Speckle Observations of Composite Spectrum Stars. II. Differential Photometry of the Binary Components.

Multicolor differential photometry measurements of the two components of 18 close binary stars, mostly composite spectrum stars, are presented. They are based on observations made at Pic du Midi Observatory with the speckle camera PISCO between 1993 and 1998. Optical bench experiments were also performed to assess the validity of the whole process from the data acquisition with the ICCD detector to the final photometry measurements. The results are discussed and compared with (1) Hipparcos and speckle photometry, (2) spectroscopic measurements, and (3) composite spectra computed with a spectral library. Our measurements are in good agreement with other observations. We also determined the evolution stage of the individual components: the absolute visual magnitudes of the cool giant stars that we found are compatible with the calibrations made by other authors. This work shows that PISCO is well adapted to efficiently perform relative photometry of close binary stars.