645 research outputs found
Limits to the presence of transiting circumbinary planets in CoRoT data
The CoRoT mission during its flight-phase 2007-2012 delivered the
light-curves for over 2000 eclipsing binaries. Data from the Kepler mission
have proven the existence of several transiting circumbinary planets. Albeit
light-curves from CoRoT have typically lower precision and shorter coverage,
CoRoT's number of targets is similar to Kepler, and some of the known
circumbinary planets could potentially be detected in CoRoT data as well. The
aim of this work has been a revision of the entire CoRoT data-set for the
presence of circumbinary planets, and the derivation of limits to the
abundances of such planets. We developed a code which removes the light curve
of the eclipsing binaries and searches for quasi-periodic transit-like features
in a light curve after removal of binary eclipses and instrumental features.
The code needs little information on the sample systems and can be used for
other space missions as well, like Kepler, K2, TESS and PLATO. The code is
broad in the requirements leading to detections, but was tuned to deliver an
amount of detections that is manageable in a subsequent, mainly visual,
revision about their nature. In the CoRoT sample we identified three planet
candidates whose transits would have arisen from a single pass across the
central binary. No candidates remained however with transit events from
multiple planetary orbits. We calculated the upper limits for the number of
Jupiter, Saturn and Neptune sized planets in co-planar orbits for different
orbital period ranges. We found that there are much less giant planets in
short-periodic orbits around close binary systems than around single stars.Comment: Accepted for publication in A&A, 11 pages, 4 figures and 4 tables.
Updated to fix error in acknowledgemen
The contribution of secondary eclipses as astrophysical false positives to exoplanet transit surveys
We investigate in this paper the astrophysical false-positive configuration
in exoplanet-transit surveys that involves eclipsing binaries and giant planets
which present only a secondary eclipse, as seen from the Earth. To test how an
eclipsing binary configuration can mimic a planetary transit, we generate
synthetic light curve of three examples of secondary-only eclipsing binary
systems that we fit with a circular planetary model. Then, to evaluate its
occurrence we model a population of binaries in double and triple system based
on binary statistics and occurrence. We find that 0.061% +/- 0.017% of
main-sequence binary stars are secondary-only eclipsing binaries mimicking a
planetary transit candidate down to the size of the Earth. We then evaluate the
occurrence that an occulting-only giant planet can mimic an Earth-like planet
or even smaller planet. We find that 0.009% +/- 0.002% of stars harbor a giant
planet that present only the secondary transit. Occulting-only giant planets
mimic planets smaller than the Earth that are in the scope of space missions
like Kepler and PLATO. We estimate that up to 43.1 +/- 5.6 Kepler Objects of
Interest can be mimicked by this new configuration of false positives,
re-evaluating the global false-positive rate of the Kepler mission from 9.4%
+/- 0.9% to 11.3% +/- 1.1%. We note however that this new false-positive
scenario occurs at relatively long orbital period compared with the median
period of Kepler candidates.Comment: 9 pages, 4 figures, accepted for publication in A&
Recommended from our members
Optimización heurística con criterios de error de control TMD en turbinas marinas flotantes
Among the current deployment of renewable energy systems, floating wind turbines are a promising resource. They take advantage of the wind at deep seas, where it reaches higher and more constant speed. However, being located in deep waters they are subject to heavy loads, caused mainly by waves and wind. To reduce the vibrations in the structure, passive control devices can be used, which come from civil engineering. But its design and tuning are not a simple task due to the diverse goals that coexist in the application of these passive control systems. In this work the use of different methods of signal analysis for the optimization of TMD devices (Tuned Mass Damper) is explored through genetic algorithms. Various error criteria have been applied for the optimization in order to obtain a greater reduction of vibrations in the various elements of the floating turbine
Improved parameters of seven Kepler giant companions characterized with SOPHIE and HARPS-N
Radial-velocity observations of Kepler candidates obtained with the SOPHIE
and HARPS-N spectrographs have permitted unveiling the nature of the five giant
planets Kepler-41b, Kepler-43b, Kepler-44b, Kepler-74b, and Kepler-75b, the
massive companion Kepler-39b, and the brown dwarf KOI-205b. These companions
were previously characterized with long-cadence (LC) Kepler data. Here we aim
at refining the parameters of these transiting systems by i) modelling the
published radial velocities (RV) and Kepler short-cadence (SC) data that
provide a much better sampling of the transits, ii) performing new spectral
analyses of the SOPHIE and ESPaDOnS spectra, and iii) improving stellar
rotation periods hence stellar age estimates through gyrochronology, when
possible. Posterior distributions of the system parameters were derived with a
differential evolution Markov chain Monte Carlo approach. Our main results are
as follows: a) Kepler-41b is significantly larger and less dense than
previously found because a lower orbital inclination is favoured by SC data.
This also affects the determination of the geometric albedo that is lower than
previously derived: Ag < 0.135; b) Kepler-44b is moderately smaller and denser
than reported in the discovery paper; c) good agreement was achieved with
published Kepler-43, Kepler-75, and KOI-205 system parameters, although the
host stars Kepler-75 and KOI-205 were found to be slightly richer in metals and
hotter, respectively; d) the previously reported non-zero eccentricities of
Kepler-39b and Kepler-74b might be spurious. If their orbits were circular, the
two companions would be smaller and denser than in the eccentric case. The
radius of Kepler-39b is still larger than predicted by theoretical isochrones.
Its parent star is hotter and richer in metals than previously determined.
[ABRIDGED]Comment: 17 pages, 9 figures, accepted for publication in Astronomy and
Astrophysic
TRUFAS, a wavelet based algorithm for the rapid detection of planetary transits
Aims: We describe a fast, robust and automatic detection algorithm, TRUFAS,
and apply it to data that are being expected from the CoRoT mission. Methods:
The procedure proposed for the detection of planetary transits in light curves
works in two steps: 1) a continuous wavelet transformation of the detrended
light curve with posterior selection of the optimum scale for transit
detection, and 2) a period search in that selected wavelet transformation. The
detrending of the light curves are based on Fourier filtering or a discrete
wavelet transformation. TRUFAS requires the presence of at least 3 transit
events in the data. Results: The proposed algorithm is shown to identify
reliably and quickly the transits that had been included in a standard set of
999 light curves that simulate CoRoT data. Variations in the pre-processing of
the light curves and in the selection of the scale of the wavelet transform
have only little effect on TRUFAS' results. Conclusions: TRUFAS is a robust and
quick transit detection algorithm, especially well suited for the analysis of
very large volumes of data from space or ground-based experiments, with long
enough durations for the target-planets to produce multiple transit events.Comment: 9 pages, 10 figures, accepted by A&
PASTIS: Bayesian extrasolar planet validation II. Constraining exoplanet blend scenarios using spectroscopic diagnoses
The statistical validation of transiting exoplanets proved to be an efficient
technique to secure the nature of small exoplanet signals which cannot be
established by purely spectroscopic means. However, the spectroscopic diagnoses
are providing us with useful constraints on the presence of blended stellar
contaminants. In this paper, we present how a contaminating star affects the
measurements of the various spectroscopic diagnoses as function of the
parameters of the target and contaminating stars using the model implemented
into the PASTIS planet-validation software. We find particular cases for which
a blend might produce a large radial velocity signal but no bisector variation.
It might also produce a bisector variation anti-correlated with the radial
velocity one, as in the case of stellar spots. In those cases, the full width
half maximum variation provides complementary constraints. These results can be
used to constrain blend scenarios for transiting planet candidates or radial
velocity planets. We review all the spectroscopic diagnoses reported in the
literature so far, especially the ones to monitor the line asymmetry. We
estimate their uncertainty and compare their sensitivity to blends. Based on
that, we recommend the use of BiGauss which is the most sensitive diagnosis to
monitor line-profile asymmetry. In this paper, we also investigate the
sensitivity of the radial velocities to constrain blend scenarios and develop a
formalism to estimate the level of dilution of a blended signal. Finally, we
apply our blend model to re-analyse the spectroscopic diagnoses of HD16702, an
unresolved face-on binary which exhibits bisector variations.Comment: Accepted for publication in MNRA
Limits to the planet candidate GJ 436c
We report on H-band, ground-based observations of a transit of the hot
Neptune GJ 436b. Once combined to achieve sampling equivalent to archived
observations taken with Spitzer, our measurements reach comparable precision
levels. We analyze both sets of observations in a consistent way, and measure
the rate of orbital inclination change to be of 0.02+/-0.04 degrees in the time
span between the two observations (253.8 d, corresponding to 0.03+/-0.05
degrees/yr if extrapolated). This rate allows us to put limits on the relative
inclination between the two planets by performing simulations of planetary
systems, including a second planet, GJ 436c, whose presence has been recently
suggested (Ribas et al. 2008). The allowed inclinations for a 5 M_E super-Earth
GJ 436c in a 5.2 d orbit are within ~7 degrees of the one of GJ 436b; for
larger differences the observed inclination change can be reproduced only
during short sections (<50%) of the orbital evolution of the system. The
measured times of three transit centers of the system do not show any departure
from linear ephemeris, a result that is only reproduced in <1% of the simulated
orbits. Put together, these results argue against the proposed planet candidate
GJ 436c.Comment: Replaced with accepted version. Minor language corrections. 4 pages,
4 figures, to appear in A&A Letter
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