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Detection of Potential Transit Signals in the First Three Quarters of Kepler Mission Data
We present the results of a search for potential transit signals in thefirst three quarters of photometry data acquired by the Kepler mission.The targets of the search include 151,722 stars which were observed overthe full interval and an additional 19,132 stars which were observed foronly one or two quarters. From this set of targets we find a total of5392 detections which meet the Kepler detection criteria: those criteriaare periodicity of signal, an acceptable signal-to-noise ratio, and acomposition test which rejects spurious detections which containnon-physical combinations of events. The detected signals are dominatedby events with relatively low signal-to-noise ratio and by events withrelatively short periods. The distribution of estimated transit depthsappears to peak in the range between 40 and 100 parts per million, witha few detections down to fewer than 10 parts per million. The detectionsexhibit signal-to-noise ratios from 7.1σ, which is the lowercutoff for detections, to over 10,000σ, and periods ranging from0.5 days, which is the lower cutoff used in the procedure, to 109 days,which is the upper limit of achievable periods given the length of thedata set and the criteria used for detections. The detected signals arecompared to a set of known transit events in the Kepler field of viewwhich were derived by a different method using a longer data interval;the comparison shows that the current search correctly identified 88.1%of the known events. A tabulation of the detected transit signals,examples which illustrate the analysis and detection process, adiscussion of future plans and open, potentially fruitful, areas offurther research are included.
| Transit Timing Observations from Kepler. I. Statistical Analysis of the First Four Months
The architectures of multiple planet systems can provide valuableconstraints on models of planet formation, including orbital migration,and excitation of orbital eccentricities and inclinations. NASA's Keplermission has identified 1235 transiting planet candidates. The method oftransit timing variations (TTVs) has already confirmed seven planets intwo planetary systems. We perform a transit timing analysis of theKepler planet candidates. We find that at least ~11% of planetcandidates currently suitable for TTV analysis show evidence suggestiveof TTVs, representing at least ~65 TTV candidates. In all cases, thetime span of observations must increase for TTVs to provide strongconstraints on planet masses and/or orbits, as expected based on N-bodyintegrations of multiple transiting planet candidate systems (assumingcircular and coplanar orbits). We find the fraction of planet candidatesshowing TTVs in this data set does not vary significantly with thenumber of transiting planet candidates per star, suggesting significantmutual inclinations and that many stars with a single transiting planetshould host additional non-transiting planets. We anticipate that Keplercould confirm (or reject) at least ~12 systems with multiple transitingplanet candidates via TTVs. Thus, TTVs will provide a powerful tool forconfirming transiting planets and characterizing the orbital dynamics oflow-mass planets. If Kepler observations were extended to at least sevenyears, then TTVs would provide much more precise constraints on thedynamics of systems with multiple transiting planets and would becomesensitive to planets with orbital periods extending into the habitablezone of solar-type stars.
| The Kepler characterization of the variability among A- and F-type stars. I. General overview
Context. The Kepler spacecraft is providing time series of photometricdata with micromagnitude precision for hundreds of A-F type stars. Aims: We present a first general characterization of the pulsationalbehaviour of A-F type stars as observed in the Kepler light curves of asample of 750 candidate A-F type stars, and observationally investigatethe relation between ? Doradus (? Dor), ? Scuti(? Sct), and hybrid stars. Methods: We compile a databaseof physical parameters for the sample stars from the literature and newground-based observations. We analyse the Kepler light curve of eachstar and extract the pulsational frequencies using different frequencyanalysis methods. We construct two new observables, "energy" and"efficiency", related to the driving energy of the pulsation mode andthe convective efficiency of the outer convective zone, respectively. Results: We propose three main groups to describe the observedvariety in pulsating A-F type stars: ? Dor, ? Sct, andhybrid stars. We assign 63% of our sample to one of the three groups,and identify the remaining part as rotationally modulated/active stars,binaries, stars of different spectral type, or stars that show no clearperiodic variability. 23% of the stars (171 stars) are hybrid stars,which is a much higher fraction than what has been observed before. Wecharacterize for the first time a large number of A-F type stars (475stars) in terms of number of detected frequencies, frequency range, andtypical pulsation amplitudes. The majority of hybrid stars showfrequencies with all kinds of periodicities within the ? Dor and? Sct range, also between 5 and 10 d-1, which is achallenge for the current models. We find indications for the existenceof ? Sct and ? Dor stars beyond the edges of the currentobservational instability strips. The hybrid stars occupy the entireregion within the ? Sct and ? Dor instability strips andbeyond. Non-variable stars seem to exist within the instability strips.The location of ? Dor and ? Sct classes in the(Teff, log g)-diagram has been extended. We investigate twonewly constructed variables, "efficiency" and "energy", as a means toexplore the relation between ? Dor and ? Sct stars. Conclusions: Our results suggest a revision of the current observationalinstability strips of ? Sct and ? Dor stars and imply aninvestigation of pulsation mechanisms to supplement the ?mechanism and convective blocking effect to drive hybrid pulsations.Accurate physical parameters for all stars are needed to confirm thesefindings.
| On the Low False Positive Probabilities of Kepler Planet Candidates
We present a framework to conservatively estimate the probability thatany particular planet-like transit signal observed by the Kepler missionis in fact a planet, prior to any ground-based follow-up efforts. We useMonte Carlo methods based on stellar population synthesis and Galacticstructure models, and report false positive probabilities (FPPs) forevery Kepler Object of Interest, assuming a 20% intrinsic occurrencerate of close-in planets in the radius range 0.5 R ⊕< Rp < 20 R ⊕. Nearly 90% of the 1235candidates have FPP <10%, and over half have FPP <5%. Thisprobability varies with the magnitude and Galactic latitude of thetarget star, and with the depth of the transit signal—deepersignals generally have higher FPPs than shallower signals. We establishthat a single deep high-resolution image will be an effective follow-uptool for the shallowest (Earth-sized) transits, providing the quickestroute toward probabilistically validating the smallest candidates bypotentially decreasing the FPP of an Earth-sized transit around a faintstar from >10% to <1%. Since Kepler has detected many moreplanetary signals than can be positively confirmed with ground-basedfollow-up efforts in the near term, these calculations will be crucialto using the ensemble of Kepler data to determine populationcharacteristics of planetary systems. We also describe how our analysiscomplements the Kepler team's more detailed BLENDER false positiveanalysis for planet validation.
| Characteristics of Planetary Candidates Observed by Kepler. II. Analysis of the First Four Months of Data
On 2011 February 1 the Kepler mission released data for 156,453 starsobserved from the beginning of the science observations on 2009 May 2through September 16. There are 1235 planetary candidates withtransit-like signatures detected in this period. These are associatedwith 997 host stars. Distributions of the characteristics of theplanetary candidates are separated into five class sizes: 68 candidatesof approximately Earth-size (R p < 1.25 R?), 288 super-Earth-size (1.25 R ?<= R p < 2 R ?), 662 Neptune-size (2 R? <= R p < 6 R ?),165 Jupiter-size (6 R ? <= R p < 15 R?), and 19 up to twice the size of Jupiter (15 R? <= R p < 22 R ?).In the temperature range appropriate for the habitable zone, 54candidates are found with sizes ranging from Earth-size to larger thanthat of Jupiter. Six are less than twice the size of the Earth. Over 74%of the planetary candidates are smaller than Neptune. The observednumber versus size distribution of planetary candidates increases to apeak at two to three times the Earth-size and then declines inverselyproportional to the area of the candidate. Our current best estimates ofthe intrinsic frequencies of planetary candidates, after correcting forgeometric and sensitivity biases, are 5% for Earth-size candidates, 8%for super-Earth-size candidates, 18% for Neptune-size candidates, 2% forJupiter-size candidates, and 0.1% for very large candidates; a total of0.34 candidates per star. Multi-candidate, transiting systems arefrequent; 17% of the host stars have multi-candidate systems, and 34% ofall the candidates are part of multi-candidate systems.
| Characterization of Kepler early-type targets *
Context. Stellar pulsation offers a unique opportunity to constrain theintrinsic parameters of stars and unveil their inner structure. TheKepler satellite is collecting an enormous amount of data of unprecedentphotometric precision, which will allow us to test theory and obtain avery precise tomography of stellar interiors. Aims: We attempt todetermine the stars' fundamental parameters (Teff, log g, vsin i, and luminosity) needed for computing asteroseismic models andinterpreting Kepler data. We report spectroscopic observations of 23early-type Kepler asteroseismic targets, 13 other stars in the Keplerfield, that had not been selected to be observed. Methods: Wemeasured the radial velocity by performing a cross-correlation withtemplate spectra to help us identify non-single stars. Spectralsynthesis was performed to derive the stellar parameters of our targetstars, and the state-of-the-art LTE atmospheric models were computed.For all the stars of our sample, we derived the radial velocity,Teff, log g, v sin i, and luminosities. For 12 stars, weperformed a detailed abundance analysis of 20 species, for 16, we couldderive only the [Fe/H] ratio. A spectral classification was alsoperformed for 17 stars in the sample. Results: We identify twodouble-lined spectroscopic binaries, HIP 96299 and HIP 98551, the formerof which is an already known eclipsing binary, and two single-linedspectroscopic binaries, HIP 97254 and HIP 97724. We also report twosuspected spectroscopic binaries, HIP 92637 and HIP 96762, and thedetection of a possible variability in the radial velocity of HIP 96277.Two of our program stars are chemically peculiar, namely HIP 93941,which we classify as B2 He-weak, and HIP 96210, which we classify as B6Mn. Finally, we find that HIP 93522, HIP 93941, HIP 93943, HIP 96210 andHIP 96762, are very slow rotators (v sin i < 20 km s-1)which makes them very interesting and promising targets forasteroseismic modeling.Based on observations collected with the telescope at the M.G.Fracastoro station of the INAF - Osservatorio Astrofisico diCatania.Reduced spectra are only available in electronic form atthe CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/517/A3
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Dades d'Observació i Astrometria
| Constel·lació: | Draco |
| Ascensió Recta: | 18h48m00.08s |
| Declinació: | +48°32'32.0" |
| Magnitud Aparent: | 9.187 |
| Moviment propi RA: | 9.5 |
| Moviment propi Dec: | 10.1 |
| B-T magnitude: | 9.55 |
| V-T magnitude: | 9.217 |
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