Extended gas clouds have been previously detected surrounding the brightest known close-in transiting hot Jupiter exoplanets, HD 209458 b and HD 189733 b; we observed the distant but more extreme ...close-in hot Jupiter system, WASP-12, with Hubble Space Telescope (HST). Near-UV (NUV) transits up to three times deeper than the optical transit of WASP-12 b reveal extensive diffuse gas, extending well beyond the Roche lobe. Our spectra reveal significantly enhanced absorption (greater than 3sigma below the median) at ~200 individual wavelengths on each of two HST visits; 65 of these wavelengths are consistent between the two visits, using a strict criterion for velocity matching that excludes matches with velocity shifts exceeding ~20 km s super(-1). Our Visit 2 NUV light curves show evidence for a stellar flare. We show that some of the possible transit detections in resonance lines of rare elements may be due instead to non-resonant transitions in common species. We present optical observations and update the transit ephemeris.
We report on the discovery of WASP-12b, a new transiting extrasolar planet with R pl = 1.79+0.09 -0.09 RJ and M pl = 1.41+0.10 -0.10 M J. The planet and host star properties were derived from a Monte ...Carlo Markov Chain analysis of the transit photometry and radial velocity data. Furthermore, by comparing the stellar spectrum with theoretical spectra and stellar evolution models, we determined that the host star is a supersolar metallicity (M/H = 0.3+0.05 -0.15), late-F (T eff = 6300+200 -100 K) star which is evolving off the zero-age main sequence. The planet has an equilibrium temperature of T eq = 2516 K caused by its very short period orbit (P = 1.09 days) around the hot, twelfth magnitude host star. WASP-12b has the largest radius of any transiting planet yet detected. It is also the most heavily irradiated and the shortest period planet in the literature.
We present a general framework for matching the point-spread function (PSF), photometric scaling and sky background between two images, a subject which is commonly referred to as difference image ...analysis (DIA). We introduce the new concept of a spatially varying photometric scale factor which will be important for DIA applied to wide-field imaging data in order to adapt to transparency and airmass variations across the field-of-view. Furthermore, we demonstrate how to separately control the degree of spatial variation of each kernel basis function, the photometric scale factor and the differential sky background. We discuss the common choices for kernel basis functions within our framework, and we introduce the mixed-resolution delta basis functions to address the problem of the size of the least-squares problem to be solved when using delta basis functions. We validate and demonstrate our algorithm on simulated and real data. We also describe a number of useful optimizations that may be capitalized on during the construction of the least-squares matrix and which have not been reported previously. We pay special attention to presenting a clear notation for the DIA equations which are set out in a way that will hopefully encourage developers to tackle the implementation of DIA software.
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
Recenzirano
Odprti dostop
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 a transiting planet with an orbital period of 3.05 days orbiting the star TYC 7247-587-1. The star, WASP-41, is a moderately bright G8
V
V
star (
V = 11.6
V
=
11.6
) with a ...metallicity close to solar (Fe/H = -0.08 ± 0.09
Fe
/
H
=
-
0.08
±
0.09
). The star shows evidence of moderate chromospheric activity, both from emission in the cores of the Ca iiH and K ines and photometric variability with a period of 18.4 days and an amplitude of about 1%. We use a new method to show quantitatively that this periodic signal has a low false-alarm probability. The rotation period of the star implies a gyrochronological age for WASP-41 of 1.8 Gyr with an error of about 15%. We have used a combined analysis of the available photometric and spectroscopic data to derive the mass and radius of the planet (0.92 ± 0.06 M
Jup
0.92
±
0.06
M
Jup
,1.20 ± 0.06 R
Jup
1.20
±
0.06
R
Jup
). Further observations of WASP-41 can be used to explore the connections between the properties of hot Jupiter planets and the level of chromospheric activity in their host stars.
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.
Transiting extrasolar planets constitute only a small fraction of the range of stellar systems found to display periodic, shallow dimmings in wide-field surveys employing small-aperture camera ...arrays. Here we present an efficient selection strategy for follow-up observations, derived from analysis of the light curves of a sample of 67 SuperWASP targets that passed the selection tests we used in earlier papers, but which have subsequently been identified either as planet hosts or as astrophysical false positives. We determine the system parameters using Markov-chain Monte Carlo analysis of the SuperWASP light curves. We use a constrained optimization of χ2 combined with a Bayesian prior based on the main-sequence mass and radius expected from the Two Micron All Sky Survey J−H colour. The Bayesian nature of the analysis allows us to quantify both the departure of the host star from the main-sequence mass–radius relation and the probability that the companion radius is less than 1.5 Jupiter radii. When augmented by direct light-curve analyses that detect binaries with unequal primary and secondary eclipses, and objects with aperture blends that are resolved by SuperWASP, we find that only 13 of the original 67 stars, including the three known planets in the sample, would qualify for follow-up. This suggests that planet discovery ‘hit rates’ better than one-in-five should be achievable. In addition, the stellar binaries that qualify are likely to have astrophysically interesting stellar or substellar secondaries.
New semiconducting polymers reach record mobility despite apparently lower structural order.
Polymer semiconductors have picked up the pace in the constant search for new and better electronic ...materials. High carrier mobility is an essential figure-of-merit for their applications as thin-film transistors (TFTs), solar cells, and light-emitting diodes. Polymers are disordered materials with partial crystallinity, and disorder introduces localized electronic states at the band edges—the so-called band tail—that trap electrons and reduce mobility. Reaching a mobility of 1 cm
2
V
−1
s
−1
was the result of engineering polymers with increased crystallinity to reduce the effect of band tail states. Reported mobilities have recently surged to between about 5 and 10 cm
2
V
−1
s
−1
(
1
), but the polymers are less ordered, according to some structural measurements. Two recent papers help resolve this puzzle. Zhang
et al.
(
2
) use a combination of structural probes to show that the high-mobility polymers gain longer-range structural order, if not high crystallinity, by having a more rigid backbone. Noriega
et al.
(
3
) provide a careful analysis of the role of disorder in charge transport for the specific case of polymers, and conclude that high crystallinity is not essential for high mobility.
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