Astrometric excess noise in Gaia EDR3 and the search for X-ray binaries

Abstract

Astrometric noise (ε) in excess of parallax and proper motion is a potential signature of orbital wobble (ω) of individual components in binary star systems. The combination of X-ray selection with astrometric noise could then be a powerful tool for robustly isolating accreting binaries in large surveys. Here, we mine the Gaia EDR3 catalogue for Galactic sources with significant values of astrometric noise over the parameter space expected for known and candidate X-ray binaries (XRBs). Cross-matching our sample with the Chandra Source Catalogue returns a primary sample of ≈6500 X-ray sources with significant ε. X-ray detection efficiency for objects with significant ε is a factor of ≈4.5 times higher than in a matched control sample exhibiting low ε. The primary sample branches off the main sequence much more than control objects in colour-mag space, and includes a higher fraction of known binaries, variables and young stellar object class types. However, values of ε reported in the Gaia pipeline releases so far can exceed expectations for individual XRBs with known semi-major axis size and other system parameters. It is likely that other factors (possibly attitude and modelling uncertainties, as well as source variability) currently dominate the observed excess noise in such systems. Confirmation of their nature must therefore await future Gaia releases. The full X-ray matched catalogue is released here to enable legacy follow-up.

TOI-3757 b: A Low-density Gas Giant Orbiting a Solar-metallicity M Dwarf

“…For the single-star astrometric solution in use for GAIA EDR3, this astrometric motion of the primary star around the center of mass would manifest as noise (Kervella et al 2019), especially for orbital periods much shorter than the observing baseline for GAIA EDR3 (∼34 months). The commonly accepted threshold in literature for this is RUWE  1.4, which correlates with the presence of a bound stellar companion in recent studies of stellar binaries (Penoyre et al 2020;Belokurov et al 2020;Gandhi et al 2021). For TOI-3757, GAIA EDR3 reports a RUWE of ∼1.1, which is in agreement with a single-star astrometric solution.…”

Ninety-seven Eclipsing Quadruple Star Candidates Discovered in TESS Full-frame Images

“…The Gaia EDR3 catalog (Gaia Collaboration et al 2021) provides such measurements in terms of an astrometric excess noise above a single star model, that is, AEN, with a corresponding significance AENS, as well as an indicator for the astrometric goodness of fit in terms of an RUWE. The method has been demonstrated for known spectroscopic binaries, which are used to measure binarity fraction across the Hertzprung-Russell diagram and detect hierarchical triples and X-ray binary stars (e.g., Belokurov et al 2020;Penoyre et al 2020;Stassun & Torres 2021;Gandhi et al 2022, and references therein). Figure 12 shows Gaia's EDR3 AEN, AENS, and RUWE for those targets in our catalog with measured AEN (91 out of 97).…”

How to search for mirror stars with Gaia

“…For this reason we apply the astrometric_excess_noise < 1 cut. The suspect population is significantly reduced, presumably because many binary and crowded or confused sources are rejected [60]. The resulting HR and CC diagrams are shown in figure 2 (middle).…”