The Multicolor "Lyra" Photometric System for Variable stars and Halo Studies

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The space photometric project "Lyra" is developed now in Russia.The project purpose is determination of the photometric information and coordinates of the natural and artificial space objects, from the brightest ones to 16ᵐ in visual lights. It is supposed to obtain the data for about 40-400 million objects from board of International Space Station, using an astronomical telescope with diameter of the main mirror of 0.5 m. The observations will be carried out in a scanning mode. Photometry will be obtained in 10 spectral bands. The expected uncertainty of magnitudes for objects of 16ᵐ in the V-band is 0.001ᵐ. The main results of experiment should become: 1) creation of spatial model of the Galaxy on distances to 3 kpc from the Sun; 2) specification of physical parameters of stars and models of star evolution; 3) discovering of a huge number (to several millions) of variable stars and determination of their variability parameters. The central wavelengths of the 10 bands of "Lyra" photometric system will be at 195, 218, 270, 350, 440, 550, 700, 825, 930 and 1000 nm. It is shown that combinations of various colour indices will allow to determine confidently both effective temperature and metallicity of stars. The presence of a 218 nm band allows to determine confidently interstellar extinction on stars of O-F spectral classes. The photometric system will make it possible to separate halo stars from disk stars and to define physical parameters of their atmospheres.