Context. A series of studies have demonstrated that the Gaia multipeak (GMP) method is a very efficient technique for selecting active galactic nucleus (AGN) pair candidates. The number of candidates is determined by the size of the input AGN catalog, and is usually limited to spectroscopically confirmed objects. Aims. The objective of this work is to compile a larger and highly reliable catalog of GMP AGN pair candidates extracted from the six million objects of the Gaia AGN catalog, the majority of which lack spectroscopic information. Methods. In order to ascertain the differences between GMP AGN pair candidates and normal AGNs in terms of their properties, we conducted an investigation using samples of GMP AGNs. These differences were employed to establish optimal selection criteria, which ultimately led to the identification of a highly reliable candidate catalog. Results. We find significant differences between normal AGNs and GMP AGN pair candidates in terms of their astrometry and multi-band color distribution. We compiled the DUal and Lensed AGN candidate catalog with the GMP method (DULAG), which comprises 5286 sources, and is accompanied by a highly reliable Golden sample of 1867 sources. A total of 37 sources in the Golden sample have been identified as dual AGN or lensed AGN. For the majority of sources in the Golden sample, we provide reference redshifts and find three close AGN pair candidates among them.

Quasars are very important in materializing the reference frame. The excess emission of active galactic nuclei (AGNs) in the mid-infrared band can be used to identify quasar candidates. As extremely distant and point-like objects, quasars also could be further selected by an astrometry method. Increasing the number of reliable quasar candidates is necessary in characterizing the properties of Gaia astrometric solution and evaluating the reliability of Gaia's own quasars classification. We identify quasars by using appropriate AllWISE [W1-W2] color and different combinations of astrometric criteria. Together with the contamination and completeness, the magnitude, astrometric properties, density distribution, and the morphological indexes of these selected quasars are evaluated. We obtain a quasar candidate catalog of 1,503,373 sources, which contains 1,186,690 candidates (78.9%) in common with the Gaia EDR3_AGN catalog and 316,683 newly identified quasar candidates. The completeness of this catalog is around 80% compared to LQAC5, and the purity of the overall catalog is about 90%. We also found that the purity of quasar candidates selected by this method will decrease in the crowded sky area and the region with less WISE observations.

Context . Orbital inclination is crucial in determining the binary mass. The astrometric excess noise contains the orbital motion information, which can be used to constrain the inclination. Aims . We aim to constrain the orbital inclination of a binary system by combining radial velocity measurements with the astrometric excess noise from the Gaia DR3 solution. Methods . The astrometric excess noise is directly related to the orbital parameters. For a binary system with a radial velocity solution, it can be treated as a function of the orbital inclination. Using the Gaia nominal scanning law and the estimated centroid uncertainties, we simulate Gaia astrometric epoch observations to reproduce the expected excess noise. By sampling different inclinations and comparing the resulting simulated excess noise with the value reported in Gaia DR3, we can constrain the inclination to a specific interval. Results . We have developed a method to constrain the orbital inclination within a specific range, enabling a more accurate determination of the binary mass, particularly for spectroscopic binaries. Internal and external validations demonstrate the robustness of the method, although certain limitations remain. It is most reliable for systems exhibiting a strong astrometric signal of binary motion, while caution is required when applying it to binaries with weak astrometric wobbles or poorly sampled orbits.

In the optical band, very few pulsars can be directly detected, but some of the pulsar binary companions can be observed. This study leverages high-precision astrometric data from Gaia Data Release 3 (DR3) to identify pulsar companions in binary systems. Cross-matching the Australia Telescope National Facility (ATNF) Pulsar Catalogue with Gaia DR3 yielded 58 astrometric pairs, including 9 newly confirmed companions—primarily in the southern hemisphere—expanding the known pulsar distribution there. Among these, 8 are redback pulsars, offering insights into millisecond pulsar evolution and companion composition. All 58 companions are classified as main-sequence stars, neutron stars, white dwarfs, or ultra-light companion stars, with $\sim$40\% being spider pulsars. Gaia’s exceptional astrometric precision advances pulsar studies, enabling gravitational wave detection via Pulsar Timing Arrays (PTAs) and improved reference frame link. Future multi-wavelength research will benefit from Gaia DR4, International Pulsar Timing Array (IPTA) collaborations (including Five-hundred-meter Aperture Spherical radio Telescope (FAST)), and Very Long Baseline Interferometry (VLBI) networks like the Chinese VLBI Network (CVN).

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.

Radio-loud high-redshift quasars (RHRQs) provide crucial insights into the evolution of relativistic jets and their connection to the growth of supermassive black holes. Beyond the extensively studied population at $z\ge 5$, the cosmic morning epoch ($3\lesssim z\lesssim 5$) marks the peak of active galactic nucleus (AGN) activity and black hole accretion, yet remains relatively unexplored. In this work, we compiled the radio high-redshift quasar catalog (RHzQCat) by cross-matching the SDSS DR16Q catalog with four major radio surveys—FIRST, NVSS, RACS, and GLEAM. Our tier-based cross-matching framework and visual validation ensured reliable source identification across surveys with diverse beam sizes. The catalog included 1629 reliable and 315 candidate RHRQs, with radio luminosities uniformly spanning ${10}^{25.5}$–${10}^{29.3}$ W Hz⁻¹. About 95% of the confirmed sources exhibited compact morphologies, consistent with Doppler-boosted or young AGN populations at high redshifts. Our catalog increases the number of known RHRQs at $z\ge 3$ by an order of magnitude, representing the largest and most homogeneous catalog of radio quasars at cosmic morning, filling the observational gap between the early ($z>6$) and local Universe. It provides a robust reference for future statistical studies of jet evolution, AGN feedback, and cosmic magnetism with next-generation facilities such as the Square Kilometer Array (SKA).