328 research outputs found
MDia and POTS - The Munich Difference Imaging Analysis for the pre-OmegaTranS Project
We describe the Munich Difference Imaging Analysis pipeline that we developed
and implemented in the framework of the Astro-WISE package to automatically
measure high precision light curves of a large number of stellar objects using
the difference imaging approach. Combined with programs to detect time
variability, this software can be used to search for planetary systems or
binary stars with the transit method and for variable stars of different kinds.
As a first scientific application, we discuss the data reduction and analysis
performed with Astro-WISE on the pre-OmegaTranS data set, that we collected
during a monitoring campaign of a dense stellar field with the Wide Field
Imager at the ESO 2.2m telescope.Comment: 10 pages, 5 figures, accepted for publication in topical issue of
Experimental Astronomy on Astro-WISE information syste
Microlensing events from the 11-year observations of the Wendelstein Calar Alto Pixellensing Project
We present the results of the decade-long M31 observation from the
Wendelstein Calar Alto Pixellensing Project (WeCAPP). WeCAPP has monitored M31
from 1997 till 2008 in both R- and I-filters, thus provides the longest
baseline of all M31 microlensing surveys. The data are analyzed with the
difference imaging analysis, which is most suitable to study variability in
crowded stellar fields. We extracted light curves based on each pixel, and
devised selection criteria that are optimized to identify microlensing events.
This leads to 10 new events, and sums up to a total of 12 microlensing events
from WeCAPP, for which we derive their timescales, flux excesses, and colors
from their light curves. The color of the lensed stars fall between (R-I) =
0.56 to 1.36, with a median of 1.0 mag, in agreement with our expectation that
the sources are most likely bright, red stars at post main-sequence stage. The
event FWHM timescales range from 0.5 to 14 days, with a median of 3 days, in
good agreement with predictions based on the model of Riffeser et al. (2006).Comment: 44 pages, 16 figures, 5 tables. ApJ accepte
Bias-Free Shear Estimation using Artificial Neural Networks
Bias due to imperfect shear calibration is the biggest obstacle when
constraints on cosmological parameters are to be extracted from large area weak
lensing surveys such as Pan-STARRS-3pi, DES or future satellite missions like
Euclid. We demonstrate that bias present in existing shear measurement
pipelines (e.g. KSB) can be almost entirely removed by means of neural
networks. In this way, bias correction can depend on the properties of the
individual galaxy instead on being a single global value. We present a
procedure to train neural networks for shear estimation and apply this to
subsets of simulated GREAT08 RealNoise data. We also show that circularization
of the PSF before measuring the shear reduces the scatter related to the PSF
anisotropy correction and thus leads to improved measurements, particularly on
low and medium signal-to-noise data. Our results are competitive with the best
performers in the GREAT08 competition, especially for the medium and higher
signal-to-noise sets. Expressed in terms of the quality parameter defined by
GREAT08 we achieve a Q = 40, 140 and 1300 without and 50, 200 and 1300 with
circularization for low, medium and high signal-to-noise data sets,
respectively.Comment: 19 pages, 8 figures; accepted for publication in Ap
Multiband Transit Light Curve Modeling of WASP-4
We report on the simultaneous g′,r′,i′,z′ multiband, high time sampling (18-24s) ground-based photometric observations, which we use to measure the planetary radius and orbital inclination of the extrasolar transiting hot Jupiter WASP-4b. We recorded 987 images during three complete transits with the GROND instrument, mounted on the MPG/ESO-2.2m telescope at La Silla Observatory. Assuming a quadratic law for the stellar limb darkening we derive system parameters by fitting a composite transit light curve over all bandpasses simultaneously. To compute uncertainties of the fitted parameters we employ the Bootstrap Monte Carlo Method. The three central transit times are measured with precision down to 6 s. We find a planetary radius Rp = 1.413 ± 0.020RJup, an orbital inclination i = 88.°57 ± 0.45° and calculate new ephemeris, a period P = 1.33823144 ± 0.00000032 days and reference transit epoch T0 = 2454697.798311 ± 0.000046 (BJD). The analysis of the new transit mid-times in combination with previous measurements imply a constant orbital period and no compelling evidence for TTVs due to additional bodies in the syste
WASP-4b Transit Observations With GROND
This is the author accepted manuscript. The final version is available from EDP Sciences via the DOI in this recordGround-based simultaneous multiband transit observations allow an accurate system parameters determination and may lead to the detection and characterization of additional bodies via the transit timing variations (TTVs) method. We aimed to (i) characterize the heavily bloated WASP-4b hot Jupiter and its star by measuring system parameters and the dependence of the planetary radius as a function of four (Sloan g', r', i', z') wavelengths and (ii) search for TTVs. We recorded 987 images during three complete transits with the GROND instrument, mounted on the MPG/ESO-2.2m telescope at La Silla Observatory. Assuming a quadratic law for the stellar limb darkening we derive system parameters by fitting a composite transit light curve over all bandpasses simultaneously. To compute uncertainties of the fitted parameters, we employ the Bootstrap Monte Carlo Method. The three central transit times are measured with precision down to 6 s. We find a planetary radius Rp = 1.413+/-0.020 RJup, an orbital inclination i = 88deg57'+/-0.45deg and calculate a new ephemeris, a period P = 1.33823144+/-0.00000032days and a reference transit epoch T0 = 2454697.798311+/-0.000046 (BJD). Analysis of the new transit mid-times in combination with previous measurements shows no sign of a TTV signal greater than 20s. We perform simplified numerical simulations to place upper-mass limits of a hypothetical perturber in the WASP-4b system.Part of the funding for GROND (both hardware as well as
personnel) was generously granted from the Leibniz-Prize to Prof. G. Hasinger
(DFG grant HA 1850/28-1). N.N. acknowledges the Klaus Tschira Stiftung
(KTS) and the Heidelberg Graduate School of Fundamental Physics (HGSFP)
for the financial support of his Ph.D. research. G.M. acknowledges the financial
support from the Polish Ministry of Science and Higher Education through the
Iuventus Plus grant IP2010 023070
Search for giant planets in M67 IV: survey results
We present the results of a seven-year-long radial velocity survey of a
sample of 88 main-sequence and evolved stars to reveal signatures of
Jupiter-mass planets in the solar-age and solar-metallicity open cluster M67.
We aim at studying the frequency of giant planets in this cluster with respect
to the field stars. In addition, our sample is also ideal to perform a
long-term study to compare the chemical composition of stars with and without
giant planets in detail. We analyzed precise radial velocity (RV) measurements
obtained with five different instruments. We conducted Monte Carlo simulations
to estimate the occurrence rate of giant planets in our radial velocity survey.
All the planets previously announced in this RV campaign with their properties
are summarized here: 3 hot Jupiters around the main-sequence stars YBP1194,
YBP1514, and YBP401, and 1 giant planet around the evolved star S364. Two
additional planet candidates around the stars YBP778 and S978 are also analyzed
in the present work. We discuss stars that exhibit large RV variability or
trends individually. For 2 additional stars, long-term trends are compatible
with new binary candidates or substellar objects, which increases the total
number of binary candidates detected in our campaign to 14. Based on the
Doppler-detected planets discovered in this survey, we find an occurrence of
giant planets of ~18.0%(+12.0/-8.0%) in the selected period-mass range. This
frequency is slightly higher but consistent within the errors with the estimate
for the field stars, which leads to the general conclusion that open cluster
and field statistics agree. However, we find that the rate of hot Jupiters in
the cluster (~5.7%(+5.5/-3.0%)) is substantially higher than in the field.Comment: Accepted by A&
Transit observations at the observatory in Grossschwabhausen: XO-1b and TrES-1
We report on observations of transit events of the transiting planets XO-1b
and TrES-1 with the AIU Jena telescope in Grossschwabhausen. Based on our IR
photometry (in March 2007) and available transit timings (SuperWASP, XO and
TLC-project-data) we improved the orbital period of XO-1b (P =
3.9414970.000006) and TrES-1 (P = 3.03007370.000006), respectively.
The new ephemeris for the both systems are presented.Comment: 4 pages, 2 figure
A hot Jupiter transiting a mid-K dwarf found in the pre-OmegaCam Transit Survey
We describe the pre-OmegaTranS project, a deep survey for transiting
extra-solar planets in the Carina region of the Galactic Disk. In 2006-2008 we
observed a single dense stellar field with a very high cadence of ~2min using
the ESO Wide Field Imager at the La Silla Observatory. Using the Astronomical
Wide-field System for Europe and the Munich Difference Imaging Analysis
pipeline, a module that has been developed for this project, we created the
light curves of 16000 stars with more than 4000 data points which we searched
for periodic transit signals using a box-fitting least-squares detection
algorithm. All light curves are publicly available. In the course of the
pre-OmegaTranS project we identified two planet candidates - POTS-1b and
POTS-C2b - which we present in this work. With extensive follow-up observations
we were able to confirm one of them, POTS-1b, a hot Jupiter transiting a mid-K
dwarf. The planet has a mass of 2.31+-0.77M_Jup and a radius of 0.94+-0.04R_Jup
and a period of P=3.16d. The host star POTS-1 has a radius of 0.59+-0.02R_Sun
and a mass of 0.70+-0.05M_Sun. Due to its low apparent brightness of I=16.1mag
the follow-up and confirmation of POTS-1b was particularly challenging and
costly.Comment: 18 pages, 23 figures, accepted for publication in MNRA
Searching for transits in the Wide Field Camera Transit Survey with difference-imaging light curves
The Wide Field Camera Transit Survey is a pioneer program aiming at for searching extra-solar planets in the near-infrared. The images from the survey are processed by a data reduction pipeline, which uses aperture photometry to construct the light curves. We produce an alternative set of light curves using the difference-imaging method for the most complete field in the survey and carry out a quantitative comparison between the photometric precision achieved with both methods. The results show that differencephotometry light curves present an important improvement for stars with J > 16. We report an implementation on the box-fitting transit detection algorithm, which performs a trapezoid-fit to the folded light curve, providing more accurate results than the boxfitting model. We describe and optimize a set of selection criteria to search for transit candidates, including the V-shape parameter calculated by our detection algorithm. The optimized selection criteria are applied to the aperture photometry and difference-imaging light curves, resulting in the automatic detection of the best 200 transit candidates from a sample of ~475 000 sources. We carry out a detailed analysis in the 18 best detections and classify them as transiting planet and eclipsing binary candidates. We present one planet candidate orbiting a late G-type star. No planet candidate around M-stars has been found, confirming the null detection hypothesis and upper limits on the occurrence rate of short-period giant planets around M-dwarfs presented in a prior study. We extend the search for transiting planets to stars with J ≤ 18, which enables us to set a stricter upper limit of 1.1%. Furthermore, we present the detection of five faint extremely-short period eclipsing binaries and three M-dwarf/M-dwarf binary candidates. The detections demonstrate the benefits of using the difference-imaging light curves, especially when going to fainter magnitudes.Peer reviewe
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