Transiting Planet Candidates Research Articles

TRANSIT TIMING OBSERVATIONS FROMKEPLER. II. CONFIRMATION OF TWO MULTIPLANET SYSTEMS VIA A NON-PARAMETRIC CORRELATION ANALYSIS

We present a new method for confirming transiting planets based on the combination of transit timingn variations (TTVs) and dynamical stability. Correlated TTVs provide evidence that the pair of bodies are in the same physical system. Orbital stability provides upper limits for the masses of the transiting companions that are in the planetary regime. This paper describes a non-parametric technique for quantifying the statistical significance of TTVs based on the correlation of two TTV data sets. We apply this method to an analysis of the transit timing variations of two stars with multiple transiting planet candidates identified by Kepler. We confirm four transiting planets in two multiple planet systems based on their TTVs and the constraints imposed by dynamical stability. An additional three candidates in these same systems are not confirmed as planets, but are likely to be validated as real planets once further observations and analyses are possible. If all were confirmed, these systems would be near 4:6:9 and 2:4:6:9 period commensurabilities. Our results demonstrate that TTVs provide a powerful tool for confirming transiting planets, including low-mass planets and planets around faint stars for which Doppler follow-up is not practical with existing facilities. Continued Kepler observations will dramatically improve the constraints on the planet masses and orbits and provide sensitivity for detecting additional non-transiting planets. If Kepler observations were extended to eight years, then a similar analysis could likely confirm systems with multiple closely spaced, small transiting planets in or near the habitable zone of solar-type stars.

Planetary transit candidates in the CoRoT-SRc01 field

Context. The space mission CoRoT is devoted to the analysis of stellar variability and the photometric detection of extrasolar planets.

Planetary transit candidates in the CoRoT LRa01 field

Context: CoRoT is a pioneering space mission whose primary goals are stellar seismology and extrasolar planets search. Its surveys of large stellar fields generate numerous planetary candidates whose lightcurves have transit-like features. An extensive analytical and observational follow-up effort is undertaken to classify these candidates. Aims: The list of planetary transit candidates from the CoRoT LRa01 star field in the Monoceros constellation towards the Galactic anti-center is presented. The CoRoT observations of LRa01 lasted from 24 October 2007 to 3 March 2008. Methods: 7470 chromatic and 3938 monochromatic lightcurves were acquired and analysed. Instrumental noise and stellar variability were treated with several filtering tools by different teams from the CoRoT community. Different transit search algorithms were applied to the lightcurves. Results: Fifty-one stars were classified as planetary transit candidates in LRa01. Thirty-seven (i.e., 73 % of all candidates) are "good" planetary candidates based on photometric analysis only. Thirty-two (i.e., 87 % of the "good" candidates) have been followed-up. At the time of this writing twenty-two cases have been solved and five planets have been discovered: three transiting hot-Jupiters (CoRoT-5b, CoRoT-12b, and CoRoT-21b), the first terrestrial transiting planet (CoRoT-7b), and another planet in the same system (CoRoT-7c, detected by radial velocity survey only). Evidences of another non-transiting planet in the CoRoT-7 system, namely CoRoT-7d, have been recently found.

Identifying non-resonant Kepler planetary systems

Abstract The Kepler mission has discovered a plethora of multiple transiting planet candidate exosystems, many of which feature putative pairs of planets near mean motion resonance commensurabilities. Identifying potentially resonant systems could help guide future observations and enhance our understanding of planetary formation scenarios. We develop and apply an algebraic method to determine which Kepler two-planet systems cannot be in a first—fourth order resonance, given the current, publicly available data. This method identifies when any potentially resonant angle of a system must circulate. We identify and list 70 near-resonant systems which cannot actually reside in resonance, assuming a widely used formulation for deriving planetary masses from their observed radii and that these systems do not contain unseen bodies that affect the interactions of the observed planets. This work strengthens the argument that a high fraction of exoplanetary systems may be near resonance but not actually in resonance.

Kepler-22b: A 2.4 EARTH-RADIUS PLANET IN THE HABITABLE ZONE OF A SUN-LIKE STAR

A search of the time-series photometry from NASA's Kepler spacecraft reveals a transiting planet candidate orbiting the 11th magnitude G5 dwarf KIC 10593626 with a period of 290 days. The characteristics of the host star are well constrained by high-resolution spectroscopy combined with an asteroseismic analysis of the Kepler photometry, leading to an estimated mass and radius of 0.970 +/- 0.060 MSun and 0.979 +/- 0.020 RSun. The depth of 492 +/- 10ppm for the three observed transits yields a radius of 2.38 +/- 0.13 REarth for the planet. The system passes a battery of tests for false positives, including reconnaissance spectroscopy, high-resolution imaging, and centroid motion. A full BLENDER analysis provides further validation of the planet interpretation by showing that contamination of the target by an eclipsing system would rarely mimic the observed shape of the transits. The final validation of the planet is provided by 16 radial velocities obtained with HIRES on Keck 1 over a one year span. Although the velocities do not lead to a reliable orbit and mass determination, they are able to constrain the mass to a 3{\sigma} upper limit of 124 MEarth, safely in the regime of planetary masses, thus earning the designation Kepler-22b. The radiative equilibrium temperature is 262K for a planet in Kepler-22b's orbit. Although there is no evidence that Kepler-22b is a rocky planet, it is the first confirmed planet with a measured radius to orbit in the Habitable Zone of any star other than the Sun.

ARCHITECTURE AND DYNAMICS OF KEPLER 'S CANDIDATE MULTIPLE TRANSITING PLANET SYSTEMS

About one-third of the ~1200 transiting planet candidates detected in the first four months of \ik data are members of multiple candidate systems. There are 115 target stars with two candidate transiting planets, 45 with three, 8 with four, and one each with five and six. We characterize the dynamical properties of these candidate multi-planet systems. The distribution of observed period ratios shows that the vast majority of candidate pairs are neither in nor near low-order mean motion resonances. Nonetheless, there are small but statistically significant excesses of candidate pairs both in resonance and spaced slightly too far apart to be in resonance, particularly near the 2:1 resonance. We find that virtually all candidate systems are stable, as tested by numerical integrations that assume a nominal mass-radius relationship. Several considerations strongly suggest that the vast majority of these multi-candidate systems are true planetary systems. Using the observed multiplicity frequencies, we find that a single population of planetary systems that matches the higher multiplicities underpredicts the number of singly-transiting systems. We provide constraints on the true multiplicity and mutual inclination distribution of the multi-candidate systems, revealing a population of systems with multiple super-Earth-size and Neptune-size planets with low to moderate mutual inclinations.

Potential biases in the detection of planetary systems with large transit timing variations

Abstract The transit timing variations (TTVs) technique provides a powerful tool to detect additional planets in transiting exoplanetary systems. In this Letter, we show how transiting planets with significant TTVs can be systematically missed, or catalogued as false positives, by current transit search algorithms, unless they are in multitransit systems. If the period of the TTVs, PTTV, is longer than the time baseline of the observations and its amplitude, ATTV, is larger than the timing precision limit of the data, transiting planet candidates are still detected, but with incorrect ephemerides. Therefore, they will be discarded during follow-up. When PTTV is shorter than the time baseline of the observations and ATTV is sufficiently large, constant period search algorithms find an average period for the system, which results in altered transit durations and depths in the folded light curves. Those candidates can get subsequently discarded as eclipsing binaries, grazing eclipses or blends. Also, for large enough ATTV values, the transits can get fully occulted by the photometric dispersion of the light curves. These detection biases could explain the observed statistical differences between the frequency of multiple systems among planets detected via other techniques and those detected via transits. We suggest that new transit search algorithms allowing for non-constant period planets should be implemented.

CoRoT LRa02_E2_0121: Neptune-size planet candidate turns into a hierarchical triple system with a giant primary

This paper presents the case of CoRoT LRa02_E2_0121, which was initially classified as a Neptune-size transiting-planet candidate on a relatively wide orbit of 36.3 days. Follow-up observations were performed with UVES, Sandiford, SOPHIE and HARPS. These observations revealed a faint companion in the spectra. To find the true nature of the system we derived the radial velocities of the faint companion using TODMOR - a two-dimensional correlation technique, applied to the SOPHIE spectra. Modeling the lightcurve with EBAS we discovered a secondary eclipse with a depth of ~0.07%, indicating a diluted eclipsing binary. Combined MCMC modeling of the lightcurve and the radial velocities suggested that CoRoT LRa02_E2_0121 is a hierarchical triple system with an evolved G-type primary and an A-type:F-type grazing eclipsing binary. Such triple systems are difficult to discover.

TRANSIT TIMING OBSERVATIONS FROM KEPLER . I. STATISTICAL ANALYSIS OF THE FIRST FOUR MONTHS

The architectures of multiple planet systems can provide valuable constraints on models of planet formation, including orbital migration, and excitation of orbital eccentricities and inclinations. NASA's Kepler mission has identified 1235 transiting planet candidates (Borcuki et al 2011). The method of transit timing variations (TTVs) has already confirmed 7 planets in two planetary systems (Holman et al. 2010; Lissauer et al. 2011a). We perform a transit timing analysis of the Kepler planet candidates. We find that at least ~12% of planet candidates currently suitable for TTV analysis show evidence suggestive of TTVs, representing at least ~65 TTV candidates. In all cases, the time span of observations must increase for TTVs to provide strong constraints on planet masses and/or orbits, as expected based on n-body integrations of multiple transiting planet candidate systems (assuming circular and coplanar orbits). We find that the fraction of planet candidates showing TTVs in this data set does not vary significantly with the number of transiting planet candidates per star, suggesting significant mutual inclinations and that many stars with a single transiting planet should host additional non-transiting planets. We anticipate that Kepler could confirm (or reject) at least ~12 systems with multiple transiting planet candidates via TTVs. Thus, TTVs will provide a powerful tool for confirming transiting planets and characterizing the orbital dynamics of low-mass planets. If Kepler observations were extended to at least six years, then TTVs would provide much more precise constraints on the dynamics of systems with multiple transiting planets and would become sensitive to planets with orbital periods extending into the habitable zone of solar-type stars.

LOW-MASS ECLIPSING BINARIES IN THE INITIALKEPLERDATA RELEASE

We identify 231 objects in the newly released Cycle 0 dataset from the Kepler Mission as double-eclipse, detached eclipsing binary systems with Teff < 5500 K and orbital periods shorter than ~32 days. We model each light curve using the JKTEBOP code with a genetic algorithm to obtain precise values for each system. We identify 95 new systems with both components below 1.0 M_sun and eclipses of at least 0.1 magnitudes, suitable for ground-based follow-up. Of these, 14 have periods less than 1.0 day, 52 have periods between 1.0 and 10.0 days, and 29 have periods greater than 10.0 days. This new sample of main-sequence, low-mass, double-eclipse, detached eclipsing binary candidates more than doubles the number of previously known systems, and extends the sample into the completely heretofore unexplored P > 10.0 day period regime. We find preliminary evidence from these systems that the radii of low-mass stars in binary systems decrease with period. This supports the theory that binary spin-up is the primary cause of inflated radii in low-mass binary systems, although a full analysis of each system with radial-velocity and multi-color light curves is needed to fully explore this hypothesis. As well, we present 7 new transiting planet candidates that do not appear among the recently released list of 706 candidates by the Kepler team, nor in the Kepler False Positive Catalog, along with several other new and interesting systems. We also present novel techniques for the identification, period analysis, and modeling of eclipsing binaries.

Characterisation of extrasolar planetary transit candidates

We present a second paper of a complete characterization of stars whose low-depth transits were discovered by the OGLE-III campaign to select the most promising candidates for spectroscopic confirmation. This paper follows a similar analysis to one previously performed in Gallardo et al. (2005, A&A, 431, 707). We present new optical and near-IR photometry and derive physical parameters such as effective temperature (T eff ), distance (d ), the stellar radii (R *), and the companion radii (R c ). We selected eight M (2800 K ≤ T eff ≤ 3850 K) or K (3850 K ≤ T eff ≤ 5150 K) stellar objects as potential candidates to host exoplanets, even though, considering the radii of their companions, only the stars OGLE-TR-61, OGLE-TR-74, OGLE-TR-123, and OGLE-TR-173 are the most promising M-type transit candidates to host planets. A confirmation of the planetary nature of any of these objects would be extremely valuable in providing a means of characterizing planets transiting M-type dwarfs with effective temperatures down to only 2900 K.

New planetary transit candidates in Carina

We have searched for planetary transits in Carina where the Optical Gravitational Lensing Experiment (OGLE) found many transits. The data that we analyzed were taken with the ESO VLT/VIMOS instrument for 4 continuous nights in 2005. We have detected several new transiting events. We recommend some of them for spectroscopic follow-up. For seven OGLE transits we present light curves. Our search also led us to discover hundreds of new variable stars.

DISCOVERY OF A TRANSITING PLANET AND EIGHT ECLIPSING BINARIES IN HATNet FIELD G205

We report the discovery of HAT-P-8b, a transiting planet with mass Mp = 1.52+0.18−0.16 MJ, radius Rp = 1.50+0.08−0.06 RJ, and photometric period P = 3.076 days. HAT-P-8b has a somewhat inflated radius for its mass, and a somewhat large mass for its period. The host star is a solar-metallicity F dwarf, with mass M⋆ = 1.28 ± 0.04 M☉ and R⋆ = 1.58+0.08−0.06 R☉. HAT-P-8b was initially identified as one of the 32 transiting-planet candidates in HATNet field G205. We describe the procedures that we have used to follow up these candidates with spectroscopic and photometric observations, and we present a status report on our interpretation for 28 of the candidates. Eight are eclipsing binaries with orbital solutions whose periods are consistent with their photometric ephemerides; two of these spectroscopic orbits are single-lined and six are double-lined.

Planetary transit candidates in Corot-IRa01 field

Context: CoRoT is a pioneering space mission devoted to the analysis of stellar variability and the photometric detection of extrasolar planets. Aims: We present the list of planetary transit candidates detected in the first field observed by CoRoT, IRa01, the initial run toward the Galactic anticenter, which lasted for 60 days. Methods: We analysed 3898 sources in the coloured bands and 5974 in the monochromatic band. Instrumental noise and stellar variability were taken into account using detrending tools before applying various transit search algorithms. Results: Fifty sources were classified as planetary transit candidates and the most reliable 40 detections were declared targets for follow-up ground-based observations. Two of these targets have so far been confirmed as planets, COROT-1b and COROT-4b, for which a complete characterization and specific studies were performed.

Planetary transit candidates in CoRoT-LRc01 field

Planetary transit candidates in CoRoT-LRc01 field

Planetary transit candidates in the CoRoT initial run: resolving their nature

With the release of CoRoT lightcurves of the Initial Run IRa01, 50 transiting planetary candidates have been published in a companion paper. About twenty of them were identified as binary stars from the CoRoT lightcurve itself. Complementary observations were conducted for 29 candidates, including ground-based photometry and radial-velocity measurements. Two giant planets were identified and fully characterized. Nineteen binaries are recognized, from which 10 are background eclipsing binaries in the CoRoT mask or triple systems, diluted by the main CoRoT target. Eight cases remain of unclear origin, one of them still being a planetary candidate. Comparison with simulations shows that the actual threshold of confirmed planet detection in this field does not yet fulfill the expectations, and a number of reasons are invoked, like the ranking process based on lightcurve analyses, and the strategy and limits of follow-up observations for targets fainter than magnitude 15.

OGLE2-TR-L9b: an exoplanet transiting a rapidly rotating F3 star

Context. Photometric observations for the OGLE-II microlens monitoring campaign have been taken in the period 1997−2000. All light curves of this campaign have recently been made public. Our analysis of these data has revealed 13 low-amplitude transiting objects among∼15700 stars in three Carina fields towards the galactic disk. One of these objects, OGLE2-TR-L9 (P∼2.5 days), turned out to be an excellent transiting planet candidate. Aims. In this paper we report on our investigation of the true natur e of OGLE2-TR-L9, by re-observing the photometric transit with the aim to determine the transit parameters at high precision, and by spectroscopic observations, to estimate the properties o f the host star, and to determine the mass of the transiting object through radial velocity measurements.

Stellar Proper Motions in the Galactic Bulge from DeepHubble Space TelescopeACS WFC Photometry

We present stellar proper motions in the Galactic bulge from the Sagittarius Window Eclipsing Extrasolar Search (SWEEPS) project using ACS WFC on HST. Proper motions are extracted for more than 180,000 objects, with >81,000 measured to accuracy better than 0.3 mas yr−1 in both coordinates. We report several results based on these measurements: (1) Kinematic separation of bulge from disk allows a sample of >15,000 bulge objects to be extracted based on ≥6 σ detections of proper motion, with <0.2% contamination from the disk. This includes the first detection of a candidate bulge blue straggler population. (2) Armed with a photometric distance modulus on a star-by-star basis, and using the large number of stars with high-quality proper-motion measurements to overcome intrinsic scatter, we dissect the kinematic properties of the bulge as a function of distance along the line of sight. This allows us to extract the stellar circular speed curve from proper motions alone, which we compare with the circular speed curve obtained from radial velocities. (3) We trace the variation of the {l, b} velocity ellipse as a function of depth. (4) Finally, we use the density-weighted {l, b} proper-motion ellipse produced from the tracer stars to assess the kinematic membership of the 16 transiting planet candidates discovered in the Sagittarius Window; the kinematic distribution of the planet candidates is consistent with that of the disk and bulge stellar populations.

Characterization of terrestrial planets identified by the Kepler mission

I outline some of the plans for following up transiting-planet candidates identified by NASA's Kepler mission. An initial spectroscopic reconnaissance will be used to sort out most of the candidates that involve eclipsing binaries instead of transiting planets. Very precise radial velocities will then be obtained for the survivors, with the goal of deriving spectroscopic orbits and planetary masses. When combined with the planetary radii derived from the transit light curves, this will provide critical information for the characterization of the planets discovered with Kepler.

Precision radial velocities of double-lined binary stars and the spectroscopic follow-up of circumbinary transiting planet candidates

AbstractWe present a new iodine cell based approach that allows one to obtain radial velocities of the components of double-lined spectroscopic binary stars (SB2s) with a precision reaching 5 m/s. Such an RV precision is up to 100 times better than what is currently available in the literature for the SB2s. We discuss the applications of our method to the radial velocity searches for circumbinary planets and spectroscopic follow-up of transiting planet candidates around eclipsing binary stars.