Current Status of Astrometry Satellite missions in Japan: JASMINE project series

Abstract

Astrometry satellites have common technological issues. (A) Astrometry satellites are required to measure the positions of stars with high accuracy from the huge amount of data during the observational period. (B) The high stabilization of the thermal environment in the telescope is required. (C) The attitude-pointing stability of these satellites with sub-pixel accuracy is also required. Measurement of the positions of stars from a huge amount of data is the essence of astrometry. It is needed to exclude the systematic errors adequately for each image of stars in order to obtain the accurate positions. We have carried out a centroiding experiment for determining the positions of stars from about 10 000 image data. The following two points are important issues for the mission system of JASMINE in order to achieve our aim. For the small-JASMINE, we require the thermal stabilization of the telescope in order to obtain high astrometric accuracy of about 10 micro-arcsec. In order to accomplish a measurement of positions of stars with high accuracy, we must make a model of the distortion of the image on the focal plane with the accuracy of less than 0.1 nm. We have investigated numerically that the above requirement is achieved if the thermal variation is within about 1 K / 0.75 h. We also require the accuracy of the attitude-pointing stability of about 200 mas / 7 s. The utilization of the Tip-tilt mirror will make it possible to achieve such a stable pointing.