We independently determine the zero-point offset of the Gaia early Data Release-3 (EDR3) parallaxes based on ∼110,000 W Ursae Majoris (EW)-type eclipsing binary systems. EWs cover almost the entire sky and are characterized by a relatively complete coverage in magnitude and color. They are an excellent proxy for Galactic main-sequence stars. We derive a W1-band period–luminosity relation with a distance accuracy of 7.4%, which we use to anchor the Gaia parallax zero-point. The final, global parallax offsets are −28.6 ± 0.6 μas and −25.4 ± 4.0 μas (before correction) and 4.2 ± 0.5 μas and 4.6 ± 3.7 μas (after correction) for the five- and six-parameter solutions, respectively. The total systematic uncertainty is 1.8 μas. The spatial distribution of the parallax offsets shows that the bias in the corrected Gaia EDR3 parallaxes is less than 10 μas across 40% of the sky. Only 15% of the sky is characterized by a parallax offset greater than 30 μas. Thus, we have provided independent evidence that the parallax zero-point correction provided by the Gaia team significantly reduces the prevailing bias. Combined with literature data, we find that the overall Gaia EDR3 parallax offsets for Galactic stars are [−20, −30] μas and 4–10 μas, respectively, before and after correction. For specific regions, an additional deviation of about 10 μas is found.
We present an independent examination of the parallax zero-point of the Third Gaia Early Data Release (hereafter EDR3), using the LAMOST primary red clump (PRC) stellar sample. A median parallax offset of around 26 μas, slightly larger than that found by examination of distant quasars, is found for both the five- and six-parameter solutions in EDR3, based on samples of over 63,000 and 2000 PRC stars, respectively. Similar to the previous investigation of Lindegren et al., to which we compare our results, the parallax zero-point exhibits clear dependencies on the G magnitudes, colors, and positions of the objects. Based on our analysis, the zero-point of the revised parallax can be reduced to a few μas, and some significant patterns, e.g., discontinuities with stellar magnitude, can be properly removed. However, relatively large offsets (>10 μas) are still found for the revised parallaxes over different positions on the sky.
We present a value-added catalog containing stellar parameters estimated from 7.10 million low-resolution spectra for 5.16 million unique stars with spectral signal-to-noise ratios (S/N) higher than 10 obtained by the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) Galactic spectroscopic surveys. The catalog presents values of stellar atmospheric parameters (effective temperature T eff, surface gravity log g, metallicity [Fe/H]/[M/H]), α-element to metal abundance ratio [α/M], carbon and nitrogen to iron abundance ratios [C/Fe] and [N/Fe], and 14 bands’ absolute magnitudes deduced from LAMOST spectra using the neural network method. The spectrophotometric distances of those stars are also provided based on the distance modulus. For stars with a spectral S/N larger than 50, precisions of T eff, log g, [Fe/H], [M/H], [C/Fe], [N/Fe], and [α/M] are 85 K, 0.098 dex, 0.05 dex, 0.05 dex, 0.052 dex, 0.082 dex, and 0.027 dex, respectively. The errors of 14 band’s absolute magnitudes are 0.16–0.22 mag for stars with a spectral S/N larger than 50. The spectrophotometric distance is accurate to 8.5% for stars with a spectral S/N larger than 50 and is more accurate than the geometrical distance for stars with a distance larger than 2.0 kpc. Our estimates of [Fe/H] are reliable down to [Fe/H] ∼−3.5 dex, significantly better than previous results. The catalog provides 26,868 unique very metal-poor star candidates ([Fe/H] ≤−2.0). The catalog would be a valuable dataset to study the structure and evolution of the galaxy, especially the solar neighborhood and the outer disk.
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