Development of a hybrid algorithm for time resolved stellar photometry from space images

The CoRoT satellite, inserted in a low Earth polar orbit, is exposed to a radioactive environment that affects the instrumental components. Effects of charged particle impacts on the onboard electronics and optics have been minimized by the use of radiation-hard components and proper data reduction techniques. However, when the satellite crosses the South Atlantic Anomaly, the CCDs are exposed to up to 10 minutes of strong radiation, subjecting up to 9% of the whole satellite’s imaging duty cycle to some kind of impact damage. This work presents an innovative hybrid photometry algorithm that takes advantage of a high-resolution instrumental point spread function and of the high signal-to-noise-ratio obtained in the onboard aperture photometry, to extract a more accurate photometric signal from the observed stars. It also takes into account the total standard deviation in each pixel, formed by Poissonian and readout noises. This methodology has proven to achieve gains in photometric precision and increase the duty cycle up to 97%, enabling robust and accurate data exploitation. Keywords— Stellar Photometric Reduction, Hybrid Algorithm, SF-fitting, Optimal Aperture.