A million binaries from Gaia eDR3: sample selection and validation of Gaia parallax uncertainties

Abstract

We construct from Gaia eDR3 an extensive catalog of spatially resolved binary stars within ≈ 1 kpc of the Sun, with projected separations ranging from a few au to 1 pc. We estimate the probability that each pair is a chance alignment empirically, using the Gaia catalog itself to calculate the rate of chance alignments as a function of observables. The catalog contains 1.3 (1.1) million binaries with >90% (>99%) probability of being bound, including 16,000 white dwarf -main sequence (WD+MS) binaries and 1,400 WD+WD binaries. We make the full catalog publicly available, as well as the queries and code to produce it. We then use this sample to calibrate the published Gaia DR3 parallax uncertainties, making use of the binary components' near-identical parallaxes. We show that these uncertainties are generally reliable for faint stars (𝐺 18), but are underestimated significantly for brighter stars. The underestimates are generally ≤ 30% for isolated sources with well-behaved astrometry, but are larger (up to ∼80%) for apparently well-behaved sources with a companion within 4 arcsec, and much larger for sources with poor astrometric fits. We provide an empirical fitting function to inflate published 𝜎 𝜛 values for isolated sources. The public catalog offers wide ranging follow-up opportunities: from calibrating spectroscopic surveys, to precisely constraining ages of field stars, to the masses and the initial-final mass relation of white dwarfs, to dynamically probing the Galactic tidal field.

RR Lyrae-based Distances for 39 Nearby Dwarf Galaxies Calibrated to Gaia eDR3

“…Although Gaia parallax uncertainties for most sources improved by only 30% on average (Lindegren et al 2020b), the typical improvement for sources in this sample is more than a factor of 2, due to better control of systematics for bright sources. Even in eDR3, parallax uncertainties for stars of this brightness are typically underestimated by up to 30% (El-Badry et al 2021;Zinn 2021). We inflate the reported eDR3 parallax uncertainties as recommended by El-Badry et al (2021, their Equation 16).…”

“…For ease of reference, we summarize the MW RRL in the calibration sample in Appendix D, with updated parallaxes from Gaia eDR3, and corrected parallax errors based on El-Badry et al (2021).…”

“…There is little doubt that applying the Lindegren et al (2020a) zerpoint correction results in more reliable parallaxes than using the uncorrected values, but there is some evidence that systematics remain at the 0.01 mas level (e.g. El-Badry et al 2021;Zinn 2021;Riess et al 2021), corresponding to distance modulus errors of order 0.01 mag. Further reduction of parallax systematics with future Gaia data releases is one avenue along which our model could be improved.…”

Unbound Close Stellar Encounters in the Solar Neighborhood

“…With distances, relative angular separations, and relative velocities, we may try to project the encounter histories of pairs of stars into the near future and recent past, to estimate how close they have/will come. Several studies have investigated the sample of wide binaries identifiable in the GAIA data (Hartman & Lépine 2020;Gaia Collabora-tion et al 2021c;El-Badry et al 2021). Our interest is in the systems these analyses reject, in that we wish to identify systems that are in close physical proximity but which are not gravitationally bound to one another.…”

“…At the separations of interest, the orbital velocity of stellar mass binaries is much less the expected magnitude of relative velocities of unbound disk stars, so we expect that genuinely bound objects should exhibit common proper motions to a level that distinguishes them from unbound pairs. The quantification of proper motion errors has its own uncertainties, but these are small enough that one can identify binary samples of high fidelity (El-Badry et al 2021).…”