# Yahalomi et al. release simulated Gaia DR4 epoch astrometry for 15,120,984 injected systems

- Published: 2026-11-05 11:28 UTC
- Section: Sky & Space › Astronomy
- Tags: Gaia DR4, epoch astrometry, simulated astrometry, orbit-modeling benchmark, substellar companions, kepmodel periodogram, G23H catalog, injected companions, false-positive rate, high-SNR sub-catalog
- URL: https://realtech.media/news/rt-63f6233f2c1722e437db5f08_yahalomi_et_al/

**The dataset injects zero, one and two companions into 5,040,328 main-sequence stars within 500 pc, with known parameters for testing orbit-modeling pipelines.**

![Yahalomi et al. release simulated Gaia DR4 epoch astrometry for 15,120,984 injected systems](https://sgzwpqqelzmajkcubgkl.supabase.co/storage/v1/object/public/rt-media/2026/11/c3381e65fe01b77f.jpg)
*Jeremy Harbeck, Wikimedia Commons, Public domain*

Yahalomi et al. (2026) published, via doi.org, a record of simulated Gaia DR4-like epoch astrometry. It is meant for testing orbit-modeling pipelines on a common set of injected systems with known parameters [1]. Into each of the 5,040,328 main-sequence Gaia stars within 500 pc in the G23H catalog, the authors injected a zero-, one- and two-companion system, for 15,120,984 systems in total [1].

## Injection and detection setup

Companion masses and semimajor axes are drawn log-uniformly over 1 M_Mars to 80 M_Jup and 0.03 to 100 au [1]. The set uses no occurrence model and no detectability cut, so the companion-free population serves as a matched null [1]. The one- and two-companion populations each carry a high-SNR sub-catalog, in which every companion has SNR_tot of at least 5. These contain 439,503 and 26,379 systems, respectively [1].

Every system was characterized with the kepmodel astrometric periodogram on a grid of 15,777 trial periods [1]. The detection thresholds were calibrated on the companion-free population to a 1% false-positive rate and applied to all three populations [1]. The characterization tables give the five-parameter chi2, best period, class (undetected, unimodal, multimodal or broad), peak powers, delta-BIC, acceleration test, calibrated detected and period_reliable flags, and FAP [1].

## Files and tools

The stellar sample, stars.csv, holds G23H astrometry, Gaia DR3 photometry and astrometric metadata, Hipparcos-Gaia proper motions, per-star noise-model terms, and interpolated main-sequence mass and radius [1]. The injected truth for every system is stored in injected_solutions parquet files. For each companion they list sma, ecc, mass, inc, Omega, omega, M_anom, period and several signal-to-noise values [1].

Each population has 640 parquet shards: 320 epoch shards and 320 matching truth shards. An epoch row contains the observation time, scan position angle, parallax factor, along-scan centroid position and its error, and the field of view [1].

The generator, the periodogram characterization, the notebooks for the paper figures and an orbit-fitting tutorial based on NumPyro and jaxoplanet are available at github.com/dyahalomi/epochalypse [1]. The script download_catalog.sh fetches the record into the expected layout and unpacks the epoch shards on request. MD5SUMS.txt lists an MD5 for every file [1].

## Sources

1. [doi.org](https://doi.org/10.5281/zenodo.23789041)
2. [arXiv · препринт](https://arxiv.org/abs/2611.06915v1)

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Source: RealTech, realtech.media — https://realtech.media/news/rt-63f6233f2c1722e437db5f08_yahalomi_et_al/