A fast hybrid algorithm for exoplanetary transit searches

Abstract

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 LeastSquares (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 boxcarsmoothing 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.

MML 53: a new low-mass, pre-main sequence eclipsing binary in the Upper Centaurus-Lupus region discovered by SuperWASP

“…The light curves, which were detrended along with other stars in the field using the SysRem algorithm (Tamuz et al 2005), were then run through our implementation of the box least squares (BLS) algorithm (Kovács et al 2002;Collier Cameron et al 2006). The BLS algorithm is designed specifically to detect square shaped dips in brightness in an otherwise flat light curve.…”

The follow-up observations for the transit events of WASP-12b

“…The magnitude of selected objects in CCD frames is measured with APPHOT task of IRAF. 26 and 24 "reference stars" for 1m and 2.4m observations, respectively, are used to simulate systematic errors in photometric data with the methods of Collier Cameron et al (2006) and Tamuz et al (2005). Then these simulated systematic effects are removed from the WASP-12b's photometric data.…”

Refined System Parameters and TTV Study of Transiting Exoplanetary System Hat-P-20

“…The transit signal of an exoplanet is normally small. In order to enhance the signal of transit events (Tamuz et al 2005;Collier Cameron et al 2006;Wang et al 2013), we correct the systematic errors in the photometric data based on the coarse decorrelation and SYSREM algorithm. However, there still are several systematic trends left in the transit light curves because of differing extinction between target and reference stars and even the flux modulation induced by starspots on the stellar surface of the rotation of the host star.…”