Delta Scorpii 2011 periastron: visual and digital photometric campaign

Abstract

Hundred observations of Delta Scorpii, from April to September 2011, made for AAVSO visually and digitally with a commercial CMOS camera have been plotted. The three most luminous pixels either of the target star and the two reference stars are used to evaluate the magnitude through differential photometry. The main sources of errors are outlined. The system of Delta Scorpii, a spectroscopic double star, has experienced a close periastron in July 2011 within the outer atmospheres of the two giant components. The whole luminosity of Delta Scorpii increased from about Mv=1.8 to 1.65 peaking around 5 to 15 July 2011, but there are significant rapid fluctuations of 0.2-0.3 magnitudes occuring in 20 days that seem to be real, rather than a consequence of systematic errors due to the changes of reference stars and observing conditions. This method is promising for being applied to other bright variable stars like Betelgeuse and Antares.