A recent study led by the astrometry team at the Shanghai Astronomical Observatory (SHAO) of the Chinese Academy of Sciences (CAS) has developed a high-precision hybrid calibration method to eliminate spatial systematic errors in the Gaia Data Release 3 (GDR3) parallaxes.

The study, published in the Monthly Notices of the Royal Astronomical Society, provides a more reliable data baseline for measuring stellar distances, mapping the structure of the Milky Way, and establishing celestial reference frames.

By integrating a global parametric pre-correction with a data-driven local refinement, the new scheme successfully suppresses persistent, large-scale spatial patterns and "striping" artifacts caused by the Gaia scanning law. These localized residual errors, which reach amplitudes of 10 to 30 microarcseconds under standard official calibration models, are reduced to nearly zero across the entire celestial sphere.

To address the drastic variations in calibrator density across different magnitudes, the research team adopted a targeted approach based on a data-driven threshold at G = 18.0.

For the faint regime (G > 18.0), the method uses a continuous, non-parametric Sliding Window technique driven by a purified sample of approximately 1.4 million extragalactic quasars, which serve as absolute geometric anchors with near-zero physical parallax.

For brighter stars (G < 18.0), the scheme incorporates relative spatial constraints from wide physical binaries, helping compensate for the sparse distribution of absolute extragalactic indicators in the bright regime.

"The Gaia catalog provides unprecedented astrometric precision, but at this extreme level of accuracy, subtle systematic errors on the microarcsecond scale become highly significant," said DING Ye, a PhD candidate at SHAO and the first author of the study. "Our work is designed to expose and eradicate these hidden, localized biases across different regions of the sky."

LIAO Shilong, a research professor at SHAO and the corresponding author of the study, emphasized the broader impact of the framework: "This study not only provides a highly refined correction map for GDR3 users but also underscores the critical diagnostic value of massive quasar samples in space astrometry. Furthermore, it offers a proven mathematical and empirical methodology that can serve as a vital reference for addressing the parallax zero-point issue in the upcoming Gaia Data Release 4 (GDR4)."

Co-corresponding author Dr. QI Zhaoxiang at SHAO added that advancing high-precision astrometric catalogs demands a profound understanding of underlying physical and instrumental systematic errors.

The team's hybrid calibration approach represents a crucial step toward pushing the boundaries of reliable data application in both galactic archaeology and modern astrophotonics, QI said.

Sky maps present the mean parallaxes of the quasar sample (top row) and the mean parallax differences of the wide binary sample (bottom row). (Image by SHAO)