Work

A pilot study on the astrometric capability of CSST

Year: 2026

Type: article

Abstract: Context. The China Space-station Survey Telescope (CSST) will provide deep, wide-field epoch astrometry over its 10-year mission. Accurate recovery of binary orbits requires both high-precision astrometry and sufficient orbital-phase coverage, enabling dynamical constraints on the masses of stellar and compact-object companions. Combining CSST and Gaia epoch astrometry extends the temporal baseline and improves orbital phase coverage, thereby enhancing binary detection and orbital characterization. Aims. We evaluate CSST, Gaia , and joint epoch astrometry for binary-candidate selection and 12-parameter (12p) orbit fitting at faint magnitudes ( g > 17.8). We also test how a more regular CSST cadence affects the number of 12p fits satisfying our criteria. Methods. We constructed a mock catalog, simulated CSST and Gaia epoch astrometry, and fitted five-parameter (5p) singlestar models. We used astrometric diagnostics, proper-motion anomaly features, and observational-sampling features in a four-stage histogram-based gradient-boosting classifier. Selected candidates were then fitted with a 12p orbital model and assessed using two nested selection tiers. Results. On the independent test set, the classifier reached a precision of 0.802 and a recall among eligible true binaries of 0.181. In the scenario-specific fitted samples, joint astrometry raised the fiducial fraction from 6.76% for Gaia alone to 10.46%; for fitted binaries with P true > 15 yr, it rose from 2.37% to 6.78%. The current CSST schedule yields few fiducial fits, while idealized regular cadences increase the yield mainly at g ≲ 21. Conclusions. In the simulation, joint CSST and Gaia epoch astrometry yields higher fractions of fitted unresolved binaries satisfying the stated criteria than Gaia alone. A practical strategy would be to select binary candidates from 5p diagnostics and astrometric anomalies, obtain more regular CSST follow-up observations for promising binaries, and then fit 12p orbital models and apply the selection criteria.

Source: Astronomy and Astrophysics

DOI: 10.1051/0004-6361/202558478