# Dynamical Mass of the Exoplanet Host Star HR 8799

**Authors:** Aldo G. Sepulveda, Brendan P. Bowler  
**arXiv:** [2111.12090](https://arxiv.org/abs/2111.12090)  
**Date:** 2021-11-23  
**Summary page:** https://www.summarizepaper.com/en/paper/2111.12090v1/

## Key points

- HR 8799 is an A5/F0 star with four directly imaged giant planets
- The planets are located at wide separations of approximately 16-78 au and are undergoing orbital motion
- The authors present a dynamical mass measurement of HR 8799 using 130 epochs of relative astrometry of its planets, including new medium-band 3.1 $\mu$m observations acquired with NIRC2 at Keck Observatory
- Each orbiting planet was treated as a massless particle and fit with a Keplerian orbit using Markov chain Monte Carlo to measure the host star's mass
- A Bayesian framework was used to combine each independent total mass measurement into a cumulative dynamical mass using all four planets
- The resulting dynamical mass of HR 8799 is found to be 1.47$^{+0.12}_{-0.17}$ \Msun assuming a uniform stellar mass prior or 1.46$^{+0.11}_{-0.15}$ \Msun with a weakly informative prior based on spectroscopy

## Summary

HR 8799 is an A5/F0 star that has been continuously monitored with adaptive optics imaging since the discovery of its four directly imaged giant planets over a decade ago. These planets are located at wide separations of approximately 16-78 au and are undergoing orbital motion. In this study, the authors present a dynamical mass measurement of HR 8799 using 130 epochs of relative astrometry of its planets, which include both published measurements and new medium-band 3.1 $\mu$m observations acquired with NIRC2 at Keck Observatory. To measure the host star's mass, each orbiting planet was treated as a massless particle and fit with a Keplerian orbit using Markov chain Monte Carlo. The authors then used a Bayesian framework to combine each independent total mass measurement into a cumulative dynamical mass using all four planets. The resulting dynamical mass of HR 8799 is found to be 1.47$^{+0.12}_{-0.17}$ \Msun assuming a uniform stellar mass prior or 1.46$^{+0.11}_{-0.15}$ \Msun with a weakly informative prior based on spectroscopy.