A Spatially Dependent Correction of Gaia EDR3 Parallax Zero-point Offset based on 0.3 million LAMOST DR8 Giant Stars

Abstract

We have studied the zero-point offset of Gaia Early Data Release 3 (EDR3) parallaxes based on a sample of 0.3 million giant stars built from the LAMOST data with distance accuracy better than 8.5%. The official parallax zero-point corrections largely reduce the global offset in the Gaia EDR3 parallaxes: the global parallax offsets are -27.9 μas and -26.5 μas (before correction) and +2.6 μas and +2.9 μas (after correction) for the five- and six-parameter solutions, respectively. The bias of the raw parallax measurements is significantly dependent on the G magnitudes, spectral colors, and positions of stars. The official parallax zero-point corrections could reduce parallax bias patterns with G magnitudes, while could not fully account the patterns in the spaces of the spectral colors and positions. In the current paper, a spatially dependent parallax zero-point correction model for Gaia EDR3 five-parameter solution in the LAMOST footprint is first provided with the advantage of huge number of stars in our sample.