Modeling the interior of exoplanets is essential to go further than the conclusions provided by mean density measurements. In addition to the still limited precision on the planets' fundamental ...parameters, models are limited by the existence of degeneracies on their compositions. Here, we present a model of internal structure dedicated to the study of solid planets up to ∼10 Earth masses, i.e., super-Earths. When the measurement is available, the assumption that the bulk Fe/Si ratio of a planet is similar to that of its host star allows us to significantly reduce the existing degeneracy and more precisely constrain the planet's composition. Based on our model, we provide an update of the mass-radius relationships used to provide a first estimate of a planet's composition from density measurements. Our model is also applied to the cases of two well-known exoplanets, CoRoT-7b and Kepler-10b, using their recently updated parameters. The core mass fractions of CoRoT-7b and Kepler-10b are found to lie within the 10%-37% and 10%-33% ranges, respectively, allowing both planets to be compatible with an Earth-like composition. We also extend the recent study of Proxima Centauri b and show that its radius may reach 1.94 in the case of a 5 planet, as there is a 96.7% probability that the real mass of Proxima Centauri b is below this value.
Context. With only two functional reaction wheels, Kepler cannot maintain stable pointing at its original target field and has entered a new mode of observation called K2. Aims. We describe a new ...pipeline to reduce K2 pixel files into light curves that are later searched for transit like features. Methods. Our method is based on many years of experience in planet hunting for the CoRoT mission. Owing to the unstable pointing, K2 light curves present systematics that are correlated with the target position in the charge coupled device (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. Results. 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.
A large fraction of the smallest transiting planet candidates discovered by the Kepler and CoRoT space missions cannot be confirmed by a dynamical measurement of the mass using currently available ...observing facilities. To establish their planetary nature, the concept of planet validation has been advanced. This technique compares the probability of the planetary hypothesis against that of all reasonably conceivable alternative false positive (FP) hypotheses. The candidate is considered as validated if the posterior probability of the planetary hypothesis is sufficiently larger than the sum of the probabilities of all FP scenarios. In this paper, we present pastis, the Planet Analysis and Small Transit Investigation Software, a tool designed to perform a rigorous model comparison of the hypotheses involved in the problem of planet validation, and to fully exploit the information available in the candidate light curves. pastis self-consistently models the transit light curves and follow-up observations. Its object-oriented structure offers a large flexibility for defining the scenarios to be compared. The performance is explored using artificial transit light curves of planets and FPs with a realistic error distribution obtained from a Kepler light curve. We find that data support the correct hypothesis strongly only when the signal is high enough (transit signal-to-noise ratio above 50 for the planet case) and remain inconclusive otherwise. PLAnetary Transits and Oscillations of stars (PLATO) shall provide transits with high enough signal-to-noise ratio, but to establish the true nature of the vast majority of Kepler and CoRoT transit candidates additional data or strong reliance on hypotheses priors is needed.
Since the discovery of the transiting super-Earth CoRoT-7b, several investigations have yielded different results for the number and masses of planets present in the system, mainly owing to the ...star's high level of activity. We re-observed CoRoT-7 in 2012 January with both HARPS and CoRoT, so that we now have the benefit of simultaneous radial-velocity and photometric data. This allows us to use the off-transit variations in the star's light curve to estimate the radial-velocity variations induced by the suppression of convective blueshift and the flux blocked by starspots. To account for activity-related effects in the radial velocities which do not have a photometric signature, we also include an additional activity term in the radial-velocity model, which we treat as a Gaussian process with the same covariance properties (and hence the same frequency structure) as the light curve. Our model was incorporated into a Monte Carlo Markov Chain in order to make a precise determination of the orbits of CoRoT-7b and CoRoT-7c. We measure the masses of planets b and c to be 4.73 ± 0.95 and 13.56 ± 1.08 M⊕, respectively. The density of CoRoT-7b is (6.61 ± 1.72)(R
p
/1.58 R⊕)−3 g cm−3, which is compatible with a rocky composition. We search for evidence of an additional planet d, identified by previous authors with a period close to 9 d. We are not able to confirm the existence of a planet with this orbital period, which is close to the second harmonic of the stellar rotation at ∼7.9 d. Using Bayesian model selection, we find that a model with two planets plus activity-induced variations is most favoured.
ABSTRACT
The knowledge of the ages of stars hosting exoplanets allows us to obtain an overview on the evolution of exoplanets and understand the mechanisms affecting their life. The measurement of ...the ages of stars in the Galaxy is usually affected by large uncertainties. An exception are the stellar clusters: For their coeval members, born from the same molecular cloud, ages can be measured with extreme accuracy. In this context, the project PATHOS is providing candidate exoplanets orbiting members of stellar clusters and associations through the analysis of high-precision light curves obtained with cutting-edge tools. In this work, we exploited the data collected during the second year of the Transiting Exoplanet Survey Satellite mission. We extracted, analysed, and modelled the light curves of $\sim 90\, 000$ stars in open clusters located in the Northern ecliptic hemisphere in order to find candidate exoplanets. We measured the frequencies of candidate exoplanets in open clusters for different orbital periods and planetary radii, taking into account the detection efficiency of our pipeline and the false positive probabilities of our candidates. We analysed the age–RP distribution of candidate and confirmed exoplanets with periods <100 d and well constrained ages. While no peculiar trends are observed for Jupiter-size and (super-)Earth-size planets, we found that objects with $4 \lesssim R_{\rm P} \lesssim 13R_{\rm Earth}$ are concentrated at ages ≲200 Myr; different scenarios (atmospheric losses, migration, etc.) are considered to explain the observed age–RP distribution.
Context.
Super-Earths present compositions dominated by refractory materials. However, there is a degeneracy in their interior structure between a planet that has no atmosphere and a small Fe ...content, and a planet that has a thin atmosphere and a higher core mass fraction. To break this degeneracy, atmospheric characterisation observations are required.
Aims.
We present a self-consistent interior–atmosphere model to constrain the volatile mass fraction, surface pressure, and temperature of rocky planets with water and CO
2
atmospheres. The parameters obtained in our analysis can be used to predict observations in emission spectroscopy and photometry with JWST, which can determine the presence of an atmosphere and, if present, its composition.
Methods.
We coupled a 1D interior model with a supercritical water layer to an atmospheric model. In order to obtain the bolometric emission and Bond albedo for an atmosphere in radiative-convective equilibrium, we used a low-resolution
k
-correlated atmospheric model. We generated emission spectra with the same atmospheric model at a higher resolution (
R
= 200–300). An adaptive Markov chain Monte Carlo was employed for an efficient sampling of the parameter space at low volatile mass fractions.
Results.
From our interior structure retrieval, we conclude that TRAPPIST-1 c most likely has a bare surface, although the presence of an atmosphere cannot be ruled out. We estimate a 1
σ
confidence interval of the surface pressure for a water-dominated atmosphere of
P
surf
= 40 ± 40 bar. We generated spectra for these two scenarios to compare with the emission flux of TRAPPIST-1 c recently observed in the MIRI F1500W filter. This is compatible with bare rock surfaces or a thin atmosphere with little or no CO
2
. In the case of 55 Cancri e, a combined spectrum with NIRCam and MIRI LRS may present high uncertainties at wavelengths between 3 and 3.7 µm. However, this does not affect the identification of H
2
O because it does not present spectral features in this wavelength range.
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 a 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 anticorrelated with the radial velocity one, as in the case of stellar spots. In those cases, the full width at 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 HD 16702, an unresolved face-on binary which exhibits bisector variations.
Using spectropolarimetry, we investigate the large-scale magnetic topologies of stars hosting close-in exoplanets. A small survey of 10 stars has been done with the twin instruments Télescope Bernard ...Lyot /NARVAL and Canada-France-Hawaii Telescope/ESPaDOnS between 2006 and 2011. Each target consists of circular polarization observations covering 7-22 d. For each of the seven targets in which a magnetic field was detected, we reconstructed the magnetic field topology using Zeeman-Doppler imaging. Otherwise, a detection limit has been estimated. Three new epochs of observations of τ Boo are presented, which confirm magnetic polarity reversal. We estimate that the cycle period is 2 yr, but recall that a shorter period of 240 d cannot still be ruled out. The result of our survey is compared to the global picture of stellar magnetic field properties in the mass-rotation diagram. The comparison shows that these giant planet-host stars tend to have similar magnetic field topologies to stars without detected hot Jupiters. This needs to be confirmed with a larger sample of stars.
ABSTRACT
The scope of the project ‘A PSF-based Approach to TESS High Quality data Of Stellar clusters’ (PATHOS) is the extraction and analysis of high-precision light curves of stars in stellar ...clusters and young associations for the identification of candidate exoplanets and variable stars. The cutting-edge tools used in this project allow us to measure the real flux of stars in dense fields, minimizing the effects due to contamination by neighbour sources. We extracted about 200 000 light curves of stars in 645 open clusters located in the Southern ecliptic hemisphere and observed by TESS during the first year of its mission. We searched for transiting signals and we found 33 objects of interest, 11 of which are strong candidate exoplanets. Because of the limited SNR, we did not find any Earth or super-Earth. We identified two Neptune-size planets orbiting stars with $R_{\star }\lt 1.5\, \mathrm{\it R}_{\odot }$, implying a frequency $f_{\star }=1.34 \pm 0.95\, {{\ \rm per\ cent}}$, consistent with the frequency around field stars. The seven Jupiter candidates around stars with $R_{\star }\lt \, 1.5\, \mathrm{\it R}_{\odot }$ imply a frequency $f_{\star }=0.19\pm 0.07\, {{\ \rm per\ cent}}$, which is smaller than in the field. A more complete estimate of the survey completeness and false positive rate is needed to confirm these results. Light curves used in this work will be made available to the astronomical community on the Mikulski Archive for Space Telescope under the project PATHOS.
Context.
LHS 1140 is an M dwarf known to host two transiting planets at orbital periods of 3.77 and 24.7 days. They were detected with HARPS and
Spitzer
. The external planet (LHS 1140 b) is a rocky ...super-Earth that is located in the middle of the habitable zone of this low-mass star. All these properties place this system at the forefront of the habitable exoplanet exploration, and it therefore constitutes a relevant case for further astrobiological studies, including atmospheric observations.
Aims.
We further characterize this system by improving the physical and orbital properties of the known planets, search for additional planetary-mass components in the system, and explore the possibility of co-orbitals.
Methods.
We collected 113 new high-precision radial velocity observations with ESPRESSO over a 1.5-yr time span with an average photon-noise precision of 1.07 m s
−1
. We performed an extensive analysis of the HARPS and ESPRESSO datasets and also analyzed them together with the new TESS photometry. We analyzed the Bayesian evidence of several models with different numbers of planets and orbital configurations.
Results.
We significantly improve our knowledge of the properties of the known planets LHS 1140 b (
P
b
~ 24.7 days) and LHS 1140 c (
P
c
~ 3.77 days). We determine new masses with a precision of 6% for LHS 1140 b (6.48 ± 0.46
M
⊕
) and 9% for LHS 1140 c (
m
c
= 1.78 ± 0.17
M
⊕
). This reduces the uncertainties relative to previously published values by half. Although both planets have Earth-like bulk compositions, the internal structure analysis suggests that LHS 1140 b might be iron-enriched and LHS 1140 c might be a true Earth twin. In both cases, the water content is compatible to a maximum fraction of 10–12% in mass, which is equivalent to a deep ocean layer of 779 ± 650 km for the habitable-zone planet LHS 1140 b. Our results also provide evidence for a new planet candidate in the system (
m
d
= 4.8 ± 1.1
M
⊕
) on a 78.9-day orbital period, which is detected through three independent methods. The analysis also allows us to discard other planets above 0.5
M
⊕
for periods shorter than 10 days and above 2
M
⊕
for periods up to one year. Finally, our co-orbital analysis discards co-orbital planets in the tadpole and horseshoe configurations of LHS 1140 b down to 1
M
⊕
with a 95% confidence level (twice better than with the previous HARPS dataset). Indications for a possible co-orbital signal in LHS 1140 c are detected in both radial velocity (alternatively explained by a high eccentricity) and photometric data (alternatively explained by systematics), however.
Conclusions.
The new precise measurements of the planet properties of the two transiting planets in LHS 1140 as well as the detection of the planet candidate LHS 1140 d make this system a key target for atmospheric studies of rocky worlds at different stellar irradiations.
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