407 research outputs found
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&
SOPHIE velocimetry of Kepler transit candidates VI. An additional companion in the KOI-13 system
We report the discovery of a new stellar companion in the KOI-13 system.
KOI-13 is composed by two fast-rotating A-type stars of similar magnitude. One
of these two stars hosts a transiting planet discovered by Kepler. We obtained
new radial velocity measurements using the SOPHIE spectrograph at the
Observatoire de Haute-Provence that revealed an additional companion in this
system. This companion has a mass between 0.4 and 1 Msun and orbits one of the
two main stars with a period of 65.831 \pm 0.029 days and an eccentricity of
0.52 \pm 0.02. The radial velocities of the two stars were derived using a
model of two fast-rotating line profiles. From the residuals, we found a hint
of the stellar variations seen in the Kepler light curve with an amplitude of
about 1.41 km/s and a period close to the rotational period. This signal
appears to be about three order of magnitude larger than expected for stellar
activity. From the analysis of the residuals, we also put a 3-sigma upper-limit
on the mass of the transiting planet KOI-13.01 of 14.8 Mjup and 9.4 Mjup,
depending on which star hosts the transit. We found that this new companion has
no significant impact on the photometric determination of the mass of KOI-13.01
but is expected to affect precise infrared photometry. Finally, using dynamical
simulations, we infer that the new companion is orbiting around KOI-13B while
the transiting planet candidate is expected to orbit KOI-13A. Thus, the
transiting planet candidate KOI-13.01 is orbiting the main component of a
hierarchical triple system.Comment: Accepted in A&A Letters. 4 pages including 4 figures and the RV tabl
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
SOPHIE velocimetry of Kepler transit candidates IX. KOI-415 b: a long-period, eccentric transiting brown dwarf to an evolved Sun
We report the discovery of a long-period brown-dwarf transiting companion of
the solar-type star KOI-415. The transits were detected by the Kepler space
telescope. We conducted Doppler measurements using the SOPHIE spectrograph at
the Observatoire de Haute-Provence. The photometric and spectroscopic signals
allow us to characterize a 62.14+-2.69 Mjup, brown-dwarf companion of an
evolved 0.94+-0.06 Msun star in a highly eccentric orbit of P =
166.78805+-0.00022 days and e = 0.698+-0.002. The radius of KOI-415 b is 0.79
(-0.07,+0.12) Rjup, a value that is compatible with theoretical predictions for
a 10 Gyr, low-metallicity and non-irradiated object.Comment: accepted in A&A Letter
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
SOPHIE velocimetry of Kepler transit candidates XIV. A joint photometric, spectroscopic, and dynamical analysis of the Kepler-117 system
As part of our follow-up campaign of Kepler planets, we observed Kepler-117
with the SOPHIE spectrograph at the Observatoire de Haute-Provence. This
F8-type star hosts two transiting planets in non-resonant orbits. The planets,
Kepler-117 b and c, have orbital periods and days,
and show transit-timing variations (TTVs) of several minutes. We performed a
combined Markov chain Monte Carlo (MCMC) fit on transits, radial velocities,
and stellar parameters to constrain the characteristics of the system. We
included the fit of the TTVs in the MCMC by modeling them with dynamical
simulations. In this way, consistent posterior distributions were drawn for the
system parameters. According to our analysis, planets b and c have notably
different masses ( and M) and low
orbital eccentricities ( and ). The
uncertainties on the derived parameters are strongly reduced if the fit of the
TTVs is included in the combined MCMC. The TTVs allow measuring the mass of
planet b, although its radial velocity amplitude is poorly constrained.
Finally, we checked that the best solution is dynamically stable.Comment: 16 pages, of whom 5 of online material.12 figures, of whom 2 in the
online material. 7 tables, of whom 4 in the online material. Published in A&
Characterization of the four new transiting planets KOI-188b, KOI-195b, KOI-192b, and KOI-830b
The characterization of four new transiting extrasolar planets is presented
here. KOI-188b and KOI-195b are bloated hot Saturns, with orbital periods of
3.8 and 3.2 days, and masses of 0.25 and 0.34 M_Jup. They are located in the
low-mass range of known transiting, giant planets. KOI-192b has a similar mass
(0.29 M_Jup) but a longer orbital period of 10.3 days. This places it in a
domain where only a few planets are known. KOI-830b, finally, with a mass of
1.27 M_Jup and a period of 3.5 days, is a typical hot Jupiter. The four planets
have radii of 0.98, 1.09, 1.2, and 1.08 R_Jup, respectively. We detected no
significant eccentricity in any of the systems, while the accuracy of our data
does not rule out possible moderate eccentricities. The four objects were first
identified by the Kepler Team as promising candidates from the photometry of
the Kepler satellite. We establish here their planetary nature thanks to the
radial velocity follow-up we secured with the HARPS-N spectrograph at the
Telescopio Nazionale Galileo. The combined analyses of the datasets allow us to
fully characterize the four planetary systems. These new objects increase the
number of well-characterized exoplanets for statistics, and provide new targets
for individual follow-up studies. The pre-screening we performed with the
SOPHIE spectrograph at the Observatoire de Haute-Provence as part of that study
also allowed us to conclude that a fifth candidate, KOI-219.01, is not a planet
but is instead a false positive.Comment: 13 pages, 4 figures, 6 tables, final version accepted for publication
in A&
SOPHIE velocimetry of Kepler transit candidates XI. Kepler-412 system: probing the properties of a new inflated hot Jupiter
We confirm the planetary nature of Kepler-412b, listed as planet candidate
KOI-202 in the Kepler catalog, thanks to our radial velocity follow-up program
of Kepler-released planet candidates, which is on going with the SOPHIE
spectrograph. We performed a complete analysis of the system by combining the
Kepler observations from Q1 to Q15, to ground-based spectroscopic observations
that allowed us to derive radial velocity measurements, together with the host
star parameters and properties. We also analyzed the light curve to derive the
star's rotation period and the phase function of the planet, including the
secondary eclipse. We found the planet has a mass of 0.939 0.085
M and a radius of 1.325 0.043 R which makes it a member
of the bloated giant subgroup. It orbits its G3 V host star in 1.72 days. The
system has an isochronal age of 5.1 Gyr, consistent with its moderate stellar
activity as observed in the Kepler light curve and the rotation of the star of
17.2 1.6 days. From the detected secondary, we derived the day side
temperature as a function of the geometric albedo and estimated the geometrical
albedo, Ag, is in the range 0.094 to 0.013. The measured night side flux
corresponds to a night side brightness temperature of 2154 83 K, much
greater than what is expected for a planet with homogeneous heat
redistribution. From the comparison to star and planet evolution models, we
found that dissipation should operate in the deep interior of the planet. This
modeling also shows that despite its inflated radius, the planet presents a
noticeable amount of heavy elements, which accounts for a mass fraction of 0.11
0.04.Comment: 11 pages, 9 figure
SOPHIE velocimetry of Kepler transit candidates. XV. KOI-614b, KOI-206b, and KOI-680b: a massive warm Jupiter orbiting a G0 metallic dwarf and two highly inflated planets with a distant companion around evolved F-type stars
We report the validation and characterization of three new transiting
exoplanets using SOPHIE radial velocities: KOI-614b, KOI-206b, and KOI-680b.
KOI-614b has a mass of and a radius of
, and it orbits a G0, metallic
([Fe/H]=) dwarf in 12.9 days. Its mass and radius are familiar and
compatible with standard planetary evolution models, so it is one of the few
known transiting planets in this mass range to have an orbital period over ten
days. With an equilibrium temperature of K, this places
KOI-614b at the transition between what is usually referred to as "hot" and
"warm" Jupiters. KOI-206b has a mass of and a
radius of , and it orbits a slightly evolved F7-type
star in a 5.3-day orbit. It is a massive inflated hot Jupiter that is
particularly challenging for planetary models because it requires unusually
large amounts of additional dissipated energy in the planet. On the other hand,
KOI-680b has a much lower mass of and requires less
extra-dissipation to explain its uncommonly large radius of . It is one of the biggest transiting planets characterized so far,
and it orbits a subgiant F9-star well on its way to the red giant stage, with
an orbital period of 8.6 days. With host stars of masses of
and , respectively, KOI-206b,
and KOI-680b are interesting objects for theories of formation and survival of
short-period planets around stars more massive than the Sun. For those two
targets, we also find signs of a possible distant additional companion in the
system
- …