The WASP Project and the SuperWASP Cameras Pollacco, D. L.; Skillen, I.; Cameron, A. Collier ...
Publications of the Astronomical Society of the Pacific,
10/2006, Letnik:
118, Številka:
848
Journal Article
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The SuperWASP cameras are wide‐field imaging systems at the Observatorio del Roque de los Muchachos on the island of La Palma in the Canary Islands, and at the Sutherland Station of the South African ...Astronomical Observatory. Each instrument has a field of view of some 482 deg2with an angular scale of 13
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7 pixel−1, and is capable of delivering photometry with accuracy better than 1% for objects having
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. Lower quality data for objects brighter than
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are stored in the project archive. The systems, while designed to monitor fields with high cadence, are capable of surveying the entire visible sky every 40 minutes. Depending on the observational strategy, the data rate can be up to 100 Gbytes per night. We have produced a robust, largely automatic reduction pipeline and advanced archive, which are used to serve the data products to the consortium members. The main science aim of these systems is to search for bright transiting exoplanet systems suitable for spectroscopic follow‐up observations. The first 6 month season of SuperWASP‐North observations produced light curves of ∼6.7 million objects with 12.9 billion data points.
We report the discovery of the transiting giant planet WASP-17b, the least-dense planet currently known. It is 1.6 Saturn masses but 1.5-2 Jupiter radii, giving a density of 6-14 per cent that of ...Jupiter. WASP-17b is in a 3.7-day orbit around a sub-solar metallicity, V = 11.6, F6 star. Preliminary detection of the Rossiter-McLaughlin effect suggests that WASP-17b is in a retrograde orbit (lambda ~ -150 deg), indicative of a violent history involving planet-planet or planet-star scattering. WASP-17b's bloated radius could be due to tidal heating resulting from recent or ongoing tidal circularisation of an eccentric orbit, such as the highly eccentric orbits that typically result from scattering interactions. It will thus be important to determine more precisely the current orbital eccentricity by further high-precision radial velocity measurements or by timing the secondary eclipse, both to reduce the uncertainty on the planet's radius and to test tidal-heating models. Owing to its low surface gravity, WASP-17b's atmosphere has the largest scale height of any known planet, making it a good target for transmission spectroscopy.
We present a fast and efficient hybrid algorithm for selecting exoplanetary candidates from wide-field transit surveys. Our method is based on the widely used SysRem and Box Least-Squares (BLS) ...algorithms. Patterns of systematic error that are common to all stars on the frame are mapped and eliminated using the SysRem algorithm. The remaining systematic errors caused by spatially localized flat-fielding and other errors are quantified using a boxcar-smoothing method. We show that the dimensions of the search-parameter space can be reduced greatly by carrying out an initial BLS search on a coarse grid of reduced dimensions, followed by Newton–Raphson refinement of the transit parameters in the vicinity of the most significant solutions. We illustrate the method's operation by applying it to data from one field of the SuperWASP survey, comprising 2300 observations of 7840 stars brighter than V= 13.0. We identify 11 likely transit candidates. We reject stars that exhibit significant ellipsoidal variations caused indicative of a stellar-mass companion. We use colours and proper motions from the Two Micron All Sky Survey and USNO-B1.0 surveys to estimate the stellar parameters and the companion radius. We find that two stars showing unambiguous transit signals pass all these tests, and so qualify for detailed high-resolution spectroscopic follow-up.
Context. To determine the physical parameters of a transiting planet and its host star from photometric and spectroscopic analysis, it is essential to independently measure the stellar mass. This is ...often achieved by the use of evolutionary tracks and isochrones, but the mass result is only as reliable as the models used. Aims. The recent paper by Torres et al. (2010, A&ARv, 18, 67) showed that accurate values for stellar masses and radii could be obtained from a calibration using Teff, log g and Fe/H. We investigate whether a similarly good calibration can be obtained by substituting log ρ – the fundamental parameter measured for the host star of a transiting planet – for log g, and apply this to star-exoplanet systems. Methods. We perform a polynomial fit to stellar binary data provided in Torres et al. (2010) to obtain the stellar mass and radius as functions of Teff, log ρ and Fe/H, with uncertainties on the fit produced from a Monte Carlo analysis. We apply the resulting equations to measurements for seventeen SuperWASP host stars, and also demonstrate the application of the calibration in a Markov Chain Monte Carlo analysis to obtain accurate system parameters where spectroscopic estimates of effective stellar temperature and metallicity are available. Results. We show that the calibration using log ρ produces accurate values for the stellar masses and radii; we obtain masses and radii of the SuperWASP stars in good agreement with isochrone analysis results. We ascertain that the mass calibration is robust against uncertainties resulting from poor photometry, although a good estimate of stellar radius requires good-quality transit light curve to determine the duration of ingress and egress.
We report the discovery and initial characterization of Qatar-1b, a hot Jupiter-orbiting metal-rich K dwarf star, the first planet discovered by the Qatar Exoplanet Survey. We describe the strategy ...used to select candidate transiting planets from photometry generated by the Qatar Exoplanet Survey camera array. We examine the rate of astrophysical and other false positives found during the spectroscopic reconnaissance of the initial batch of candidates. A simultaneous fit to the follow-up radial velocities and photometry of Qatar-1b yields a planetary mass of 1.09 ± 0.08 M
J and a radius of 1.16 ± 0.05 R
J. The orbital period and separation are 1.420 033 ± 0.000 016 d and 0.023 43 ± 0.000 26 au for an orbit assumed to be circular. The stellar density, effective temperature and rotation rate indicate an age greater than 4 Gyr for the system.
Context. Many transiting exoplanet surveys are now in operation, observing millions of stars and searching for the periodic signals that may indicate planets orbiting these objects. Aims. We have ...tested the performance of transit detection algorithms using real WASP data, avoiding the issue of generating the appropriate level of white and red noise in simulated lightcurves. We used a two-dimensional search method, the box-least-squares (BLS) algorithm, and two- and three-dimensional versions of the analysis of variance (AoV) method. Methods. After removing any potential transiting candidate or variable objects, transits were injected into each lightcurve. We performed Monte Carlo simulations, testing the recovery of injected signals in 99 lightcurves by each algorithm. Results. In the simulations using data from one season of WASP observations, it was determined that the BLS method should detect a total of 37% of planets and the 3D AoV 23%. Simulations to explore the effects of extending survey baseline or number of hours of observations per 24 h period, i.e. longitudinally spaced observatories, were also performed. They showed that increasing the coverage via an increase in baseline or in observational hours are equally good for maximising overall detections of transiting planets. The resulting algorithm performance was combined with actual WASP-South results to estimate that 0.08% and 0.30% of stars harbour very hot Jupiters and hot Jupiters respectively.
We have performed photometric observations of nearly seven million stars with 8 < V < 15 with the SuperWASP-North instrument from La Palma between 2004 May to September. Fields in the right ascension ...range 17–18 h, yielding over 185 000 stars with sufficient quality data, have been searched for transits using a modified box least-squares (BLS) algorithm. We find a total of 58 initial transiting candidates which have high signal-to-noise ratio in the BLS, show multiple transit-like dips and have passed visual inspection. Analysis of the blending and the inferred planetary radii for these candidates leave, a total of seven transiting planet candidates which pass all the tests plus four which pass the majority. We discuss the derived parameters for these candidates and their properties and comment on the implications for future transit searches.
The Wide Angle Search for Planets (WASP) survey currently operates two installations, designated SuperWASP-N and SuperWASP-S, located in the Northern and Southern hemispheres, respectively. These ...installations are designed to provide high time-resolution photometry for the purpose of detecting transiting extrasolar planets, asteroids, and transient events. Here, we present results from a transit-hunting observing campaign using SuperWASP-N covering a right ascension (RA) range of 06h < RA < 16h. This paper represents the fifth and final in the series of transit candidates released from the 2004 observing season. In total, 729 335 stars from 33 fields were monitored with 130 566 having sufficient precision to be scanned for transit signatures. Using a robust transit detection algorithm and selection criteria, six stars were found to have events consistent with the signature of a transiting extrasolar planet based on the photometry, including the known transiting planet XO-1b. These transit candidates are presented here along with discussion of follow-up observations and the expected number of candidates in relation to the overall observing strategy.
The Wide Angle Search for Planets (WASP) photometrically surveys a large number of nearby stars to uncover candidate extrasolar planet systems by virtue of small-amplitude light curve dips on a ≲5-d ...time-scale typical of the ‘Hot-Jupiters’. Observations with the SuperWASP-North instrument between 2004 April and September produced a rich photometric data set of some 1.3 × 109 data points from 6.7 million stars. Our custom-built data acquisition and processing system produces ∼0.02 mag photometric precision at V= 13. We present the transit candidates in the 03h–06h RA range. Out of 141 895 light curves with sufficient sampling to provide adequate coverage, 2688 show statistically significant transit-like periodicities. Out of these, 44 pass a visual inspection of the light curve, of which 24 are removed through a set of cuts on the statistical significance of artefacts. All but four of the remaining 20 objects are removed when prior information at higher spatial resolution from existing catalogues is taken into account. Of the four candidates remaining, one is considered a good candidate for follow-up observations with three further second-priority targets. We provide detailed information on these candidates, as well as a selection of the false-positives and astrophysical false-alarms that were eliminated, and discuss briefly the impact of sampling on our results.
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