Determining Temperature-Corrected Gravitational Focal Length Changes of the 26-m HartRAO Radio Telescope

Abstract

The accuracy of VLBI measurements depends on the structural stability of radio telescopes. In this study we investigate deformations caused by the gravitational force of the 26 m radio tele-scope of the South African Radio Astronomy Observatory at Hartebeesthoek site (HartRAO). Special focus is put on the deformation of the main reflector in different telescope pointing positions which are defined by Hour Angle and Declination. Its fundamental deformation can be described by changes of the focal length of the paraboloid that is the main parameter for the overall shape of the telescope’s main reflector. Besides the overall shape deformations also local surface deformations of the main reflector are analyzed. The impact of these deformations on the VLBI signal delay and how the results can be used for further calculations will be described briefly.