Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userEfficient identification of exoplanetary transit candidates from SuperWASP light curves
358
0
0.0
(
0
)
Added by
Andrew Collier Cameron
Publication date
2007
fields
Physics
and research's language is
English
Ask ChatGPT about the research
No Arabic abstract
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 optimisation of chi-squared combined with a Bayesian prior based on the main-sequence mass and radius expected from the 2MASS 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 sub-stellar secondaries.
rate research
Read More
We derive solutions to transit light curves of exoplanets orbiting rapidly-rotating stars. These stars exhibit significant oblateness and gravity darkening, a phenomenon where the poles of the star have a higher temperature and luminosity than the equator. Light curves for exoplanets transiting these stars can exhibit deviations from those of slowly-rotating stars, even displaying significantly asymmetric transits depending on the systems spin-orbit angle. As such, these phenomena can be used as a protractor to measure the spin-orbit alignment of the system. In this paper, we introduce a novel semi-analytic method for generating model light curves for gravity-darkened and oblate stars with transiting exoplanets. We implement the model within the code package starry and demonstrate several orders of magnitude improvement in speed and precision over existing methods. We test the model on a TESS light curve of WASP-33, whose host star displays rapid rotation ($v sin i_* = 86.4$ km/s). We subtract the hosts $delta$-Scuti pulsations from the light curve, finding an asymmetric transit characteristic of gravity darkening. We find the projected spin orbit angle is consistent with Doppler tomography and constrain the true spin-orbit angle of the system as $varphi=108.3^{+19.0}_{-15.4}$~$^{circ}$. We demonstrate the methods uses in constraining spin-orbit inclinations of such systems photometrically with posterior inference. Lastly, we note the use of such a method for inferring the dynamical history of thousands of such systems discovered by TESS.
We present the first analysis of results from the SuperWASP Variable Stars Zooniverse project, which is aiming to classify 1.6 million phase-folded light curves of candidate stellar variables observed by the SuperWASP all sky survey with periods detected in the SuperWASP periodicity catalogue. The resultant data set currently contains $>$1 million classifications corresponding to $>$500,000 object-period combinations, provided by citizen scientist volunteers. Volunteer-classified light curves have $sim$89 per cent accuracy for detached and semi-detached eclipsing binaries, but only $sim$9 per cent accuracy for rotationally modulated variables, based on known objects. We demonstrate that this Zooniverse project will be valuable for both population studies of individual variable types and the identification of stellar variables for follow up. We present preliminary findings on various unique and extreme variables in this analysis, including long period contact binaries and binaries near the short-period cutoff, and we identify 301 previously unknown binaries and pulsators. We are now in the process of developing a web portal to enable other researchers to access the outputs of the SuperWASP Variable Stars project.
Reliable estimations of ephemeris errors are fundamental for the follow-up of CoRoT candidates. An equation for the precision of minimum times, originally developed for eclipsing binaries, has been optimized for CoRoT photometry and been used to calculate such errors. It may indicate expected timing precisions for transit events from CoRoT, as well as from Kepler. Prediction errors for transit events may also be used to calculate probabilities about observing entire or partial transits in any given span of observational coverage, leading to an improved reliability in deductions made from follow-up observations.
We have performed photometric observations of nearly 7 million stars with 8 < V < 15 with the SuperWASP-North instrument from La Palma between 2004 May-September. Fields in the RA range 17-18hr, 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 S/N in the BLS, show multiple transit-like dips and have passed visual inspection. Analysis of the blending and inferred planetary radii for these candidates leaves a total of 7 transiting planet candidates which pass all the tests plus 4 which pass the majority. We discuss the derived parameters for these candidates and their properties and comment on the implications for future transit searches.
Clouds have been shown to be present in many exoplanetary atmospheres. Cloud formation modeling predicts considerable inhomogeneities of cloud cover, consistent with optical phase curve observations. However, optical phase curves cannot resolve some existing degeneracies between cloud location and cloud optical properties. We present a conceptually simple technique to detect inhomogeneous cloud cover on exoplanets. Such an inhomogeneous cloud cover produces an asymmetric primary transit of the planet in front of the host star. Asymmetric transits produce characteristic residuals compared to a standard symmetric model. Furthermore, bisector spans can be used to determine asymmetries in the transit light curve. We apply a model of asymmetric transits to the light curves of HAT-P-7b, Kepler-7b and HD209458b and search for possible cloud signatures. The nearly uninterrupted Kepler photometry is particularly well-suited for this method since it allows for a very high time resolution. We do not find any statistically sound cloud signature in the data of the considered planets. For HAT-P-7b, a tentative detection of an asymmetric cloud cover is found, consistent with analysis of the optical phase curve. Based on Bayesian probability arguments, a symmetric model with an offset in the transit ephemeris remains, however, the most viable model. Still, this work demonstrates that for suitable targets, namely low-gravity planets around bright stars, the method can be used to constrain cloud cover characteristics and is thus a helpful additional tool to study exoplanetary atmospheres.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
