
3769 were marked as suspected variable stars and 54 from them showed clear
periodicity. From these 19 periodic stars are within the part of the CoRoT FOV
covered in our data set
Results from the Exoplanet Search Programmes with BEST and TEST
Thueringer Landessternwarte Tautenburg (TLS) has started to operate a small
dedicated telescope - the Tautenburg Exoplanet Search Telescope (TEST) -
searching for transits of extrasolar planets in photometric time series
observations. In a joint effort with the Berlin Exoplanet Search Telescope
(BEST) operated by the Institut fuer Planetenforschung of the "Deutsches
Zentrum fuer Luft- und Raumfahrt (DLR)" at the Observatoire de Haute-Provence
(OHP), France, two observing sites are used to optimise transit search. Here,
we give a short overview of these systems and the data analysis. We describe a
software pipeline that we have set up to identify transit events of extrasolar
planets and variable stars in time series data from these and other telescopes,
and report on some first results.Comment: 6 pages, 5 figures, contributed paper to the "Solar and Stellar
Physics Through Eclipses" conference, eds. O. Demircan, S.O. Selam, B.
Albayrak (Turkey, March 2006
Variability survey in the CoRoT SRa01 field: Implications of eclipsing binary distribution on cluster formation in NGC 2264
Time-series photometry of the CoRoT field SRa01 was carried out with the
Berlin Exoplanet Search Telescope II (BEST II) in 2008/2009. A total of 1,161
variable stars were detected, of which 241 were previously known and 920 are
newly found. Several new, variable young stellar objects have been discovered.
The study of the spatial distribution of eclipsing binaries revealed the higher
relative frequency of Algols toward the center of the young open cluster NGC
2264. In general Algol frequency obeys an isotropic distribution of their
angular momentum vectors, except inside the cluster, where a specific
orientation of the inclinations is the case. We suggest that we see the orbital
plane of the binaries almost edge-on.Comment: 18 pages, 8 figures, accepted for publication in Ap
Structure and dynamics of a model glass: influence of long-range forces
We vary the amplitude of the long-range Coulomb forces within a classical
potential describing a model silica glass and study the consequences on the
structure and dynamics of the glass, via molecular dynamics simulations. This
model allows us to follow the variation of specific features such as the First
Sharp Diffraction Peak and the Boson Peak in a system going continuously from a
fragile (no Coulomb forces) to a strong (with Coulomb forces) glass. In
particular we show that the characteristic features of a strong glass
(existence of medium range order, bell-shaped ring size distribution, sharp
Boson peak) appear as soon as tetrahedral units are formed.Comment: 5 pages, 4 figures. To be published in J.Phys.: C
The Berlin Exoplanet Search Telescope II. Catalog of Variable Stars. I. Characterization of Three Southern Target Fields
A photometric survey of three Southern target fields with BEST II yielded the
detection of 2,406 previously unknown variable stars and an additional 617
stars with suspected variability. This study presents a catalog including their
coordinates, magnitudes, light curves, ephemerides, amplitudes, and type of
variability. In addition, the variability of 17 known objects is confirmed,
thus validating the results. The catalog contains a number of known and new
variables that are of interest for further astrophysical investigations, in
order to, e.g., search for additional bodies in eclipsing binary systems, or to
test stellar interior models.
Altogether, 209,070 stars were monitored with BEST II during a total of 128
nights in 2009/2010. The overall variability fraction of 1.2-1.5% in these
target fields is well comparable to similar ground-based photometric surveys.
Within the main magnitude range of , we identify
0.67(3)% of all stars to be eclipsing binaries, which indicates a completeness
of about one third for this particular type in comparison to space surveys.Comment: accepted to A
Pre-discovery observations of CoRoT-1b and CoRoT-2b with the BEST survey
The BEST wide-angle telescope installed at the Observatoire de Haute-Provence
and operated in remote control from Berlin by the Institut fuer
Planetenforschung, DLR, has observed the CoRoT target fields prior to the
mission. The resulting archive of stellar photometric lightcurves is used to
search for deep transit events announced during CoRoT's alarm-mode to aid in
fast photometric confirmation of these events. The "initial run" field of CoRoT
(IRa01) has been observed with BEST in November and December 2006 for 12
nights. The first "long run" field (LRc01) was observed from June to September
2005 for 35 nights. After standard CCD data reduction, aperture photometry has
been performed using the ISIS image subtraction method. About 30,000
lightcurves were obtained in each field. Transits of the first detected planets
by the CoRoT mission, CoRoT-1b and CoRoT-2b, were found in archived data of the
BEST survey and their lightcurves are presented here. Such detections provide
useful information at the early stage of the organization of follow-up
observations of satellite alarm-mode planet candidates. In addition, no period
change was found over ~4 years between the first BEST observation and last
available transit observations.Comment: AJ, accepte
The Opinion-Policy Nexus in Europe and the Role of Political Institutions
A strong link between citizen preferences and public policy is one of the key goals and criteria of democratic governance. Yet, our knowledge about the extent to which public policies on specific issues are in line with citizen preferences in Europe is limited. This article reports on the first study of the link between public opinion and public policy that covers a large and diverse sample of concrete public policy issues in 31 European democracies. The findings demonstrate a strong positive relationship and a substantial degree of congruence between public opinion and the state of public policy. Also examined is whether political institutions, including electoral systems and the horizontal and vertical division of powers, influence the opinion‐policy link. The evidence for such effects is very limited, which suggests that the same institutions might affect policy representation in countervailing ways through different mechanisms
The BAST algorithm for transit detection
The pioneer space mission for photometric exoplanet searches, CoRoT, steadily
monitors about 12000 stars in each of its fields of view. Transit detection
algorithms are applied to derive promising planetary candidates, which are then
followed-up with ground-based observations. We present BAST (Berlin Automatic
Search for Transits), a new algorithm for periodic transit detection, and test
it on simulated CoRoT data. BAST searches for box-shaped signals in normalized,
filtered, variability-fitted, and unfolded light curves. A low-pass filter is
applied to remove high-frequency signals, and linear fits to subsections of
data are subtracted to remove the star's variability. A search for periodicity
is then performed in transit events identified above a given detection
threshold. Some criteria are defined to better separate planet candidates from
binary stars.
From the analysis of simulated CoRoT light curves, we show that the BAST
detection performance is similar to that of the Box-fitting Least-Square (BLS)
method if the signal-to-noise ratio is high. However, the BAST box search for
transits computes 10 times faster than the BLS method. By adding periodic
transits to simulated CoRoT data, we show that the minimum periodic depth
detectable with BAST is a linearly increasing function of the noise level. For
low-noise light curves, the detection limit corresponds to a transit depth
d~0.01%, i.e. a planet of 1 Earth radius around a solar-type star.Comment: 4 pages, 3 figures, to be published in A&
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