Comparison of different photometric algorithms on Pi of the Sky data.

摘要

Pi of the Sky is a system of wide field-of-view robotic telescopes, which search for short timescale astrophysical phenomena, especially for prompt optical GRB emission. The system was designed for autonomous operation, monitoring a large fraction of the sky with 12m-13m range and time resolution of the order of 1 - 100 seconds. System design and observation strategy were successfully tested with a prototype detector in Chile, operational since 2004. In July 2013 the final Pi of the Sky detector system, with 16 CCD cameras on 4 mounts, was comissioned at the INTA El Arenosillo Test Centre in Spain, resulting in a total coverage of about 6000 square degrees. LUIZA is a dedicated framework developed for efficient image processing, implemented in C++. Data analysis is divided into small, well-defined steps, which are implemented as so called processors. The framework allows to define the processor selection and their order, as well as all the required parameters at runtime, in a simple XML steering file. It was used in the presented study to compare three different photometric algorithms considered in analysis of the Pi of the Sky data. The algorithm based on the ASAS photometry was implemented in LUIZA as a sequence of three processors. First processor searches for stars in the considered images and extracts parameters of the Gaus profile describing star pointoint spread function (PSF) best. The next processor uses the PSF parameters to convolute the image with the Gaussian kernel and used to identify stars on the resulting image. In the last step the actual photometry is peformed, i.e. object brightnesses are calculated. In the presented study, results obtained from the ASAS photometry were compared with the new photometry algorithm developed within LUIZA and with the simple aperture photometry implemented previoulsly. Results are presented for analysis of single images with different exposure times, as well as for stacked frames.