High-Precision Lightcurves from Undersampled CCD Images
Abstract
We are searching for transiting extrasolar planets using the 0.5m Automated Patrol Telescope at Siding Spring Observatory. A disadvantage of using such a wide-field telescope is that the images are severely undersampled. As a consequence intra-pixel sensitivity variations on the CCD limit the photometric precision we can achieve using conventional observing and data reduction methods (to ~5mmag).
We have developed a new observing technique specifically aimed at minimising the effects of intra-pixel variations. We systematically move the telescope during intergration in a raster-type scan covering 1x1 or 2x2 pixels. Although this does broaden the PSF slightly it effectively eliminates the intra-pixel variation problem. The resulting PSF is fairly flat topped with a very rapid falloff. We therefore developed an optimised aperture photometry package to process the resulting images with co-located apertures for each object positioned to better than 1/100th of a pixel repeatability in each frame. Using this system we are obtaining differential photometric precision of ~2mmag down to V=12 in 150sec exposures. The lightcurves are further processed to find and remove periodic signals from variable stars and searched for transit signals using a variant of the Gregory-Loredo algorithm optimised for transit detection- Publication:
-
IAU Joint Discussion
- Pub Date:
- 2003
- Bibcode:
- 2003IAUJD..12E..14H