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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.
| Global stellar variability study in the field-of-view of the Kepler satellite
Aims: We present the results of an automated variability analysisof the Kepler public data measured in the first quarter (Q1) of themission. In total, about 150 000 light curves have been analysed todetect stellar variability and to identify new members of knownvariability classes. We also focus on detecting variables present ineclipsing binary systems, given the strong constraints on stellarfundamental parameters they can provide. Methods: The methodologywe use here is based on the automated variability classificationpipeline, which was previously developed for and successfully applied tothe CoRoT exofield database and to the limited subset of a few thousandKepler asteroseismology light curves. We use a Fourier decomposition ofthe light curves to describe their variability behaviour and use theresulting parameters to perform a supervised classification. Severalimprovements were made, including a separate extractor method to detectthe presence of eclipses when other variability is present in the lightcurves. We also included two new variability classes compared toprevious work: variables showing signs of rotational modulation and ofactivity. Results: Statistics are given on the number ofvariables and the number of good candidates per class. A comparison ismade with results obtained for the CoRoT exoplanet data. We present somespecial discoveries, including variable stars in eclipsing binarysystems. Many new candidate non-radial pulsators are found, mainlyδ Sct and γ Dor stars. We studied those samples in moredetail by using 2MASS colours, and the full classification results aremade available as an online catalogue.The full classification results are only available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/529/A89
| Kepler Eclipsing Binary Stars. I. Catalog and Principal Characterization of 1879 Eclipsing Binaries in the First Data Release
The Kepler space mission is devoted to finding Earth-size planetsorbiting other stars in their habitable zones. Its large, 105deg2 field of view features over 156,000 stars that areobserved continuously to detect and characterize planet transits. Yet,this high-precision instrument holds great promise for other types ofobjects as well. Here we present a comprehensive catalog of eclipsingbinary stars observed by Kepler in the first 44 days of operation, thedata being publicly available through MAST as of 2010 June 15. Thecatalog contains 1879 unique objects. For each object, we provide itsKepler ID (KID), ephemeris (BJD0, P 0), morphologytype, physical parameters (T eff, log g, E(B - V)), theestimate of third light contamination (crowding), and principalparameters (T 2/T 1, q, fillout factor, and sin ifor overcontacts, and T 2/T 1, (R 1 + R2)/a, esin ω, ecos ω, and sin i for detachedbinaries). We present statistics based on the determined periods andmeasure the average occurrence rate of eclipsing binaries to be ~1.2%across the Kepler field. We further discuss the distribution of binariesas a function of galactic latitude and thoroughly explain theapplication of artificial intelligence to obtain principal parameters ina matter of seconds for the whole sample. The catalog was envisioned toserve as a bridge between the now public Kepler data and the scientificcommunity interested in eclipsing binary stars.
| Bayesian inference of stellar parameters and interstellar extinction using parallaxes and multiband photometry
Astrometric surveys provide the opportunity to measure the absolutemagnitudes of large numbers of stars, but only if the individualline-of-sight extinctions are known. Unfortunately, extinction is highlydegenerate with stellar effective temperature when estimated frombroad-band optical/infrared photometry. To address this problem, Iintroduce a Bayesian method for estimating the intrinsic parameters of astar and its line-of-sight extinction. It uses both photometry andparallaxes in a self-consistent manner in order to provide anon-parametric posterior probability distribution over the parameters.The method makes explicit use of domain knowledge by employing theHertzsprung-Russell Diagram (HRD) to constrain solutions and to ensurethat they respect stellar physics. I first demonstrate this method byusing it to estimate effective temperature and extinction from BVJHKdata for a set of artificially reddened Hipparcos stars, for whichaccurate effective temperatures have been estimated from high-resolutionspectroscopy. Using just the four colours, we see the expected strongdegeneracy (positive correlation) between the temperature andextinction. Introducing the parallax, apparent magnitude and the HRDreduces this degeneracy and improves both the precision (reduces theerror bars) and the accuracy of the parameter estimates, the latter byabout 35 per cent. The resulting accuracy is about 200 K in temperatureand 0.2 mag in extinction. I then apply the method to estimate theseparameters and absolute magnitudes for some 47 000 F, G, K Hipparcosstars which have been cross-matched with Two-Micron All-Sky Survey(2MASS). The method can easily be extended to incorporate the estimationof other parameters, in particular metallicity and surface gravity,making it particularly suitable for the analysis of the 109stars from Gaia.
| 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
| HATNET Variability Survey in the High Stellar Density ``Kepler Field'' with Millimagnitude Image Subtraction Photometry
The Hungarian-made Automated Telescope Network (HATnet) is an ongoingproject to detect transiting extrasolar planets using small-aperture (11cm diameter) robotic telescopes. In this paper, we present the resultsfrom using image subtraction photometry to reduce a crowded stellarfield observed with one of the HATnet telescopes (HAT-5). This field waschosen to overlap with the planned Kepler mission. We obtained I-bandlight curves for 98,000 objects in a 67 square degree field of viewcentered at J2000 (α,δ) =(19h44m00s0, +37°32'00.0"), near theGalactic plane in the constellations Cygnus and Lyra. These observationsinclude 788 exposures of 5 minutes' length over 30 days. For thebrightest stars (I~8.0) we achieved a precision of 3.5 mmag, falling to0.1 mag at the faint end (I~14). From these light curves we identify1617 variable stars, of which 1439 are newly discovered. The fact thatnearly 90% of the variables were previously undetected furtherdemonstrates the vast number of variables yet to be discovered evenamong fairly bright stars in our Galaxy. We also discuss some of themost interesting cases. These include V1171 Cyg, a triple system withthe inner two stars in a P=1.462 day period eclipsing orbit and theouter star a P=4.86 day Cepheid; HD 227269, an eccentric eclipsingsystem with a P=4.86 day period that also shows P=2.907 day pulsations;WW Cyg, a well-studied eclipsing binary; V482 Cyg, an R Coronae Borealisstar; and V546 Cyg, a PV Telescopii variable. We also detect a number ofsmall-amplitude variables, in some cases with full amplitude as low as10 mmag.
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