Astronomy & Telescopes

A Generative Model for Gaia Astrometric Orbit Catalogs: Selection Functions for Binary Stars, Giant Planets, and Compact Object Companions

By Keith Cowing

Status Report

astro-ph.SR

November 7, 2024

Filed under astro-ph.SR, Astrometry, binary star, exoplanet, Gaia DR3, Gaia mission, gas giant, imaging, rock planet, Stellar Cartography

A Generative Model for Gaia Astrometric Orbit Catalogs: Selection Functions for Binary Stars, Giant Planets, and Compact Object Companions — Selection of the astrometric solutions for our mock astrometric binary catalog. This figure in inspired by Figure 3 of Halbwachs et al. (2023), who present the same quantities for the astrometric solutions of real sources published in Gaia DR3. Upper left panel shows all solutions with a₀/σa₀ > 5 and F₂ < 25. The cloud of points at long P_orb and low f_m, _ast consists mostly of good solutions, while the vertical stripes of solutions with high f_m, _ast and short periods are all spurious. In the upper right, green and gray show the distributions of solutions with fm, ast < 0.3 M_⊙ (presumed mostly reliable) and f_m, _astt > 0.3 M_⊙ (presumed mostly spurious). Black line shows the empirical cut (Equation 20) below which solutions are discarded. Bottom panels show only solutions that pass this cut. Red lines in these panels show additional cuts applied to the final solutions: only solutions below (left panel) and above (right panel) the red lines were retained. — astro-ph.GA

Astrometry from Gaia DR3 has produced a sample of ∼170,000 Keplerian orbital solutions, with many more anticipated in the next few years. These data have enormous potential to constrain the population of binary stars, giant planets, and compact objects in the Solar neighborhood.

But in order to use the published orbit catalogs for statistical inference, it is necessary to understand their selection function: what is the probability that a binary with a given set of properties ends up in a catalog?

We show that such a selection function for the Gaia DR3 astrometric binary catalog can be forward-modeled from the Gaia scanning law, including individual 1D astrometric measurements, the fitting of a cascade of astrometric models, and quality cuts applied in post-processing.

We populate a synthetic Milky Way model with binary stars and generate a mock catalog of astrometric orbits. The mock catalog is quite similar to the DR3 astrometric binary sample, suggesting that our selection function is a sensible approximation of reality.

Our fitting also produces a sample of spurious astrometric orbits similar to those found in DR3; these are mainly the result of scan angle-dependent astrometric biases in marginally resolved wide binaries. We show that Gaia’s sensitivity to astrometric binaries falls off rapidly at high eccentricities, but only weakly at high inclinations.

We predict that DR4 will yield ∼1 million astrometric orbits, mostly for bright (G≲15) systems with long periods (P_orb≳1000 d). We provide code to simulate and fit realistic Gaia epoch astrometry for any data release and determine whether any hypothetical binary would receive a cataloged orbital solution.

Kareem El-Badry, Casey Lam, Berry Holl, Jean-Louis Halbwachs, Hans-Walter Rix, Tsevi Mazeh, Sahar Shahaf

Comments: 22 pages, 17 figures, accepted to OJAp. Code at this https URL
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Earth and Planetary Astrophysics (astro-ph.EP); Astrophysics of Galaxies (astro-ph.GA); Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as: arXiv:2411.00088 [astro-ph.SR] (or arXiv:2411.00088v1 [astro-ph.SR] for this version)
https://doi.org/10.48550/arXiv.2411.00088
Focus to learn more
Related DOI:
https://doi.org/10.33232/001c.125461
Focus to learn more
Submission history
From: Kareem El-Badry
[v1] Thu, 31 Oct 2024 18:00:00 UTC (6,977 KB)
https://arxiv.org/abs/2411.00088
Astrobiology,

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

Follow on Twitter