Analysis of the Systematic Differences between the Stellar Parallaxes of the TGAS and Hipparcos Catalogues Using Spherical Harmonics

The systematic differences between the trigonometric parallaxes of the Hipparcos and TGAS catalogues have been investigated using spherical harmonics. The most significant harmonics in the expansion have been determined. The distribution of the parallax difference dispersion in various regions of the celestial sphere has also been studied. The distribution of the rms deviation has the simplest form in the ecliptic coordinate system.