Detection of four cold Jupiters through combined analyses of radial velocity and astrometry data

TL;DR

This work addresses the challenge of characterizing cold Jupiters by combining long-baseline RV measurements with Hipparcos–Gaia astrometry, enabling determination of true masses and full 3D orbits. Using a parallel-tempering MCMC framework, the authors fit RV data from multiple instruments together with Gaia and Hipparcos astrometry, including instrument offsets and jitter, to derive orbital elements for four systems. The results yield four cold Jupiters—HD 48265 b/c, HD 68475 b, HD 114386 b/c, and HD 100508 b—revealing diverse architectures, including a significant mutual inclination in HD 48265 and a potential direct-imaging target in HD 68475. The study demonstrates the power of joint RV–astrometry analyses to expand the cold Jupiter census, constrain dynamical histories, and guide future direct-imaging campaigns and Gaia-era surveys.

Abstract

Cold Jupiters play a crucial role in planet formation and dynamical evolution. Since their initial discovery around 47 UMa, they have attracted significant interest, yet their formation mechanisms remain uncertain, underscoring the need to expand the known population. In this work, we combine RV data with Gaia astrometry using Hipparcos-Gaia proper-motion anomalies over a 25-year baseline. By jointly modeling both datasets with the MCMC framework, we constrain planetary masses, orbital inclinations, and three-dimensional orbital architectures. This reduces RV degeneracies and improves mass determinations. Four cold Jupiters are reported: HD 68475 b and HD 100508 b are each the first confirmed planet in their systems, with orbital periods $7832_{-323}^{+463}$ d and $5681\pm42$ d and dynamical masses of $5.16_{-0.47}^{+0.53} M_{\text{Jup}}$ and $1.2_{-0.18}^{+0.30} M_{\text{Jup}}$, respectively. In multi-planet systems, HD 48265 c has a period of $10418_{-1400}^{+2400}$ d and a mass of $3.71_{-0.43}^{+0.68} M_{\text{Jup}}$, while HD 114386 c orbits at $444.00_{-0.88}^{+0.93}$ d with a minimum mass of $0.37 \pm 0.03 M_{\text{Jup}}$. The two planets in the HD 48265 system may exhibit a significant mutual inclination, making it a target for testing the von-Zeipel-Kozai-Lidov mechanism. HD 68475 b is a promising candidate for future direct imaging with ELT/METIS. We identified a Jupiter analog with the longest known orbital period among planets with masses between 0.5 and 2 $M_{\text{Jup}}$, implying that a substantial population of cold Jupiters likely awaits discovery by Gaia. This study expands the sample of cold Jupiters with constrained orbits and dynamical masses, demonstrating the value of combining radial velocity and astrometry in exoplanet research.

Figures (21)

• Figure 1: (a) RV curve of HD 48265. The points with error bars denote the RV measurements and associated uncertainties. The black line denotes the best-fit orbit. (b) Residual (O-C) between observation and model. Panels (c) and (d) show the RV signals from each of the two planets separately, with all data folded to the respective orbital period of each planet.
• Figure 2: RV curve of HD 68475. The symbols are the same as Figure \ref{['fig: HD48265RV']}.
• Figure 3: Comparing the five-parameter astrometry of the model prediction to GDR2 and GDR3 astrometry. The barycentric motion of the HD 68475 system has been subtracted for both the catalog Gaia data (square) and the predictions (boxplot). The inner thick line, edge of the box, and whisker, respectively, denote the median, $1 \sigma$ uncertainty and $3 \sigma$ uncertainty. The Gaia astrometric uncertainty has been adjusted for the error inflation factor. The subscripts of the label of the x-axis correspond to the Gaia release number.
• Figure 4: Boxplot for HD 48265. The symbols are the same as Figure \ref{['fig: HD68475box']}.
• Figure 5: RV curve of HD 114386. The symbols are the same as Figure \ref{['fig: HD48265RV']}.