Pre-registered Gaia DR4 predictions for nearby stars with unexplained Hipparcos–Gaia accelerations

We list six stars within 25 pc whose Hipparcos–Gaia proper-motion anomaly (PMa) is significant at 11–39σ and for which, after vetting against SIMBAD, Robo-AO imaging and recent astrometry + radial-velocity orbit catalogues, we find no published companion: HD 49095, θ Scl, HD 190771, HD 72760, BD+71 851 and HD 152606 (plus HIP 79431, whose known short-period planet cannot produce the anomaly).

For each star we give the allowed companion mass–orbital radius range and falsifiable predictions for Gaia DR4 (release 2026-12-02): the magnitude and position angle of the astrometric acceleration, and the expected companion position angle for follow-up imaging. The companions are expected to be brown dwarfs or low-mass M dwarfs at 5–50 au, too faint to appear in the DR4 residual images.

The identical pipeline is applied to seven control stars with known companions (GJ 229, 15 Sge, HD 4747, ε Ind A, HD 159062, HD 199509, HD 182488), so that DR4 provides a blind test of the method. The verification script (d_verifica_dr4.py) is fixed in this deposit before DR4.

The deposit contains the note (PDF and Markdown), the prediction tables (CSV), the mass–separation curves, and all Python code needed to reproduce the predictions and to test them against DR4.

The analysis was carried out with the assistance of an AI model (Claude, Anthropic); see the section "Author contributions and use of AI" in the note.