fainter than 18th magnitude, promising to expand Gaia's tomographic mapping of the Milky Way to much 5 fainter end, which can be up to magnitude 26 at g band. This extension will enrich astronomical databases 6 with critical data, including positions, parallaxes, distance estimates, and color-magnitude-based stellar 7 parameters. CSST is anticipated to establish the densest and deepest reference frame in the world, covering 8 magnitudes ranging from 18 to 26.
Through simulation data, the astrometric performance of CSST is assessed, revealing a remarkable 10 accuracy at such faint magnitude, see Figure 1 (Fu et al., 2023). Specifically, for sources within the 18-22 11 mag range in the g band, CSST achieves a precision better than 1 mas(• yr -1 ). Moreover, for sources falling 12 within the 22-26 mag range in the g band, CSST demonstrates a precision ranging from approximately 1 13 to 10 mas(• yr -1 ). It is noted that optimizing the survey schedule holds the potential to further enhance 14 CSST's astrometric accuracy.
Addressing the crucial matter of preserving and enhancing the Gaia catalogue, CSST proposes a novel 16 approach. By modeling the astrometric fit of sources in the extragalactic region of the Gaia sample using
In the realm of asteroid mass determination through close encounters, CSST's potential is explored.
With anticipated accuracies in the milliarcsecond range and a limiting magnitude of 26 (AB mag) or 29 higher, CSST's observations, when combined with ground-based data, promise significant enhancements 30 in asteroid mass precision. While limitations exist, including strong perturbations during close encounters, 31 the improvement brought by CSST data is evident. Dedicated observations during strong encounters, with 32 a specific focus over 7.2 observation hours spanning three years, could yield precise determinations for a 33 significant number of asteroids, with 10 expected to achieve precision better than 10% (Li et al., 2023).
