350 research outputs found
New planetary and EB candidates from Campaigns 1-6 of the K2 mission
With only two functional reaction wheels, Kepler cannot maintain stable
pointing at its original target field and entered a new mode of observation
called K2. Our method is based on many years of experience in planet hunting
for the CoRoT mission. Due to the unstable pointing, K2 light curves present
systematics that are correlated with the target position in the CCD. Therefore,
our pipeline also includes a decorrelation of this systematic noise. Our
pipeline is optimised for bright stars for which spectroscopic follow-up is
possible. We achieve a maximum precision on 6 hours of 6 ppm. The decorrelated
light curves are searched for transits with an adapted version of the CoRoT
alarm pipeline. We present 172 planetary candidates and 327 eclipsing binary
candidates from campaigns 1, 2, 3, 4, 5 and 6 of K2. Both the planetary
candidates and eclipsing binary candidates lists are made public to promote
follow-up studies. The light curves will also be available to the community.Comment: 22 pages. 5 figures, 4 tables, Accepted for publication in A&
Distinguishing the albedo of exoplanets from stellar activity
Light curves show the flux variation from the target star and its orbiting
planets as a function of time. In addition to the transit features created by
the planets, the flux also includes the reflected light component of each
planet, which depends on the planetary albedo. This signal is typically
referred to as phase curve and could be easily identified if there were no
additional noise. As well as instrumental noise, stellar activity, such as
spots, can create a modulation in the data, which may be very difficult to
distinguish from the planetary signal. We analyze the limitations imposed by
the stellar activity on the detection of the planetary albedo, considering the
limitations imposed by the predicted level of instrumental noise and the short
duration of the observations planned in the context of the CHEOPS mission. As
initial condition, we have assumed that each star is characterized by just one
orbiting planet. We built mock light curves that included a realistic stellar
activity pattern, the reflected light component of the planet and an
instrumental noise level, which we have chosen to be at the same level as
predicted for CHEOPS. We then fit these light curves to try to recover the
reflected light component, assuming the activity patterns can be modeled with a
Gaussian process.We estimate that at least one full stellar rotation is
necessary to obtain a reliable detection of the planetary albedo. This result
is independent of the level of noise, but it depends on the limitation of the
Gaussian process to describe the stellar activity when the light curve
time-span is shorter than the stellar rotation. Finally, in presence of typical
CHEOPS gaps in the simulations, we confirm that it is still possible to obtain
a reliable albedo.Comment: Accepted for publication in A&A, 14 pages, 12 figure
Constraining planet structure and composition from stellar chemistry: trends in different stellar populations
The chemical composition of stars that have orbiting planets provides
important clues about the frequency, architecture, and composition of exoplanet
systems. We explore the possibility that stars from different galactic
populations that have different intrinsic abundance ratios may produce planets
with a different overall composition. We compiled abundances for Fe, O, C, Mg,
and Si in a large sample of solar neighbourhood stars that belong to different
galactic populations. We then used a simple stoichiometric model to predict the
expected iron-to-silicate mass fraction and water mass fraction of the planet
building blocks, as well as the summed mass percentage of all heavy elements in
the disc. Assuming that overall the chemical composition of the planet building
blocks will be reflected in the composition of the formed planets, we show that
according to our model, discs around stars from different galactic populations,
as well as around stars from different regions in the Galaxy, are expected to
form rocky planets with significantly different iron-to-silicate mass
fractions. The available water mass fraction also changes significantly from
one galactic population to another. The results may be used to set constraints
for models of planet formation and chemical composition. Furthermore, the
results may have impact on our understanding of the frequency of planets in the
Galaxy, as well as on the existence of conditions for habitability.Comment: Accepted for publication in Astronomy & Astrophysic
Measuring the orbit shrinkage rate of hot Jupiters due to tides
A tidal interaction between a star and a close-in exoplanet leads to
shrinkage of the planetary orbit and eventual tidal disruption of the planet.
Measuring the shrinkage of the orbits will allow for the tidal quality
parameter of the star () to be measured, which is an important
parameter to obtain information about stellar interiors. We analyse data from
TESS for two targets known to host close-in hot Jupiters, WASP-18 and WASP-19,
to measure the current limits on orbital period variation and provide new
constrains on . We modelled the transit shape using all the available
TESS observations and fitted the individual transit times of each transit. We
used previously published transit times together with our results to fit two
models, a constant period model, and a quadratic orbital decay model, MCMC
algorithms. We find period change rates of for
WASP-18b and for WASP-19b and we do not find
significant evidence of orbital decay in these targets. We obtain new lower
limits for of in WASP-18 and
in WASP-19, corresponding to upper limits of the
orbital decay rate of and ,
respectively, with a 95% confidence level. We compare our results with other
relevant targets for tidal decay studies. We find that the orbital decay rate
in both WASP-18b and WASP-19b appears to be smaller than the measured orbital
decay of WASP-12b. We show that the minimum value of in WASP-18 is
two orders of magnitude higher than that of WASP-12, while WASP-19 has a
minimum value one order of magnitude higher, which is consistent with other
similar targets. Further observations are required to constrain the orbital
decay of WASP-18 and WASP-19.Comment: 10 pages plus 5-page appendix. To be published in Astronomy and
Astrophysic
Understanding stellar activity-induced radial velocity jitter using simultaneous K2 photometry and HARPS RV measurements
One of the best ways to improve our understanding of the stellar
activity-induced signal in radial velocity (RV) measurements is through
simultaneous high-precision photometric and RV observations. This is of prime
importance to mitigate the RV signal induced by stellar activity and therefore
unveil the presence of low-mass exoplanets. The K2 Campaign 7 and 8
field-of-views were located in the southern hemisphere, and provided a unique
opportunity to gather unprecedented simultaneous high precision photometric
observation with K2 and high-precision RV measurements with the HARPS
spectrograph to study the relationship between photometric variability and RV
jitter. We observed nine stars with different levels of activity; from quiet to
very active. We probe the presence of any meaningful relation between measured
RV jitter and the simultaneous photometric variation, and also other activity
indicators (e.g. BIS, FWHM, , and F8), by evaluating the strength
and significance of the correlation between RVs and each indicator. We found
that for the case of very active stars, strong and significant correlations
exist between almost all the observables and measured RVs; however, for lower
activity levels the correlations become random. Except for the F8 which its
strong correlation with RV jitter persists over a wide range of stellar
activity level, and thus our result suggests that F8 might be a powerful proxy
for activity induced RV jitter. Moreover, we examine the capability of two
state-of-the-art modeling techniques, namely the FF' method and SOAP2.0, in
accurately predicting the RV jitter amplitude using the simultaneous
photometric observation. We found that for the very active stars both
techniques can reasonably well predict the amplitude of the RV jitter, however,
at lower activity levels the FF' method underpredicts the RV jitter amplitude.Comment: 13 pages, 7 figures, 2 tables, accepted for publication in A&
SOPHIE velocimetry of Kepler transit candidates XVII. The physical properties of giant exoplanets within 400 days of period
While giant extrasolar planets have been studied for more than two decades
now, there are still some open questions such as their dominant formation and
migration process, as well as their atmospheric evolution in different stellar
environments. In this paper, we study a sample of giant transiting exoplanets
detected by the Kepler telescope with orbital periods up to 400 days. We first
defined a sample of 129 giant-planet candidates that we followed up with the
SOPHIE spectrograph (OHP, France) in a 6-year radial velocity campaign. This
allow us to unveil the nature of these candidates and to measure a
false-positive rate of 54.6 +/- 6.5 % for giant-planet candidates orbiting
within 400 days of period. Based on a sample of confirmed or likely planets, we
then derive the occurrence rates of giant planets in different ranges of
orbital periods. The overall occurrence rate of giant planets within 400 days
is 4.6 +/- 0.6 %. We recover, for the first time in the Kepler data, the
different populations of giant planets reported by radial velocity surveys.
Comparing these rates with other yields, we find that the occurrence rate of
giant planets is lower only for hot jupiters but not for the longer period
planets. We also derive a first measurement on the occurrence rate of brown
dwarfs in the brown-dwarf desert with a value of 0.29 +/- 0.17 %. Finally, we
discuss the physical properties of the giant planets in our sample. We confirm
that giant planets receiving a moderate irradiation are not inflated but we
find that they are in average smaller than predicted by formation and evolution
models. In this regime of low-irradiated giant planets, we find a possible
correlation between their bulk density and the Iron abundance of the host star,
which needs more detections to be confirmed.Comment: To appear in Astronomy and Astrophysic
Asymmetry in the atmosphere of the ultra-hot Jupiter WASP-76 b
Context. WASP-76 b has been a recurrent subject of study since the detection of a signature in high-resolution transit spectroscopy data indicating an asymmetry between the two limbs of the planet. The existence of this asymmetric signature has been confirmed by multiple studies, but its physical origin is still under debate. In addition, it contrasts with the absence of asymmetry reported in the infrared (IR) phase curve.
Aims. We provide a more comprehensive dataset of WASP-76 b with the goal of drawing a complete view of the physical processes at work in this atmosphere. In particular, we attempt to reconcile visible high-resolution transit spectroscopy data and IR broadband phase curves.
Methods. We gathered 3 phase curves, 20 occultations, and 6 transits for WASP-76 b in the visible with the CHEOPS space telescope. We also report the analysis of three unpublished sectors observed by the TESS space telescope (also in the visible), which represents 34 phase curves.
Results. WASP-76 b displays an occultation of 260 ± 11 and 152 ± 10 ppm in TESS and CHEOPS bandpasses respectively. Depending on the composition assumed for the atmosphere and the data reduction used for the IR data, we derived geometric albedo estimates that range from 0.05 ± 0.023 to 0.146 ± 0.013 and from <0.13 to 0.189 ± 0.017 in the CHEOPS and TESS bandpasses, respectively. As expected from the IR phase curves, a low-order model of the phase curves does not yield any detectable asymmetry in the visible either. However, an empirical model allowing for sharper phase curve variations offers a hint of a flux excess before the occultation, with an amplitude of ~40 ppm, an orbital offset of ~ â30°, and a width of ~20Âș. We also constrained the orbital eccentricity of WASP-76 b to a value lower than 0.0067, with a 99.7% confidence level. This result contradicts earlier proposed scenarios aimed at explaining the asymmetry observed in high-resolution transit spectroscopy.
Conclusions. In light of these findings, we hypothesise that WASP-76 b could have night-side clouds that extend predominantly towards its eastern limb. At this limb, the clouds would be associated with spherical droplets or spherically shaped aerosols of an unknown species, which would be responsible for a glory effect in the visible phase curves
The SOPHIE search for northern extrasolar planets. XI. Three new companions and an orbit update: Giant planets in the habitable zone
We report the discovery of three new substellar companions to solar-type
stars, HD191806, HD214823, and HD221585, based on radial velocity measurements
obtained at the Haute-Provence Observatory. Data from the SOPHIE spectrograph
are combined with observations acquired with its predecessor, ELODIE, to detect
and characterise the orbital parameters of three new gaseous giant and brown
dwarf candidates. Additionally, we combine SOPHIE data with velocities obtained
at the Lick Observatory to improve the parameters of an already known giant
planet companion, HD16175 b. Thanks to the use of different instruments, the
data sets of all four targets span more than ten years. Zero-point offsets
between instruments are dealt with using Bayesian priors to incorporate the
information we possess on the SOPHIE/ELODIE offset based on previous studies.
The reported companions have orbital periods between three and five years and
minimum masses between 1.6 Mjup and 19 Mjup. Additionally, we find that the
star HD191806 is experiencing a secular acceleration of over 11 \ms\ per year,
potentially due to an additional stellar or substellar companion. A search for
the astrometric signature of these companions was carried out using Hipparcos
data. No orbit was detected, but a significant upper limit to the companion
mass can be set for HD221585, whose companion must be substellar.
With the exception of HD191806 b, the companions are located within the
habitable zone of their host star. Therefore, satellites orbiting these objects
could be a propitious place for life to develop.Comment: 12 pages + tables, 7 figures. Accepted for publication in Astronomy &
Astrophysic
The correlation between photometric variability and radial velocity jitter, based on TESS and HARPS observations
The current and upcoming high precision photometric surveys such as TESS,
CHEOPS, and PLATO will provide the community with thousands of new exoplanet
candidates. As a consequence, the presence of such a correlation is crucial in
selecting the targets with the lowest RV jitter for efficient RV follow-up of
exoplanetary candidates. Studies of this type are also crucial to design
optimized observational strategies to mitigate RV jitter when searching for
Earth-mass exoplanets. Our goal is to assess the correlation between
high-precision photometric variability measurements and high-precision RV
jitter over different time scales. We analyze 171 G, K, and M stars with
available TESS high precision photometric time-series and HARPS precise RVs. We
derived the stellar parameters for the stars in our sample and measured the RV
jitter and photometric variability. We also estimated chromospheric Ca II H
K activity indicator , , and the stellar
rotational period. Finally, we evaluate how different stellar parameters and a
RV sampling subset can have an impact on the potential correlations. We find a
varying correlation between the photometric variability and RV jitter as
function of time intervals between the TESS photometric observation and HARPS
RV. As the time intervals of the observations considered for the analysis
increases, the correlation value and significance becomes smaller and weaker,
to the point that it becomes negligible. We also find that for stars with a
photometric variability above 6.5 ppt the correlation is significantly
stronger. We show that such a result can be due to the transition between the
spot-dominated and the faculae-dominated regime. We quantified the correlations
and updated the relationship between chromospheric Ca II H K activity
indicator and RV jitter.Comment: Accepted for publication in section 10. Planets and planetary systems
of A&
The SOPHIE search for northern extrasolar planets VIII. A warm Neptune orbiting HD164595
High-precision radial velocity surveys explore the population of low-mass
exoplanets orbiting bright stars. This allows accurately deriving their orbital
parameters such as their occurrence rate and the statistical distribution of
their properties. Based on this, models of planetary formation and evolution
can be constrained. The SOPHIE spectrograph has been continuously improved in
past years, and thanks to an appropriate correction of systematic instrumental
drift, it is now reaching 2 m/s precision in radial velocity measurements on
all timescales. As part of a dedicated radial velocity survey devoted to search
for low-mass planets around a sample of 190 bright solar-type stars in the
northern hemisphere, we report the detection of a warm Neptune with a minimum
mass of 16.1 +- 2.7 Mearth orbiting the solar analog HD164595 in 40 +- 0.24
days . We also revised the parameters of the multiplanetary system around
HD190360. We discuss this new detection in the context of the upcoming space
mission CHEOPS, which is devoted to a transit search of bright stars harboring
known exoplanets.Comment: 11 pages, 9 figure
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