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

Abstract

Astrometry satellites have common technological issues. (A) Astrometry satellites arerequired to measure the positions of stars with high accuracy from the huge amount of dataduring the observational period. (B) The high stabilization of the thermal environment inthe telescope is required. (C) The attitude-pointing stability of these satellites withsub-pixel accuracy is also required.

Measurement of the positions of stars from a huge amount of data is the essence ofastrometry. It is needed to exclude the systematic errors adequately for each image ofstars in order to obtain the accurate positions. We have carried out a centroidingexperiment 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 orderto achieve our aim. For the small-JASMINE, we require the thermal stabilization of thetelescope in order to obtain high astrometric accuracy of about 10 micro-arcsec. In orderto accomplish a measurement of positions of stars with high accuracy, we must make a modelof 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 thermalvariation is within about 1 K / 0.75 h. We also require the accuracy of theattitude-pointing stability of about 200 mas / 7 s. The utilization of the Tip-tilt mirrorwill make it possible to achieve such a stable pointing.