240 research outputs found
III.6 Exploration of the brown dwarf regime around solar-like stars by CoRoT
This book is dedicated to all the people interested in the CoRoT mission and the beautiful data that were delivered during its six year duration. Either amateurs, professional, young or senior researchers, they will find treasures not only at the time of this publication but also in the future twenty or thirty years. It presents the data in their final version, explains how they have been obtained, how to handle them, describes the tools necessary to understand them, and where to find them. It also highlights the most striking first results obtained up to now. CoRoT has opened several unexpected directions of research and certainly new ones still to be discovered
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
Stable and habitable systems with two giant planets
We have studied planetary systems which are similar to the Solar System and
built up from three inner rocky planets (Venus, Earth, Mars) and two outer gas
giants. The stability of the orbits of the inner planets is discussed in the
cases of different masses of the gas planets. To demonstrate the results
stability maps were made and it was found that Jupiter could be four times and
Saturn could be three times more massive while the orbits of the inner planets
stay stable. Similar calculations were made by changing the mass of the Sun. In
this case the position of the rocky planets and the extension of the liquid
water habitable and the UV habitable zones were studied for different masses of
the Sun. It was found that the orbits of the planets were stable for values
greater than 0.33 M_Sun where M_Sun is the mass of the Sun and at lower masses
of the Sun (at about 0.8 M_Sun) only Venus, but for higher mass values (at
about 1.2 M_Sun) Earth and also Mars are located in both habitable zones.Comment: 8 page
The Anticorrelated Nature of the Primary and Secondary Eclipse Timing Variations for the Kepler Contact Binaries
We report on a study of eclipse timing variations in contact binary systems,
using long-cadence lightcurves in the Kepler archive. As a first step,
'observed minus calculated' (O-C) curves were produced for both the primary and
secondary eclipses of some 2000 Kepler binaries. We find ~390 short-period
binaries with O-C curves that exhibit (i) random-walk like variations or
quasi-periodicities, with typical amplitudes of +/- 200-300 seconds, and (ii)
anticorrelations between the primary and secondary eclipse timing variations.
We present a detailed analysis and results for 32 of these binaries with
orbital periods in the range of 0.35 +/- 0.05 days. The anticorrelations
observed in their O-C curves cannot be explained by a model involving mass
transfer, which among other things requires implausibly high rates of ~0.01
M_sun per year. We show that the anticorrelated behavior, the amplitude of the
O-C delays, and the overall random-walk like behavior can be explained by the
presence of a starspot that is continuously visible around the orbit and slowly
changes its longitude on timescales of weeks to months. The quasi-periods of
~50-200 days observed in the O-C curves suggest values for k, the coefficient
of the latitude dependence of the stellar differential rotation, of
~0.003-0.013.Comment: Published in The Astrophysical Journal, 2013, Vol. 774, p.81; 14
pages, 12 figures, and 2 table
Long-term evolution of FU Orionis objects at infrared wavelengths
We investigate the brightness evolution of 7 FU Orionis systems in the 1-100
micrometer wavelength range using data from the Infrared Space Observatory
(ISO). The ISO measurements were supplemented with 2MASS and MSX observations
performed in the same years as the ISO mission (1995-98). The spectral energy
distributions (SEDs) based on these data points were compared with earlier ones
derived from the IRAS photometry as well as from ground-based observations
carried out around the epoch 1983. In 3 cases (Z CMa, Parsamian 21, V1331 Cyg)
no difference between the two epochs was seen within the measurement
uncertainties. V1057 Cyg, V1515 Cyg and V1735 Cyg have become fainter at
near-infrared wavelengths while V346 Nor has become slightly brighter. V1057
Cyg exhibits a similar flux change also in the mid-infrared. At lambda >= 60
micrometer most of the sources remained constant; only V346 Nor seems to fade.
Our data on the long-term evolution of V1057 Cyg agree with the model
predictions of Kenyon & Hartmann (1991) and Turner et al. (1997) at near- and
mid-infrared wavelengths, but disagree at lambda > 25 micrometer. We discuss if
this observational result at far-infrared wavelengths could be understood in
the framework of the existing models.Comment: 9 pages, 3 figures, to be published in Astronomy & Astrophysic
The effect of stellar limb darkening values on the accuracy of the planet radii derived from photometric transit observations
We study how the precision of the exoplanet radius determination is affected
by our present knowledge of limb darkening in two cases: when we fix the limb
darkening coefficients and when we adjust them. We also investigate the effects
of spots in one-colour photometry. We study the effect of limb darkening on the
planetary radius determination both via analytical expressions and by numerical
experiments. We also compare some of the existing limb darkening tables. When
stellar spots affect the fit, we replace the limb darkening coefficients,
calculated for the unspotted cases, with effective limb darkening coefficients
to describe the effect of the spots. There are two important cases. (1) When
one fixes the limb darkening values according to some theoretical predictions,
the inconsistencies of the tables do not allow us to reach accuracy in the
planetary radius of better than 1-10% (depending on the impact parameter) if
the host star's surface effective temperature is higher than 5000 K. Below 5000
K the radius ratio determination may contain even 20% error. (2) When one
allows adjustment of the limb darkening coefficients, the a/Rs ratio, the
planet-to-stellar radius ratio, and the impact parameter can be determined with
sufficient accuracy (<1%), if the signal-to-noise ratio is high enough.
However, the presence of stellar spots and faculae can destroy the agreement
between the limb darkening tables and the fitted limb darkening coefficients,
but this does not affect the precision of the planet radius determination. We
also find that it is necessary to fit the contamination factor, too. We
conclude that the present inconsistencies of theoretical stellar limb darkening
tables suggests one should not fix the limb darkening coefficients. When one
allows them to be adjusted, then the planet radius, impact parameter, and the
a/Rs can be obtained with the required precision.Comment: Astronomy & Astrophysics Vol. 549, A9 (2013) - 11 page
An estimate of the Love number of WASP-18Ab from its radial velocity measurements
Context. Increasing our knowledge of the interior structure, composition and
density distribution of exoplanets is crucial to make progress in the
understanding of exoplanetary formation, migration and habitability. However,
the directly measurable mass and radius values offer little constraint on
interior structure, because the inverse problem is highly degenerate. Therefore
there is a clear need for a third observable of exoplanet interiors. This third
observable can be the fluid Love number which measures the central mass
concentration of an exoplanet. Aims. The aims of this paper are (i) to develop
a basic model to fit the long-term radial velocity and TTV variations caused by
tidal interactions, (ii) to apply the model to the WASP-18Ab system, and (iii)
to estimate the Love number of the planet. Methods. Archival radial velocity,
transit and occultation timing data are collected and fitted via the model
introduced here. Results. The best model fit to the archival radial velocity
and timing data of WASP-18Ab was obtained with a Love number of the massive
() hot Jupiter WASP-18Ab: . This causes apsidal motion in the system, at a rate of
arcseconds/day. When checking possible causes of periastron precession, other
than the relativistic term or the non-spherical shape of the components, we
found a companion star to the WASP-18 system, named WASP-18B which is a
probable M6.5V dwarf with at 3519 AU distance from the
transit host star. We also find that small orbital eccentricities may be real,
rather than an apparent effect caused by the non spherical stellar shape.Comment: Accepted for publication in Astronomy and Astrophysic
A study of the performance of the transit detection tool DST in space-based surveys. Application of the CoRoT pipeline to Kepler data
Context. Transit detection algorithms are mathematical tools used for
detecting planets in the photometric data of transit surveys. In this work we
study their application to space-based surveys. Aims: Space missions are
exploring the parameter space of the transit surveys where classical algorithms
do not perform optimally, either because of the challenging signal-to-noise
ratio of the signal or its non-periodic characteristics. We have developed an
algorithm addressing these challenges for the mission CoRoT. Here we extend the
application to the data from the space mission Kepler. We aim at understanding
the performances of algorithms in different data sets. Methods: We built a
simple analytical model of the transit signal and developed a strategy for the
search that improves the detection performance for transiting planets. We
analyzed Kepler data with a set of stellar activity filtering and transit
detection tools from the CoRoT community that are designed for the search of
transiting planets. Results: We present a new algorithm and its performances
compared to one of the most widely used techniques in the literature using
CoRoT data. Additionally, we analyzed Kepler data corresponding to quarter Q1
and compare our results with the most recent list of planetary candidates from
the Kepler survey. We found candidates that went unnoticed by the Kepler team
when analyzing longer data sets. We study the impact of instrumental features
on the production of false alarms and false positives. These results show that
the analysis of space mission data advocates the use of complementary
detrending and transit detection tools also for future space-based transit
surveys such as PLATO.Comment: 18 pages, 23 figures, published in A&A, solved issue with reference
Exoplanet Research with the Stratospheric Observatory for Infrared Astronomy (SOFIA)
When the Stratospheric Observatory for Infrared Astronomy (SOFIA) was
conceived and its first science cases defined, exoplanets had not been
detected. Later studies, however, showed that optical and near-infrared
photometric and spectrophotometric follow-up observations during planetary
transits and eclipses are feasible with SOFIA's instrumentation, in particular
with the HIPO-FLITECAM and FPI+ optical and near infrared (NIR) instruments.
Additionally, the airborne-based platform SOFIA has a number of unique
advantages when compared to other ground- and space-based observatories in this
field of research. Here we will outline these theoretical advantages, present
some sample science cases and the results of two observations from SOFIA's
first five observation cycles -- an observation of the Hot Jupiter HD 189733b
with HIPO and an observation of the Super-Earth GJ 1214b with FLIPO and FPI+.
Based on these early products available to this science case, we evaluate
SOFIA's potential and future perspectives in the field of optical and infrared
exoplanet spectrophotometry in the stratosphere.Comment: Invited review chapter, accepted for publication in "Handbook of
Exoplanets" edited by H.J. Deeg and J.A. Belmonte, Springer Reference Work
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