A Planetary Illusion's Funeral: Non-detection of a Gaia DR3 Exoplanet Candidate, and the Role of Intermediate-precision Radial Velocities in Gaia Exoplanet Follow-up

TL;DR

This study investigates the non-detection of a Gaia DR3 exoplanet candidate around HD 12800 using radial velocity measurements, highlighting the importance of intermediate-precision RV spectrographs in Gaia exoplanet follow-up efforts.

Contribution

It demonstrates the role of intermediate-precision radial velocities in confirming or refuting Gaia astrometric exoplanet candidates, especially for stars with certain brightness levels.

Findings

Radial velocity observations did not detect the proposed planet.

The proposed planet would have been detectable with the RV data if it existed.

Intermediate-precision RV spectrographs are valuable for Gaia exoplanet confirmation.

Abstract

The detection of exoplanets using astrometry has long been an area of interest, but is fraught with challenges. The Gaia mission is fundamentally reshaping this field thanks to its unprecedentedly precise all-sky astrometric observations. The 2022 release of Gaia DR3 brought the first exoplanets discovered from the Gaia astrometry, including a new candidate around the bright ($V=6.6$) solar-type star HD 12800. However, two years after announcement, the Gaia exoplanet candidate was retracted. In this work we report radial velocity observations of HD 12800 acquired with the TRES spectrograph, which we began immediately after the release of Gaia DR3. Our observations failed to detect the planet candidate; nonetheless, we emphasise that the originally proposed companion would have been easily detected in our radial velocity observations. We conclude with a discussion on the role of intermediate-precision ($\approx$10 m s$^{-1}$) RV spectrographs in the follow-up of Gaia astrometric exoplanet candidates, relevant to the forthcoming release of Gaia DR4. We argue that such observations may play an important role in planet confirmation for stars between approximately $8<G<12$, likely to represent a significant fraction of Gaia exoplanet discoveries.