I derive the physical properties of 30 transiting extrasolar planetary systems using a homogeneous analysis of published data. The light curves are modelled with the jktebop code, with special ...attention paid to the treatment of limb darkening, orbital eccentricity and error analysis. The light from some systems is contaminated by faint nearby stars, which if ignored will systematically bias the results. I show that it is not realistically possible to account for this using only transit light curves: light-curve solutions must be constrained by measurements of the amount of contaminating light. A contamination of 5 per cent is enough to make the measurement of a planetary radius 2 per cent too low. The physical properties of the 30 transiting systems are obtained by interpolating in tabulated predictions from theoretical stellar models to find the best match to the light-curve parameters and the measured stellar velocity amplitude, temperature and metal abundance. Statistical errors are propagated by a perturbation analysis which constructs complete error budgets for each output parameter. These error budgets are used to compile a list of systems which would benefit from additional photometric or spectroscopic measurements. The systematic errors arising from the inclusion of stellar models are assessed by using five independent sets of theoretical predictions for low-mass stars. This model dependence sets a lower limit on the accuracy of measurements of the physical properties of the systems, ranging from 1 per cent for the stellar mass to 0.6 per cent for the mass of the planet and 0.3 per cent for other quantities. The stellar density and the planetary surface gravity and equilibrium temperature are not affected by this model dependence. An external test on these systematic errors is performed by comparing the two discovery papers of the WASP-11/HAT-P-10 system: these two studies differ in their assessment of the ratio of the radii of the components and the effective temperature of the star. I find that the correlations of planetary surface gravity and mass with orbital period have significance levels of only 3.1σ and 2.3σ, respectively. The significance of the latter has not increased with the addition of new data since Paper II. The division of planets into two classes based on Safronov number is increasingly blurred. Most of the objects studied here would benefit from improved photometric and spectroscopic observations, as well as improvements in our understanding of low-mass stars and their effective temperature scale.
Binary stars are crucial laboratories for stellar physics, so have been photometric targets for space missions beginning with the very first orbiting telescope (OAO-2) launched in 1968. This review ...traces the binary stars observed and the scientific results obtained from the early days of ultraviolet missions (OAO-2, Voyager, ANS, IUE), through a period of diversification (Hipparcos, WIRE, MOST, BRITE), to the current era of large planetary transit surveys (CoRoT, Kepler, TESS). In this time observations have been obtained of detached, semi-detached and contact binaries containing dwarfs, sub-giants, giants, supergiants, white dwarfs, planets, neutron stars and accretion discs. Recent missions have found a huge variety of objects such as pulsating stars in eclipsing binaries, multi-eclipsers, heartbeat stars and binaries hosting transiting planets. Particular attention is paid to eclipsing binaries, because they are staggeringly useful, and to the NASA Transiting Exoplanet Survey Satellite (TESS) because its huge sky coverage enables a wide range of scientific investigations with unprecedented ease. These results are placed into context, future missions are discussed, and a list of important science goals is presented.
I calculate the physical properties of 32 transiting extrasolar planet and brown-dwarf systems from existing photometric observations and measured spectroscopic parameters. The systems studied ...include 15 observed by the CoRoT satellite, 10 by Kepler and five by the Deep Impact spacecraft. Inclusion of the objects studied in previous papers leads to a sample of 58 transiting systems with homogeneously measured properties. The Kepler data include observations from Quarter 2, and my analyses of several of the systems are the first to be based on short-cadence data from this satellite.
The light curves are modelled using the jktebop code, with attention paid to the treatment of limb darkening, contaminating light, orbital eccentricity, correlated noise and numerical integration over long exposure times. The physical properties are derived from the light-curve parameters, spectroscopic characteristics of the host star and constraints from five sets of theoretical stellar model predictions. An alternative approach using a calibration from eclipsing binary star systems is explored and found to give comparable results whilst imposing a much smaller computational burden.
My results are in good agreement with published properties for most of the transiting systems, but discrepancies are identified for CoRoT-5, CoRoT-8, CoRoT-13, Kepler-5 and Kepler-7. Many of the error bars quoted in the literature are underestimated. Refined orbital ephemerides are given for CoRoT-8 and for the Kepler planets. Asteroseismic constraints on the density of the host stars are in good agreement with the photometric equivalents for HD 17156 and TrES-2, but not for HAT-P-7 and HAT-P-11.
Complete error budgets are generated for each transiting system, allowing identification of the observations best-suited to improve measurements of their physical properties. Whilst most systems would benefit from further photometry and spectroscopy, HD 17156, HD 80606, HAT-P-7 and TrES-2 are now extremely well characterized. HAT-P-11 is an exceptional candidate for studying starspots. The orbital ephemerides of some transiting systems are becoming uncertain and they should be re-observed in the near future.
The primary results from the current work and from previous papers in the series have been placed in an online catalogue, from where they can be obtained in a range of formats for reference and further study. TEPCat is available at http://www.astro.keele.ac.uk/~jkt/tepcat/
Detecting the atmospheres of low-mass, low-temperature exoplanets is a high-priority goal on the path to ultimately detecting biosignatures in the atmospheres of habitable exoplanets. High-precision ...HST observations of several super-Earths with equilibrium temperatures below 1000 K have to date all resulted in featureless transmission spectra, which have been suggested to be due to high-altitude clouds. We report the detection of an atmospheric feature in the atmosphere of a 1.6 transiting exoplanet, GJ 1132 b, with an equilibrium temperature of ∼600 K and orbiting a nearby M dwarf. We present observations of nine transits of the planet obtained simultaneously in the griz and JHK passbands. We find an average radius of 1.43 0.16 for the planet, averaged over all the passbands, and a radius of 0.255 0.023 for the star, both of which are significantly greater than previously found. The planet radius can be decomposed into a "surface radius" at ∼1.375 overlaid by atmospheric features that increase the observed radius in the z and K bands. The z-band radius is 4 higher than the continuum, suggesting a strong detection of an atmosphere. We deploy a suite of tests to verify the reliability of the transmission spectrum, which are greatly helped by the existence of repeat observations. The large z-band transit depth indicates strong opacity from H2O and/or CH4 or a hitherto-unconsidered opacity. A surface radius of 1.375 0.16 allows for a wide range of interior compositions ranging from a nearly Earth-like rocky interior, with ∼70% silicate and ∼30% Fe, to a substantially H2O-rich water world.
ABSTRACT
I measure the physical properties of 38 transiting extrasolar planetary systems, bringing the total number studied within the Homogeneous Studies project to 82. Transit light curves are ...modelled using the jktebop code, with careful attention paid to limb darkening, orbital eccentricity and contaminating light. The physical properties of each system are obtained from the photometric parameters, published spectroscopic measurements and five sets of theoretical stellar model predictions. Statistical errors are assessed using Monte Carlo and residual permutation algorithms and propagated via a perturbation algorithm. Systematic errors are estimated from the interagreement between results calculated using five theoretical stellar models.
The headline result is a major upward revision of the radius of the planet in the OGLE‐TR‐56 system, from 1.23–1.38 to 1.734 ± 0.051 ± 0.029 RJup (statistical and systematic errors, respectively). Its density is three times lower than previously thought. This change comes from the first complete analysis of published high‐quality photometry. Significantly larger planetary radii are also found for Kepler‐15, KOI‐428, WASP‐13, WASP‐14 and WASP‐21 compared to previous work.
I present the first results based on Kepler short‐cadence data for Kepler‐14, Kepler‐15 and KOI‐135. More extensive long‐cadence data from the Kepler satellite are used to improve the measured properties of KOI‐196, KOI‐204, KOI‐254, KOI‐423 and KOI‐428. The stellar component in the KOI‐428 system is the largest known to host a transiting planet, at 2.48 ± 0.17 ± 0.20 R⊙. Detailed analyses are given for HAT‐P‐3, HAT‐P‐6, HAT‐P‐9, HAT‐P‐14 and WASP‐12, based on more extensive data sets than considered in previous studies.
Detailed analyses are also presented for the CoRoT systems 17, 18, 19, 20 and 23; Kepler‐7, ‐12 and ‐17; KOI‐254; OGLE‐TR‐111, ‐113, ‐132 and L9 and TrES‐4.
I revisit the correlations between orbital period and surface gravity, and orbital period and mass of the transiting planets, finding both to be significant at the 4σ level. I conclude by discussing the opportunities for follow‐up observations, the sky positions and the discovery rate of the known transiting planets.
I present a homogeneous analysis of the transit light curves of 14 well-observed transiting extrasolar planets. The light curves are modelled using jktebop, random errors are measured using Monte ...Carlo simulations and the effects of correlated noise are included using a residual-permutation algorithm. The importance of stellar limb darkening on the light-curve solutions and parameter uncertainties is investigated using five different limb darkening laws and including different numbers of coefficients as fitted parameters. The linear limb darkening law cannot adequately fit the Hubble Space Telescope (HST) photometry of HD 209458, but the other four laws give very similar results to each other for all transit light curves. In most cases fixing the limb darkening coefficients at theoretically predicted values does not bias the results, but does cause the error estimates to be too small. The available theoretical limb darkening coefficients clearly disagree with empirical values measured from the HST light curves of HD 209458; limb darkening must be included as fitted parameters when analysing high-quality light curves. In most cases the results of my analysis agree with the values found by other authors, but the uncertainties I find can be significantly larger (by factors of up to 3). Despite these greater uncertainty estimates, the analyses of sets of independent light curves for both HD 189733 and HD 209458 lead to results which do not agree with each other. This discrepancy is worst for the ratio of the radii (6.7σ for HD 189733 and 3.7σ for HD 209458), which depends primarily on the depth of the transit. It is therefore not due to the analysis method but is present in the light curves. These underlying systematic errors cannot be detected from the reduced data alone unless at least three independent light curves are available for an individual planetary system. The surface gravities of transiting extrasolar planets are known to be correlated with their orbital periods. New surface gravity values, calculated from the light-curve results and the stellar spectroscopic orbits, show that this correlation is still present. New high-precision light curves are needed for HD 149026, OGLE-TR-10, OGLE-TR-56, OGLE-TR-132 and GJ 436, and new radial velocity curves for the XO-1, WASP-1, WASP-2 and the OGLE (Optical Gravitational Lensing Experiment) planetary systems.
Abstract
Even though tens of directly imaged companions have been discovered in the past decades, the number of directly confirmed multiplanet systems is still small. Dynamical analysis of these ...systems imposes important constraints on formation mechanisms of these wide-orbit companions. As part of the Young Suns Exoplanet Survey we report the detection of a second planetary-mass companion around the 17 Myr-old, solar-type star TYC 8998-760-1 that is located in the Lower Centaurus Crux subgroup of the Scorpius–Centaurus association. The companion has a projected physical separation of 320 au and several individual photometric measurements from 1.1 to 3.8 microns constrain a companion mass of 6 ± 1
M
Jup
, which is equivalent to a mass ratio of
q
= 0.57 ± 0.10% with respect to the primary. With the previously detected 14 ± 3
M
Jup
companion that is orbiting the primary at 160 au, TYC 8998-760-1 is the first directly imaged multiplanet system that is detected around a young, solar analog. We show that circular orbits are stable, but that mildly eccentric orbits for either/both components (
e
> 0.1) are chaotic on gigayear timescales, implying in situ formation or a very specific ejection by an unseen third companion. Due to the wide separations of the companions TYC 8998-760-1 is an excellent system for spectroscopic and photometric follow-up with space-based observatories such as the James Webb Space Telescope.
We show that the surface gravity of a transiting extrasolar planet can be calculated from only the spectroscopic orbit of its parent star and the analysis of its transit light curve. This does not ...require additional constraints, such as are often inferred from theoretical stellar models or model atmospheres. The surface gravity of the planet can therefore be measured precisely and from only directly observable quantities. We outline the method and apply it to the case of the first known transiting extrasolar planet, HD 209458b. We find a surface gravity of gp= 9.28 ± 0.15 m s−2, which is an order of magnitude more precise than the best available measurements of its mass, radius and density. This confirms that the planet has a much lower surface gravity than that predicted by published theoretical models of gas giant planets. We apply our method to all 14 known transiting extrasolar planets and find a significant correlation between surface gravity and orbital period, which is related to the known correlation between mass and period. This correlation may be the underlying effect as surface gravity is a fundamental parameter in the evaporation of planetary atmospheres.
The CoRoT and Kepler satellites were the first space platforms designed to perform high-precision photometry for a large number of stars. Multiple systems display a wide variety of photometric ...variability, making them natural benefactors of these missions. I review the work arising from CoRoT and Kepler observations of multiple systems, with particular emphasis on eclipsing binaries containing giant stars, pulsators, triple eclipses and/or low-mass stars. Many more results remain untapped in the data archives of these missions, and the future holds the promise of K2, TESS and PLATO.
ABSTRACT The Kepler mission has provided unprecedented, nearly continuous photometric data of ∼200,000 objects in the ∼105 deg2 field of view (FOV) from the beginning of science operations in May of ...2009 until the loss of the second reaction wheel in May of 2013. The Kepler Eclipsing Binary Catalog contains information including but not limited to ephemerides, stellar parameters, and analytical approximation fits for every known eclipsing binary system in the Kepler FOV. Using target pixel level data collected from Kepler in conjunction with the Kepler Eclipsing Binary Catalog, we identify false positives among eclipsing binaries, i.e., targets that are not eclipsing binaries themselves, but are instead contaminated by eclipsing binary sources nearby on the sky and show eclipsing binary signatures in their light curves. We present methods for identifying these false positives and for extracting new light curves for the true source of the observed binary signal. For each source, we extract three separate light curves for each quarter of available data by optimizing the signal-to-noise ratio, the relative percent eclipse depth, and the flux eclipse depth. We present 289 new eclipsing binaries in the Kepler FOV that were not targets for observation, and these have been added to the catalog. An online version of this catalog with downloadable content and visualization tools is maintained at http://keplerEBs.villanova.edu.
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